Recycling heat energy

[Metallover]

Well, When gas burns in an ICE engine, 40% is wasted as heat and 30% is used to cool the engine. Only about a quarter of the energy in the gas is converted to mechanical energy.

Do you think there would be some pretty big gains if someone came up with an efficient way to recycle the heat? Is there already a way?

[NeilBlanchard]

Hi,

Sure, heat can be used to produce electricity, so you could replace the alternator.

But it would be much better to convert more of the fuel's energy to mechanical motion in the first place -- and produce less waste heat. The cam driven Revetec engine is ~2X as efficient (39.5%) as the typical piston engine, since the mechanical leverage of the cams can be designed -- crankshaft and connecting rod engines are locked into sinusoidal motion, which wastes a lot of energy.

Also, the weight of the vehicle is a huge drain -- check out Amory Lovins on the specifics:
Amory Lovins on winning the oil endgame | Video on TED.com

[Ryland]

thermo electric generators can turn about 3-5% of the waste heat from a source like your exhaust in to electricity at a cost of about $2,000-3,000 for a single car to elimenate the alternator.

[jesse.rizzo]

Turbochargers have been used for a long time to capture waste energy from the exhaust.

[Daox]

BMW came up with a 'turbosteamer' engine that used the heat from the exhaust and coolant to provide propulsion power. I don't think it ever went anywhere though.

[NiHaoMike]

What about inject water into the exhaust after the cat and spin a turbine with the mixture of exhaust gas and steam?

[Metallover]

If 30% of the energy in gasoline is wasted keeping the engine cool, can something like a "mesh" hood help mpg? Something made out of a material that allowed heat to rise up through it yet keep most of the passing air from creating drag would be perfect.

Imagine your car without a hood on. All the heat from the engine could rise out of the opening.

You could even go as far as putting heatsinks on the engine.

Anyone want to try this out?

[Christ]

Nope, because it won't work. The fuel used to keep your engine cool is primarily designed to keep it from knocking, which can't be helped by external cooling. You can help it with water injection, though.

A tight enough mesh probably wouldn't affect aero too much, but it would let the engine overcool between trips, meaning that you'd probably spend more time in open loop operation, which is less efficient overall, as a general rule.

[DonR]

Engine bay vents in the bodywork (hoods/fenders) with coolant temp. controlled shut off valves. The valves would open at the same time the grill blocks open. Hope they don't stick closed like a thermostat.

Don