In an internal combustion engine how much pressure ?

Question

( Pounds per square inch ) is exerted on the piston when the sparkplug fires?

The formula does not match the listed specifications .

Answer 1

The formula for determining Mean Effective Pressure in the cylinder is 2 times the power in Watts (.0012 times horsepower), divided by the product of the rotating speed in Hertz (the same as rpms) times the volume of the cylinder.

The answer comes out in Pascals (Newton Meters squared). Multiply by 0.0014504 to get pounds per square inch.

Answer 2

Normal atmospheric pressure is about 14 psi. My car is a low compression version quoted as 8.3 to 1, other cars are 9 to 1, sometimes more. Diesel motors, which do not have spark plugs, are much more. For a 9 to 1 compression ratio, neglecting the heating effect of rapidly compressing the air in the cylinder, the pressure will be 9 times 14. However the temperature increase will be significant. For every degree centigrade temperature rise the pressure will increase by about 1/273. Because the pressure rise occurs within a fraction of a second, it is essentially adiabatic.

Gas Law PV=nRT

P =pressure
V=volume
n=quantity of gas in moles
R=gas constant
T=absolute temperature=273= temperature in Celsius.

So you see, it depends.

Answer 3

That is an excellent question that I cannot find an answer to. It is obviously much more than compression pressure that the the previous posters stated. Otherwise, an engine wouldn't run. (if the power stroke had the same psi as the compression stroke the engine wouldn't have any reason to keep turning much less develop extra power) You have piqued my curiosity and I hope somebody can answer this. Does Yahoo give points for best question?

Answer 4

That depends on the engine. They can range all the way from 8.7:1 psi to 10.5:1 psi depending on the make and model engine with a few even being lower. Older pre unleaded gas engines had compression ratios of 9.5:1 psi to 10.5:1 psi with a few high performance engines going as high as 12.5:1 psi.
Diesel engines run around 15:1 to 17:1 psi

But here is the kicker: Namely supercharged and turbo charged engines. Their operating compression is a lot higher but they get most of that from air being rammed into them. If you were to measure the compression ratio of a turbo charged engine with a compression Gage it will normally indicate a lower compression that an engine which is not turbo charged. But when running the operating compression is up around 15:1 to 16:1 psi.
These are all ball park figures taken as a general average.

Answer 5

depends on the engine. A diesel(internal combustion engine) it is much more than a gas that is say blowing the "blues".

Answer 6

On a 'mom and pop' car, about 150# per cyclinder.