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Cylinder temps

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Going through the "Understanding Knock" lecture on EFI

Question: Are cylinder temps around ~1000F (~538C)?

*Either way, adding fuel (richening the mixture decreases the temps, right? But by how much?

*And this begs the question of what is the OPTIMAL cylinder temp the car is happy with/operates at?

*Actually, what is the optimal temperature and pressure that a cylinder likes to operate at?

*And does this number change if we have our engine cylinders "sleeved" with aftermarket sleeves per se..

Sorry for all the questions; I am really enjoying these lectures.

Far from an expert, but...

Depends on what you mean by "cylinders"? I don't know the specific reference, but they cylinder walls, head, and piston surfaces are probably around the 250f mark - that's a guess considering the coolant temp's, thermal transfer through the engine's material, and piston temperature tolerance. Combustion temperatures can be well over 2000f. So I expect the reference is to the temperature increase due to compression, which can easily reach that - this is important because the fuel used may reach the temperature where it self-ignites, usually explosively rather than as a "burn", and this can cause severe engine damage. The compression temperature rise is also critical for diesels, known as "compression ignition" engines, as the fuel is added to the hot air and that is what ignites it.

Depends on the fuel, and how much is used. For example, gaseous fuels like CNG get hotter as it's run richer, as do diesels as a general rule. In context, petroleum based and alcohol fuels are introduced to the engine in liquid form - fine droplets - and it's the evaporation of these into a gas that cools the charge (same principle as water injection). The volumes of the fuel required, and the energy needed to evaporate them, can vary a great deal, so it's not really possible to give an estimate without further investigation.

Again, depends on definition. It also depends a great deal on the engine and fuel characteristics. In theory you want the least heat loss from the combustion into the engine which means running high coolant temperatures and/or using thermal barriers; the densest charge drawn into the cylinder, which means keeping it as cold as possible; and minimising the energy lost out the exhaust, which means burning the fuel as quickly as possible within the limits of the engine construction.

Not really - except it may change the thermal qualities of the cylinder walls - how much heat passes from the combustion into the cooling medium. The primary reasons for using sleeves are to provide a stronger cylinder wall and/or to re-condition worn engines by providing a fresh cylinder bore - there is also a small number of times it's used to reduce the bore diameter, such as to meet engine capacity limits.

Hopefully, someone else will comment to clarify/correct that as required.

This is pretty helpful; and thoughtful.

Thank you for taking the time to respond, Gord.


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