Internal expansion steam engine?

[ynot]

I have often wondered if it could be possible to make an internal expansion steam engine where the steam is created directly in the piston chamber (similar to a diesel engine). Diesel engines heat air with compression to an extent that it causes the diesel to ignite (explode). Could compression cause enough heat to turn water in to steam. I realise that pressure also raises the boiling point of water and this could mean that the pressure would always prevent the water from turning in to steam. If this is so, could the pressure be quickly released after the heat has been created? I also realise that a sudden drop in pressure causes a drop in temperature so this may not work either. Yet another silly water for fuel idea?

 

[casebro]

No water needed. Just building a compound engine ought to make an extra 20% efficiency. That is when you use the exhaust pressure form the primary cylinder to push a second, bigger piston down. The advantage of using water would be that condensing the exhaust from the second cylinder back into water will create a vacuum, sucking the last cylinder down. The problem with all this low tech efficiency is that it all weighs a bunch compared to an internal combustion engine. 10 horsepower today weighs 100 pounds. A steam system with boiler and condenser would weigh well over 1,000. Okay if you live in the backwoods and can chop firewood, not good for diving a car to the convenience store. Google for "live steam".

There were compound internal combustion engines 100 years ago. But using my guestimates above, the 100 pound engine making 10 hp, would need to double it's weight for an additional 2 hp. Also not good for a trip to the liqour store.

 

[ynot]

No water needed. Just building a compound engine ought to make an extra 20% efficiency. That is when you use the exhaust pressure form the primary cylinder to push a second, bigger piston down. The advantage of using water would be that condensing the exhaust from the second cylinder back into water will create a vacuum, sucking the last cylinder down. The problem with all this low tech efficiency is that it all weighs a bunch compared to an internal combustion engine. 10 horsepower today weighs 100 pounds. A steam system with boiler and condenser would weigh well over 1,000. Okay if you live in the backwoods and can chop firewood, not good for diving a car to the convenience store. Google for "live steam".

There were compound internal combustion engines 100 years ago. But using my guestimates above, the 100 pound engine making 10 hp, would need to double it's weight for an additional 2 hp. Also not good for a trip to the liqour store.

Thanks - very interesteing. I'm suggesting using water as the sole power source. I guess the engery required to turn water in to steam always exceeds the energy created.

 

[TjW]

<snippage by TjW>
10 horsepower today weighs 100 pounds.

[nitpick]

I think you'll find that two-strokes can do considerably better than this.
For example, the Hirth F33 can make 28 HP @ 6000 RPM, and it weighs 33 lbs.
[/nitpick]

 

[Asolepius]

To a small extent this has already been done, with water injection. WW2 aircraft commonly used water-methanol injection, mainly to allow much higher boost pressures without detonation, but the water also of course boiled into steam internally.

BTW are you seriously suggesting water as a sole fuel? Of course the input energy will always exceed the output energy, which I think you have realised. Also, because the output is steam it contains latent heat of evaporation so there is a very big energy loss in the system, not anywhere near a gain. This is the main reason that steam engines without regenerative condensers are very inefficient. I think about 10% for a typical locomotive compared with over 30% for a petrol engine.