Four stroke waste heat engine?

Could we build a four-stroke engine that runs on the exhaust heat of another engine? My idea is to have a four stroke engine **** in the exhaust from another running engine, instead of fresh air. Compress that hot exhaust on it’s compression stroke, then at TDC inject a burst of steam, through some kind of injector. The boiler water could be preheated by the cooling system of the first running engine. Does this sound at all feasible?

5 comments

Comments (5)

justincorhad

Aug 09, 2022

Thanks for the reply! I’m curious how the combined efficiency would be less? Wouldn’t the efficiency of the system go up as whole since more of the fuel energy is being extracted?

Thermodynamics Forum

Aug 09, 2022

Replying to

I mean to say if we consider the energy that had been put into making of the waste heat recovery system (like for example the energy that would be required in making steel components).

I mean to say the impact on environment as a whole because of the additional components. This is my guess though.

You would need to do a 'Life Cycle Assessment (LCA)' to quantify the impact.

Yes, you are right. At the local system level the thermal efficiency would increase slightly.

justincorhad

Aug 09, 2022

Replying to

Okay I see what you’re saying now, and I completely agree with that! Actually when I originally had this idea it was to take a v8 engine, have one bank run on gas or diesel, feed that exhaust to the other bank which would then compress and steam inject. I wonder if it might be a better option To do it that way?

Thermodynamics Forum

Aug 09, 2022

Replying to

You should find out the pressure and temperature at the time of spark plug igniting the fuel. The temperature is in the range of 2500 degrees Celsius just after fuel ignites. So the steam should also be able create that much amount of energy to push the piston towards BDC. If somehow its possible to produce such a high pressure and temperature steam then it should be feasible.

Thermodynamics Forum

Aug 09, 2022

Hi,

Thermodynamically speaking this system is possible. It does not violate the first or second law of thermodynamics as long as you are providing the gasoline/diesel into the first engine.

But,

The thermal efficiency (gains) of the combined system would be far less.
The gains you would make will not be economically feasible. (The cost you incur making such a system - fixed as well as running costs).

The exhaust heat has less potential to get converted into power(work). The more and more chemical conversions any substance goes through, the lesser its capacity to convert it into work becomes.(also called 'availability' or 'exergy')

Considering all of this, you can still make possible this system. But making it economically feasible would be challenging but not impossible.

The I.C. engine has been the result of decades of improvements and research, somebody might have thought about it and there must be scientific material available.

Do try to find the papers on Google Scholar

Let everyone else here know if you find something.

Cheers!