Question

A petrol engine consumes 20.4 kg of petrol per hour of calorific value 43 mj/kg. The thermal efficiency of the engine is 20 %. Determine the power output of the engine and the energy rejected/min.

Answer 1

Answer:

Explanation:

Given A petrol engine consumes 20.4 kg of petrol per hour of calorific value 43 mj/kg. The thermal efficiency of the engine is 20 %. Determine the power output of the engine and the energy rejected/min.

So 20.4 kg /hr needs to be converted to kg/s, so divide by 60 x 60

Now 20.4/3600  

So consumed petrol = 20.4/3600 x 43 x 10^6 J/s

So efficiency is 20% = 0.2

Now power output will be 20.4/3600 x 43 x 10^6 x 0.2 J/s

We know that 1 j/s = 1.00 w

 Power output = 48733.33 w

                         = 48.7 kw

Now to find energy rejected  

So energy rejected = (1 – thermal ɳ) x energy received

(1 – 0.2)(20.4/60 x 43 x 10^6)J/min

0.8 x 0.34 x 43 = 11.69 J/min

So energy rejected will be 11.7 J/min