Forum » Diesel Tuning Fundamentals » Egt vs injection timing vs combustion chamber temperature

Egt vs injection timing vs combustion chamber temperature

Diesel Tuning Fundamentals

Discussion and questions related to the course Diesel Tuning Fundamentals


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During the practical demonstration we notice the effect of the EGT increasing as the main injection is retarded and lowering when advanced. However would it be fair to assume that even though the EGT is lower, actually more heat is being absorbed by the cylinder head and piston with advanced injection timing?

I guess to expand on this what I am asking is if you are running a fairly aggressive tune on your diesel with big boost and fuel. Tuning solely off EGT reading may not be enough to know that it would be safe as by advancing the injection timing too far may lower the egt but actually raise the chance of melting something?

When you advance the injection timing, it's like advancing the spark timing on a gasoline engine. The engine increases thermal efficiency and more energy is converted to motion, rather than waste heat. However cylinder pressures increase, and that could strain components.

For a given injection mass the boost actually leans it out and cools it down.

Hopefully Andre can chime in and give a more detailed explanation.

Yeah that's what I would have guessed.

I found some other forum posts with very similar topics and as you have mentioned the increase in thermal efficiency and hence torque output also comes at the expense of increased heat into the piston and cylinder head.

Sorry for the slow reply. Your point is exactly right and I delve into this in the section on EGT - The EGT is measuring the byproduct of the combustion process, rather than the combustion temperature itself. When it comes to engine safety and reliability it's the heat the piston is exposed to that is the worrying factor and for this reason it's difficult to put an exact line in the sand and say X EGT is safe but Y EGT will result in parts failure.