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I need your vote for a new Rotary HCCI engine !

I need your vote for a new Rotary HCCI engine !

(OP)
Fellow engineers,

This post promotes my design, but it's also informative for those curious about new developments in engine design, so I hope it's OK. Please accept my apologies if not.

I have submitted my patent pending design for a "Hybrid Miller Cycle Rotary HCCI Engine for RQ-7 Class Drones" in the "Create the Future" contest. You may find it by googling the engine name above or by visiting https://contest.techbriefs.com/2017/entries/aerosp....

Preliminary analysis indicates power density (3 HP per pound) and efficiency (45% with 0.300 BSFC) comparable to a turbofan when operated at full equivalency. When operated in Low Temperature Combustion (LTC) mode, the engine still produces nearly 1 HP per pound but creates very few emissions. Because of its small 10" diameter and 6.5" thickness, multiple engines can be arranged in a clover-leaf pattern around a common shaft to yield 380 HP in a 24" by 6.5" volume. Another set of engines can be arranged behind the first to yield 760 HP in 24" by 16" volume. Note it's not mechanically efficient to add a third engine set due to limitations in my design.

I would greatly appreciate your support of my contest entry. Viewing my entry helps, but voting for it (which requires simple e-mail verification) helps even more. As it stands, I'm only one vote ahead of a "free energy" device ! That's just wrong ! Please circulate the link as widely as possible and encourage all your engineering friends and colleagues to help me win this contest! If I win the contest 100% of the money will go to funding 3D modeling of CFD/Combustion/Heat Loss by a consultant.

Thank you very much for your time and any support you can offer. If you have questions or comments, please post them here or on the contest site and I will answer them to the best of my abilities. I view criticism as being more valuable than praise when it comes to design, so don't hesitate to challenge my design (but please keep it respectful per normal engineering tradition).

Respectfully,

Rod Newstrom

P.S. Some may wonder why I targeted my contest entry at military drones. I would have preferred to emphasize the efficiency and low emissions qualities of my engine when operating in Low Temperature Combustion (LTC) mode. I targeted the military application instead because the administration wants to zero funding at the DOE/ARPA-E (who would normally fund such advances) while simultaneously increasing military budgets. I mention the RQ-7 drone, an unarmed surveillance drone, specifically because my engine fits in the volume and weight envelope of its current engine (the AR-741 Wankel), and the Army issued a Request For Information in 2016 for a replacement engine.

RE: I need your vote for a new Rotary HCCI engine !

Do you have a running prototype?

RE: I need your vote for a new Rotary HCCI engine !

I could use an engine similar to that for a project I am working on , however I only need 45 hp not 90
You can keep me posted on here as to your progress . I have seen and investigated a great many engines that look promising , only to find that they fail to deliver promised horsepower and weight savings when actually built.
B.E.

You are judged not by what you know, but by what you can do.

RE: I need your vote for a new Rotary HCCI engine !

I answered my own question ... "If I win the contest 100% of the money will go to funding 3D modeling of CFD/Combustion/Heat Loss by a consultant." In other words, this is currently a CAD exercise.

But the question was more of a shot across the bow before firing the main volleys.

This thing has A LOT of finicky little bits and pieces. It has A LOT of opportunities for leakage past seals. Those hydrodynamic cam followers are going to have a lot of friction. It has A LOT of surface area relative to displacement which means lots of heat loss. All of this means the claimed efficiency is a pipe dream. The claim of low emissions is also a pipe dream.

Why should this mechanical layout be any better at operating in HCCI mode than any other (e.g. conventional) layout is?

RE: I need your vote for a new Rotary HCCI engine !

Very nice rendering and lots of effort in detail design. Unfortunately Brian is spot on.

Why the stepped bore in the power cylinders?

Does the rapid compression piston really have a stroke of 0.048 (1/10th of the other piston?)

I assume the dimensions are inches? If so, the use of mixed unit systems (masses in g) is not recommended.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Berkshire, I will develop different sizes based on demand, but only *after* this one is in production. I estimate that will take between 3-5 years, and that assumes it's funded (DARPA, ARPA-E, or private investors) and everything goes well. Yes, there are a ton of "new engine designs" out there that turn out to be rubbish. In my experience, this is due to publication before formal analysis (much less prototype) by non-engineers. I am an engineer, and I spent several years after the concept was finalized performing mechanical design and analysis (tolerances and FEA) as well as thermodynamics and inertial loads (Excel). Even then, I feel I am publishing early, but I got an estimate for the next phase of analysis (which has to be done in KIVA to be accepted by the HCCI community), and it's too much for me to bear without investment. I can't get investment without publishing my work thus far, of course, so it's a Catch-22 of sorts. I'm not hoping to win the contest so much as I am using it to publish. Many of the votes for my design come from respected experts in the field (who notified me by LinkedIn that they had voted).

--------------------------------------

Brian, Yes, it's still in the analysis phase. All new engines go through this phase.

The design may appear to have a lot of "finicky little bits and pieces," but relative to what? It has no valve train. No timing gear or belt, cam shafts, no valves, no valve spring retainers, no valve springs, no valve bushings, and no valves. Imagine how many "finicky little bits and pieces" a double overhead cam, 4 valve per cylinder, 4 cylinder engine has. Mine engine has less.

I have seal losses high on my risk register due to the tremendous pressure of HCCI at full power (equivalence 1). I am using soft steel rings on tool steel pistons in tool steel liners. Though I have a lot of rings, the total surface area is small, and my expansion stroke is very quick specifically to reduce the amount of time available for blow-by and heat loss. The side seals are another area of concern, but I am much more confident in them than I would be if I were using the kind of seals in the Wankel rotary.

I'd be interested in substantiation of your statement "Those hydrodynamic cam followers are going to have a lot of friction." Do you believe they result in substantially greater FMEP than the combination of sources I lack (valve train, piston skirts, oil pump, water pump) relative to a high performance engine running at 16,000 RPM (Ref 1)? If you wish to do some back of envelope work, the cam surfaces are micro-polished H-13 tool steel, the combined contact length is 1 inch, the average track length is 22.9 inches, the RPM is 7800, and the average pressure is 1142 pounds. Tell me what FMEP you came up with and we can compare and discuss our results.

My current analysis calculates heat loss in 0.5 degree steps using Hohenberg's heat transfer coefficient (which has been shown to be more accurate than Woschni's for HCCI (Ref 2, 3, and 4). These calculations incorporate the surface area of the combustion chamber. I want to do full 3D analysis using KIVA or similar because those models are well recognized in the community (DOE's HCCI consortium of academia, national labs, and industry). If I fail to obtain funding for the KIVA work, I will use Solidworks to do the same work with lower fidelity then conduct critical experiments and take measurements.

Claims of HCCI efficiency and low emissions in Low Temperature Combustion (LTC) mode are not mine, they are those of numerous researchers (Ref 5). I only claim low emissions when operating in Low Temperature Combustion (LTC) mode. In this mode, the maximum temperature is under 2100K, and this is low enough to prevent formation of NO2 (Ref 5). HCCI is also very efficient due to it's near instantaneous combustion, lack of a flame front, etc. (Ref 5). Granted, if my engine fails to perform according to my analysis due to heat loss, friction, etc., it won't attain the HCCI ideal. I have addressed your concerns in these areas in the above paragraphs.

If you are familiar with HCCI, you know what the challenges are: control of timing over a wide range of operating conditions, extreme pressure and ringing during full load operation, lean miss-fire limiting operation at low load and creating difficulty in starting (Ref 6). I address each of these in my contest submission. The core innovation of my design is the means by which I manage intake temperature by controlling supercharger pressure and the way I generate the auto-ignition event using an "ignition piston" such that the engine is insensitive to timing variance. If you read the literature, you will find nearly all HCCI research focuses on its use in existing engine designs, and the difficulties people are having is proof of the HCCI's incompatibility with those designs; big bores, uncontrolled intake temperature, and efforts to time combustion without any special means of initiating it are critical weaknesses. I set out to design an HCCI engine from the bottoms-up, and the resulting design is uniquely suited to HCCI combustion (hence the patent application).

-----------------------------------

gruntguru, the bores are stepped because that was required to ensure the reverse torque generated by the ignition piston during combustion is less than the forward torque of the expansion piston during combustion. This is only an issue during starting. Once the engine is running, the rotational inertia of the rotor is sufficient to prevent engine reversal.

Yes, the stroke of the ignition piston is very short. It's only purpose is to initiate ignition (it's my spark plug so to speak). When the ignition process starts, the larger piston is at TDC, so there's very little volume in the larger bore cylinder and the entire combustion chamber is defined by the smaller cylinder's volume. At this point, the charge temperature is just 100K below auto-ignition temperature. The ignition piston then performs a full stroke as the expansion piston begins moving slowly away to start its expansion stroke. The speed at which the expansion piston moves is determined by its bore vs that of the ignition piston and the radius of its cam versus that of the ignition piston, factors relating to prevention of reverse rotation. The final factor is the angle of contact (mechanical advantage) of the cams associated with each piston. Because the expansion piston has great advantage in its product of bore and lever length (cam radius), it can have a much more shallow cam angle with less displacement and lower speed. As a result of these dynamics, the expansion piston doesn't move far as the ignition piston rapidly approaches and the resulting compression ratio is very high, sufficient to cause auto-ignition. This is the most difficult part of the design to understand. Hopefully my explanation helps. Let me know if I failed.

Finally, you are correct, I shouldn't have mixed units. The weights were so small in pounds I switched the weight unit in Solidworks' "mass properties" dialog box to grams without thinking. I suppose I should have used ounces. Sorry !

Rod

------------------------------------------------------

Ref 1: Ricardo friction analysis of high performance engine: Slide 38, https://studylib.net/doc/18063895/calculation-of-f...
Ref 2: Heat transfer equation includes surface area: http://www.engineeringtoolbox.com/convective-heat-...
Ref 3: Hohenberg's heat transfer coefficient: Page 149, http://www.ni.com/pdf/manuals/NICASUM.pdf
Ref 4: Heat transfer predictions in HCCI: http://lib.ugent.be/fulltxt/RUG01/002/153/552/RUG0...
Ref 5: HCCI Efficiency and Emissions: http://www.iosrjournals.org/iosr-jmce/papers/vol11...
Ref 6: HCCI Challenges: https://en.wikipedia.org/wiki/Homogeneous_charge_c...

RE: I need your vote for a new Rotary HCCI engine !

How does air get in and how does exhaust get out? Is there a cross-section or a schematic diagram? Is it a piston-ported two-stroke or it somehow a four-stroke? It's hard to follow from the CAD model how this is actually supposed to work.

RE: I need your vote for a new Rotary HCCI engine !

My initial thoughts concur with Brian in this case. Apologies if this sounds rude or I am mistaken, but making claims without even the first attempt at a proper combustion analysis is out in the realm of powerpoint engineering, most in engine development consider that rather unethical. The irony is that its another HCCI project, aka the blackhole that many billions in corporate research have disappeared into due to powerpoint engineering.

RE: I need your vote for a new Rotary HCCI engine !

Sorry but I really couldn't see much. And as far as a rotary engine, I thought I saw mention of pistons? Rotary engines don't have pistons.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
BrianPeterson, I apologize for the limited drawings in the contest submission; they only allow 3 figures and 500 words. I'm in Europe right now responding by phone, so I can't get you more drawings. Words will have to do.

As I note in Figure 3, the outermost cylinder, which contains the air pump piston, is capped by a reed valve assembly through which pump intake air is drawn. The reed valve assembly has a sheet of spring steel laser cut to form 8 small reeds bound in an alumininum frame. On intake the 8 reeds open to pass air into the cylinder. On output, the 8 intake reeds close and another pair opens to pass pressirized air into chambers within the sideplates. Each sideplate contains two chambers, one for scavenge air and the other for intake charge air.

The engine has 36 pistons arranged as 12 radial sets of 3. Each set of three pistons form a modified Doxford Engine... esentially Junkers' opposed piston two-stroke with uniflow scavenging augmented by Doxford with an air pump piston. Modifications include deletion of diesel fuel injectors or spark plugs, non-symettric stroke of the opposed piston pair, and augmentation of the normal piston-gated in-cylinder ports with rotary side ports. The rotary side ports are essentially *ANDed* with the traditional ports. On intake, this allows seperate management of intake charge air and scavenge air. On exhaust, this allows continued expansion after the piston passes the in-cylinder port.

Exhaust blow-down occurs when the expansion piston reachs the end of it's stroke, well after it opened the in-cylinder exhaust port. At this time the exhaust sideports open and residual gas pressure escapes out the in-cylinder port, though the side port, and into the exhaust manifolds in the sideplates. The piston then pushes exhaust gasses out until it is just below the in-cylinder exhaust port. At this time, the scavenge side port opens and air travels from the pressurized scavenge chamber in the sideplate, through the sideport and in-cylinder intake port, through the combustion chamber, out the in-cylinder exhaust port, through the exhaust side port and into the exhaust manifolds of the side-plate.

Hopefully my many words have painted a picture that clarifies things. If not, I'll try again.

--------------

CWB1, Your apology for being rude is accepted. All you have seen is a contest entry. It is limited by the contest rules to 500 words and 3 illustrations. I have answered what challenges and questions I can here and really can't do much more at this point. I *do* have 24 months of extensive analysis backing my claims. If I send it to you, are you going to provide a resume with qualifications, sign the NDAs, then put a couple of months effort into checking it? That's what my consultant with advanced degrees in combustion, chemical kinetics, and heat transfer is charging me to review my work and perform independent analysis. He hasn't completed his independent analysis but he has completed his initial review of my work. He said it looked good and felt there was little risk of misrepresentation in going public at the time I entered the contest.

Yes, it would certainly be unethical to sell shares or seek investment without proper analysis. I have completed initial peer review and am funding independent analysis so I can present an ethical and trasparent proposal to investors. At this point, however, I'm not soliciting investment, I'm simply asking people in this forum to vote for my design so I can beat the numerous "free energy" machines entered in the contest. I don't feel that's unethical in the least.

Yes, I am intimately aware of the effort that's been put into HCCI and the poor results obtained thus far. Using your train of logic, I suppose everyone should stop trying because so many before have tried and failed. I explained why others have failed and how mine is different.

---------------

dicer, I happen to own a 3rd Gen RX-7 with the twin turbo Wankel Rotary. I also thought there was no such thing as a piston based rotary engine. Both the US and international patent classification systems as well as Wikipedia taught me otherwise. See https://en.m.wikipedia.org/wiki/Rotary_engine

---------------

VE1BLL, My patent pending number is 62,485,227 with a filing date of April 20, 2017. It wont be available for public viewing for 18 months after filing per normal USPTO policy. See https://www.uspto.gov/web/offices/pac/mpep/s1120.h... . I haven't received a number for my international filing under the Patent Cooperation Treaty (PCT). Am I supposed to get one or does that only happen upon national filing ?

Rod

RE: I need your vote for a new Rotary HCCI engine !

So how does the fuel get in?

It doesn't look like it uses timed solenoid-fired direct-injection. Good thing, because I don't think one small enough for this has been developed.

Is it just squirting the fuel, untimed, into the scavenge air somehow?

If that's the case, some of it is going to get out the exhaust unburned - it's inevitable.

If it is somehow timing the fuel delivery to happen late in scavenging, you might have a chance of not having too much unburned fuel going through to the exhaust. The Bombardier SDI (semi direct injection) two-strokes that pre-dated their current direct-injection two-strokes were like this. Injection (via a more-or-less conventional automotive solenoid-operated injector) happened into the transfer port partway through the scavenging process with the hope that the early part of the scavenge was most likely to be the part that got out the exhaust but didn't have much fuel in it, and the late part of the scavenge with the fuel in it wasn't as likely to make it all the way across the piston and out the exhaust.

How are you handling atomisation/vaporisation? It's a problem area even for automotive 4-stroke spark ignition engines.

What about lubrication? This engine appears to be at least partially reliant on piston-porting. The means by which the piston rings cross the ports has historically been problematic. Some oil will inevitably end up going out the exhaust, or into the intake stream (or both). If adequate lubrication is supplied, the engine is an oil-burner and has exhaust emissions to show it. If lubrication is sparse, piston ring and cylinder wall life will be shortened. This was always a problem with the old two-stroke Detroit Diesel engines.

Now about that HCCI ...

Cold starting?

Light load, heavy load on the engine?

Pre-ignition due to running hot?

Or are you planning to use HCCI all the time simply because there's nowhere to put any spark plugs in places where you can get access to them ...

I just don't see this working out. Too many cylinders that are each too small, too many moving parts, too many surfaces that need to be sealed and lubricated and cooled, too many uncertainties what with both the mechanical arrangement and the proposed HCCI operation.

But, what do I know. I don't have the fancy thermodynamic and fluid dynamic analysis tools that your consultant does. I've only had about 15 or 20 motorcycle engines apart over the years, sometimes for fixing something that's broken, sometimes to prevent something from breaking before it does, sometimes in an attempt (not always successful) to "make faster" ...

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian, the fuel injectors are unit type (100% mechanical) driven by axial cams incorporated into the side faces of the rotor. You can't see the cam lobes because the stroke is so small (because the fuel load is so small).

You seem to have missed the significance of separate side ports and chambers for scavenge and intake; it keeps the two processes separate and allows early injection into the intake air charge held in the intake chamber pressurized by the air pump.

The Junkers style opposed piston engines like mine don't work like those you've seen in motorcycles. There is no "crankcase" where the intake charge is stored, and oil is squirted directly onto cylinder walls and the bottom of pistons. Ports nearly circle the cylinder and are comprized of many slots with ring support metal between. Take a close look at some of modern opposed piston engines on the web (Achates, OPOC, etc).

My HCCI approach came first and is stated in general terms within separate patent claims because it is applicable to engines of all configurations. It was only after I developed that idea that I realized It simplified (if not enabled) construction of the rotating-cylinder radial engine.

My HCCI approach has a built in heater, extreme compression (even more than a traditional diesel). It also has an integral electric motor/generator. In arctic conditions, the engine is run without fuel until everything has exited cold-soak condition. Light load/lean burn is enhanced by excess compression and minimized by stopping fuel injection (and venting air pump pressure) into pairs of cylinders on opposite sides of the rotor such that the remaining cylinders can operate under heavier load. Full load HCCI is enabled by use of very small bore steel pistons which allow operation at very high pressure.

You keep coming back to how many parts and seals I have. I'm guessing you must absolutely hate V-12 overhead cam engines ! Hopefully you do acknowledge they work, however.

I've had more than a few engines apart on the bench over the years too. Most were motorcycles (Kawasaki Mach III, Yamaha RD-350, the venerable Honda 750, Kawasaki Z1, Pontiac 400 HO, and a Fiat 124 Spider. I ported and polished the RD-350 (making it unridable LOL!). The rest were just straight rebuilds with the occasional new cam, manifold, carb, and headers. I've always been an engine enthusiast but stopped working on them when they became cluttered with emissions controls and mods were all but banned in California.

Yes, there are a lot of uncertainties and issues I will be working through on my way to a working engine. Who knows what unforeseen challenges will pop up along the way. All the tools do is help us identify and address some of the basic issues in a computer (far cheaper than hardware builds) so we can focus hardware builds on other issues. As an engine builder you know how much simpler things become once you get the darned thing running, even if it's coughing and spitting a bit. Once running, you can start tuning.

I'll be the first to admit my engine may never make it to production for any number of reasons. I didn't come here to ask for money, I only asked for your vote in an inventors contest in which I am competing with ideas far less thought out than mine.

Do I get your vote ? clown

RE: I need your vote for a new Rotary HCCI engine !

Is my reasoning incorrect or is the tangential rate on the sliding surfaces 247 feet/second or nearly 15,000 feet per minute?

That seems high for a pin that will be constrained between two cam surfaces.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
3DDave,

Yes, it's around 15,000 fpm assuming the average radius of the outer cam (0.304 ft) at 7800 RPM (130 rev/s). For comparison, the big end rod bearing of a Formula 1 engine has a diameter of about 1.34 inches or 0.11 ft. We know the crankshaft mains are larger, but I couldn't find the spec off hand, so let's go with around 2.5 inches or 0.208 ft. These engines run near 20,000 RPM (333 RPS), so the surface speed of the mains is around 13,000 fpm, not that much different than mine.

It's misleading to think of the cam follower being captive between the two surfaces of the cam track. Analysis indicates that the combination of centripetal and gas pressures are sufficient to hold the follower against the outer surface of the cam track even at 500 RPM. Thus the inner surface is really only being used during start, and there's no need for tight clearances between the follower and both track surfaces. Note, by the way, calculation of loads on the outer cam resulting from acceleration, gas pressure, and centripetal forces shows minimum 74% margin to material yield limits for H-13 tool steel.

By performing the surface speed calculation, you have discovered the rational for the hydrodynamic tilting pad followers (an independent claim in my patent); there are no roller bearings that will run at those speeds under high load. Even if there were, they'd be unattractive due to their cost and impact on reciprocating mass. As it stands, the outer piston assembly (expansion piston, pump piston, cam shaft, and both hydrodynamic bearings) only weigh about 50 grams. Note these issues of surface speed and reciprocating mass are not addressed in any existing patent of radial cam driven engines.

Note one of the earliest critical experiments on actual hardware will be stability, vibration, and friction of the outer cam at speed.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Detroit Diesels had a full ring of small ports all the way around the cylinder as you describe for yours. They still had tradeoffs between having enough lubrication and the oil consumption and emissions that came along with it, and piston ring and cylinder wear. They eventually had to give up with that engine design and go to 4-strokes.

What's the contact stress in your cam followers - particularly in view of your high compression ratio (and bear in mind that combustion will send peak cylinder pressure waaaay up)? Is it (approaching) point contact, line contact, or surface contact? To me it looks like line contact ...

The connecting rod to crank pin interface in a normal engine approaches surface contact.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian,

I suppose I may have issues with the ports. Nobody using them is reporting any, but I suppose that's to be expected. I guess I'll just have to find out for myself !

Did Detroit Diesel use separate paths for charge air and scavenge air ? If they didn't, I'm not surprised they had an emissions problem. I wonder if they didn't cut lubrication in order to try and mitigate that emissions problem. Do you have any useful links that will help me better understand the issues they found ?

I've completed comprehensive cam design and analysis. The analysis includes acceleration of the assemblies, gas pressure during all phases of operation including combustion at 7,000 psi (but only producing max 4200 pound force on the cam followers, 2100 pounds each, due to my small bore), and centripetal force. The surfaces undergo elastic deformation and the contact patch is 0.074 in2 at full load. This results in a minimum 74% margin to the yield limit of H-13 tool steel.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Detroit Diesel of course used only scavenging air (supplied by an external Roots blower - crankcase has oil in it) since fuel was supplied via direct-injection in those diesel engines.

The issue is that a wee bit of the oil supplied to the piston rings from the lubricated space underneath the piston, escapes into the port as the ring passes the port, and then on the subsequent scavenging operation, that oil gets blown into the cylinder. It will of course participate, at least partially, in the subsequent diesel combustion process, but Detroit Diesel was never able to get those engines to meet modern emission standards despite going to electronic unit injection in the later years.

As for issues "Nobody using them is reporting any" ...

The Detroit Diesel on-road two-stroke diesels went out of production decades ago and were never called upon to meet today's emission standards.
Many locomotive and ship engines still use the blower-scavenged piston-ported two-stroke diesel design, but they're not called upon to meet automotive emission standards. And those are very large low-RPM engines.
Modern fuel-injected spark-ignition two-strokes such as the Bombardier E-Tec snowmobile and outboard engines don't have to meet automotive emission standards ... and they have short service lives between rebuilds compared to anything automotive.
The various proposed opposed-piston two-stroke engines of various designs (OPOC etc) have yet to make it into production. I have the same reservations about those.

As for your safety factor to the yield stress ... what's your safety factor to the infinite-life fatigue limit?

Do you have radial clearance in that cam groove between the follower and each side of the groove? (Hope so, otherwise it will bind from thermal expansion!) Are load reversals going to cause "slop" and backlash leading to repeated impacts? This isn't necessarily a disaster; any valve mechanism in a 4-stroke using mechanical lifters (be it shim-bucket or manual threaded adjusters) has a repeated impact every time the cam hits the lifter and every time the valve gets set down on the valve seat ... but it requires careful design consideration to not be noisy and not break stuff.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian,

Your explanation finally set off the light bulb. Thanks !

After reviewing Achate's technical publication list ( http://achatespower.com/media-center/proven-result... ), I suppose it's obvious that emissions are a challenge in their opposed-piston two-stroke engine architecture, so I have to concede your point. They claim to meet emission standards (and have broadly published their test results), but their performance *may* be partially due to the fact their efficiency so high (they claim a 9% improvement). If that's the case, then I may be OK because my efficiency is also high. I'll review their work more closely to see whether they are doing anything special to address oil being dragged and blown into the exhaust port and assess my design accordingly. Hopefully they haven't found the *only* solution and patented it!

I haven't completed fatigue analysis. If I find a problem there, I will likely reduce the bore of the expansion piston to compensate. While this will reduce power out, it will also reduce size. I'll post results of fatigue analysis once I'm back home from Europe in late August.

Yes, there is clearance between the followers and the cam track, and I believe the geometry works in my favor in regards thermal expansion.

The loads on the outer cam are exclusively on the outer track once RPM exceeds 1,250. At 500 RPM (lowest likely idle), the maximum load on the inner track is only 31 pounds. Since it's only present for 0.5 degrees in my model, it likely indicates a need to slow the piston a bit more before reversal (I'll have to tweak the NURBS angle there and see if I can eliminate it). Thus, I don't think I'll have an issue with load transfer. Note the planned critical experiments encompass this phenomenon.

I'm finding this conversation very useful and thank you for your inputs thus far !

Rod

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian,

It tool little research before I found out that Achates assumes use of emissions control that *includes* urea (see http://achatespower.com/wp-content/uploads/2017/07... and http://www.jmdpf.com/diesel-particulate-filter-sys... ). It's the urea used to treat NOx emissions that's of greatest concern as tests have shown folks who own cars that require it don't actually fill the urea tank except when going in for emissions testing. It's also, of course, a pain having to deal with another routine task when fueling.

When running at equivalency of 0.439 (Air to Fuel ratio of 33:1), my combustion temperatures are below 2150K, so I won't be making much if any soot or NOx, only C02.



Reducing after treatments to CO2 puts my engine in a category similar to traditional auto engines.

In this LTC mode, my engine only produces 30 HP and efficiency comparable to a standard engine (31%), but it has the power to weight ratio of a Wankel (1 HP per pound). Because my engine is only 20" in diameter and 7" in depth, four of them can be arranged around a common shaft in a cloverleaf pattern to produce 120 HP in a 24" x 7" volume. Adding another set of such cylinders yields 240 HP in a 24" x 15" volume. That's in the sweet spot of low end low emissions vehicles. Each of my engines is a hybrid, so mileage and emissions in daily use will be better than I'm citing here.

I'm still going to go off and make sure I understand how people are addressing the emissions and lubrication challenges inherent to this design, but feel I likely have a marketable product here (from the emissions and power density perspective) even for on-road use. Of course, *all* ground use vehicles are likely to go electric anyway, so the real benefit would be in the EPA's "off-road" category (ATVs, farm equipment, snowmobiles, etc. that are operated far from electric charging/servicing infrastructure such that emerging to service on-road vehicles). I expect I may also have a market in portable power generation, but *all* these ground opportunities will require I get the price way down.

Overall, I think my best bet is still going to be aviation. My engine runs on diesel, and general aviation aircraft are still using *leaded* avgas. The EPA says these small piston-driven planes are responsible for nearly *all* remaining lead emissions in the US ! The improved fuel economy and very high power to weight ratio (even including emissions after-treatments such as being used by Achates) combined with the ability to retain significant power at altitude are big discriminators in my favor. Fortunately, aviation engines are *very* expensive; if I can meet *any* price target, it's in aviation.

Rod

RE: I need your vote for a new Rotary HCCI engine !

"gruntguru, the bores are stepped because that was required to ensure the reverse torque generated by the ignition piston during combustion is less than the forward torque of the expansion piston during combustion. This is only an issue during starting. Once the engine is running, the rotational inertia of the rotor is sufficient to prevent engine reversal.

Yes, the stroke of the ignition piston is very short. It's only purpose is to initiate ignition (it's my spark plug so to speak). When the ignition process starts, the larger piston is at TDC, so there's very little volume in the larger bore cylinder and the entire combustion chamber is defined by the smaller cylinder's volume. At this point, the charge temperature is just 100K below auto-ignition temperature. The ignition piston then performs a full stroke as the expansion piston begins moving slowly away to start its expansion stroke. The speed at which the expansion piston moves is determined by its bore vs that of the ignition piston and the radius of its cam versus that of the ignition piston, factors relating to prevention of reverse rotation. The final factor is the angle of contact (mechanical advantage) of the cams associated with each piston. Because the expansion piston has great advantage in its product of bore and lever length (cam radius), it can have a much more shallow cam angle with less displacement and lower speed. As a result of these dynamics, the expansion piston doesn't move far as the ignition piston rapidly approaches and the resulting compression ratio is very high, sufficient to cause auto-ignition. This is the most difficult part of the design to understand. Hopefully my explanation helps. Let me know if I failed."


There are several misconceptions in your analysis of velocities, pressure, torque and mechanical advantage.

Everything you need to know is contained in a volume/crankangle diagram regardless of how many pistons are doing the displacement or what their relationship to the crankshaft ("mechanical advantage") is.

"I will develop different sizes based on demand, but only *after* this one is in production"

Your design will never get into production. You have a great deal of talent and energy - I strongly suggest you get a mechanical engineering degree or enlist the help of someone who has one.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Guru,

You *could* say "Your explanation makes no sense to me because... Can you address this and clarify?" rather than take the stance that *I'm* an idiot because *you* don't understand.

Yes, PV work is a complete description that encompasses mechanical advantage. In this case, however, we're not discussing the work of a single piston but that of two subjected to the same combustion pressure and controlled by independent cams (or cranks if you prefer). Thus it's convienient to talk of the forces each applies to the ouput shaft. You know full well (I assume) that both approaches are valid, it's just easier to visualize it using force applied to levers.

The faster piston, by definition *because* it's moving faster, has greater mechanical advantage on the output shaft. At the same time its smaller bore results in less surface area (square inches), so combustion gas pressure (pounds-per-square-inch) produces less pound-force on the lever. Thus, though its mechanical advantage is greater, it exerts less torque on the output shaft.

To make it even simpler, imagine I'm trying to turn a shaft one way using a lever and you're trying to turn it the other way. My lever is shorter but the pressure I apply is normal to the lever. You have the longer lever but the force you apply is at an angle far from normal. Thus, even though your lever is longer, a given force applied to your lever will produce less torque on the shaft than if that same force is applied to mine, so I will win. I want *you* to win, however, so I need you to apply more force on your lever than I do to mine. In the engine, both pistons are exposed to the same combustion pressure but the force applied to their respective levers differs according to their bore. I arrange the bores such that you get more force and win.

Hopefully this clarifies whats going on for you.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Quote (RodRico)

The faster piston, by definition *because* it's moving faster, has greater mechanical advantage on the output shaft.

It appears to me that you're confusing mechanical advantage with velocity ratio. They are not the same thing.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
JgKRI,

Velocity Ratio and Mechanical Advantage are the same in an ideal system (efficiency=100%). I wasn't analyzing detailed machine performance (and never mentioned efficiency), I was only explaining its operation *in theory*. I'm sorry if you found it confusing.

Rod

RE: I need your vote for a new Rotary HCCI engine !


Rod - I find the whole thing hard to make a judgement on as it is so complex - more and simpler diagrams and drawings are needed - at least by me.

RE: I need your vote for a new Rotary HCCI engine !

Rod. I did not say your explanation makes no sense to me. I said it is flawed.

The statement below tells us everything we need to know. If a single piston is connected to a mechanism which produces the same Volume/theta diagram as your multiple piston layout - the result will be the same. There is no need for the extra complexity. Similarly there is no need to "step" the bores to prevent reversal. The actuation mechanism can be tuned for any desired piston-motion profile so the desired rate of volume change can be produced regardless of bore size. Likewise any volume/theta profile can be produced with a single piston layout (With identical torque profile).

"Everything you need to know is contained in a volume/crankangle diagram regardless of how many pistons are doing the displacement or what their relationship to the crankshaft ("mechanical advantage") is."

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

(OP)
BigClive,

The contest only allows 3 illustrations and 500 words. I'm traveling Europe for the next couple of months, but plan to put up my own website when I'm back home. I'll post a link in the forums when done.

Thanks for taking a look !

Rod

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Gruntguru,

Granted, I could replicate the volume/theta diagram with one pistion, but it would result in autoignition occuring while compression was still increasing just as with commonplace detonation. With two pistons, I can initiate autoignition with both moving in the same direction (toward BDC expansion) as long as I ensure forward torque dominates.

This conversation would be much easier face-to-face over a beer !

Rod

RE: I need your vote for a new Rotary HCCI engine !

One of the problems with HCCI is that autoignition happens whenever it wants to happen. If that happens when the net volume is decreasing (it makes no difference whether it's one piston or two or whether they're the same area) there is going to be net reverse torque while the engine has to continue to compress the already-detonating charge. If this happens soon enough before effective TDC (minimum net volume - doesn't matter how it's arranged) your engine is going to have a bad day.

RE: I need your vote for a new Rotary HCCI engine !

It would have been much clearer if there was a 2-D graph of all the operating characteristics against angle. I can't help but think this was generated at some point, but maybe it's trapped in a spreadsheet.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian,

We don't seem to be converging on agreement. Let's suspend the discussion until I have time to generate some figures annotated with forces.

3DDave,

Yes, it would be clearer. I maintain the whole design and analysis in Excel (from which I export parameters and dimensions to Solidworks). Cams are designed on one tab, side port timing on another, volume and surface area on a third, and PVT thermodynamics on a fourth. There are plots of every aspect over a full cycle in 0.5 degree steps. I'm in Europe at present and can't access them until I get home.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Definitely be easier over a beer. You don't need figures annotated with forces.

Its all in the V/Theta diagram. Likewise if you take the next step and draw a P/V diagram you can see the work and recognise whether it is negative or positive - regardless of how many pistons, what size and which direction they are travelling.

Volume decreasing -> work (and torque) is negative.
Volume increasing -> work (and torque) is positive.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !


Whether it works well or - you can still make a million dollars out of it. Promote it hard enough and somebody will invest - plenty of other people have done this - I can think of half a dozen at least. If you can make a running prototype - even better. Bill Gates has invested more than $30,000,000 (total investments are over $60,000,000) in the OPOC engine - which (to me at least) doesn't seem to be anything new.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Grunt, I have PV diagrams and calculate work in 0.5 degree steps. I suspect the communication breakdown is occuring in my use of terms here.

BigClive, I'm not out to make millions, I'm out to make a better motor. If money comes in as a result, great. I would feel terrible if I wasted others' money on nothing.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Quote (gruntguru)

Volume decreasing -> work (and torque) is negative.
Volume increasing -> work (and torque) is positive
gg, I expect you're referring to the compression and expansion phases.
Yet as you know, work can be negative during {at least part of) the induction stroke (but not necessarily). I can't think of any mainstream examples where the work is positive during the exhaust stroke, though certainly two-stroke extraction systems and exotic race headers strive in this direction.
...Or did I misunderstand something?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: I need your vote for a new Rotary HCCI engine !

Hemi - "I almost added "assuming positive pressure at all times". Should have.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

(OP)
gruntguru,

I had a moment on a computer in London and drew this up for you. It's the simplest explanation I can provide.

RE: I need your vote for a new Rotary HCCI engine !

Ooooh, so it's a variable compression ratio mechanism.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian,

The shaft angle at which it crosses autoignition threshold is optimized using knock sensors much like a spark engine varies ignition timing. Neither is properly called "variable compression ratio."

Rod

RE: I need your vote for a new Rotary HCCI engine !

Rod. I understand your explanation but dispute your statement "P.dV doesn't fully describe the mechanism. Must use F.dX of each piston to fully describe it".

P.dV = F.dX

This relationship applies for each piston individually and for both pistons combined.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Grunt,

Yes, P.dV = F.dX both in theory and in my Excel workbook calculations. P.dV accurately predicts work and performance, but it is agnostic as to the direction of rotation. Each piston generates rotation force in a different direction than the other in my engine, and I need to know what those forces are so I know the engine won't counter-rotate. It eludes me how I would determine that examining P.dV (which represents the bulk condition of the combustion chamber of which each piston is only a part) rather than the P.dX for each piston alone ? Assuming it can be done, why would it be superior given we agree they are the same ?

You have repeated several times that I don't need the two pistons and that a single piston developing the same PV diagram would achieve the same result. I still disagree. Combustion occurs *during* compression in my engine... that's how I eliminate the vulnerability to factors affecting ignition delay that make it so hard for a "normal" HCCI engine to ensure combustion occurs shortly after TDC. If combustion were to occur before TDC in a single-piston engine, it would drive the engine backwards. In my engine, it occurs before TDC of one piston (which would be intolerable if it were the only piston) but not the other, and they are arranged such that the F.dX of the proper piston exceeds that of the other. Granted it's undesirable to continue compression during combustion, but this only occurs during start and warm-up. Once the engine is running and stable, I start shifting the timing of the combustion point near TDC of the ignition piston to minimize compression during combustion.

Rod

RE: I need your vote for a new Rotary HCCI engine !

There is only one TDC. In multi-piston engines like yours, "TDC" is the point at which minimum cylinder volume occurs. If combustion occurs prior to that point, the pressure increase is tending to drive the engine backwards (Work, P.dV, Sum of F.dX, Sum of T.dTheta etc are all negative) - regardless of how complex you design the pistons and actuating mechanisms.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

I don't know it anybody else has all ready said it - but I don't know how wise it is to try and develop a new engine architecture (if that is the word) and an experimental engine process (the HCCI) at the same time. Maybe develop each separately?

RE: I need your vote for a new Rotary HCCI engine !

(OP)
gruntguru,

Top-Dead-Center describes a position. If you want to redefine it as Min-Cylinder-Volume, you can, but then you're left having to come up with terms for positions. No matter, it's semantics. We're just going to have to agree to disagree on the "you could do this with one piston" assertion. It's OK, it happens. I'll come back and let you know one way or the other if and when I get thru prototype.

--------------------------

BigClive,

You're right. I plan incremental hardware builds and will likely get the HCCI working first using stationary cylinders and rotating cams.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Quote (RodRico)

Top-Dead-Center describes a position. If you want to redefine it as Min-Cylinder-Volume, you can, but then you're left having to come up with terms for positions. No matter, it's semantics. We're just going to have to agree to disagree on the "you could do this with one piston" assertion. It's OK, it happens. I'll come back and let you know one way or the other if and when I get thru prototype.

You're correct in that TDC is a defined position of components- but Guru is correct in that this defined position of components is take as the point where cylinder volume is minimized. You are not the first person to design an engine with more than one cylinder acting on a single combustion volume, and those other people use this known, standard definition of TDC as well.

This is an industry convention that, if you want people that design and invest in engines to take you seriously, you should be using as well. You're already doing work to make your documentation align with known conventions, the terminology should align as well. It makes your ideas easier to understand and, more importantly to you, easier to sell.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
JgKRI,

I can't find that definition anywhere. Every one I see is a positional description. Nonetheless, I'll work on a description of my engine that doesn't violate the common use of TDC.

Thanks for the tip.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Who here didn't understand the description of combustion occurring when one piston was past it's TDC point and the other piston was before it's TDC point?

RE: I need your vote for a new Rotary HCCI engine !

I figured that out with the simplified diagram, and established (in my mind) that the adjustable phase-shift between the two pistons is essentially a variable compression ratio mechanism (despite the original poster's protestations), and I understand the point of having a variable compression ratio mechanism if you are attempting to use HCCI since it is one of the few means available to be able to (poorly) control the moment of ignition.

I just don't think the reality is going to work out the way it is imagined. I still consider this to be a SolidWorks exercise backed up by unrealistic theoretical calculations.

RE: I need your vote for a new Rotary HCCI engine !

I remember as a teenager using " Diesel" model aircraft motors ,and having to screw down on the compression screw to get the thing to start , then as the motor warmed up, backing the screw off, since adjusting the compression ratio was the only means of adjusting the timing and adjusting for best rpms, does this engine have that sort of adjustment?
B.E.

You are judged not by what you know, but by what you can do.

RE: I need your vote for a new Rotary HCCI engine !

Evidently, adjusting the phase angle between the inner and outer cams, and therefore the pistons, is intended to have that effect.

I forgot about the model airplane engines - the "glow plug" engines. Those are a simple form of HCCI engine with (manually) adjustable compression ratio in order to coarsely tune the moment of ignition. (I refuse to call it "fine tune")

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian,

You haven't seen my calculations. They are indeed theoretical... as are about 90% of the hundreds of published papers I have read regarding HCCI. I will obviously have a more compelling story once hardware demonstations are completed. In the meantime, I'll take your meaning to be simply, "I haven't seen enough evidence to convince me it will work as claimed."

-------------

Berkshire,

One of the earliest HCCI engines was, in fact, a diesel model engine that used a premixed charge. Read the "History" section at https://en.m.wikipedia.org/wiki/Homogeneous_charge... .

This engine is designed to operate without changing the compression ratio. It does have the ability to shift the relative phase of the two pistons to adjust timing, but this does not neccesarily change compression ratio; I'm really just shifting the whole process such that combustion occurs when both pistons are further along in their trajectory... the expansion piston is further into its expansion stroke and the compression piston closer to its full stroke. This costs a small bit of expansion but reduces negative work by the compression piston and allows the engine to accomodate varying fuel characteristics, engine temperatures, operating load, etc. just as spark advance is used in conventional gas engines.

Rod

RE: I need your vote for a new Rotary HCCI engine !

shift the relative phase of the two pistons to adjust timing, but this does not necessarily change compression ratio
It does actually.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

shift the relative phase of the two pistons to adjust timing, but this does not necessarily change compression ratio
It does actually.


Depends on what the valve timing does.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
guru,

We're debating terms again.

A modern spark ignition engine could delay spark causing combustion to occur later in the expansion stroke. The net result would be a reduction in compression ratio. Modern spark engines don't generally do this, however. Instead, they adaptively move spark timing to try and hold it at the optimum position at the start of the expansion stroke. The fact that they *could* delay the spark enough to yield reduction in compression ratio doesn't make them variable compression engines.

Like a spark engine, my engine *can* vary it's compression ratio, but in actual operation, it has one and only one compression ratio, that required to cause auto-ignition. Any more and it's wasted energy, any less and it doesn't work. At start-up, it's uncertain what compression ratio is necessary, so the engine is designed to ensure the proper value falls somewhere in the range of the compression piston stroke. The margin used to encompass uncertainty inevitably leads to some "spare" compression, meaning the compression piston continues compressing after combustion, resulting in lost efficiency. As soon as the engine fires, it delays the start of the compression piston stroke relative to the receding expansion piston to shed the "spare" compression. The compression ratio at which combustion occurs is constant within a narrow window regardless of when it occurs. If you want to focus on one limited case, start-up, you could say the engine is variable compression. It is, however, operating at a fixed compression ratio with very little variation over time the overwhelming majority of the time.

Note, by the way, that the optimization of operating point after start up can also be effected using the waste-gate on the output of each supercharger piston. This is, in fact, the cheapest and simplest way to accomplish the desired state. Though its latency is greater than that of the shaft phase adjuster, the rate of variation while running is low, so I'm pretty confident this method will be determined sufficient during testing. Many engines employ waste-gates, as you know, and they effectively change compression in aircraft engines in order to compensate for reduced air density at altitude. We don't call *those* engines variable compression either.

Rod

RE: I need your vote for a new Rotary HCCI engine !

I suspect you will find that the "one and only one compression ratio, that required to cause auto-ignition" will be different depending on altitude, intake air temperature, lambda, residual exhaust percentage, temperature of surfaces in contact with the charge, and fuel properties. Lambda, residual exhaust percentage, and temperature of surfaces in contact with the charge are dependent on how much load is on the engine. The temperature of surfaces in contact with the charge is additionally dependent on HOW LONG a given load is on the engine.

RE: I need your vote for a new Rotary HCCI engine !

'Compression ratio' has nothing to do with when combustion does or doesn't occur.

No one that designs engines uses the term 'compression ratio' to describe the combined net effect of mechanical dimensions, valve event timing, and ignition timing in the way that you're using it.

You're not having a 'debate' about the meaning of compression ratio- you're using the term incorrectly.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian,

I'll post a link to a paper on HCCI response to the conditions you mention tomorrow (gotta dig the link back up). As I recall, it shows HCCI at high intake pressure to be less sensitive to many of the conditions you mention than one might expect. I'll elaborate when I post the link.

-----------

JgKRI,

You apparently aren't familiar with HCCI. "Homogeneous Charge" (HC) means fuel and air are premixed at intake (like a gasoline spark engine). "Compression Ignition" (CI) means the mixed charge is ignited by compression. Compression has *everything* to do with when combustion occurs in an HCCI engine.

We weren't debating the meaning of compression ratio. We were debating whether my manipulation of piston stroke phase is rightly called a "variable compression ratio" process.

I never said valves had anything to do with compression ratio in my engine (though they cetainly can in some engines... consider the modern direct injection engines with variable valve timing that hold the intake valve open in the early portion of what would normally be the compression stroke to reduce intake volume and compression while increasing expansion ratio). Note, by the way, that my engine is a uniflow scavenged opposed-piston two-stroke (ala Junkers) augmented with rotary side ports. It uses ports, not poppet valves, and it has no means to vary port timing or duration.

Rod

RE: I need your vote for a new Rotary HCCI engine !

I am intimately familiar with HCCI. I've bit my tongue a lot in this thread, mostly because Brian has frequently said very nearly exactly what I would've said had he not posted first.

The point I was making is that your interpretation of what the term 'compression ratio' means is incorrect.

I said this:

Quote ('Compression ratio' has nothing to do with when combustion does or doesn't occur.)


Which you apparently interpreted as 'combustion timing of compression ignition engines is not affected by compression ratio'.

That statement would be incorrect, but that isn't the point I was making

The point I WAS making is that compression ratio is a mechanical characteristic, dictated by geometry. Theoretical compression ratio by piston bore/stroke and combustion chamber size; actual or dynamic compression ratio by piston bore/stroke, combustion chamber size, and timing of valve events.

Changing ignition timing does not change compression ratio, period, regardless if the engine is an HCCI design or not. If you think it does you're simply not talking about compression ratio.

The only spark ignition engines that can change compression ratio are those with complicated mechanical arrangements that change some or all parts of the geometric factors listed above.

If you're changing BDC or TDC volume, you're changing compression ratio, unless you're doing it in a way maintains the relationship between them.

It's a little pedantic to go back and forth about terms in such detail- but if you want people to understand your concept, and you want to appear to know what you're talking about, you can't redefine technical terms on the fly.

RE: I need your vote for a new Rotary HCCI engine !


"Glow-plug" model engines don't have adjustable CR - only model "diesel" engines do - the CR can be as 40:1. The model "diesels" are notably more fuel efficient and quieter than "glows" but usually less powerful.
A glow engine with adjustable CR would be quite possible - but I have never heard of it being done.

RE: I need your vote for a new Rotary HCCI engine !

Unlike the silly argument over the use of TDC, you used the term compression ratio wrong. Compression ratio IS exactly as described by jgKRI.

Quote (jgKRI)

The point I WAS making is that compression ratio is a mechanical characteristic, dictated by geometry. Theoretical compression ratio by piston bore/stroke and combustion chamber size; actual or dynamic compression ratio by piston bore/stroke, combustion chamber size, and timing of valve events.

What you wrote here

Quote (RodRico)

A modern spark ignition engine could delay spark causing combustion to occur later in the expansion stroke. The net result would be a reduction in compression ratio.

is completely wrong. Spark timing does not change the compression ratio. You probably could have said that retarding the spark timing has the same effect as reducing the compression ratio. You certainly can't say that retarding the timing reduces the compression ratio.

And your engine is variable compression ratio.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian,

The paper I was referring to is titled "A reduced chemical kinetic model for HCCI combustion of primary reference fuels in a rapid compression machine" and it's available at http://citeseerx.ist.psu.edu/viewdoc/download?doi=... . Figures 8 through 13 figure prominently in my thinking. Note in reviewing this paper that my intake is at about 1.0 MPa and 770K at the start of the ignition process. By the end of the process, motoring pressure and temperature are around 1.4 MPa and 830K respectively. With this input state, predicted ignition delay is under 1 degree at 7800 RPM. At these given octane, intake pressure, and intake temperature, the chemical reaction rates are extremely fast and don't vary much over load. Altitude certainly affects the input state, but I regulate the supercharger piston output pressure/temperature via a computer controlled wastegate. Cylinder temperature should come up quickly and fluctuate pretty slowly due to the thermal mass of the rotor. All of this will be the focus of the next phase of work. My consultant will be building a multi-physics model (CFD, heat transfer, chemical kinetics, etc.), and engineering will construct controlled experiments to ensure everything tracks expectation (within reason). We'll iterate this process until we're happy then go into prototype to start peeling the next layer of the onion.

-------------------------------------

jgKRI,

Sorry for misunderstanding your comment. My engine is, in fact, "variable compression" during the very short transition period between cold start and run state. Making a variable compression engine with opposed-pistons and a third supercharger piston is not complex (or at least not much more complex than building the same engine with fixed compression). There are two ways to accomplish this: Manipulate the supercharger piston's wastegate to change intake charge pressure/temperature, or change the phase of the two cams. The engine already needs a wastegate for other reasons, so manipulating that wastegate is cheaper and is the preferred approach. Nonetheless, let's look at how one can make a comparatively simple and robust variable compression engine using opposed pistons alone without a supercharger piston...

Forget my cams for a moment and just imagine the two opposed-pistons are on separate crankshafts. If the two cranks are in phase, maximum compression will occur when both are at maximum stroke. If they are 180 degrees out of phase, the compression ratio will be zero as the pistons will just move a fixed volume up and down in the cylinder. The phases between 0 and 180 degrees yield different compression ratios. The mechanism to control the phase of one crank relative to the other is where the mechanical challenges come in. My engine, however, doesn't use crankshafts, it uses cam shafts, and their relative phase can be adjusted using a cam phase adjuster identical to those used in several modern engines (i.e. Ecotec). If I have trouble with attaining the desired result via manipulation of the wastegate, I will use the cam phasor approach.

My engine has more compression than needed to initiate autoignition even under lean cold start conditions. The first few combustion cycles are inefficient because compression continues after combustion. I eliminate this inefficiency once running by dumping some supercharger pressure or by shifting the relative phase of the two cams. Once established, this setting should change very slowly (certainly not cycle to cycle) per my response to Brian above. Thus, once running in steady state, compression ratio remains stable.

--------------------------------

BigClive,

See my discussion above for two comparatively simple ways to effect variable compression ratio in an opposed-piston engine. One requires presence of a supercharger, the other does not.

The reasons diesels produce more torque and better efficiency are related, as you know... High compression ratio yields efficiency and torque but the long stroke of the engine (and, to a lessor degree, the time to complete fuel injection) yields detrimental impacts on RPM and power. I address these issues in two ways. First, the radial arrangement of my cylinders naturally facilitates a supercharger piston bore that is much larger than the bore of the other two pistons which form the combustion chamber, and this facilitates very high compression ratio with little stroke. Second, HCCI ignition delay and heat release rate are extremely fast when the intake pressure and temperature are as high as they are in my engine (see the paper I linked to in my response to Brian above). By my analysis at 7800 RPM, combustion completes within a degree of crossing the autoignition temperature. This rapid combustion also improves efficiency as it is about as close to constant volume as possible using petroleum fuels. HCCI also, of course, improves efficiency simply due to its lack of a flame front. Watch the video at https://www.youtube.com/watch?v=oNCBbcINHuk to get an idea of how much faster HCCI is than spark combustion with a flame front (imagine how much faster than a diesel fuel spray it would be). The rapid heat release does, of course, come with a price. It yields extremely high combustion pressures. I had to downsize the pistons and use steel to get stresses in bounds with margin. The downsized pistons cost me a bit of efficiency, but it appears the other gains outweigh the cost of the small cylinders with high surface area to charge ratio.

Rod

RE: I need your vote for a new Rotary HCCI engine !

No harm done on the misunderstanding- your interpretation of my comment wasn't what I intended to convey, but it was a reasonable interpretation of the actual phrasing I used. My comment was a little bit vague in terms of what I actually meant, which is why I felt I should explain.

Back to technical discussion...

How exactly are you calculating compression ratio?

Quote (RodRico)

and this facilitates very high compression ratio with little stroke

This phrase is.. confusing.

I also noticed when I looked at your submission the first time, that your stated compression ratio is very high and the stated expansion ratio is lower than I would have expected given the quoted compression ratio.

So.. How exactly did you calculate this theoretical 70:1 ratio?

And is that compression ratio the value you are using to calculate efficiencies? Lumping the various stages of your combustion process together seems to me to be a little dubious.

I understand your combustion phasing concept; what I don't understand at this point is how the combustion volume and 'supercharger' piston interact.

If the 'supercharger' piston is never exposed to combustion pressure, than its expansion does not contribute to positive work- in fact it represents pumping loss and thus negative work- in which case it does not contribute to dynamic compression.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
LionelHutz,

Imagine you're doing thermodynamic analysis of a classic four stroke engine. What compression ratio do you use in working through to efficiency ? Do you use that establihed by the compression stroke or that at time of combustion ? It matters.

I apologize if I have deviated from normal use of some terms. That being said, are you trolling on terminology or truly trying to understand how my engine works? If it's the former, I will stop responding to you. If it's the latter, please read everyting and tell me what you need clarified.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Regardless of terminology used, how is the voting going RR?

RE: I need your vote for a new Rotary HCCI engine !

You have to use terminology that is consistent with what is used in industry and in combustion-engine research if you want to be taken seriously.

Obviously, in a real internal combustion engine, the "instantaneous", or "effective", compression at the moment that a given fuel particle burns is what effects the thermodynamic analysis and, at least in theory, the total is the integration of that over the entire fuel mass. But this isn't what is normally considered to be the "compression ratio". The nominal compression ratio is the ratio of maximum chamber volume to minimum chamber volume - period. (No consideration of moment of ignition or speed of combustion.) The effective, or dynamic, compression ratio is the ratio of trapped chamber volume (at the moment that it becomes trapped - whether by valve closure in a poppet-valve engine or port closure in a piston-ported engine) to minimum chamber volume - period. Again there is no consideration of the moment of ignition or speed of combustion. Forced induction is not taken into account.

I think we could use a better diagram of how the gas-flow works relative to the motions of the various pistons, ports, and valves. Focus on one cylinder's piston motions.

RE: I need your vote for a new Rotary HCCI engine !

Rod,

"Figures 8 through 13 figure prominently in my thinking. Note in reviewing this paper that my intake is at about 1.0 MPa and 770K at the start of the ignition process. By the end of the process, motoring pressure and temperature are around 1.4 MPa and 830K respectively. With this input state, predicted ignition delay is under 1 degree at 7800 RPM. "

The paper gives curves for initial pressures up to 0.1 MPa, so you are extrapolating the ignition delay curves from those shown (typ. 1 to 10 ms) to your expected pressure. By my math, (7800 rev/min)*(360 degrees/rev)/(60 sec/min) = 46,800 degrees/sec, or the reciprocal about 2x10-5 seconds per degree. I'm not sure I buy a 5 orders of magnitude reduction in ignition delay for a one order of magnitude pressure increase? Can you explain your reasoning here?

RE: I need your vote for a new Rotary HCCI engine !

(OP)
btrueblood,

I extrapolated the curves of Figure 8 for PRF63, the midpoint betwwen PRF75 and PRF50. Note PRF50 looks to average around 1 ms, so I think your orders of magnitude is too large. Anyway, I contacted the author to see if he had data further down and he replied he did not. I asked if he felt extrapolation would be valid and he replied yes, for first order estimates. I have hired a consutant experienced in all aspects of combustion (worked on Skyactive team at Mazda) to check the fuel characteristics in his chemical model and review my thermodynamics work. He should be done soon.

Rod

RE: I need your vote for a new Rotary HCCI engine !

(OP)
djhurayt,

Not as well as I hoped. All of my contacts are engineers, and most said it looked interesting, but they couldn't vote for it until they did analysis. LOL! Typical engineers! The guys pitching free energy machines obviously don't suffer the same problem. No matter. Votes and views can get me a small prize, but the big one is determined by a panel of judges. Last year's winner had fewer votes than I currently have.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Quote (BigClive)

Glow-plug" model engines don't have adjustable CR - only model "diesel" engines do - the CR can be as 40:1. The model "diesels" are notably more fuel efficient and quieter than "glows" but usually less powerful.
That's consistent with the model (airplane) engine landscape when I was fooling around with them in the 70s. By then, the diesel variant was obsolescent, I guess. I never saw one first hand, but the technology was still well known at the time. The sealing mechanism for the variable CR screw boggles the mind.

From a thermodynamic perspective, there are at least two additional interesting volume ratios in addition to the mechanical compression ratio. One has been discussed already, the "dynamic compression ratio". The other is effective expansion ratio (EER). Engine layouts and combustion systems that can at least partially decouple these two ratios are interesting, because a high EER is always beneficial for efficiency, while keeping the dynamic compression ratio to a lower value is beneficial for reducing peak temperatures and hence NOx formation, in all engines; and thereby also adding knock margin, in spark ignited engines. The Miller cycle concept is probably the best known and simplest engine layout commercially applied today that achieves this goal. Lest anyone think I'm ignorant of the Atkinson cycle, as applied today it is simply a variation on the Miller theme, albeit that Atkinson predates Miller.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: I need your vote for a new Rotary HCCI engine !

Atkinson/Miller cycle is relatively simple to emulate with a 4 stroke engine of conventional layout ... either close the intake valve really early (VW) or really late (Toyota) and make the mechanical compression ratio quite high. The effective compression ratio is lower (i.e. "normal") because part of the charge either never gets into the cylinder to begin with (early intake valve closure) or part of it gets pushed back out again (late intake valve closure).

It's not normally so easy if you use piston porting, but I wonder if this is what our OP (original poster) is attempting to achieve but has not been able to explain correctly. If the piston that is handling the exhaust ports is bigger in displacement (either via bore or stroke) than the one that is handling the intake ports, AND the piston that is handling the exhaust ports "leads" the timing of the piston that is handling the intake ports (i.e. exhaust opens first and closes first, intake opens second and closes second but by which time the "big" exhaust-side piston has come partway up) it will have the effect of a two-stroke Atkinson cycle.

I read the paper that was linked to which concerned HCCI combustion in a rapid-compression device. The long delay between initiation of slow combustion and the "explosion" (~ 10 ms in some cases) is something of an issue - in an engine spinning at just 3000 rpm, the expansion stroke is done in that time. The variable amount of that delay depending on fuel characteristics and intake air temperature is another headache to deal with. If that's the situation with HCCI combustion, I don't see much hope for it (and it may be why, since that paper was published in 2003 and it is now 2017, we have not seen HCCI in production yet). I realize that the delay can be shortened by overcompressing, but then if operating conditions (fuel, temperature, load) change so that the delay is less, combustion will happen before TDC and peak cylinder pressure will skyrocket. I don't see a hope for this without variable compression ratio of some sort ... Which the original poster's concept design is capable of doing, even though the original poster himself is denying its use smile

RE: I need your vote for a new Rotary HCCI engine !

Hemi - most of the sealing of these small model engines is by the excess oil from the fuel mixture after combustion. These engines are notable "droolers" of oil from the exhaust ports.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Guys,

I found an old movie I made showing engine operation on my phone. It doesn't reflect the current configuration in a couple of ways (there are no cam valves for the intake and scavenge paths as each now has its own side port, and all of the numbers relate to a different instantiation of the engine), but it should help you visualize what's going on. I'll be updating the movie when I get back to the states to reflect the same configuration as shown in the contest entry.



Someone asked how I calculated compression and expansion ratios and suggested I use them to calculate performance.

I don't use compression and expansion ratio in my performance calculations. I calculate in-cylinder port state (intake, exhaust) as well as side port state (pump out, scavenge and intake in, exhaust) along with volume, pressure, temperature, ratio of specific heats, and work in 0.5 degree steps. I then sum work and derive performance from there.

I only *report* compression and expansion ratio. I calculate compression ratio by dividing the max volume of the air pump by the volume at first burn and expansion ratio as the volume when the exhaust side port first opens divided by volume at first burn. The calculation of compression ratio is pretty course; it doesn't include incremental losses as the gas moves through all the ports from the air pump to the combustion chamber. The expansion ratio number should be solid as it involves no transfers.

Someone said my pump piston has a cost. Of course it does. I calculate a loss of 1.8 joules over that piston's cycle. Another 5.2 joules is lost between the compression and expansion piston, and 18.8 joules gained during combustion/expansion. The result is a net gain of 11.8 joules out from 25.1 joules of fuel energy in.

Rod

RE: I need your vote for a new Rotary HCCI engine !

To me, that looks like a sealing nightmare, a gas-transfer nightmare, a heat-loss nightmare, and a friction-loss nightmare all rolled into one. Maybe I'm wrong.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Brian, It's not going to be easy, that's for sure !

Greg, Every design goes through the steps I'm taking. Nobody exits System Concept Review saying "were're done!" All they can say is "we haven't found anythng in concept development that indicates it won't work, so we're going to proceed into preliminary design."

RE: I need your vote for a new Rotary HCCI engine !

The thing is anything that looks like a pump can be made into an engine. This not exactly earth shattering revelation means that you can start from almost any pumping concept and then try and make an engine of it. Thermodynamics give some pretty harsh limits on what you'll be able to achieve efficiency wise, and the other operating parameters are more a matter of detail than concept. Read up on this one, its been running for years http://www.revetec.com/latestnews.htm

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Greg,

I guess you missed the part where I described what thermodynamic and mechanical analysis has (and hasn't) been completed thus far. I have hired an expert in combustion, heat transfer, chemical kinetics, etc. to reveiw my analysis. If it passes muster, I'll proceed to full 3D multi-physics analysis. Only after that will I cut metal.

I'm fully aware that many have tried and failed. I examined the many engines that came before including Wankel, Revetec, Duke, OPOC, Scudiere, Nautilus, Achates, etc. I wouldn't have taken it this far if I didn't believe it offers something different and valuable. Mine is comparatively simple and offers efficiency and power density of a turbofan.

I have long experience in risk driven technology development. Some pretty radical concepts that few experts beleived were possible suceeded, and a number that seemed simple failed well into development due to unknown unknowns. My engine has passed my own thermodynamics and stress analysis. If it fails that of my consultant it stops. If it fails in 3D multi-physics, it stops. If it is too costly to manufacture it stops. If at any point it fails to offer performance vs cost value at least twice that of competing engines, it will stop.

I have no illusions that my engine is a slam dunk. Heck, even if it *does* work as well as hoped and proves to be manufacturable and affordable, it may be too late to suceed commercially in a world where many see only electric vehicles.

Rod

RE: I need your vote for a new Rotary HCCI engine !

2
I believe the point that many in this thread are attempting to make Rod is that you are going about this contrary to accepted engineering practice while lecturing others on basic concepts and verbiage which you are mistaken about. In engine development an initial combustion analysis via CFD is literally the first step, it drives hardware design, gives a rough estimate of possible performance, and also lends credibility to your design. Without this you are still in the realm of the many hobbyist dreamers that attempt to break into engine development every year, insisting on all manner of free energy and easy efficiency. I am sure you put a lot of effort into your paper study however without correlation to significant testing its highly unlikely to even get you in the ballpark due to efficiency losses and combustion trends beyond your current understanding and analysis capability. JMO as someone who works in this niche but you are still at step zero in a very long process.

RE: I need your vote for a new Rotary HCCI engine !


Roller followers might be better than your "plain" followers.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
CWBI,

Thank you for pointing that out. As I noted in prior comments, the next phase of development will be 3D Multi-Physics modeling encompassing CFD, combustion, heat transfer, etc. Perhaps I should have started with 3D Multi-Physics. It's time consuming and costly, however, so I started with basic feasibility analysis of first order thermodynamics, heat transfer, materials and stresses.

Rod

RE: I need your vote for a new Rotary HCCI engine !

I haven't seen anything that goes past this being yet another 3-D CAD experiment. So, I'm really not seeing much else useful to comment on besides your poor use of terminology.

RE: I need your vote for a new Rotary HCCI engine !

How detailed have your gas flow analyses been to this point?

Your ports appear to have a very high area/perimeter ratio. Have you checked for localized supersonic limits on flow?

Checked for effects on charge homogeneity and droplet size during pumping through these highly restrictive orifices?

RE: I need your vote for a new Rotary HCCI engine !

(OP)
JgKRI,

Port sizing was rudimentary, and I have done no spray analysis. My consultant is performing only first order analysis at present, suitable for a sanity check. Assuming it checks out, I'll fund him to do full CFD of gas and spray along with combustion, heat transfer, etc. I hope to offset the cost of that work by winning the contest mentioned in my original post. I'll fund it out of pocket if I don't win. I was fortunate in my career as an engineer, retired early, and can afford to carry this to prototype if need be. I'd rather not, however.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Just wow ! I see some critical heat treated hard parts with high contact stress, and a device that will be in need of constant low hour overhauls, and super costly parts to keep them in operation. Its kind of funny all the ideas that attempt to replace the crank chain in the reciprocating engine, and how it hasn't been done and will not be done until everyone settles on electric motors. Its just not me, but I vote for the electric motor its just way less monkey motion than that engine design and little to none wear parts that need constant attention.

RE: I need your vote for a new Rotary HCCI engine !

IC reciprocating engines, turbines, and electric motors each have their strengths and weaknesses, and are applied accordingly.
I don't expect to see an electric motor generating electric power anytime soon. ponderwink

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Lithium ion battery: 0.8 MJ/kg, motor efficiency: 95%
Diesel #2/JP-8: 45.5 MJ/kg, engine efficiency: 40%
Try to design a drone to carry a 1,000 pound payload for 24+ hours.
Electric needs better batteries to compete in aviation.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
At under 20,000 feet so radar and cameras can be used to observe the ground?

RE: I need your vote for a new Rotary HCCI engine !

Yup, and they're doing it with a traditional layout that will go down a standard production line and will be completely familiar to any technicians that may have to work on it.

I've known about this for a while. Other manufacturers have been attempting to get HCCI to operate over the whole speed and load range. Mazda did the common sense thing, "screw it" just put in spark plugs and use them as a redundant ignition source when the engine doesn't feel like operating in compression-ignition mode.

RE: I need your vote for a new Rotary HCCI engine !

Greg,

They are working on a plane that can reach 70,000 feet without a propulsion system, with a pilot, while not weighing less than one.

Thus far, high-endurance electrical aerial vehicles have been very limited. The Zephyr has no cargo capacity to speak of, low maneuverability, limited scaleability. Electrics are far from general purpose and occupy a niche similar in size to LTA.

RE: I need your vote for a new Rotary HCCI engine !

Being an engine person my vote for electric motor was against this engine idea, not against ICR engines.
Hemi, Lincoln built a welder where the motor did run a generator for power, and there are many other such examples for generating power at other than 60Hz. When fuel cell technology is better they will generate the electricity.
Again has the TBO for this engine on paper been addressed?
I would like to know what the HP requirement is for this special drone engine?
As long as there are no special emissions requirements and restrictions it will be easier, to get the efficiency and power needed. Approximately what is the fuel load allowed in the drone?
So is there a video of a model of this engine that you propose running? If there are no running examples you are looking at many hours of time spent to find out it may not be feasible. I personally feel the materials will not last from the stresses. Its difficult to get solid tappets to last, how do you expect to transfer major HP through that cam and keep it lubricated? The side loads on the pistons and lack of advantage that recip crank arm has by using a cam ramp? ]
In this engine design you have lots to learn, and won't happen till you make the metal parts and give it a go.

RE: I need your vote for a new Rotary HCCI engine !

I don't think you can call this engine "rotary" as the pistons undergo cyclic acceleration. In a rotary piston engine the pistons travel in a circular path and only undergo a constant centrifugal force.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Enginesrus,

The targeted drone is the RQ-7. It currently uses the AR-741 Wankel producing 38 HP at 7800 RPM. The Army issued an RFI in 2016 seeking an improved engine. You can google the drone and engine to learn more. There are no emissions requirements in the military application. Note the pistons in this engine are are under constant preload, and FEA has been completed on the preliminary design with normal 4x safety factor. There are no side loads on the pistons. Lateral thrust is from the camshaft behind the followers to the slot in the rotor. The engine is not built or running yet. It is still in preliminary anaysis. I hope to commence full 3D analysis with CFD, chemical kinetics, and heat transfer this year. I am hoping to use the contest prize money to fund that analysis, but will fund it myself if need be. Yes it will be a long slog, and it may end in failure, but I'm retired and have plenty of time and money.

BigClive,

You lost me when you said my engine is not like a rotating cylinder radial piston engine. Other than the fact I replace the crank mechanism with cams, I see no difference. Perhaps you can clarify further.

Rod

RE: I need your vote for a new Rotary HCCI engine !

There will be side loads on the pistons - even if the cam is frictionless the force is applied to the piston normal to the cam contact.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

(OP)
grunt,

I'm probably screwing up terminology again. There are large lateral forces on the assemblies. The lateral travel is constrained, however, by support structures; the follower that's integral to the small inner piston rides between supports, and the outer cam shaft rides in a slot of the rotor. The intent of these supports is to take the load related to the cam so the piston rings aren't compressed against one side of the cylinder. The figures below show the assembly of the rotor and expose the supports around the inner piston cam follower as well as the cam shafts of the outer piston assemblies which pass through slots in the rotor. Note the supports around the inner piston follower are the soft metal of the rotor body while the slots containing the cam shafts have polished tool steel inserts. Also note the center of mass of the outer piston assemblies is centered on the cam shaft.




Rod

RE: I need your vote for a new Rotary HCCI engine !


To continue on the theme of whether the engine is rotary or not: - with the use of a four-cornered cam ring the pistons wouldn't follow a circular path - thus they would accelerate back and forth. Having the pistons travel in a circle would be my definition of a "rotary" engine. If you had just one circular cam ring - then the engine would be rotary.
I may have missed it - but just why are you proposing a rotating-block engine? Rotating block engines (even if they are true rotaries) have many disadvantages and very few advantages.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
BigClive,

I see what you're saying, but personally feel it's a legitimate rotary. Patents are filed with classifications to help folks find those that are relevent to a field. Each classification is accompanied by a description, and mine complies with the description of a rotating cylinder, radial engine. If you look for other engines in that class, you find the classic radial rotaries of years gone by.

Rotating cylinder engines do have one key advantage... only one fuel injector is needed per cycle to service any number of cylinders. Though I show 12 cylinders in the illustrated instantiation, there are only four fuel injectors (one per complete cycle separated by 90 degrees). The mechanical aspects are also simpler with a rotating block. Visualize how to spin that central shaft *and* the outer cam rings while plumbing air passeges from the outer cylinders to the inner *and* incorporating an electric motor/generator into the engine. It's a complicated mess!

Traditional rotating cylinder engines have two key disadvantages IMHO. The largest is getting the devices that initiate combustion (spark plug or fuel injector) into the cylinders. The common approach is to spin the spark plug/fuel injector with the cylinder or to have the cylinders rotate past a stationary "head." The former leads to challenges in passing fuel or spark energy to the rapidly rotating spark plug or injector while the later creates complications in high pressure seals and combustion. I sidestep these problems using HCCI.

Another problem with rotating block engines is, of course, centripetal forces and rotational inertia. Centripetal forces are included in my stress analysis which looks OK, but it *will* limit the diameter/RPM of the engine... The 7800 RPM engine doesn't scale well up to larger sizes, for example. Rotational inertia will certainly affect acceleration, but the rotor is made of aluminum or titanium (depending on RPM) and doesn't weigh any more than flywheels and balancers commonly found on 100 HP class engines. In versions equipped with the electric motor/gen, I will also have the torque of the electric motor to aid acceleration.

Bottom line: the rotating block just emerged as the cleanest answer given use of HCCI. Note that my patent explicity states that the core claims apply to an engine with a rotating *or* stationary block (as do most patents in this class).

Rod

RE: I need your vote for a new Rotary HCCI engine !

Very expensive and difficult parts to manufacture. And many wear points to lubricate, and saying nothing about the
lack of proper tribological design for the bearing areas. So what is max weight the engine design can be, and hp? Maybe I should enter, how and where to do that? My design has way less parts.

edit "the -->to"

RE: I need your vote for a new Rotary HCCI engine !

RodRico,

The engine you are competing against, the successor to the Midwest/Norton rotary , basically only has 3 moving parts not counting the accessories. and still costs over $10,000.0 , with all of the parts in your engine , how are you going to get to a manufactured cost that competes with this engine ?
If not the only other path is efficiency.
B.E.

You are judged not by what you know, but by what you can do.

RE: I need your vote for a new Rotary HCCI engine !

(OP)
enginesrus,

How can you assess my tribological design based on the information provided? You must be a seer! :)
Yes I have a lot of parts. I have a lot fewer than a modern 6 cylinder four stroke, however. Note my pistons are about the same weight as valves in a conventional engine and are driven by cams.
Estimated performance is given at https://contest.techbriefs.com/2017/entries/aerosp.... My preliminary analysis shows 95 HP at 7800 RPM in 31.4 pounds including all accessories.

Entry for this year's context closed on 1 July. You should enter next year!

I love looking at engine concepts! Is yours online anywhere?

-----------------------------------------------------------------------------------

berkshire,

One reason I chose the military drone market as an entry point is their tolerance for cost. They currently pay over $25,000 for a 100 HP engine not including the accessories that are built into my motor. The real challenge will be in the commercial markets such as the 15 million unit per year scooter market (which I will target with a 6 cylinder version running in LTC mode producing about 1 HP/LB). My engine will be built on a 5 axis CNC machining center. Using this kind of technology, set-up is a major factor in cost, so the number of *unique* parts has great bearing. Though I have many parts, I don't have many unique parts, so I'm hopeful. I will certainly develop cost models before seriously considering markets beyond military UAVs.

Sorry for the delay in responding... I just got back from Europe and have been catching up on other things!

Rod

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Bershire,

I did a bit of research on the Midwest/Norton rotary. Wikipedia has scant information (https://en.wikipedia.org/wiki/MidWest_AE_series#Th...), but does mention the Midwest is closely related to the Norton for which more information is available. Here's a picture of the Norton's guts...



I see a lot more than three moving parts in that image, and that's of the engine alone sans accessories such as the oil pump, starter, and generator. Eliminating accessories from the comparison is silly IMHO as they are all part of the final system. My engine as shown includes all necessary accessories except the battery and fuel tank, and I feel part of its attractiveness is the synergy attained between the accessories and the ICE components proper. Granted, my engine isn't running yet (much less demonstrating the desired performance), but the *concept* stands up well under comparison in my humble opinion.

In prior comments I mentioned that my original objective was to fix the shortcomings of the Wankel such as in my 1993 RX-7. The more I learned, the more dire the outcome seemed; while it's fantastic in terms of power per unit weight and volume, the engine just has too many shortcomings where emissions, reliability, and efficiency are concerned. I won't bother detailing the issues here, I'll simply point you to this excellent report by the Army Research Lab: http://www.arl.army.mil/arlreports/2011/ARL-TR-554.... The report was generated as part of the Army's long history working to improve the Wankels used on air vehicles such as the RQ-7 drone. While the titular subject of the report is heavy fuel operation, it contains a lot of great discussion of the Wankel in general.

Rod

RE: I need your vote for a new Rotary HCCI engine !

Rodrico,
The AR-741 Wankel that you cite was developed from the Midwest rotary which in turn was developed from the Norton rotary . I should of course mentioned that the 3 moving parts are of course assemblies not just individual components.
B.E.

You are judged not by what you know, but by what you can do.

RE: I need your vote for a new Rotary HCCI engine !

<<<<<I have a lot fewer than a modern 6 cylinder four stroke, however. Note my pistons are about the same weight as valves in a conventional engine and are driven by cams>>>>

So then your pistons are driven by cams? Most IC engines I have been around the pistons are being driven by combustion pressure and then the pistons are driving a crankshaft. Oh a special note the radius of the crank throw turns that pressure to torque. A cam in a normal piston 4 stroke engine is something you try not to over load with pressure.
It will not matter what your cam follower system is that is going to be the weakest link and along with the crazy high pressures needed to create torque into that cam system. So how is the proto type going? Any parts made yet?

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Enginesrus,

LOL! You're the master of syntax!

In the spirit of your piston comment...
What drives *your* pistons during start, compression and exhaust?
What parts *do* you try to overload?
Torque = BMEP x Displacement x PPR/75.4

Prototypes follow analysis. The cam loading is easy to assess, and it's fine. My consultant (who has worked with Mazda, Honda, and Liquid Piston during engine development) just sent me his mid-task report a few days ago in which he performed feasibility and risk assessments. He found no mistakes and his error analysis said I was with a few percentage points one way or the other. His biggest concern was port fill time which drove him to suggest I increase port height. I asked whether this engine was viable and worth pursuing further, and he replied in the affirmative adding "this is pretty exciting." He's now moving on to independent bottoms up analysis just to be sure. We also discussed next steps, and I am now making the simplified break-out models we'll need for 3D analysis (chemical kinetics, CFD, heat transfer, cooling). Only once everything is tweaked up in the 3D analysis will metal be cut, and it won't be an engine, but critical experiment fixtures, instrumentation, and engine subsystems. I'll start building the shop and my son (also an engineer) will be tweaking the mechanical design for manufacturability while our consultant is working the 3D analysis. I expect experiments and design refinements will occur in 2018 and the first prototype in 2019.

Rod

RE: I need your vote for a new Rotary HCCI engine !

May I suggest some some 1D modelling of a single cylinder? Some of the innovative features of your engine are based on invalid assumptions around P/V and T/Theta. (The contra-pistons, stepped bore and different stroke/piston motion are unnecessary)

A lot of effort goes into dead-end designs for lack of basic consultation and intervention at the concept design stage. OPOC and Achates are good examples.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

(OP)
gruntguru,

My consultant identified nothing wrong in my work, and he's quite experienced; he helped design Mazda's SkyActive, LiquidPiston's engine, and an unspecified engine for Honda. He's also worked with a number of well known shops including WERC, ESI, CdAdapco, Mahle, and AVL. That being said, we *do* plan to do 1D followed by 3D analysis. At the bottom of this message is a screen grab of the plan (sans hours and costs) we're working to.

My consultant has checked all my work and found it to be complete and "within plus or minus a few percentage points." As I noted, he's currently doing an independent top-down analysis just to be sure. Assuming his conclusion regarding my analysis holds up after he finishes his own top-down analysis, we'll move into more sophisticated modeling and simulation.

No offense, but I'm going to have to go with my consultant's opinion over yours. It's what I pay him for. He has the entire set of design and analysis files which you don't have. I'm confident you know what you're talking about when it comes to engines, so I assume the errors are being introduced in my poor communication of the design.

FYI, I can't find a free copy of this paper, but you might find Morton, R., Riviere, R., and Geyer, S., "Understanding Limits to the Mechanical Efficiency of Opposed Piston Engines," SAE Technical Paper 2017-01-1026, 2017, doi:10.4271/2017-01-1026 illuminating. In this paper, the authors (who work for Volvo) say:

"In the case of the opposed piston engine, it is important to keep in mind that the P-V diagram applies to the gas volume, while the standard indicator calculations compute the volume from the piston displacement. In conventional single piston architecture, the change in volume is simply cylinder area times piston displacement. In the opposed piston design, the two pistons may be moving at different rates and directions, but there is only a single working volume and pressure. The indicator diagram and P-V diagram are different in this case... The difference between the loads on the two cranks is not due any difference in pressure on the pistons, but the transform of thermodynamic work to mechanical work for each piston-rod-crank system... The work is not evenly distributed between the two cranks because of this phasing, even if the basic geometries are similar (stroke, rod length, piston area, offsets). In a typical case with crank phasing between 10 and 20 degrees, the minimum volume does not occur at TDC for either crank, but at a point after TDC as the leading piston starts to accelerate out of the cylinder and before the trailing piston, which is still traveling inward in the cylinder, reaches its TDC. Note that the sign of the work terms is not necessarily the same at any instant in time. Since expanding gas work is positive, the positive x direction is outward from the center of the cylinder for both pistons. Thus inward motion of the pistons consistent with compression results in negative work while outward motion results in positive work. This piston work translates into positive (or negative) shaft work by contributing torque to the respective crankshaft. The trailing crank is producing a negative torque throughout the pressure rise until about the location of peak cylinder pressure, and due to kinematics, produces less torque throughout the cycle... The conventional approach to opposed piston engine design is to simply sum the resultant torques from each crank system. It must be recognized that these negative torque excursions on the trailing crank are clearly subtractions from the torque of the leading crank. There are additional losses such as the friction losses that are a function of the absolute loads on the components. The friction of the connecting gear train is higher due to the two cranks fighting each other with the transmitted torque being the sum of the instantaneous driving and restraining torques."

The authors are describing what I have attempted to communicate, albeit poorly.

Rod

The plan:

RE: I need your vote for a new Rotary HCCI engine !

Yes the quote is a correct analysis. However, with the exception of variable compression, there is nothing in the OP design with or without stepped bore (in terms of PV and work) that could not be accomplished with a single piston - especially one which is cam driven.

je suis charlie

RE: I need your vote for a new Rotary HCCI engine !

We all will be waiting for the proto type and the results of hundreds of hours of dyno time.

RE: I need your vote for a new Rotary HCCI engine !

Rotary engine:
One in which the crank is stationary and the cylinders revolve around the crank.
Rotary engine:
An engine that uses a rotor in a chamber rather than pistons and cylinders. Some similarities to a vane pump.
One word, two completely different meanings. Both valid.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: I need your vote for a new Rotary HCCI engine !

waross, Its more of a radial engine he has, but I guess they don't teach that subject. So ?? Nomenclature is at a loss.

RE: I need your vote for a new Rotary HCCI engine !

A rotating radial? OK
Can I call V type engines truncated radials?
More fun with words. grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Y'all better go edit Wikipedia. They call rotating cylinder radials "rotary" and so do the US and international patent classification systems. Mine is in the rotating cylinder class. I'm an RX-7 owner. I'm familiar with what the public generally calls a "rotary." The literal definition is wider, however. https://en.m.wikipedia.org/wiki/Rotary_engine

RE: I need your vote for a new Rotary HCCI engine !

(OP)
Waross,

As long as the cylinders rotate around the central shaft, you can call your v-type engine a "rotary." You'll need a pretty large balance with a v-type cylinder arrangement, however. ūüėĀ

Rod

RE: I need your vote for a new Rotary HCCI engine !

I said radial, not rotary.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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