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diesel exhaust heat recovery

diesel exhaust heat recovery

Besides known EGR principle to lower NOx and partly to heat up engine quicker will there be any benefit to warm air intake throuh exhaust heat exchanger. By ideal gas law higher than compression ratio higher the efficiency of the engine (of course CR engines in practise has retard injection to some point thus extraction of heat does not start at TDC). If the air itake is warm up by the hot exhaust the overal efficieny would'n increase since from the gas law thermal efficiency is difference of temperatures at TDC and BDC and if the intake air is hotter that only means that exhaust would be hoter but temp differences of TDC and BDC would stay the same (in theory).

So this would only gain efficiency if we used combined cycle where we'll use exhaust heat to make steam and run steam turbine.

Also some exhaust kinetic energy (when exhaust valve opens there are still some pressure, round 5 bar) can be extracted via turbogenerator (turbine wheel powering alternator).

RE: diesel exhaust heat recovery

I'd think it would be adverse, at least looking at things just as the thermodynamic cycle, you want your initial state to be as close to the dead state as possible. Adding heat pre-cylinder heat will also push up the high temp, and promote NOx formation. EGR limits NOx formation by reducing the %O2 in the intake charge, IIRC. My old benz diesel has a duct to get cold air from the crack between the valence and the hood, instead of warm air from the engine compartment. IDK if this is supposed to help power, NOx or both.

I was thinking the above,

And then saw this:
so, confused.

RE: diesel exhaust heat recovery

Are you asking if it would be beneficial to heat the intake air of an engine?

In general, no. You generally want the intake air as cold as is feasible, for increased charge energy density.

Yes, you could use exhaust heat to create steam and drive a turbine- but you'd be asking the ICE engine to do more work than it is already doing. The air that carries that heat must be pumped, and the engine is going to provide that pumping power.

There is no free lunch.

RE: diesel exhaust heat recovery

It is Done on at least one form of "engine": gas turbines can be fitted with a recuperator, which operates as you say to transfer energy from exhaust to inlet and improve the plant efficiency.

This is not used on RICE (reciprocating internal combustion engines) for the reasons given by others above.

RE: diesel exhaust heat recovery


I didn't watch that entire video, but it appears to me that by accelerating the EVC event they are just creating 'passive' EGR behavior.

This does cause some charge heating- but after the charge is inside the cylinder and the IV is closed. That's a different animal than heating the charge and then having to pump that lower-density air at the same mass flow rate.

RE: diesel exhaust heat recovery

There may be some advantage to intake air heating in the odd situation for cold weather applications, very common to use an electric intake air heater for cold starting. I have seen just about every other fluid heated via exhaust in these applications, everything from various engine/trans/hydraulic oils to coolant however intake air isnt one of them.

RE: diesel exhaust heat recovery

Heat recovery is done on stationary diesels that drive generators.
The typical scheme is to boil a low boiling point organic (butane) and then drive a small turbine with this working fluid.
These systems are referred to as ORC and common in recovering energy from low value sources (also used in generating power from geothermal heat).
It takes a lot of equipment and controls to run these systems well.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: diesel exhaust heat recovery


Yes one can recover heat from the engine, but this this is not what the op raised.

Heat recovery from exhaust, jacket water, lube oil etc is common and known as combined heat and power / cogeneration.

Using exhaust heat to raise combustion air inlet temperature is a different principle.

RE: diesel exhaust heat recovery

For waste heat recovery I think scroll expanders with an ORC cycle hold a lot of potential. This company is doing a lot with scroll expanders/compressors

Air Squared :

RE: diesel exhaust heat recovery

I can't find a reference to it on the internet - but I seem to recall that Volvo had what they called a "adiabatic" diesel engine where the exhaust heated the intake air. Plus there were other heating saving measures like ceramic piston tops and cylinders - the idea being that as little heat as possible was lost. I think they got pretty good results from it but (as far as I know) it never went into production.

There was also Smokey Yunick's "Mystery Engine".

RE: diesel exhaust heat recovery

I was thinking that any ICE has wery low thermal efficiency. Even modern diesels with common rail technology hardly achive 40% thermal efficiency. EURO 5 diesels has lower compression ratio 1:18 (Mazda skyactive for example) and by the ideal gas law they should be less fuel efficient but as they say injectors open earlier, giving more time for diesel fuel to atomize and when combustion ocurs it takes less time for the fuel molecules to react with oxygen so heat released occurs quicker meaning that more energy is extracted by the piston. I read that BMW is working on engines exuiped with small stem generator to improve fuel efficiency (up to 15%). Combined cycle is well known and used in power plants or large marine diesel but tending to be integrated even in small car's power plants. And when we talk about diesel steam combined cycle, higher than exhaust temp more steam can be generated, so could preheating air intake make any difference?

Also turbogenerators like found in F1 race cars could be used on either petrol or diesel engines, since there are sufficient pressure and kinetic energy of exhaust gases that could be extracted (by the studies round 5 to 10kW alternators could be fitted to turbine on average petrol car's engine).

RE: diesel exhaust heat recovery

Regarding the "adiabatic" diesel engine that BigClive mentioned:

Roy Kamo did a lot of work on this, most of it government funded. I saw him give his sales pitch once in the 1990's. He founded a little company that still does stuff related to thermal barrier coatings, etc.

Also, Toyota claimed back in about 1993 that they would have an adiabatic diesel engine in production within five years. Once again, the revolution never happened.

Maybe Volvo did something similar but I never saw anything on that engine.

On the original post:

For max efficiency on an engine cycle, whenever you are compressing a fluid, the fluid should be as cold as possible.

Why? So that there is less work done compressing the fluid. If you are doing the compression in two stages, cool the fluid between the stages.

Bottom line:

Unless you are trying to warm up the engine quicker, don't heat up intake air on an IC engine.


RE: diesel exhaust heat recovery

If the intake air temp is hotter, then less heat from the cylinder and combustion chamber will be transferred into the intake charge prior to ignition. The combustion chamber would probably maintain hotter temperatures, but the cooling system might compensate for it to keep the coolant temp at equilibrium. By heating the charge prior to that, you would be changing the temperature gradient in the engine to have higher combustion chamber temps prior to ignition. The negative impact is the decrease in charge density.

As it is, the intake charge is heated as it is being drawn into the engine. Heat is transferred into the intake charge from the combustion chamber, piston, and cylinder. It then heats up more under compression, but some of the heat during combustion is transferred into the metals that compose the combustion chamber.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: diesel exhaust heat recovery

If I recall correctly, the upshot for so-called "adiabatic engines", apart from the temperature issues affecting materials and lube oil, was that most of the heat that was prevented from escaping via the walls of the combustion chamber ended up escaping with the exhaust instead.
Incidentally, as a new graduate from UBC in 1986, I met Roy Kamo when he visited as a judge for the Expo 86 IVDC (innovative vehicle design competition, hosted by UBC Engineering), and I ended up applying and getting an offer for a job with his outfit, Adiabatic Engines. While they were prepared to sponsor my application for a green card, it fell through because there were too many out of work mechanical engineers in the Indianapolis area at the time, which effectively blocked the sponsorship of an inexperienced would-be immigrant.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: diesel exhaust heat recovery

I'm in the turbomachinery business BTW; thermodynamically all that heat in the exhaust looks like juicy low hanging fruit, but when you figure the cost of a system to turn it into useful work and deliver it, the price/kW is pretty horrendous compared with the basic prime mover. Especially with energy prices as they are today, I don't see mainstream turbocompound systems entering the market in a big way in the next 5 years at least (niche players like Bowman notwithstanding).

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

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