Question

In a certain automobile engine with an efficiency of 21.6%, combustion of gasoline in one cylinder releases 510 J of heat.

(a) Find the work done by the system of gasoline vapor and air on the surroundings during one cycle.


(b) Find the total mechanical power produced by all four cylinders, operating at 48 cycles/s, or 2880 rpm.

Answer 1

If the engine were 100% efficient, all of the heat energy would be converted to mechanical energy.
We have 21.6 % efficiency, so 510J*0.216 = 110.16 joules of work donees   

power is work divided by time. We have 110.16 joules J for each cylinder, and each cylinder fires 48 times per second.

All together
110.16 joulesJ/cylinder*4cylinders/engine*48cycles/second =21150.72 J/s for the engine or
21150.72 Watts
The mechanical power of the engine is 21150.72 W