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Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?
5

Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
I was recently reading the research of Prof Dr-Ing Gerhard Schmitz into compound expansion ICEs, and Mr Bruce Crower into water injection. So I'd like your advice as to whether this is feasible, as I am merely a community college student planning on entering automotive or mechanical engineering.

Most ICEs waste a whole bunch of power by having the exhaust expand into the outside world. And they require massive radiators to keep the parts from getting heat-damaged. And they also require camshafts to open and close the valves, which adds a whole bunch of weight. And Otto cycle engines require spark plugs and have to use lower compression ratios to prevent detonation, which adds weight as well and decreases power.

We can solve this by starting with a basic four stroke Diesel cycle engine. We replace the camshaft with electronically-controlled solenoids to actuate the valves. Then we can dispense with the timing belt as well.

We then add a low pressure cylinder that the exhaust is directed to. This cylinder will be at TDC when the exhaust valves on the combustion cylinder are open, and when it's at BDC, it's contents will be directed into the air. Steam engine designers figured out the concept of compound expansion centuries ago, why has it taken ICE engineers this long?

Finally, the next time the combustion cylinder is at TDC, instead of injecting diesel, we inject distilled water. This will a) provide an extra power stroke, as water expands 1600x when it turns into steam, and b) cool the engine. We could also increase power-to-weight ratio, depending on the weight of water needed to replace the weight of the radiator. Once again, steam engines don't need radiators, as they produce power, they also dissipate heat. You'd just have to ensure ) that the water is very pure, and b) use steam engine lubricant.

And to ensure the engine will always be operating at peak efficiency, we couple it to a continuously-variable transmission.

So we have the benefits of a) the very efficient Diesel cycle which doesn't require spark plugs and produces more torque, b) use electronically-controlled solenoids to actuate the valves, which saves the weight of the camshaft, c) compound expansion to extract extra power from the exhaust, d) steam power, which keeps the engine cool and adds extra power, and e) a CVT, which eliminates the inefficiency involved in gear-shifting.

If we build the engine out of carbon fiber, this engine will be very light and strong, and able to survive the high temperatures involved. And a lighter engine means it can rev higher and have larger cylinders. It's better to produce torque at a higher rpm, because then you can take full advantage of the CVT's gearing to produce optimum power, and there's no replacement for displacement.

So thanks for advising me!

Lexi

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

"Most ICEs waste a whole bunch of power by having the exhaust expand into the outside world"
"adds a whole bunch of weight"

Engineers like numbers, not bunches.

"We replace the camshaft with electronically-controlled solenoids to actuate the valves"
Been around for 20 years, never made it into production. Why not?

"why has it taken ICE engineers this long? "
because there is a better way, within the constraints of the design at the time. Exactly how much is this bunch of power, and is it worth increasing engine weight and complexity by 50% to harvest it?

"the next time the combustion cylinder is at TDC, instead of injecting diesel, we inject distilled water."
and wash all the oil off the cylinder walls.


No problem with you asking questions, but try and do some homework first.








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: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

"....the next time the combustion cylinder is at TDC, instead of injecting diesel, we inject distilled water...."

That's a great question. Injecting distilled water into the compressed air charge at TDC will lower the temperature of the air charge through the latent heat effect of the water vaporizing. But how will this add energy to the working fluid that can be recovered to produce a positive output of work? Injecting diesel fuel into the hot air charge results in combustion and a release of thermal energy. Injecting distilled water does not.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Well, a camshaft weighs about 4 lbs. And unnecessary weight does reduce power-to-weight ratio. The goal is to make the engine as light as possible, and as powerful as possible, and as fuel-efficient as possible.

And you can prevent the oil from being washed off by using Mobil 600W Super Cylinder oil, which is what they use in steam cylinders, as it resists the washing action of the steam.

We get extra power from the steam stroke and compound expansion, but the main gain is an increase in fuel-efficiency and a decrease in operating temperature, which means we can run the engine at higher rpm, as it won't overheat as quickly. It's better to produce torque at higher rpm, as then you can take advantage of gearing.

Koenigsegg is developing an engine with electronically-actuated valves.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
tbuelna, the heat of the compressed air will cause the water to turn to steam, which pushes the piston down.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Quote (TSLexi)

tbuelna, the heat of the compressed air will cause the water to turn to steam, which pushes the piston down.

If the compressed air mass contains enough heat energy, it will indeed cause the injected water to vaporize. But how does this add energy to the working fluid?

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
The water itself is the working fluid.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
1st stroke: intake of air.
2nd stroke: compression of air.
3rd stroke: injection of diesel and combustion, producing power
4th stroke: exhaust into LP cylinder when it's at TDC, producing power
5th stroke: injection of water (LP cylinder releases exhaust)
6th stroke: steam power stroke
7th stroke: exhaust steam into LP cylinder when it's at TDC, producing power
8th stroke: 1st stroke (LP cylinder releases steam)

So we have 8 strokes, 4 of which produce power.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

For more on electric valves, see 'Lucas Helenoid'.
Given the amount of iron and copper that had to be present for magnetoelectrical reasons, an engine set had to weigh a bunch more than a mechanical valve train does, possibly without even including the high current power supply.

Practical steam cars, like the Doble Model E, did indeed have radiators; they were called condensers.

I think Bruce Crower reported that he couldn't limit cylinder corrosion in his SteamOline engine.
Come to think of it, it may have been spalling induced by thermal fatigue from the alternating hot and cold strokes. We may need another century of cylinder development to get that under control, longer if such a thing never goes into real production.

Steam cylinder oil was developed for a particular environment, generally hot and wet. Motor oil was developed for a different environment, generally much hotter and not as wet. SteamODiesel oil will have to perform in a different environment from either, damn hot, pretty cool, and fairly wet. ExxonMobil can't really make it happen until they can buy some crate engines to destroy in testing. ... and the crate engines will need special oil to survive, so there's kind of a chicken and egg problem to be wrestled.


I salute your enthusiasm. Try to hold onto that. Positive Mental Attitude is a wonderful thing; it can catalyze amazing progress, usually by loosening up a money flow.

The people who hang out here are generally responsible for turning that money flow into a bigger money flow. That takes hard science and hard math. ... both so called because they are, hard.

You are not yet well equipped to go bench racing with these guys. Do study hard.




Mike Halloran
Pembroke Pines, FL, USA

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
I know. I just wanted some advice on whether this is feasible at all, not advice on how to actually build one. Yet. I'll learn how to do that in MechE school.

I think silicone oil could be used, as it can't dissolve in water and resists heat.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Yeah, silicone oil >resists< heat, but when it decomposes from the heat it can't resist, one of the decomposition products is fine white sand, which doesn't do engines any good.

Hydrocarbons, OTOH, decompose to, among other things, elemental carbon, which is soft enough to not bother an engine, at least not as much as silica does.

Mike Halloran
Pembroke Pines, FL, USA

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
And I think spalling can be solved by using carbon fiber. If it works at high altitudes for jet engine blades, it can work here. Jets have freezing cold air that gets compressed into extremely hot air.

You could dispense with the engine oil entirely, and coat the moving parts in hexagonal boron nitride, which has a high melting point (2900C, well above the cylinder temps of 1000C), and is a very slick aerospace lubricant, and can survive oxidizing environments.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Governments throw large amounts of money at companies researching new and novel engine and power-gen concepts (or old ones, dusted down). Most (if any) don't make it into production, but the people working on them probably have a lot of fun and an education, taxpayer funded. The US government seems more keen on this than most, for example: http://energy.gov/eere/vehicles/vehicle-technologi...

If you read the trade rags, there are always glossy one-pagers boasting of a brand new technology with awesome potential. Some have even built working prototypes.

Spending a few years of ones early career with one of the start-ups that are spending this money may be interesting.

- Steve

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

I know people that have made careers out of it. Moving from one failed startup to another, rising up the company ladder and salary. The key is to jump just before each crash. Good money if you are good at whitewashing a pig.

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

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: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Or, you could work for a '___ Research Institute', and whitewash other people's pigs without having to move. You'll probably need at least a Masters degree to get in.

Mike Halloran
Pembroke Pines, FL, USA

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Hmmm...I wonder if using an 20:1:1 diesel:water:methanol emulsion would be better than using a separate water injection stroke, as it will provide the same advantages with less complexity. Lower cylinder temperatures, less diesel use, and more torque, as have three expansion processes going on: diesel combustion, methanol combustion, and water vaporization.

And according to this article, water-in-fuel emulsions decrease emissions, especially NOx and PM: http://www.hindawi.com/journals/tswj/2014/527472/

So we should set the dynamic CR so it will be high enough to autoignite the methanol, as it has a higher autoignition temperature then diesel, around double. And higher CRs increase efficiency.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

I'm not going to try much to burst your bubble; but there have been gobs of people pondering ICE issues, and if something doesn't exist, there are probably plenty of sound, rational, and practical reasons for not doing it.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

2
Injecting water together with the fuel will just cool down the charge as a whole - and at the worst possible time, the time when you want to be RAISING the temperature of the charge. The heat that it takes to vaporize the water doesn't come from nowhere. Boiling water makes it expand (into steam), but cooling off hot air makes it shrink, and because of the latent heat of vaporization, the shrinking is more than the boiling ... this is not what you want to be doing. The air and the water/steam are in the same chamber. You can't tell the expanding steam to push the piston down while simultaneously telling the shrinking (cooling) air to act like it hadn't cooled off and shrunk (or lost pressure) ...

Water injection CAN be effective in some circumstances but I strongly urge the original poster to understand the thermodynamics. In a normal application of water injection, the water goes in BEFORE the air is compressed, i.e. it goes in during the intake stroke (typically, upstream of the intake valve ... or upstream of a turbocharger that is in front of said intake valve.) In that situation, the latent heat of vaporization comes from the air as it is compressed ... thus reducing the work of compression. By reducing the temperature of the charge at the end of the compression stroke, this also reduces the work of expansion on the following expansion stroke - there is no free lunch. But with a spark-ignition engine, it allows a higher compression ratio to be used without detonation - or higher boost pressure without detonation - and *that* is where the efficiency and/or power boost can come from.

Addressing various other random points that have been made ...

Regarding electronic solenoids for valve actuation ... Know how I know that you have never built an engine? When the cam lobe compresses the valve spring (taking mechanical energy out of the camshaft) that energy is stored up, and when the valve spring expands on the other side of the cam lobe, it sends a good chunk of that energy right back into the camshaft, so there is not as much loss as you might think there would be. If you've built an engine - particularly a single cylinder engine! - you would know this! If you open a valve using a solenoid, it took electrical energy to accelerate that valve. How do you get that energy back?

One of the reasons that electric/electronic valve actuation has never gone into production is that when you build such a system in the real world, the energy that it takes to actuate the valves is excessive.

You CAN, on the other hand, devise a mechanism to vary the timing of valve opening and closing within certain rather wide bounds, and you can even devise a mechanism to vary the amount of valve lift ... and such systems are in production on engines that you can buy today.

You criticize the weight of a camshaft and valve buckets or rocker arms. I can assure you that a set of solenoids to do the same thing, plus the increased size of the alternator that would be required to supply power to them, will weigh more and cost more.

I know about the Koenigsigg system and find it interesting; it may yet change things. It is not relying fully on electric actuation - as I recall, it appears more like pneumatic actuation under solenoid control. Still, "there is no free lunch". They've demonstrated the system; it remains to be seen if the benefits outweigh the downsides - and you can rest assured that there will be downsides that the inventors perhaps are not telling the world about.

The secondary "low pressure cylinder" - the secondary expansion - can be achieved in a more efficient manner - by simply changing the valve timing events so that the effective power stroke is longer than the effective compression stroke. And, this is in production today - a good many of the gasoline hybrid-electric cars already do this. A good many gasoline engines with variable valve timing play with the cam timing to achieve this effect at part throttle. It's better to do it this way than to use a secondary expansion cylinder ... because it avoids the very substantial fluid flow losses that would be associated with transferring the fluid from one cylinder to the other. Current mass-production engines known to use simulation of the Atkinson cycle at part throttle: Honda Civic (base engine, not SI), Fiat 500 (and all the other Fiats and Chryslers that use MultiAir), BMW (all that use the current turbocharged and Valvetronic-equipped 4 cylinder 2.0 litre engine), Toyota Corolla with the "eco" optional engine, and I'm quite sure there are others.

I won't address the materials-compatibility and lubrication issues associated with the water-injection-stroke system for the simple reason that I don't know enough about it, aside from noting that others have touched on this issue. Suffice it to say that "there is no such thing as a free lunch".

I hate continuously-variable transmissions.

Carbon-fiber engine block??

It's great to be enthusiastic ... but it is also very important to be realistic, and to understand that it's often better to make one small advancement at a time (and hopefully succeeding, and in any event, limiting the amount of damage in case it does not succeed) as opposed to trying for a technological moon-shot with an exponentially greater risk of failure. In today's market all it takes is for ONE small aspect of your design to be wrong.

What happens to your fancy distilled-water-injection system when someone leaves the car overnight in -30 C and starts the engine in the morning? (Some diesels are having issues with the water-based DEF NOx control systems because of this)

What happens to your electronic-valve-actuation system if the system voltage is out of spec? What happens if a fuse blows or a wire breaks with the engine running? If you use the Koenigsigg compressed-air-assisted system, what happens if the compressor fails? In any of these situations, does the piston come up and smash into the valve? Oops, that's an expensive warranty claim - or worse, if the sudden loss of power causes an accident ... a number of auto manufacturers are currently in a wee bit of a pickle because of this right now.

Can your carbon-fiber engine block catch fire?

If your engine relies on some super exotic chemical concoction in place of normal engine oil, what happens when your mother dutifully takes the car to the garage on the corner for its 3000 mile oil change as she has always done for the last 30 years (because that's the only thing she knows about car maintenance), and the flunkie with the toolbox fails to read and pay heed to the massive warning sticker that you applied to the engine in the hope that they will use the correct exotic fluid instead of Quaker State 5w30?

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Thanks Brian! Also, I now realize injecting water along with the fuel would be a bad idea. But I was originally talking about injecting water after the exhaust stroke when the cylinder is at TDC, letting it expand, get exhausted, and THEN have the next air intake stroke.

And Atkinson cycles engines sacrifice power density, as it can't take in the air needed to fully combust the fuel. But that can be remedied by adding a supercharger and/or turbocharger (or NOS if you really want it), making it a Miller cycle engine. Cold air is more oxygen-dense then warm air, and the steam strokes will cool the cylinders, cooling the air charge. You'd probably still need a radiator, but it could be much smaller than usual.

And carbon fiber can survive temperatures of up to 1200C. They use it in clutches and brake pads for racing cars.

So thanks for giving me constructive criticism, instead of calling me stupid like a friend of mine did.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

"Atkinson cycles sacrifice power density"

Indeed. What do you think the displacement of your secondary expansion cylinder needs to be, relative to the size of the normal conventional power production cylinder? How much contribution to power output do you think that cylinder would add, relative to the increase in size of the engine as a whole? How would this compare to the additional friction? What about the fluid (pumping) losses of that extra-big cylinder? How big would the valves have to be - how much friction would they add?

The hybrid cars (various Toyota and Ford models) that use Atkinson cycle, use the hybrid system to top-up the torque and power output of the engine. There's nothing wrong with that, and you can't argue with the results.

The non-hybrid cars that emulate the Atkinson cycle do so by using VVT so that it uses Atkinson during periods of moderate torque output - which, for most drivers in most cars, accounts for most of the time. They shift the valve timing back to normal when high torque output is demanded. OK so it loses a bit of efficiency during full-torque operation ... but perhaps that's better than dragging along the friction and heat loss of a much-bigger-displacement secondary expansion cylinder ALL the time.

And speaking of which, I suspect that the amount of secondary expansion for maximum benefit might be smaller than you think it is. At a certain point, it becomes not worthwhile because of the extra friction. At part-load operation, ideally, less extra expansion is needed than at full torque. But if the engine is spending most of its life at part load, it's better to optimize for that. It is a trade-off.

Turbocharging and supercharging are no free lunch, either, as I am sure you are aware. A number of manufacturers (*cough* Ford!) seem to be experiencing a rather large discrepancy in fuel consumption between the ideal conditions associated with the various EPA, Transport Canada, NEDC, etc government testing cycles, and the way people actually drive in the real world. My sister has a Ford Escape 1.6 Ecoboost, so this is a situation that we have rather personal awareness of ...

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Well, my idea of having a steam stroke is to decrease the amount of diesel needed. Twincharging can be utilized to decrease the amount of diesel needed, as higher oxygen density means more complete combustion, which means more work can be extracted from a given amount of diesel, and less emissions of UHCs. And to reduce power losses from the chargers, I think we can use carbon fiber, as it's lighter and very heat resistant, which means it will take less work from the engine to spin it fast enough. GE uses it as fan blades in their GEnx family of turbofans, and it's used on F1 brake pads and clutches.

Having the compression ratio able to differ from the expansion ratio also allows more work to be extracted from a given amount of diesel (although forced induction is required to keep power density the same).

The cooling effect from the steam strokes will decrease cylinder temperatures, so less NOx will form, and the engine can rev higher, since it runs cooler, although we do have to work out the effects of thermal shock and fatigue on the parts from the constant heating and cooling.

And since we're using diesel to provide the main power stroke, and steam to provide an additional power stroke, 33% of the six strokes are devoted to power, making it more efficient then a normal four stroke IC, where only 25% of the strokes generate power. And since we use steam to provide one of the power strokes, we can use less diesel, so the exhaust would be mainly steam, which will decrease the total percentage of exhaust that is PM, UHC, and NOx. The solution to pollution is dilution.

I think this could be workable, but that's just me. I wish I had a friend with a CAE package to virtually prototype this.

I guess with engines their are four things, power, fuel efficiency, weight, and cost, and you can only have three.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
I guess I could get some money together to build a small W4 motorcycle engine from this concept.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
I think carbon fiber-reinforced silicon carbide would be a great material to build this engine, as it has a high melting point, high thermal shock resistance, and a high strength/weight ratio. I mean, if it can be used in high-performance brake pads, why can't you use it for the engine's moving parts?

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

There was an SAE paper on this subject.
B.E.

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

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
So, from reading that, water injection increases power while decreasing BFSC, and water contamination of the oil can be avoided by aiming the water at the piston head rather than at the bore walls. And it decreases NOx. And I believe the problem of SOx and UHC and CO emissions can be solved by using ULSD, and using forced induction to increase the amount of oxygen present to fully-combust the diesel.And having a higher dynamic CR will increase the oxygen density and temperature, leading to more complete combustion.

And that paper was written in 1975, and fuel and engine technology has drastically increased since then. Does that paper indicate the effect on BMEP?

And, no matter what, I still stand by that using a CVT will make any engine more efficient, as the engine can always operate at peak efficiency.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Having the engine go from idle to screaming WOT in a quiet residential parking lot is not necessarily a desirable feature.

How do you sell the idea of adding water at every fuel stop, when people are already getting annoyed about adding DEF?
How do you keep the water from freezing? How easily do you repair your system after it does?

Mike Halloran
Pembroke Pines, FL, USA

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Keep it from freezing by adding methanol to it. And the sound...that's a feature. some people like loud engines. You could dampen it with active noise cancellation technology as an option.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
I think you could sell the idea of having to add water by the savings on fuel.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
I also wonder if placing a squirrel cage generator between the turbines of the chargers, will help recover some of the energy lost, as we could use it to charge the car battery, and when the engine's exhaust speed is too low to drive the turbine fast enough to provide the desired boost, we could use the battery to run the generator in reverse to spin the blades fast enough to provide boost.

Then we solve the whole problem of not having boost during low rpms, but we also drain the battery a bit when we're at low rpms.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Back in the '40s, water injecting carburetor were available for gasoline engines. I haven't seen a water injecting carburetor since I was a little boy and the one I saw was in a box, not on a vehicle.
NOX generation is related to the dynamic effects of the high temperature in the center of the burning mixture in the cylinder. The farther from the cylinder walls, the higher the temperature of the burning gasses may be with more NOX produced. Water injected during a previous or subsequent cycle will have little effect. Water may be more effective if it is injected with the diesel fuel.
Many statements here may demonstrate a lack of understanding of the basic laws of the conservation of energy.
More study of basic principles may yield negative answers to many of the questions here.
Over-spinning the turbo at low speeds may have merit. Faster forward, not in reverse. Google "super charger".
In practice the actual savings rather than the percentage savings may be so little as to be almost pointless.
Taking energy from the turbo will, in many cases, reduce the efficiency of the turbo.
There may appear to be a saving at WOT if energy extraction is used to reduce dumping of excess volume of charge air, but only if the extracted energy may be used efficiently. Batteries on a running engine are usually back up to full charge shortly after the engine is started. The excess energy extracted from a turbo may be used to supply electrical loads such as daytime running lights and other loads, but a charged battery is not an effective place to store recaptured energy.

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

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Yeah, perhaps trying to use the turbo as an alternator would be wasteful. Although using an ultracapacitor may have merit. A variable-geometry turbo would be better.

So in order to reduce NOx emissions, we need to reduce hot spots in the cylinder, by making sure the air and fuel are thoroughly mixed. I was reading Somender Singh's research about roughening the combustion chamber to ensure maximum turbulence of the air-fuel mixture, and thus maximum mixing.

And the way to minimize energy loss is to make sure all reciprocating and rotating parts are as light as possible. Carbon fiber-reinforced silicon carbide is extremely light, extremely strong, and has high thermal shock resistance. If the parts are lighter, more torque is transmitted to the crankshaft, and if the stroke is also shortened, they can rev higher.

Also, my main reason to have two extra strokes for steam power was to cool the engine in a way that also increase BMEP, and potentially decrease BSFC wrt diesel. That's it. Water is already used to cool engines, why not have it do some work as well. I mean, all you have to do is, after the first power stroke, keep the exhaust valve closed, inject water when the piston is at TDC, and then open it when the piston is at BDC.

I wonder why so many people don't like CVTs? They're more efficient, and you don't have to waste time shifting.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Please explain how injecting water into the cylinder long after combustion has taken place will reduce peak combustion temps and reduce NOx formation in a diesel engine.

The reduced exhaust gas temps will also complicate the performance of the various exhaust emission devices used on modern automotive diesel engines.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

It may be difficult to get the piston back o top dead center with the exhaust valves closed. Something will probably break.

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

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

As this is a blue-sky discussion, I don't think it makes sense to assume that contemporary exhaust emissions technology has a place. Where we stand now is a result of incremental reaction to legislative changes. Evolution does not always provide the best solution. The gasoline people saddled with the three-way cat and all the compromises that brings will attest to that.

This statement: "If the parts are lighter, more torque is transmitted to the crankshaft" is flat-out wrong though.

Regarding CVTs. Not everyone hates them. It's mostly those that have driven them. Human brains find the disconnect between the senses disconcerting. Personally I find even a typical torque converter auto fitted to a small engine to be impossible to live with.

- Steve

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
tbuelna, my reasoning is that the exhaust gases from combustion are quite hot (EGTs are routinely 1200+ degC), and by having the piston recompress those gases, and then injecting water, the water will be vaporized, which will provide force to push the piston back down, and also reduce EGT. High EGT is a sign the engine is not as efficient, as energy that could be used to perform work is instead being rejected as exhaust heat.

This means that both BSFC wrt diesel can be increased, as you can use less diesel to provide a given amount of power, and emissions are decreased because of the same.

And SomptingGuy, my mistake. Lighter parts will allow the engine to rev higher, as less mass needs to be accelerated. So we get more power. If we have enough power at enough speed, gearing can solve the issue of torque. And waross, I believe the flywheel will conserve enough angular momentum to return the piston to TDC with the exhaust valve closed. Also, lighter engines are good in general, as they, all other things being equal, decrease weight, increasing power to weight ratio.

Bruce Crower of Crower Cams has actually built an engine on this design, with great results, and unfortunately he has fallen ill, so someone needs to continue development for him. http://www.popsci.com/scitech/article/2007-05/inve...

High BMEP and low BSFC is what all engine designs strive for.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Recompressing the gases takes work - the work that you just extracted by expanding them! Error - does not compute!

I appreciate the enthusiasm shown here but I sense a lack of understanding and appreciation of why some things are the way they are and why they have become that way over the last century or so of development, and a certain lack of understanding of thermodynamics and heat transfer.

Ceramics have been tried in engines. One thing is for sure; they are expensive. Even if you can get certain parts of the engine to work with ceramic, it is unlikely that you can make the WHOLE engine out of ceramic. Piston rings may be a challenge, for example. Valves would be another. If there is a ceramic material out there that is not brittle, I have not seen it. Just because a given material has the temperature resistance doesn't mean it will play nice with everything else in the engine. Run things at very high temperature, and lubrication becomes a challenge.

And then ... Running things at high temperature might not necessarily raise the efficiency of the engine, anyhow. Just because you are not taking heat out of the engine doesn't mean that heat transfer is not occurring. It just might be transferring heat to the intake charge (bad) rather than to the cooling system.

Diesel engines nowadays have been trying to RAISE the exhaust temperature in order to make particulate filters work, and a diesel engine that conforms to today's emission standards without a particulate filter has not been developed. I'm not saying it's impossible, but it's something that thousands of engineers have been working on for the last decade or two, and they have not found a way yet. If you need that particulate filter then you need to have the exhaust temperature to regenerate it, at least under SOME engine operating conditions.

I would encourage the original poster to look up HCCI. While the truest form of HCCI has practical implementation problems, close relatives of it - call it "almost-HCCI" - are where internal combustion engines are headed. Those have at least the potential for getting away from the diesel engine DPF and NOx aftertreatment systems, although a 3-way catalyst is likely still needed (and needs a certain amount of heat in order to operate ...)

The HCCI and similar combustion systems that I am aware of, rely on re-using a portion of the previous cycle's exhaust gas to raise the temperature of the intake charge of the next cycle, as a means of controlling the self-ignition timing in the next cycle.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
OK, but my theory based around recovering some energy from that hot exhaust. As long as the EGT is 500-800 degF, the catalytic converter will operate. Any temperature above that is wasted energy.

Also, perhaps a way to extract more work would be to have opposing pistons linked together by their heads (i.e. the piston heads are facing on another) with a lightweight yet strong, heat resistant rod, and the strokes timed so that whenever one cylinder is being forced down in it's cylinder, it pulls the other one up in it's the cylinder. Not like the Stelzer cycle though, that's asthmatic.

So the diesel power stroke of one is compression stroke of the other, and the steam power stroke of one is the exhaust stroke of the other. The size of the engine will have to increase a bit to make up for the lost combustion surface due to the rod taking up some space in the combustion chambers, but if we can find a material with a high enough tensile strength to specific volume, this can be minimized.

You know, if you can use less diesel to get the same power, emissions decrease, all other things being equal, because it's happening in lower quantities.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

@OP: If you like opposed-piston diesel engines, take a look at what those crazy people at Achates Power are doing. In common with all the start-ups, their WWW site is packed with fun and games. Educational too. They might even be hiring.

- Steve

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Wow, Achates Power and me have the same idea kinda (theirs seems more thought out though)! I mean, about the cylinder design.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

The turbo charger goes a long way to recover some of the otherwise waste heat of the exhaust gases. It also cools the exhaust gases and improves the efficiency of the engine. Water cooling of the exhaust gases will interfere with the operation of the turbo and lose some of the efficiencies that the turbo delivers.
You are not the first one to look at the hot exhaust gas as a possible source of energy. The turbo is one solution.
Another solution is to use the hot exhaust to boil water in a steam generator. The steam is then used to drive a steam turbine and generator. This is often used with gas turbine generators. The principle is valid for diesel sets also, but diesel installations are seldom large enough to make exhaust gas steam generation economically feasible.

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

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

A third option is to use a thermoelectric generator, or peltier device.

All of these improve the thermodynamic efficiency, but at non cost effective premium.

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: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Since the exhaust will be too cool to activate the turbo, couldn't we just use a supercharger for forced induction instead? Sure, we lose some percentage of power, but it should be made up.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Maybe we could inject hydrogen peroxide after the power stroke when the piston is at TDC to oxidize any UHCs, PMs, and CO remaining after the diesel combusts. You then have to deal with the nitric and sulfuric acid formed from the oxidation of the NOx and SOx, but you could probably neutralize them. And if you have enough nitrogen dioxide and hydrogen peroxide, you should be able to generate enough nitric acid to passivate the combustion chamber and exhaust system.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

OK, i think we've dredeed through many cockeyed theories here. Do you actually have a work related point, or are you just randomly typing stuff in?

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: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Basically, the same idea as before, but using hydrogen peroxide, a powerful oxidizer, instead of water, which I'm no realizing wouldn't quite do as much, as all it does is boil, still leaving contaminants.

We could also inject the hydrogen peroxide during the intake stroke, right before the diesel is injected, which should provide the same effect. Unlike water, H2O2 increases the oxygen content, resulting in more complete combustion. If after combustion of ULSD, you have anything other than carbon dioxide, water, and NOx, your oxygen-fuel ratio is too low.

It's like nitrous, but industrial-strength hydrogen peroxide doesn't require pressurization, and is about $4/gallon. And you only need a bit more than 1 liter to react with 1 mole of cetane, as hydrogen peroxide is a liquid, vs over a 1000 liters of O2 gas for the same reaction.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
My main point, Greg, is trying to extract has much work from fuel as possible, and the best way to do that is to make sure the fuel combusts completely, and all the energy from the heat is used as well.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Hydrogen peroxide is significantly energy-intensive to produce. Think about the big picture. It's also chemically unstable when stored in a high enough concentration to be useful.

I do get the feeling that you are randomly throwing out thoughts without thinking them through. Please do that.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
I have checked the prices of industrial-strength 70% hydrogen peroxide. It's $0.45/lb. Diesel is a bit more expensive per pound, around $0.57/lb. If the hydrogen peroxide is 70% or above, it's hypergolic with organic materials. You just need to keep it away from light, in aluminum containers.

Isn't the point of a turbocharger or supercharger to increase the amount of oxygen available to burn the fuel? The former steals hp, the second requires exhaust modification.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

I suspect just about every man (and his dog) has seen an exhaust manifold glowing red hot and had the idea of recovering all or some of this lost energy by means of a steam engine. Many people and companies have had an attempt - for example BMW in recent times:
http://www.dvice.com/archives/2011/09/bmws_turbost...
In the past probably the most notable example was the Still Engine:
http://www.douglas-self.com/MUSEUM/POWER/still/sti...

For various reasons, it never seems to be really practical.

I was under the impression that Bruce Crower abandoned his work and patents on the very clever Six-Stroke Engine because testing showed that the power recovered was not worth the added complexity etc.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Actually, BigClive, Mr Crower fell ill, so he couldn't finish development. And no-one's figured out yet how to deal with the corrosion from the hot steam, and make sure the steam doesn't wash away the oil.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

HI TsLexi,

Send my regards to Mr Crower. For the hot steam corrosion, there are several coatings used by the steam turbine engines that you can apply to the piston top surface, combustion chamber and valves. It will also help for you to inject the water upward rather than downward. Attach the water injector to the cylinder block rather than the cylinder head. Make sure that your expansion ratio is properly designed to avoid the cylinder temperature dropping too low at the end of expansion stroke that the hot steam will condense. Even when some steam condenses, if you coat the piston rings with diamond like carbon coating and skirt with anti scuffing coating, you will get away from from accelerated wear and seizure. I see big potentials in what you believe in thus I will be more than happy to resolve the challenges that you will surely face.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
Yeah, azmio3. And if we use hydrogen peroxide to augment the oxygen from the forced induction system, we can get more complete combustion, which means higher power and lower BSFC.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

If what you want is to generate steam to power a heat engine using hydrogen peroxide, why don't you simply flow the hydrogen peroxide over a metal catalyst bed to produce high temperature steam?

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

(OP)
That's a better idea. We can divert the steam into a turbine, and use the oxygen to power a gas turbine, and connect the two shafts.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

TSLexi,

Why not use oxygen. The chinese researchers use onboard oxygen generator for the oxygen supply. You can burn low quality fuels without HC, CO and PM problems.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Think about the energy that it took to make the hydrogen peroxide in the first place.

"There is no such thing as a free lunch"

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

The Crower 6-stroke is an interesting engine. But, it uses water as a consumable, NO GOOD for a mobile powerplant, unless you recover the water by condensing it, NO GOOD for a mobile powerplant. Also, the power gain from the extra 2 strokes is on the order of 10-20% for a loss of 1/3 the 4-stroke power strokes -equivalent to wasting 1/3 the mass of the engine; NO GOOD for a mobile powerplant.
For a stationary plant with a continuous supply of fresh water it may be fine. Cooling costs become power from cooling -provided you don't insist on distilled water.

Past efforts at solenoid valve actuation have not been impressive. However, the ones I have seen use a magnetic core attached to the valve stem with a coil around it -classic solenoid. Do you think the voice coil model may offer better performance???? Look at hard drive head actuators. Super magnets keep getting stronger.

RE: Compound expansion plus water injection to increase fuel efficiency of a Diesel cycle engine?

Compound expansion recovers energy "dumped" by the single expansion process. However, it costs mechanical weight and complexity. The old compound piston steam engines were WAY larger and heavier than the 1st, single expansion stage.
The stages that follow the 1st stage are "bottom cycle" stages. The energy they recover is normally only a fraction of the energy recovered by the 1st stage and the volume of gasses they process is MUCH greater.
If the bottom cycle stages are of the same design as the 1st stage this is a big time looser for a mobile powerplant. However, the exhaust turbine is a relatively very small device for recovering bottom cycle energy behind a piston engine.

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