Diesel EGT's

[SMOKNZ]

I'm pretty new to Diesels (as you can see by my post #'s) and had a few questions about EGT's. I have been afiliated with gas engines and pcm tuning for a few years now with my camaro, and was just curious if the temps with gas and diesel correlate. I have always been told if tuning a gas engine that the EGT limit is 1600 deg F. why is it 1250 with a diesel? As the EGT is rising in a gas motor, it is a signal that it is running lean. However on a diesel I have read that it is getting more fuel that causes the rise in EGT's. Boost leaks (less air in the combustion chamber) can also cause EGT's to go up. I know these are 2 way different combustion methods, but do they correlate at all? What happens when a Diesel is smoking, way rich???

Thanks

Bill

 

[CSIPSD]

The 1250 on our trucks is to protect the Aluminum pistons, EGT on a diesel will go up with more fuel, also with less boost. Smoke is a product of too much fuel, but to get a diesel to not smoke yet still make lots of HP is very expensive. Turbos, intercoolers, intakes, exhausts, injectors, and HPOP's all play a big part... Then there is tuning...

 

[oi8228oi]

less boost less cool air into the cumbustion mixture... everything runs hotter....
smoke on a diesel does mean rich... older diesels smoke because of large amount of carbon build up... if there lottsa smoke comming out its the perfect setting to use NOS, Propain, or Methonol injection

 

[Hoss 350]

I'm pretty new to Diesels (as you can see by my post #'s) and had a few questions about EGT's. I have been afiliated with gas engines and pcm tuning for a few years now with my camaro, and was just curious if the temps with gas and diesel correlate.

No, they do not. Lean gassers run high EGTs (less fuel=more heat). EGT's in a diesel have an inverse relation. The more fuel you add, the higher the EGTs.

I have always been told if tuning a gas engine that the EGT limit is 1600 deg F. why is it 1250 with a diesel?

I've often wondered this very thing myself. Considering a diesel piston and a gas piston are more or less the same as far as heat resistance, I have no clue why EGTs can be higher on a gasser than a diesel. If you find out, please let me know, because I'm curious.

As the EGT is rising in a gas motor, it is a signal that it is running lean. However on a diesel I have read that it is getting more fuel that causes the rise in EGT's.

Right. More fuel=more heat in a diesel. Inverse to a gasser.

Boost leaks (less air in the combustion chamber) can also cause EGT's to go up.

Yes. It depends on more variables than that, but the general idea is that the more cool intake air you can get in, the cooler you run. But this is true in a gasser, too. Cool intake air cools them off, also, so there is no difference there.

I know these are 2 way different combustion methods, but do they correlate at all? What happens when a Diesel is smoking, way rich???

Diesels, by nature, typically run lean from the factory. Very lean. Since the DI technology does not require the fuel to be mixed with air at stociometric. If you see black smoke, that means the diesel is running OVER stochiometric, which means it is running rich. All the black smoke is is incompletely burned fuel (like soot from a cold fire). There was not enough oxygen in the cylinder to completely burn all of the fuel injected. Black smoke is typically viewed as wasteful, since it is dumping unburned fuel out the exhaust, instead of burning it all in the engine.

 

[95_stroker]

I've often wondered this very thing myself. Considering a diesel piston and a gas piston are more or less the same as far as heat resistance, I have no clue why EGTs can be higher on a gasser than a diesel. If you find out, please let me know, because I'm curious.

Me too, could it be something to do with the way the engines are designed? Particularly the head, intake/exhaust valve arrangement and the different fuels they are intended to burn?

If you see black smoke, that means the diesel is running OVER stochiometric, which means it is running rich.

Nit pickyness but if you are rolling black smoke you are sub-stoich.