5 stroke engine

[vederstein]

I was continuing to think about this engine that GG created.

First of all sir, congrats on such a cool design and without any plans! So what I say isn't any type if criticism on your work, I'm just pondering ways of making engines more thermally efficient.

There's a company that's working on a crazy efficient opposed piston two stroke diesel engine. Per the video below, properly outfitted, they're approaching thermal efficiencies of around 50%. This is phenomenal!! (For example a gasoline engine in a car is about thermally 25% efficient. A nuclear power plant about 35% efficient. A steam locomotive about 5% efficient.)

I was thinking of an addition to this engine and again it's not a new idea. In fact, this idea was used in WWII aircraft engines: Water Injection. Just after ignition, inject a small amount of water into the engine. The heat of combustion will then not only push the pistons apart, but will create steam to push on the pistons as well.

The balance would be to inejct only enough water to counteract the amount of heat removed via a traditional water jacketed cooling system. What I'm envisioning would have no cooling system. What is currently waste heat would be converted to steam to push on the cylinder creating power.

Also, If the engine could run about 150 celsius with the exhaust the same temperature, opportunities abound for weight reduction. There are industrial plastics that can easily withstand these temperatures which would replace what are now metal components.

Comments?

...Ved.

 

[Anatol]

Ved

when I was a college - in Australia - there was talk of hottrodders using water injection to increase compression, so its a known technology. Seems obvious, I've always wondered why I've never seen it used commercially. Wikipedia - of course - has page on it (this is why I give money to Wikipedia). Turns out it was used in aviation and is in currently active development "In 2015 BMW has introduced a version of their high performance M4 coupe, the M4 GTS, that combines water injection with intercooling."

Another post noted the similarity to the steam compound engine, as a method of energy scavenging. I've been thinking about compounds again recently - has anyone here built one? They went out of fashion as faster uniflows took over, but stayed relevant for big stationary and marine applications - a couple of Great Lakes ferries (still?) use them.

Love the opposed piston engine! Clever use of ports for both inlet and exhaust! But again, (afaik) the two-stroke exhaust port was an adaption of the prior and well developed steam uniflow design.

hmmm, just noticed this is a very old thread.

 

[Steamchick]

I would like to counter your hypothesis of water injection using thermodynamic theory... .but I don't know enough to even try. And if BMW are doing something they have the expertise (and money!) that would support your ideas. But I do think Otto (a very clever lad!) got it right with high compression - synonymous with high temperature - for efficiency. So I am strugging to understand how water-injection to combustion chambers can increase effecency? It doesn't add energy so how can it increase power?
But late water injection (perhaps after the catalyst?) to cool exhaust could extract more heat.. or rather cool the gas flow by making low pressure steam from added water, but at the expense of water handling equipment.. and I can't figure how to extract the power from low temperature, low pressure steam and gas at very high volumes...? But BMW have some reason... "better men than I"...
K2

 

[Richard Hed]

Ved

when I was a college - in Australia - there was talk of hottrodders using water injection to increase compression, so its a known technology. Seems obvious, I've always wondered why I've never seen it used commercially. Wikipedia - of course - has page on it (this is why I give money to Wikipedia). Turns out it was used in aviation and is in currently active development "In 2015 BMW has introduced a version of their high performance M4 coupe, the M4 GTS, that combines water injection with intercooling."

Another post noted the similarity to the steam compound engine, as a method of energy scavenging. I've been thinking about compounds again recently - has anyone here built one? They went out of fashion as faster uniflows took over, but stayed relevant for big stationary and marine applications - a couple of Great Lakes ferries (still?) use them.

Love the opposed piston engine! Clever use of ports for both inlet and exhaust! But again, (afaik) the two-stroke exhaust port was an adaption of the prior and well developed steam uniflow design.

hmmm, just noticed this is a very old thread.

There was a man who developed a 6 stroke engine that had four conventional strokes for gasoline and two strokes for water injection which cooled the engine and of course created steam pressure. The engine did not need a radiator system, nor was it air cooled. I don't know what happened, I suspect the felllow died. I'll see if I can find the stuff to show you.

 

[Anatol]

Today at 8:56 AMI would like to counter your hypothesis of water injection using thermodynamic theory... .but I don't know enough to even try.

I am strugging to understand how water-injection to combustion chambers can increase effecency? It doesn't add energy so how can it increase power?

I'm not an applied physics PhD or engineer either, but my intuition (which can often be wrong) is that hot exhaust gas is wasted energy. Using that heat to turn expand atomised water into steam, thus creating extra compression in the cylinder.

 

[Steamchick]

OK... I hear you but I don't understand. Does it mean that the "exhausted heat energy" is actually less if you add the water during the power stroke? - Or just more molecules at a lower temperature? Because (with my limited brain and education) - the heat "energy" is the compound of mass and temperature... not temperature alone. (Anyone understand thermodynamics to help us understand this one?). I would have GUESSED that injecting water into the combustion chamber part way through the power stroke would lower the pressure by cooling the combustion gas. Below 350 deg C it stops burning (and releasing chemical energy as heat). So I suspect it may work on an engine at very high output (full throttle) but not at lower powered conditions - which is possibly why it has been used as you suggest. Also, modern engines for road use (maybe not large marine plant etc.) need catalyst exhaust after-treatment - which needs to be up around 600 deg. C to ignite and function as a 3-way or 2-way catalyst. So cooling the exhaust means dirtier exhaust.... contrary to many National laws since the mid-1970s. As a lad... - before catalysts in exhausts were thought of... - I was taught that cars and motor-bikes run better in damp air - but this was explained as the cooler intake air, being cooler at point of ignition, so less susceptible to pre-ignition, as well as the combustion being slower as it was heating a tiny amount of water as well as the fuel and air, which again reduces the chance of pre-ignition.
Teach me more please, I'm curious to improve my understanding!
K2

 

[Anatol]

> (Anyone understand thermodynamics to help us understand this one?).

Don't take my notes as anything but idle speculation over a beer...

> I would have GUESSED that injecting water into the combustion chamber part way through the power stroke would lower the pressure by cooling the combustion gas.

so - any conversion of water vapor to steam will increase pressure, and ... I don't know if the pressure generated by combustion is due to thermal expansion of combustion products or if combustion produces bigger molecules (that sounds about as juvenile as my understanding of combustion chemistry/physics is).

> Also, modern engines for road use (maybe not large marine plant etc.) need catalyst exhaust after-treatment - which needs to be up around 600 deg. C to ignite and function as a 3-way or 2-way catalyst.

> I was taught that cars and motor-bikes run better in damp air

I heard this too. But the explanation I heard was that excess heat turned water vapor into steam, creating more pressure in the cylinder and cooling it at the same time - but I'm repeating myself and repeating stuff I heard 30+ year ago.

Actual thermodynamics engineers, please chime in

 

[Richard Hed]

OK... I hear you but I don't understand. Does it mean that the "exhausted heat energy" is actually less if you add the water during the power stroke? - Or just more molecules at a lower temperature? Because (with my limited brain and education) - the heat "energy" is the compound of mass and temperature... not temperature alone. (Anyone understand thermodynamics to help us understand this one?). I would have GUESSED that injecting water into the combustion chamber part way through the power stroke would lower the pressure by cooling the combustion gas. Below 350 deg C it stops burning (and releasing chemical energy as heat). So I suspect it may work on an engine at very high output (full throttle) but not at lower powered conditions - which is possibly why it has been used as you suggest. Also, modern engines for road use (maybe not large marine plant etc.) need catalyst exhaust after-treatment - which needs to be up around 600 deg. C to ignite and function as a 3-way or 2-way catalyst. So cooling the exhaust means dirtier exhaust.... contrary to many National laws since the mid-1970s. As a lad... - before catalysts in exhausts were thought of... - I was taught that cars and motor-bikes run better in damp air - but this was explained as the cooler intake air, being cooler at point of ignition, so less susceptible to pre-ignition, as well as the combustion being slower as it was heating a tiny amount of water as well as the fuel and air, which again reduces the chance of pre-ignition.
Teach me more please, I'm curious to improve my understanding!
K2

Most materials have a "latent energy" which is an amount of energy that it needs to either melt or solidify or boil or condense. What this is is say for ice, ice melts at 0deg (or 32) but once the ice warms up from say -10 deg, to 0, it still takes MORE energy to actually melt still at 0deg. Same for boiling. For different materials, this energy is more or less than other materials. Water is very high. So for this reason when liquid water is atomized into a hot situation, it will cool the thing just in taking up the necessary energy to vaporize. However this has a good point to it in that it acts the same way alcohol in the gasoline acts, that is, it acts like octane which slows the burning of the fuel down to a point where it does not "explode" or knock the engine and thus adds engine life. Once the water passes the point where the necessary energy has overcome the latent energy needs, the water vaporizes and acts exactly as steam pressure does in a steam engine. Of course the exhaust is cooler, but I don't know how much cooler. I don't belileve you would want to put your hand in it for very long. Once the water is vaporized, it expands rapidly and easily with much less energy, as it is the Van der Waals forces which cause the high latent energy needs to vaporize.
There are other factors involved which I doesn't know much about. This is probably onlhy a partial explaination.

 

[Steamchick]

I'm a "simple physics" student (alias engineer) - and not too "hot" on chemistry and thermodynamics. But recognising it takes a lot of the heat (i.e. energy in the kinetic oscillations of the molecules) released from the chemical interaction of the fuel gases (combustion) to even vaporise the injected water, that will cause a significant pressure drop in the combustion gases. The water droplets will boil to steam at the elevated temperature matching the pressure in the combustion chamber, but as this pressure is dropping as it expands with the piston the newly created steam will condense back to water, so will only give back some of the energy that it took from the combustion gases. I can't see anything to "increase pressure" as you suggest... and it is pressure that transfers energy from gases to pistons. The net effect I can see is that injected water will capture some heat (= energy) and carry it out with the exhaust. I.E. less efficient than no water injection. So I still don't understand the reason for it. But I am not as clever as BMW and others... ?
Sorry, I can't say more than that.
K2

 

[vederstein]

As I wrote earlier, some WWII aircraft engines used water injection to get a power boost when needed (e.g. take off, dog chasing, etc).

Some of the points here are valid and injecting too much water can have detrimental effects on power by absorbing too much heat. As far as my feeble mind takes me (I had Thermodynamics courses some 27 years ago), the maximum water you'd want to inject and be vaporized would equal the heat that would otherwise be removed via the coolant.

I didn't attempt to calculated it, but my gut tells me for each power stroke, you're not really talking about large amounts of water.

For the most efficient (not necessarily powerful) engine, you want the pressure in the piston at the bottom dead center to be at or nearly atmospheric pressure. This would indicate that all available energy was extracted from the fluid and transferred the crankshaft. Ergo, the lowest exhaust temperature would be no less than the boiling temperature of water at that altitude. (about 100C)

...Ved.

 

[Steamchick]

As I wrote earlier, some WWII aircraft engines used water injection to get a power boost when needed (e.g. take off, dog chasing, etc).

Some of the points here are valid and injecting too much water can have detrimental effects on power by absorbing too much heat. As far as my feeble mind takes me (I had Thermodynamics courses some 27 years ago), the maximum water you'd want to inject and be vaporized would equal the heat that would otherwise be removed via the coolant.

I didn't attempt to calculated it, but my gut tells me for each power stroke, you're not really talking about large amounts of water.

For the most efficient (not necessarily powerful) engine, you want the pressure in the piston at the bottom dead center to be at or nearly atmospheric pressure. This would indicate that all available energy was extracted from the fluid and transferred the crankshaft. Ergo, the lowest exhaust temperature would be no less than the boiling temperature of water at that altitude. (about 100C)

...Ved.

As I said, I hear what you say, but I don't fully appreciate the maths or whatever, so (like a lot of clever ideas?) I hold my hands up and say "don't understand". An alternative idea may be that with supercharged engines in WW2 aircraft (to avoid loss of power at altitude, as well as improve max power when needed) the fuel would detonate (pinking or pre-ignition) at high boost, but water injection would delay the pre- ignition point so they could run a higher boost and revs with water injection. I.E. A combustion versus boost issue, not efficiency related? If water injection was for fuel efficiency, I can't understand "why" they used it at times of needing max power, as you describe? Dog-fighting and take-off. However if it was for fuel efficency, I would guess they would use it in cruising-mode to increase the range of aircraft...?
But I a guessing!
Any more ideas?
K2

 

[Steamchick]

Hi Ved, just re-reading your earlier message, and it confused me by "increasing pressure while reducing temperature" ??
I thought pressure and temperature were intimately related (PV=RT ?)?Except at the triple point, or when changing state.... but the boiling point of water changes with pressure.... so surely the only condition for water and steam to exist is with temperature increasing with increasing pressure? You've got me really confused here... Hence " I don't understand" message...
K2

 

[ShopShoe]

RE: Post #51, above:

That is what I have understood about water injection.

Many years ago, the U.S. TV network CBS featured an episode of their "60 minutes" magazine show (I think) in which they attempted to "one-up" a factory car to provide both reduced emissions and improved performance (of the day). The race-car builders they employed to do that added water injection to a stock Ford Fiesta (or was it a Festiva?) and possibly demonstrated it to work, but with the problems of inconvenience for the driver and reduced life of the engine.

My late father, who was a Navy carrier pilot in WWII, watched that program with me and commented that some of the planes he flew had water injection, but the pilots were instructed to use it very sparingly as it would cause other problems in the engines.

FWIW,

--ShopShoe

 

[Steamchick]

Thanks Shop Shoe. That information is worth more than you may appreciate. As US and UK had higher Octane fuel than Germany, and Japan, I had guessed it was a German thing born of an anti-knocking additive when boosting higher than normal for the engine. But if the USAF used it then probably I am wrong? - I think the UK were supplying Lead additive back across the pond to the US as the UK were big users and manufacturers of lead additive. And it was needed for the higher powered engines with supercharging. (e.g. Merlins made by Pratt and Whitney for USAF). I believe all of these tales - I just don't understand (Technically) "why inject water?" and "how it works?".
But I'll find out someday, when it becomes more important to know.
Just now I have "steam boilers" on the brain, as I have a old built boiler - that refuses to seal... - My problem - just the technique of trying to get it warmed reasonably uniformly when 3/4 buried in sand.... and using a few blowlamps. I seem to stress the boiler upon cooling - so any tiny flaws in the silver solder cause a crack - or where I repair on odd spot a pin-hole appears nearby - probably from some new dirt migrating into the joint....? Always seems to be right about the edge of the flame that made the repair.... And I can't see the pin-holes with the naked eye, but they do show tiny bubbles under soap with air pressure. I suspect a "cold-lap" condition where the liquidus meets solidus in the repaired joint.
Thanks again for tales of water injection.
K2

 

[Richard Hed]

Thanks Shop Shoe. That information is worth more than you may appreciate. As US and UK had higher Octane fuel than Germany, and Japan, I had guessed it was a German thing born of an anti-knocking additive when boosting higher than normal for the engine. But if the USAF used it then probably I am wrong? - I think the UK were supplying Lead additive back across the pond to the US as the UK were big users and manufacturers of lead additive. And it was needed for the higher powered engines with supercharging. (e.g. Merlins made by Pratt and Whitney for USAF). I believe all of these tales - I just don't understand (Technically) "why inject water?" and "how it works?".
But I'll find out someday, when it becomes more important to know.
Just now I have "steam boilers" on the brain, as I have a old built boiler - that refuses to seal... - My problem - just the technique of trying to get it warmed reasonably uniformly when 3/4 buried in sand.... and using a few blowlamps. I seem to stress the boiler upon cooling - so any tiny flaws in the silver solder cause a crack - or where I repair on odd spot a pin-hole appears nearby - probably from some new dirt migrating into the joint....? Always seems to be right about the edge of the flame that made the repair.... And I can't see the pin-holes with the naked eye, but they do show tiny bubbles under soap with air pressure. I suspect a "cold-lap" condition where the liquidus meets solidus in the repaired joint.
Thanks again for tales of water injection.
K2

The point abougt a "small" amount of water is that it is a "tiny" amount which doesn't take as much heat out as you seem to be thimking.

 

[Larry G.]

Thanks Shop Shoe. That information is worth more than you may appreciate. As US and UK had higher Octane fuel than Germany, and Japan, I had guessed it was a German thing born of an anti-knocking additive when boosting higher than normal for the engine. But if the USAF used it then probably I am wrong? - I think the UK were supplying Lead additive back across the pond to the US as the UK were big users and manufacturers of lead additive. And it was needed for the higher powered engines with supercharging. (e.g. Merlins made by Pratt and Whitney for USAF). I believe all of these tales - I just don't understand (Technically) "why inject water?" and "how it works?".
But I'll find out someday, when it becomes more important to know.

General Motors marketed production vehicles with water injection, solely for the purpose of knock prevention. The idea and application of higher compression engines was successful but the program was abandoned because of... USER FAILURE. Owners failed to add the required alcohol antifreeze to the injection water tank, allowing it to freeze, allowing the engine to knock itself to death in cold-weather climates. I had ordered research papers from SAE, before internet service.

 

[Steamchick]

Thanks Larry,
That explains a lot.
Thanks Richard. I think that your "small amount of water" makes sense with Larry's comment. I think this is a more reasonable explanation for hot-rodders et al using it, as Anatol mentions. The idea of cooling engines and steam generation transferring more power to the piston - as the 6 stroke engine - sounds intriguing... this one is on Science direct so I'll read and learn.
Thanks all.
K2

 

[NapierDeltic]

Hi,
Kerosene flame temperature is about 2400C , steam cycle high temp is slightly above 500C. There were some industrial applications of topping cycles (many retrofit in stationary plants) based on liquid metal (mercury or other) to intermediate the difference between the 2 temperatures. there were some (succesfull) trials with organic fluids to use wasted heat in steam cycles. Both were based on Rankine cycle and the overlap is named cascade cycle. So there is no real, completely "waste heat"
I have spoken about Peltier elements not because I am necessary a fan of them, but because having a theoretical efficiency much lower then Carnot cycle they still proof a real positive, tangible, output. And thermal cycles can do more! It is not Fata Morgana.

About WWII engines , as I know, the water injection was done in admision and, especially for turbocharged motors, it was the simplest version of intercooling. Vapourising water induced low temperature of air, higher density, higher power. That's why is mentioned at takeoff, where air temperature is elevated and power need is high. Anti-knock effect could be a bonus. It does not improve thermal efficiency so no extra-range for the plane.

On another hand, in normal piston engine, after exhaust phase, if piston goes to TDC and you inject water (small amount and no admission) if cylinder wall temperature is elevated (600C is required by catalytic converter, but average - admit-is lower), what will happen with water? I would say it expands 1600 times to vapour state, generate some pressure and pushes the piston down generating output. This is the 6 stroke cycle. For 5 stroke cycle the things are a bit more complex-mixing 2 strokes in one-, and harder to model in someone's mind. But at least we can figure which are the pros and cons factors and how to block or favour ones or the others. And the main processes considered are quite the same as for the 6 stroke, where there is a gain, as I have mentioned.

Anatol is right in that point and I ask myself how much power comes in IC from thermodynamics and how much from phase change - chemical reaction from liquid fuel IN to gaseous exhaust OUT.
Equal to how much expansion in explosives comes from exothermic reaction and how much from phase change of reactants? So how much IC engine is a pure thermodynamic engine.

 

[vederstein]

it confused me by "increasing pressure while reducing temperature" ??
I thought pressure and temperature were intimately related (PV=RT ?)

Gas laws and steam tables are still in effect here, but I doubt the ideal gas law works. Maybe I'm underthinking it, but an engine's cooling system is there to remove excess heat that would otherwise damage components. If that heat went into vaporizing water, then the water vapor (steam) could be used to help push down a piston.

What's to remember here is assume the energy input (gasoline flow) is constant. So we have a constant energy input (Q). Per the first law of thermodynamics, that energy must go somewhere but it cannot be created or destroyed, just changed forms. So an engine would be Q=E1 + E2 +E3 where E1=useful power generated, E2 = waste heat to the low temperature mass, and E3 = heat removed via other means (radiator).

I'm discussing taking some of E3, which goes through the radiator and use it to create a bit of steam instead.

From a thermodynamic perspective, you would never want to have a heat removed from the system except to the low temperature mass. In the case of a gas engine, the low temperature mass is the exhaust. The high temperature mass is the combustion. The ratio between the two is the Carnot efficiency. No heat engine can be more efficient at those temperatures.

Obviously there's more practical limitations to this. The whole discussion here, though interesting, is a bit academic.

Speaking of the laws of thermodynamics, here they are in layman's terms:

1st law: You can only get out what you put into it.
2nd Law: You can't even get that.
3rd Law: Things always get messier unless you work to keep them organized.

...Ved.

 

[Tim Wescott]

... I just don't understand (Technically) "why inject water?" and "how it works?". ...

Particularly after reading the relevant Wikipedia article I'm pretty sure that 90% of the answer is "because it cools the incoming charge and prevents detonation", with a teeny bit of "oh, and it cools it (like an intercooler) so you can stuff more charge in there".

It's one of the cited advantages of using alcohol fuel over gasoline -- alcohol vaporizes readily, but has a high heat of vaporization. So the charge filling the cylinder is cooler, and thus contains more molecules at the same pressure than it would be otherwise.