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Higher Compression = Lower Exhaust Gas Temp

EFI Tuning Fundamentals

Relevant Module: Fundamental Engine Principles > Engine Principles > Pressure Volume Cycle

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Refers to "Pressure Volume Cycle" (https://www.hpacademy.com/dashboard/courses/efi-tuning-fundamentals/engine-principles-pressure-volume-cycle)

I'm hesitant with my thought about ;

how a higher compression engine can produce a relative lower exhaust gas temperature ?

is it because of higher compression engine have a less cylinder pressure at the end = lower egt ?

or because of the piston absorb more energy from the combustion so less heat produce ? (conservation of energy principle)

or something else ??

It's all about Ideal gas law- volume, temperature and pressure are directly related to one another as you said. As piston goes down the bore after TDC with higher compression ratio in cylinder pressure drops much faster than lower compression ratio resulting in noticeable temperature drop as well. That is why it makes sense to install long duration exhaust camshaft since most of the energy is consumed ealier in the cycle- that would allow keeping exhaust valve of the noramal size and save room in favour of installing bigger size intake valve that should improve engine VE and power.

As Shota said, the more compressed air-fuel mixture burns faster, with the peak pressure earlier in the power stroke, and so more thermal energy (heat) is lost as it expands.

It's similar to the affect timing has on exhaust temperature.

Just saying with no offense to anyone.. I LOVE SCIENCE!

I think i didn't quite catch it...

I'll just add you may see higher EGT with higher compression, but EGT doesn't necessarily inform you of in cylinder temperature, much like ignition timing as Gord mentioned.

Just a few more screen shots to add to this topic.

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