High efficiency ICE (exhaust heat recovery)

[amnonholland]

Since ICE's reject a large deal of thermal energy from the exhaust i had the idea of utilizing this to possible improve efficiency.

Idea

Take say a 4 cylinder engine and route the exhaust from cylinder 1 and 4 to the intake of cylinder 2 and 3. Replace the spark plug in 2 and 3 with a high pressure water injector. Basically you would be converting the waste heat from the cylinder 1 and 4 exhaust to mechanical energy (i.e. a steam engine). Cylinder 1 and 4 would probably need forced induction to make enough power for compressing 2 and 3. May need a strong diesel cycle engine to withstand forces. You may be able to reach much higher thermal efficiencies.

Potential problems.
- Would have to be a low reving engine since steam expands only moderately quickely
- the compression stroke in cylinder 2 and 3 would generate really high temperatures before water is injected, which would create insanely high pressures.

Could this possibly work? Please provide comments and ideas

[Daox]

Its possible. Google the crower 6 stroke engine, it uses a similar idea.

[Dr. Jerryrigger]

I've been thinking about this since 9th grade, when I read somewhere that ICE's waist about 90% of the fuel energy. I was thinking more like a steam generator and a turbine as a pony motor. After I came up with this; i did some searching and found that Mercedes Benz has a patent on it.

[Phantom]

If you do try to do this I would recommend adding a valve or just a secondary pipe on the exhaust. That way it can vent excess gas to the exhaust if you go WOT then to 0% throttle there will be excess pressure forcing both sides on the engine to work harder.

[jdgFirefly]

I like the Idea and I think it will work, but it's not likely to work as well as you might think.

I read somewhere that a modern engine is doing good if it can get 20%eff the rest is waste. about 45% is wasted heat to the cooling system and 35% wasted heat and pressure to the exhaust.

So with your idea, you effectively cut your engine displacement in half too try for the 35% wasted in the exhaust. But you are not going to be able to recover the full 35% because the steam engine is also not 100% eff. Like all heat engines the efficiency greatly depends on the initial and the final temperature of the cycle. the greater the difference the more efficient.

Say your engine exhaust temp is 900 deg f, your are able to expand the steam and exhaust until the steam almost starts to condense at 215deg f. If this is the case than your max theoretical eff would be about 50%. So you have recovered 50% of the original 35%. Well not exactly. you now have to add your real world inefficiencies like heat loss to the block, friction, blow-by, the power needed for the injectors, yada, yada.

Also a large inefficiency would come from the fact that your cylinders are not optimized for your steam cycle. For example they might be to small and not allow full expansion or too large and cause over expansion. Optimizing cylinder size might be hard because the heat available is always changing with engine load.

Sorry for sounding so negative, I do like the idea but these are just some possible design hurdles that came to mind.

[Frank Lee]

Originally Posted by Dr. Jerryrigger

I've been thinking about this since 9th grade, when I read somewhere that ICE's waist about 90% of the fuel energy.

My waist stores about 90% of my fuel energy intake...

[amnonholland]

i understand it wont recover all the heat energy. Some is a good start.
Yea the steam cylinders would are not optimized for steam.(wont be able to have complete expansion)

In the compression stroke of cylinders 2 and 3, say air entering would be around 600K from the exhaust of the other cylinders. In the compression it would be heated to about 1200K (assuming a compression ratio of 9). When water is injected into this high temp gas it would created huge pressures. On steam expansion the exhaust(steam) of these centre cylinders would be cooler. Effectively there are only 2 cylinders exhausting heat as opposed to 4.

I would run water injectors off the spark ignition signal.
Does the the plug fire twice every 4 stokes or once? Because if it fires twice then water would be injected just before the compression which would cause the engine to lose power(due to compressing steam. we dont want this). we would only want injection once per 4 strokes right after compression. Clearly water injection time would have to be precise.
Could a diesel injector be used and a diesel pump?

Also the engine wouldn't run as smooth because of the different expansion rates and torques created by the steam pistons as opposed to the fuel pistons.

I really think its worth a try and if i can get hold of a old second hand engine i may do some experimenting.

[Piwoslaw]

Originally Posted by amnonholland

I would run water injectors off the spark ignition signal.
[...]
Could a diesel injector be used and a diesel pump?

Why do you need spark plugs in the first place? As mentioned earier, you'll need a diesel block, since it's stronger, so why not use the diesel cycle in the fuel side to begin with, and use the injector signal? Or instead of injector signals use two injector pumps, one for fuel and one for water, and you can adjust the timing of the second pump. The only downside is that diesels are more efficient, so the exhaust will be slightly cooler, but I think it'll still be more efficient than converting a gasser.

Originally Posted by amnonholland

Also the engine wouldn't run as smooth because of the different expansion rates and torques created by the steam pistons as opposed to the fuel pistons.

Use an 8 cylinder diesel in such a way that there is always a pair of cylinders in the same phase. One cylinder in each pair would be fuel fired, the other water.

[mpgx2]

Interesting discussion..

Actually I have a book from 1910 on heat engines and the
'latest' addition is actually 'the car' lol. Fascinating reading
really. Car engine designs are not changed as much as
people are led to believe.

Anyway, you can pump steam into the combustion chamber
of any cylinder. And some people claim it works really well
as a fuel saver.

Having the water right where the explosion is, enables a
transfer of heat to the water. The water turns to steam
and expands some 1800 times. Driving the piston.

To get real heat recovery, have a think about how to dispose
of the radiator altogether. Once you do that you are not
throwing heat away.

1/3 of all the fuel energy gets flushed out the radiator.

I think convenience and simplicity for motorists have dictated
a recircling heat dump system. I understand why car companies
wouldn't bother with steam cars.

but in these days of environmental sensitivity, its fun toying
with the concept of a 10% fuel, 90% water automobile.

I'm all for the idea of the choo-choo car.... lol

[Piwoslaw]

Originally Posted by mpgx2

I think convenience and simplicity for motorists have dictated a recircling heat dump system. I understand why car companies
wouldn't bother with steam cars.

Two more reasons: freezing problems and cheap oil. There are still places where oil is as cheap as water.