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2 Stroke Reverse Uni-Flow Cam Engine

2 Stroke Reverse Uni-Flow Cam Engine

Here is some info on this Fairchild-Caminez cam engine that I think has some potential for a modern make-over.
The Fairchild-Caminez 447 engine was a four-cylinder air-cooled radial intended for aircraft useage. It was designed by Harold Caminez, who had previously worked in the Engine Design Section of the US Army Air Service. The pistons acted on a leminiscate-shape cam, which made only one revolution for every two piston cycles, so for the same number of power impulses the engine ran at half speed. The pistons were connected by steel links to keep them pressed against the cam; the cylinder were steel with aluminium heads.
The Fairchild-Caminez 447 was first flown in an Avro 504 from Farmdale, Long Island, New York, in 1926. It was successfully endurance-tested in 1927, and was the first ever axial engine to receive a US Dept of commerce type certificate.

An IC engine expert speaks:
"Flight tests revealed what should have been predicted: a very large fourth-order torque variation due to the unusually heavy piston assemblies with their large ball-bearing rollers. Since the cam had two lobes, the second-order interia torque of the conventional 4-cylnder engine becomes fourth order in the arrangement in question. The engine was abandoned on this account."

(Quote from The Internal-Combustion Engine in Theory and Practice by Charles Fayette Taylor, 2nd edition, pub MIT press 1985, p579. This is a standard work on IC engines)

It was indeed abandoned due to vibration problems in 1929.


115 mm


143 mm


7.3 litres

Compression ratio:



150HP at 2400 rpm

Flying weight:

164 kg (1.1kg/HP)


20.5 HP/litre

I have written on physics forum for the last few years about a reverse uni-flow compression ignition 2 stroke engine. Here is some info i copied from LIM Technologies website:

"Once the LIM type engine has started, all four events occur in an only slightly modified sequence. As the power stroke ends, EXHAUST begins, then almost immediately, new air is forced into the cylinder; at the same time that exhaust continues. This new air displaces the remnants of the previous POWER stroke and COMPRESSION then takes place, completing the cycle.

The mechanical resemblance to a two-stroke is only that the piston acts as the exhaust valve. The major mechanical improvement, compared to a four-stroke, is the use of most of the head area for intake valves, since the exhaust leaves through the ports disposed around the girth of the cylinder.

The crank case, as in a conventional four-stroke, is home only to the bearings and crankshaft, the connecting rods and the main lubrication system. Another LIM advantage is that the main lubrication system has nothing to do with the valve train, although it may be involved with lubricating the compressor.

The compressor is external to the cylinder, but is vital to making a LIM type engine what it is. The compressor enables the LIM type engine to resemble a conventional four-stroke because it forces the fresh charge of air into the cylinder, and the coincidental displacement of the remains of the previous cycle.

The LIM Cycle is just three events: Ventilation, Compression, and Power. Two-stroke engines and four-stroke engines are explained in greater detail on other pages in this site."

So my idea is to take both of these designs and combine them, to make a 2 stroke reverse uniflow diesel cam engine. This Caminez cam design could work very well with some modifications. If you study the LIM engine, there is always downward force on the pistons, so the roller would always be forced down against the cam; it may be possible to remove those control arm things. The only time the pistons would not have down force is during start-up and engine braking. If the supercharger had a clutch and an electric motor it would be possible to spin the SC and create boost which would push the pistons down into place. With four cylinders, a motor like this would create 4 power strokes per revolution, not have a camshaft or pushrods, it would have a very high power density and actually be pretty simple mechanically. Could make use of new, lighter, ceramic ball bearings. SI or CI. For highest efficiency and power, a turbocharger and supercharger could be used along with water injection.

Here is another cam engine design that could also be used: The Daniel cam engine patent: US 817,905 of 17th April 1906.
This French engine by Paul Daniel of Levallois-Perret, near Paris, is the first to appear in the Cam-Engine Gallery because it was the subject of quite a comprehensive description in Model Engineer & Electrician for 28th April 1904. It is described as having been exhibited in "the last few days of the Paris salon", which possibly refers to the Exposition Universelle of 1900 in Paris, though that it would seem to indicate a pretty serious delay in reporting the fact. Perhaps some other exhibition is meant.
The report did not say if the engine was running.

There is a big roller d built into the bottom of the piston a which pushes on the top of the big elliptical cam e, and a little roller x' which bears on the inside of the cam. There is an automatic inlet valve p', and an exhaust valve k operated by rocking lever h, which is driven by an eccentric on the main output shaft; since this went round once per cycle, there was no need for a separate cam-shaft running at half engine speed.

The Daniel engine was a water-cooled four-stroke, the cam system allowing it to complete one cycle for each revolution of the output shaft. The patent shows a four-cylinder engine with two groups of cylinders and cams, and air-spring cylinders to take up the backlash in the cam system.

here is my sketch of a conventional crankshaft driven RUDIST (reverse uniflow direct-injection super-turbocharged) engine:


There's more info I got I just wanted to get this up here first and i'll keep adding to it. I would appreciate your thoughts on this engine design. Thank you!

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Upon which criteria are we to judge this engine?

RE: 2 Stroke Reverse Uni-Flow Cam Engine

You should also be aware of the Marchetti engine, a four stroke 8-cylinder radial using two quartered cams, each similar to those of the Caminez engine, with roller rockers controlling the pistons.

Mike Halloran
Pembroke Pines, FL, USA

RE: 2 Stroke Reverse Uni-Flow Cam Engine

I'm mainly trying to determine the feasibility of the concept and design challenges to make this engine work. This is a rough frame, but the main goal is to make a 2 stroke cam engine with minimal parts. If something like this worked it would have lots of applications where high power/efficiency is required.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

The usual thing that kills all of this type of engine mechanism that use cams to convert piston motion to shaft motion is the contact stress at the cam interface.

What's wrong with a normal crankshaft and rods? What does this accomplish that a normal crankshaft and con-rod arrangement doesn't?

RE: 2 Stroke Reverse Uni-Flow Cam Engine

You might want to work out the kinks in a Forward Uniflow ... etc., by hacking an old GMC two-stroke Diesel.

Mike Halloran
Pembroke Pines, FL, USA

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Well there are a few advantages a camshaft can have over a crankshaft. Cam engines don't have the long dwell time at tdc and bdc like crank engines do, which means a more efficient transfer of energy, and it's better for emissions too. If you consider that 4 pistons (or more) can turn one camshaft, there's considerably less rotating weight.

The reverse uniflow is superior to uniflow for 2 major reasons. First, there is no camshaft required to operate the intake valves, so no valvetrain. Second, since the intake valve can stay open during the compression stroke (once the exhaust port has closed) which enables running boost from the turbo/super and up the power density.

Putting together both of these designs yields a much more powerful and efficient engine that could actually cost less than a conventional ICE. Since there's no valvetrain there's less weight and space, and less issues with timing belt/chain issues. The pistons are in perfect counter balance to eachother, and no counter weights are needed. There are some other vibration challenges but I think with modern materials those vibrations could be drastically reduced or eliminated. Possibly connecting 2 or 3 quad modules together could reduce vibration and improve idling.

I've been going over this design on paper and in my head for years. At this point I'd rather see it get built, even if it's not by me. If we could build a motor like this it would be a game changer. I would be really excited to see it used as a range extender for an EV, in a hybrid, aviation, racing, marine; really anywhere where high power density and efficiency is required. I think the reverse uniflow and cam engine are each huge possible improvements by themselves and together could make something incredible.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Hmmm, where to start.

All of your claimed advantages about dwell time near TDC are out the window if you can't make the contact stresses at the camshaft (the one connected with the pistons, not with the valves) work out to be acceptable.

The Fairbanks engine kinda dealt with this because of the linkage between the opposed pistons. The camshaft only needs to deal with the net difference between them. It's still going to be a tough situation.

Take note of the compression ratio on that Fairbanks engine: 5.2:1. Efficiency ... Lousy. It can't have been a diesel engine, therefore it must have been spark-ignition, and would have had all of the disadvantages of a normal carbureted two-stroke. Efficiency: Lousy. Emissions: Lousy (misfiring). Smoothness: Awful (misfiring).

If you're proposing to allow the intake valves to simply operate as check valves, enjoy your very low redline before the valves are not able to close quickly enough. Yes, there are plenty of high-revving two-stroke engines that use reed valves for admitting air to the crankcase ... but reed valves don't have to withstand combustion chamber pressure!

Do some calculations ... please.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

LIM Technology did a study and proved valve bounce to be negligible. Here is a short summary of the reports findings:


Questions raised by knowledgeable people regarding valve bounce were answered in 2006, with the publication of the report by Douglas M. Baker, Ph.D. Dr. Baker describes how valve movement was measured at high speed. Valve bounce occurred on opening, and we know how to eliminate it. Time to open the valve to full lift was faster; dwell was longer, and closing was faster than conventional cam profiles can allow. Valve bounce at closing, due to the small mass of the valve and the deceleration shown in the diagram below, seems to be a non-issue.

The chart above tells the story of valve bounce in our camless engine. Blow down begins at 126 deg. after BDC. It appears that the valve begins to open at 145 deg. In the engine tested, maximum valve lift would be about 0.450 inches. In about 30 deg. of crank rotation, the valve reaches about 90% of its potential lift. After a bounce of just over 1/10 “, ending at about BDC, lift resumes, continuing for another 70 deg. As the valve retracts, its rate of closure slows to a nearly soft landing after the exhaust ports are sealed by the piston. Experts had thought that valve bounce would be a factor in closing the valve, when in fact bounce at closing is negligible. Unlike in any conventional valve train, there is some bounce in the opening, but we think it is benign."

So according to their findings valve bounce is not an issue.

From what i've read about silicon nitride ball bearings, they should be able to handle the contact stresses, the cam could be made of a similar material. I understand the fairbanks engine was an in-efficient 2 stroke, but the reverse uniflow solves all of those problems. Scavenging is done with fresh air, regardless of if it is SI or CI, so emissions should be about the same as a 4 stroke DI. I've read papers that have determined reverse uniflow to be the most efficient 2 stroke design; they didn't even investigate the potential of operating the intake valves without a camshaft.

Here are a few of those research papers you can read for yourself if interested:


A Fully Variable Valve in an Optimized 2-Stroke Diesel Engine:

Performance Tests of Reverse Uniflow-Type Two-Stroke Gasoline DI Engine: Link

Developing a 10cc Single-Valve, Reverse Uniflow, 2S Engine: Link

So maybe my head is little up in the clouds trying to combine both engine designs. How about a reverse uniflow with a conventional crankshaft? I've talked to the owner of LIM technologies, he's built 3 running prototypes, 2 were converted detroit diesel 2 strokes and the other was a DD 4s. He's put over a million dollars of his own money into building this engine; and now he's simply out of money and pretty much gave up on the project a few years ago. He did have a patent on his intake valve design but i think that expired because of non-payment of annual fee's. The cam engines are interesting and could have some potential; there are definitely a lot of issues to work out though. How about we just compare the 2 designs on their own? A reverse uniflow diesel with a conventional crank, and a cam engine as a 4s SI or CI?

Thanks for your participation!

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Also, keep in mind; the fairchild engine was originally designed and built in 1927, thats 90 year's ago! Things have changed enormously since then in regards to new higher strength materials and the more we know about engine design and efficiency now. Just the fact that they were able to make this design work with the materials they had then should be proof enough that given a modern makeover this engine could work. At least in my opinion...

RE: 2 Stroke Reverse Uni-Flow Cam Engine

A Fully Variable Valve in an Optimized 2-Stroke Diesel Engine:


RE: 2 Stroke Reverse Uni-Flow Cam Engine

What RPM was the engine running at under the conditions in which that first chart was made?

What was the compression ratio of that engine? What was the peak cylinder pressure? (Higher means needing heavier valves which means slower operation)

So you want to use gasoline direct-injection ... fair enough. Gasoline direct-injection two-strokes are in production by Bombardier for snowmobiles and outboard motors without any intake or exhaust valves at all. (They use piston porting as with normal two-strokes) They do indeed have much better fuel consumption than conventional two-strokes. But these engines are not called upon to meet automotive emission standards. Nor are they expected to last 300,000 km without an overhaul - and that's an issue with any form of piston-porting.

It seems that most inventors are blind to the downsides of their invention. Sorry for busting bubbles but you're not getting me to invest ...

You may be interested to research the design, and the eventual fate, of the Commer TS3 diesel engine. Look it up. Ask yourself what your design does that that design didn't. And that one was good enough to be in actual production for quite a few years.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

The biggest issue facing the Caminez engine was durability of the cam mechanism. The roller/cam contact had serious skidding/sliding problems due to the dynamic loading from the 4-stroke engine cycle.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Every ask yourself how wise it is to attempt a new engine design by combining "the best of" from a number of failures, especially when one has been around over 100 years yet hasn't managed to gain any traction?

RE: 2 Stroke Reverse Uni-Flow Cam Engine

I think the caminez engine would have less problems with dynamic loading if it ran on the RU 2 stroke cycle. Just because a motor failed almost one hundred years ago doesn't mean it can't work with a modern makeover. There were so many new motors being built back then, they just chose the one that was the easiest to work with, not necessarily the best one. And the RU engine was not a failure, LIM built 3 working prototypes, they have all the information about those engines and the tests that they did; so you guys should look at some of that information for your self. I've shown lots of evidence that the RU engine works and is efficient for the basic prototypes that were built. MatLab simulations showed RU engines having very good scavenging ability. Everybody wants to tell me a RU engine could never work, even though I have proof of it working with 3 engines from LIM Technology. Those were just basic prototypes, if we put a fraction of what we put into refining our current 4s engines into perfecting a RU engine, I believe it would be more powerful and efficient. I mean the 4s crankshaft engine has been perfected over a period of 100 years, so to say just because a first generation prototype can't put out better numbers than a 4s that's had billions of dollars of research and design from numerous different companies, is kind of unfair and not an accurate comparison.

Can somebody show me a failed RU engine? There has never been one put into production, so I think it would be unwise to say something can't work just because the company that produced it was not able to bring it to production. I mean it's not too unbelievable to think that maybe the engine manufacturers would not like to sell an engine that could possibly last much longer and give better mpgs. They make plenty of money selling their same old 4s engines, as long as that's the only option available to consumers, they have no competition or reason to design a new type of engine.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Explain to the rest of us why this engine should be more efficient than a Commer TS3. I can point to at least one advantage that engine would have over yours ... less surface area for heat transfer per unit volume.

Explain to the rest of us why this engine should be more efficient than a Detroit Diesel. The scavenging goes in the opposite direction on those. So what? It doesn't take all THAT much power to operate a camshaft and valves. And in any case, the energy to open and close your valves is still there ... just not coming from the same source. (It's coming from pressure drop across the scavenging path, which means it's coming from the power that it takes to operate the forced-induction scavenging blower.)

Spark ignition with gasoline direct injection? Explain to the rest of us why this engine should be more efficient than a Bombardier E-Tec snowmobile or outboard engine.

All of those engines have either been in production in the past and given up on, or are in production today. Skip how the motion of the pistons is controlled. The combustion system doesn't care. Thermodynamically and scavenging-wise, your system has analogies to all of the above.

Dwell near TDC is a bug, not a feature, if you have a good fast-burn combustion chamber. More time near TDC means more time for heat loss and more time for detonation if you are using a combustion system that uses premixed air and fuel (e.g. spark ignition).

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Did the X-Files ever have an episode explaining how the petro/industro complex buys up and kills off or gets committed all those demonstrably better engine designs? The conspiracy theorists among us ignore that capital has always been available for potential breakthroughs in most every technology. That there aren't funds pretty much means it's been looked at and judged very unlikely.

If one follows the long history of IC engine design and production, there have always been investors and engineers and corporations willing to bet millions trying any wild-hair idea which promised to obsolete the conventional IC; radials, 2-stroke, sleeve valve, opposed piston, rotary valve, turbine, Wankel, Miller-cycle, in addition to your cam-X-link-opp-slider-swash-plate whatevers which provided Popular Mechanics articles for the past hundred years.

Getting way OT, but my son is a venture capital mergers and acquisitions manager. He travels the world constantly searching for any likely idea to be funded, any emerging company to be bought. The world today is awash with liquid capital looking for a breakthrough idea. If it isn't getting funded, it can't get anyone beyond the inventor to believe in it. The entire venture capital establishment will sometimes miss a big idea on the first go, but more often they're willing to fund ten remotely possible R&D/startups, just on the chance one will hit it big.

I asked him about the likelihood of any new IC design and production funding. He said the general consensus is the existing IC are going to see us to the end of the line. Most R&D is going into electric. However, every new design is constantly evaluated, because consumer research indicates most drivers today have range anxiety about electrics and will want a fall-back IC. So compact, efficient, standby, quiet, vibrationless, bring it on.

jack vines

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Consider this bit of advice from my few decades of product development:

If your new product relies on ONE rediscovered/ breakthrough/ revolutionary/ magical/ underappreciated/ misunderstood technology, your schedule becomes even more of a fantasy than is otherwise likely, and you will surely blow your budget, but you may be able to pull it off.

If your new product relies on MORE THAN ONE such technology, teething problems with each of the rediscovered, etc. technologies will interfere with development of the other(s), and add YEARS or DECADES to the project.

I.e., you will almost surely run out of money and investors before you get your engine in any sort of production, as it has been described.

OTOH, the odds against you are not insurmountable if you limit yourself to a RU engine with a normal slider-crank, or to a normal two or four stroke top end with cams in the crankcase.

Mike Halloran
Pembroke Pines, FL, USA

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Mike - I agree. I worked for some people who started thinking all sorts of things could be done but they always failed to recognize what seems to me was a fairly simple notion.

The notion is, after analyzing the existing products and market, how did you come to believe the current competitors missed the advantage you offer?

For certain there are some cases where the incumbent has too much money tied up to change or has a malformed notion of their position, but it is pretty rare that a big gap will remain open for long. I am pretty sure the last gap like that in propulsion was filled with the turbojet engine and its variants and that gap waited for materials that could withstand the conditions.

RE: 2 Stroke Reverse Uni-Flow Cam Engine


I mean it's not too unbelievable to think that maybe the engine manufacturers would not like to sell an engine that could possibly last much longer and give better mpgs. They make plenty of money selling their same old 4s engines, as long as that's the only option available to consumers, they have no competition or reason to design a new type of engine.

Now you're just using conspiracy theory arguments to justify your posts. 100 odd years of R&D effort by countless different COMPETING companies have landed us where we are today.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Mike - I gave you a star for that one. Back in the '80s I signed on to a development project with a Fortune 100 company that they thought was going to revolutionize a certain part of the automotive industry. It involved multiple breakthrough technologies. It was a great ride with a monthly R&D budget of over two million dollars and all the bells and whistles. We did make considerable progress but the devil is always in the details and when the expenditures kept mounting and the payback kept moving farther out the ax fell. The entire program was canned and 60 engineers joined the unemployment lines. No conspiracy theory needed.


The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

BrianPetersen - You said, that higher peak cylinder pressure means needing heavier valves, can You explain why? :)

RE: 2 Stroke Reverse Uni-Flow Cam Engine

I am talking about just making a RU CI engine with a conventional crankshaft; there's just too many issues to try to combine into both designs. So could we please focus on just the RU and not the cam engine anymore please?

The Commer TS3 has too many moving parts, too much friction, and potential for breakage. Why is RU better than a DD? Valvetrains do lose a considerable amount of energy through friction, they are also expensive, require maintenance, take up space, and heavy. Yes Brian, the valve in a RU does use some energy from the pressure differential to move the valve, but it doesn't lose all that energy through friction like a valvetrain would. With a RU, whether CI or SI, it is possible to run boost, which none of the other 2s engines are able to do (at least not a significant amount of boost) that to me is a major advantage that allows the power density and efficiency to be increased. The bombardier and mercury engines cant run boost, they require the orbital air injection system, which seems like a weak link to me; those engines also have to use their REV exhaust valves, to change the volume of the exhaust port, another potential weak link. Those engines also are still a total loss oiling system, whereas the RU is lubricated like a conventional 4s. So yes, the bombardier and mercury 2s are not suitable for 100,000s of miles like a RU engine could be.

Another advantage of RU vs. uniflow, the pressure wave from combustion, which is traveling downward during the power stroke, can continue going in its natural direction and exit through the exhaust port; whereas in a uniflow that pressure wave has to be forced to turn back around and be pushed out a valve in the top, which exposes the exhaust valve to extremely hot temperatures and reduces it's lifespan.

CI would be the easiest to control with a RU engine, so I would like to focus on just CI. SI is definitely possible but gets more complicated with injecting fuel directly into the cylinder during the compression stroke. To me, the idea of not having to worry about replacing a $3,500 timing chain system after 100k miles is attractive just by itself. My mother had an Audi A4 with the 3.2L V6, the chain tensioner had a problem, which made the chain skip a tooth. Long story short, they had to pull the whole motor out to fix the timing chain system, which cost $5,000. And then the new tensioner failed, so the shop (they specialize in Euro cars) had to pull the motor and do it all over again. Timing belts break all the time, timing chains have all sorts of expensive issues, i'm a mobile mechanic so i've done plenty of timing belt jobs. If i could have a simpler engine that didn't need a valvetrain id be all for it. That's why I like 2s so much, they're high power density and mechanical simplicity. So if I could have a 2s that didn't have all the issues they normally have, like terrible emissions, poor efficiency, burning oil. Thats what the RU engine offers, the best of both worlds from 2s and 4s.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Also, in regards to conspiracy theories. Was the GM EV1 incident a conspiracy? Didn't California sue GM over that? Actually 1 million dollars of that went to the California Energy Commission which they used to start CleanTech Institute, and train engineers and mechanics to be certified EV Techs; I know that because I graduated from that program in 2012. How about the VW emissions cheating scandal, is that just a conspiracy? Manufacturers will do what is best for their bottom line, profit for shareholders; they will not do what is necessarily best for consumers and technology. To them, if it ain't broke, why fix it? I have to agree electric is the future, but I also believe hybrids can bridge the gap getting us to 100% electric; and small, powerful, efficient engines are the best for hybrids.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

OK, so now you are backtracking, to what amounts to essentially a Detroit Diesel but with the scavenging running in the other direction, and skipping the crazy cam-and-linkage piston mechanism. Good move.

Re the pressure wave ... it's not significant. The speed of the piston moving down (10 - 15 m/s) is insignificant compared to the local speed of sound (400 - 500 m/s at elevated temperature typical of the end of the expansion stroke). When the exhaust ports/valves open, the whole cylinder will "know" within a small number of crank degrees.

A cam-operated valve mechanism takes as much power to operate as you seem to think it does.

Scavenging probably takes more power than you seem to think it does. If you have to move 1 litre of air per revolution (typical of an automotive-scale engine) and the engine is spinning at 3000 rpm (which it could be) and there's 100 kPa of pressure difference because of your spring-loaded-closed valves (and it could very easily be more) that's 5 kW not accounting for compressibility effects but it will be in that range.

If the intake valve is (let's say) 30mm in diameter then 100 kPa of pressure to open the valve is about 70 N (about 15 lbs in old English units). That's not a lot. If the valve spring pressure was brought into a range normally seen, scavenging pressure would have to be A LOT higher. If the valve spring pressure was brought even lower, I have my doubts that the valve could be opened and closed quickly enough.

Again rough number, that 30mm diameter valve would have a head about 4mm thick and the stem would be about 5mm diameter (motorcycle engines have valves in this range) and let's say 100mm long - it has to get past the port and the valve spring. The valve alone would weigh about 38 grams if it's made of steel. 70 N / 0.038 kg = 1873 m/s2. Then ... d = 1/2 a T^2; let's give it 1 ms. I get almost exactly 1mm of valve movement in that time. 1 ms of crank rotation at 3000 rpm is 18 degrees. It's not going to make it. We haven't even considered the weight of the retainer and the valve spring and the keepers.

Titanium valves and pneumatic valve springs would help ...

Two-strokes with reed valves successfully operate at high RPM because the reeds are very thin and light (and are supported by a cage in the closed position). They can be that thin and light because they only have to withstand crankcase-scavenging pressure, not compression pressure and certainly not combustion pressure.

If my numbers are wrong ... please substitute your own and explain.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Thank you for the pointers.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Quote (voltech444 (Automotive) )

Also, in regards to conspiracy theories. Was the GM EV1 incident a conspiracy? Didn't California sue GM over that? Actually 1 million dollars of that went to the California Energy Commission which they used to start CleanTech Institute, and train engineers and mechanics to be certified EV Techs; I know that because I graduated from that program in 2012. How about the VW emissions cheating scandal, is that just a conspiracy? Manufacturers will do what is best for their bottom line, profit for shareholders; they will not do what is necessarily best for consumers and technology. To them, if it ain't broke, why fix it? I have to agree electric is the future, but I also believe hybrids can bridge the gap getting us to 100% electric; and small, powerful, efficient engines are the best for hybrids.

Quote (voltech444 (Automotive))

I mean it's not too unbelievable to think that maybe the engine manufacturers would not like to sell an engine that could possibly last much longer and give better mpgs. They make plenty of money selling their same old 4s engines, as long as that's the only option available to consumers, they have no competition or reason to design a new type of engine.

I can tell you that everything I underlined is completely false and it makes me question whether or not you have worked for a manufacturer. Selling an engine that is demonstrably more durable and demonstrably more fuel efficient would be the most profitable thing that an engine or auto manufacturer could ever do.

The problem with switching platforms of engines is that you would have to make it meet previously established customer expectations in power delivery, packaging dimensions, noise, vibration, user-friendliness, maintenance costs, operating speed, and initial purchase cost. Then you have to overcome challenges that come into play when designing something for mass production. Are there more efficient platforms out there? You bet, but customers don't want a 6L engine that makes 100 horsepower and 80 ft-lbs of torque just so they can get a 15% increase in thermal efficiency.

The industry has came to an engine platform that serves the widest variety of applications and expectations. These 4 cycle engines can be in anything from F1 cars to semi trucks.

Trust me, I have put a lot of effort into finding a better way. I remain certain that there is a better way, but it is certainly going to require pure genius to discover it. And don't assume that all manufacturers are running to the bank with loads of profits. Keeping up with regulations and competing with other manufacturers has actually put a lot of people out of the business and caused mergers. Notice that there aren't many successful startups in the automotive and engine industries. That's because it is a tough business to be in. Merely satisfying regulations to legally build engines for commercial sale is absurdly expensive. How much of the budget is even left over to delve into the pie-in-the-sky skunkworks projects? Let me know where and when that money exists and I'll be there asap.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Quote (Panther140)

The industry has came to an engine platform that serves the widest variety of applications and expectations.

This is the crux of the matter for me.

We are talking about an engineered product that is the result of over 100 years of development, with an always-present profit-driven motive to improve economy and power, reduce cost, increase reliability, etc etc etc. I tend to think that the current state of powertrain design is the result of 'natural selection' in many ways. It certainly is possible to build an engine that's better for a single purpose, but to change the platform entirely without having to compromise somewhere is going to require either 1) a change to the laws of thermodynamics 2) a simple massive amount of engineering effort and time with an uncertain result.

Auto manufacturers are not capable of producing the first, and are wary of undertaking the second.

In my opinion, a single man or woman in a home shop or similar situation has little or no chance of turning the tide. You're basically assuming that the majority of engine development engineers who worked over the last century are wrong.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

I think the biggest practical improvements will be gains in the ability to keep an engine running near peak efficiency under a wider variety of load/speed conditions. New methods or systems added onto engines to re-harvest waste heat and pumping losses will probably also get attention in certain applications. I don't see manufacturers straying far from poppet valves and crank/conrod/piston assemblies. Ignition and fuel systems will probably be altered to reduce pumping losses as DI becomes more common.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Ok, there must've been some kind of glitch. I posted this last night but somehow it was gone today. Took me a while to finally get back into my account.

There will be pumping loses with scavenging. 4s engines also have pumping loses; I'd have to research it more to find out which one has higher pumping loses.

The valve design is critical and the good news is this work has already been done by LIM Technology. They designed and patented the valve, although I believe the patent has expired because of non payment of fees.

Here is a picture of the valve:

It is possible to use these valves with a clock spring, or control them entirely pneumatically. I was also thinking about Samarium Cobalt magnets as the springs since they can handle high temperatures; although the temp could be too high but it's an interesting idea if it could work.

Using a valve design like these would sabe a considerable amount of space and weight. They could be light enough, to move fast enough, to work up to decently high rpms. Since I'm focusing on a CI engine the rpms shouldn't be too high anyways. Also, since it's 2s it doesn't need to Rev high to make good torque.

Another thing is the springs for the intake valves don't need to have very much force. Engine tests from LIM found that all the spring does is help the valve close faster. They were actually able to run one of their prototype engines with no pneumatic or metal springs; it ran terrible but it shows how it's really the air pressure that causes the valve to open and close, the spring just helps it return closed. By simply adjusting the force on the valve, allows the valve to open and close at higher rpms; it is similar to a VVT but obviously much simpler.

The reason why the dual charger setup is used is to provide the positive pressure necessary to operate the valves and scavenging. It is possible to use only a supercharger but I believe by having compression done in 2 stages, from the turbo compressor first and then the SC, and using water injection after the TC compressor and before the SC. The dual charged setup would have the highest power potential; it could also be more efficient.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

So what's the point of these valves? There's a lot not to like about this design- no pure mechanical retention (if the spring breaks, where does the valve go?)

What looks to me like inferior curtain area compared to a similarly sized poppet valve

More weight than a similarly sized poppet valve

The use of a clock spring, which is a more fragile arrangement with more flow restriction than a conventional stem/seat/helical spring arrangement

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Look at the Wankel Engine, seemed to be going to change the engine industry in the early 70's.

Now virtually gone. Many reasons, but the fact that the automotive and small engine industry (< 100 kW) had a huge investment in the layout of RICE (Reciprocating Internal Combustion Engines) made development of these a better investment than development of what was a new technology.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

The clock spring just illustrates the concept; you are correct they would perform poorly. Having valves with no mechanical actuation is interesting to me, but a RU engine with a camshaft would probably make the most sense. It would still have all the other advantages still. I wonder if a single cam or double cam would be better.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

If there's only one valve, what does the second camshaft do?

Mike Halloran
Pembroke Pines, FL, USA

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Bruce Crower built a uniflow engine that had intake valves and the exhaust was piston-port - a modified Triumph motorcycle engine I seem to recall. And I think there have been plenty of others.
I would also like to question the use of the word "reverse" - since the 1800s uniflow steam engines were intake through valves and exhaust piston port so GM engines should called "reverse" uniflow.
Here is a good source of odd IC engine types: If you can think up an engine layout that is not here you are doing well.

If you use two cams you can have four intake valves running at half-crankspeed to give a two-stroke effect.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Ya that's interesting some steam engines were originally reverse uniflow.

It's actually better to use 4 intake valves per cylinder with 2 cams or 2 valves with one cam. Maybe a solenoid actuated valve could work good with an RU engine. Since the pressure differential can open and close the valve, it wouldn't take much energy to just help the valve open and close sooner.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

I think your assumption that pressure differential can open the valve is dubious, at best.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

And even if it can be coaxed to work by some means, the pressure differential is associated with a large source of pumping loss.

Give it up; control the valve using a camshaft like everyone else does. There's a reason why everyone else does it that way and it's not because self-actuation of intake valves wasn't thought of before; it was thought of in the late 1800s and early 1900s and given up on it because it doesn't work well enough.

If you don't like the forces associated with valve springs then use something like Ducati's desmodromic system in which the valve is both opened and closed by cams. No valve springs.

I can tell you that the Ducati 4-stroke engines with desmodromic valve actuation are not appreciably more or less efficient than other competitive engines that use normal valve springs.

RE: 2 Stroke Reverse Uni-Flow Cam Engine

Quote (jgKRI (Mechanical))

I think your assumption that pressure differential can open the valve is dubious, at best.

Harley Davidson single cylinder engines used that concept on their intake valves until about 1912. Apparently it worked back then, but it didn't work well on their V Twin engines. I wish I had more information than that, but its proprietary information from the early 1900s. I know some guys that worked for Harley, but not in the early 1900s!

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

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