How much energy is wasted in a petrol/diesel engine....

[aceparts_com]

Pondering on from past discussions I was wondering how much waste heat energy (in KW's) could possibly be recovered from an average 100bhp petrol/diesel engine running at say half/maximum load.

I was thinking along the lines of heat exchangers on the cooling system, exhaust etc?

[Avocet]

Can't give you exact numbers but the new "Euro IV" diesels are so efficient that manufacturers struggle to find enough waste energy to work the heater on a cold day! Increasingly, they have auxillary heaters that burn diesel fuel and dump the heat into the cooling system to keep the water temperature up!

That doesn't mean to say they're 100% efficient - far from it, I think they're about 40% (i.e. 40% of the energy in the fuel goes into pushing the car around) but extracting the remainder could be very tricky...

[Pigeon]

The usual rule of thumb is that "it splits three ways". A third of the energy in the fuel comes out as useful work at the flywheel, a third comes out as heat through the cooling system and a third comes out as heat in the exhaust. The "third as work" is often a bit optimistic

The heat coming out through the cooling system is at too low a temperature to be of any use for converting to some other form of energy, but the exhaust is a different matter and you can recover a significant proportion of it with an exhaust turbine. The common and obvious example is turbochargers, and a large one can recover several tens of horsepower, but there have been engines designed such as the Napier Nomad which added the power from the exhaust turbine to the crankshaft, and achieved very good overall efficiency as a result. It does tend to get a bit complicated though...

[chuntington101]

here is one possiaable way to improve the efficeny of and engine useing the huge amount of energy thats weasted in heat! i really like the idea and really looks like it could work! and even if there was NO powere gain it wouls still mean you could bump the compresion ratio and boost (if running) on normal fuel and not worry about pinking!

www.pistonheads.co.uk/gassing/topic.asp?t=248517&f=66&h=0

also we could try running cooler running fuels like alcohol! the disadvantage with allky is you need about twice the volume! but on a turbo engine is can be amazing! you can forget radiators (or dramatically reduce there size) and intercoolers. and you can un much higher compresion with boost! and example was a drag engine is read about. it was making around 2500bhp, was runing about 40psi, had no intercoolers and ran 10:1 compresion ratio!!!!!

so if you could make alky with more energy per cc then it would be great!

thanks Chris.