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Old 07-19-2014, 12:02 PM   #10 (permalink)
peterrr
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pressures an temperatures

The temperature is kind of unknown because we don't know the inside temperature of the cylinder head. But we do know the temperature of the coolant (its a dial on the dashboard) and it is kept mostly at 80-85 C(and this varies a bit per engine type). However if you really step on it (you will have to transport a lot of heat from inside to outside) there will be a difference between the inside (which is heated) and the outside (which is cooled). My guess for the inside temperature when you really step on it constantly(going up a hill) would be 100C. But when you are accelerating and the water pump still turns slowly and the thermostats is still closed I guess it could run up to 110C.
The pressure at which the fuel condensates will vary with the temperature. The condensation pressure is something like P= 10Power(a/T). The boiling point of septane is about the same as water so as a first guess you could look the pressures for 80 100 and 110C up in a steam table. And once you've done that fill it in in the Raoult law sum.
However the car will enrich the fuel (with a acceleration pump) and with an enrichment formula for heavy loads. So you could take the condensation pressure of the fuel constant. The water vapour pressure would vary.

Last edited by peterrr; 07-19-2014 at 12:21 PM.. Reason: I'm a nitwit
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