Quote:
Originally Posted by arcosine
Humm, intake, compression, power, exhaust, that's two revolutions, one intake stroke. Piston is working agaist the vacuum 1/4 of the time, doesn't matter how many cylinders.
|
Yup, and that would be part of your pumping losses, not power. For your power equation to be correct you need to have the correct number of intake strokes, which
is dependent on the number of cylinders. And you're using pressure, not vacuum to calculate power.
Or, you can just skip the intake stroke calc and divide the engine displacement by 2 since that is the volume the intake manifold pressure is seeing each revolution.
Remember, the displacement of the engine is calculated by determining the volume of one cylinder (piston top dead center to piston bottom dead center), ignoring whether the design is 4 stroke or 2 stroke, then multiplying the volume of that one cylinder times the number of cylinders. So if you have a 2 liter 4 stroke engine it only pulls in 1 liter of air per revolution (a 2 stroke would pull in 2 liters, which is why they usually have a higher power density).