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Im trying to calculate the heat input and brake specific fuel consumption for an engine. However, Im having troubles with units lining up.

Heat Input= reaction enthalpy (J/kg) x fuel flow rate per injector (kg/s) x 4 (4 cyl engine) x 0.5 (4 stroke)

Doing it like that gives me J/s = power, which is what I want, but shouldnt the engine speed have something to do with this?

Next problem is the BSFC. Im after units of kg/MJ. It looks simple to just multiply the flow rate by time and multiply the reaction enthalpy by mass. Then divide one by the other. This would give me the correct units, however I dont really know what to do.

Can someone point me in the right direction?

Thanks.