I'd like to start with two established internal combustion engineering benchmarks:

1. In some 2-stroke, intake air is introduced to the combustion chamber via ports in the lower cylinder, which are covered and uncovered by the reciprocating piston.

2. In the Corvette engine, reverse flow cooling is used: coolant is first directed at the water jacket surrounding the hottest part of the cylinder head first, then down to the rest of the block.

Suppose we take the boost of a turbocharger and direct it to the air jacket...reverse cooling style...to the cylinder head,which den flows down to the rest of the block and encounters the intake ports; thus the cooling medium converts into pre-warmed intake air.

I figure, thermodynamically, this setup would be very efficient: instead of parasitic losses from the radiator fan and water pump, all cooling comes from free/cheap energy liberated by the turbo. In other words, energy is conserved; kinetic energy is not used up getting rid of thermal energy.

Question is...will this engine melt anyway?

From the seat of my pants, I'd say, "It will Probably still melt." but it will definetly make some extra pollution.

Turbo charger air is hot - so it still needs to get cooled off by the intercooler before entry to the engine. That will increase its density, and make the air cooler to be a better heat transfer medium.

The problem is, that even in a conventionally cooled engine (either four stroke, or two stroke as the Detroits are) the intake air charge is ALREADY helping to cool the chamber from the INSIDE.

Because diesels have no throttle valve to reduce the density of the air charge under partial load conditions, a greater portion of their heat rejection already occurs through the air compared to a gas engine. A great deal of diesel exhaust is simply hot air - not combustion products.

Modern diesel engine manufacturers already try to get the intake air as cool and dnese as they can. Not for power - which is the obvious reason for that - but for EMISSIONS. Power produced by a diesel is directly related to the amount of fuel you feed it, because they operate fuel lean under all but the highest of loads.

Lowering the temperature and increasing the density lowers the combustion temperature. Heat rejection to the exhaust remains about the same, because energy flow (Q with a dot over it in engineering terms - pronounced "Que dot") = temp change x mass flow rate ("M dot").

Q-dot = M-dot x (outlet temp - inlet temp) x C

(C is related to the specific heat of the working fluid - in this case, Air, and makes the units work out. It's "almost" constant.)

Decreasing the inlet temperature increases the density of the air charge - it weighs more per unit volume when its colder.

Because a diesel is essentially a fixed positive displacement pump, it sucks a given VOLUME of air at a given rpm - which we're holding constant for this example.

Since we've made the air denser, we've actually changed TWO variables in the energy flow equation. M-dot INCREASED because of the density increase, AND inlet temperature decreased.

The Q-dot we're looking at here is actually the heat rejected by the engine. It's primarily a function of compression ratio, and for a given power output pretty constant for an engine.

That means that when we drop the intake temperature, the exhaust temperature has to drop EVEN MORE to maintain the same heat rejection.

Reducing combustion chamber temperatures is the BEST way to reduce NOx emmisions.

That's why engine makers dump as much of the coolest air they can through the engine, and try to cool off the EGR gasses before they pump them in. Every extra bit of heat that goes into the air charge raises the temperature in the exhaust - and the combustion process - and makes more NOx.

All the modern diesels are easy to tweak to get more power for just this reason - there's already a TON more air there than required for effective combustion. The hot rodders just have to put more fuel in - the air is already there.

for getting more fuel in, there's really only three variables to chase.

They have to make sure they don't squirt the fuel too early - causing essentially the same condition as spark knock in a gas engine - excessive pressure too early in the cycle.

They have to make sure they shut the fuel squirt off soon enough - so that the fuel has time to completely burn in the cylinder AND expand to do useful work.

Once the start time and end time are defined - the ONLY thing left to get more fuel in is to SQUIRT FASTER - which is why there are high flow injectors on the market for most of the common diesels.

There you have it - diesel engine theory in one long rambling post.

Eric K

personally, I found it a very informative and interesting post. Thanks!

Okay...how about we utilize this engine in an ultra-low ambient temperature environment?

Say, a generator at an Arctic/Antarctic outpost, or maybe a propeller engine for a high-altitude airplane?
Yeah, I know, at low altitudes the air would be too warm...maybe starting the engine with water injection or nitrous?