Question

An automobile engine consumes fuel at a rate of 22 L/h and delivers 85 kW of power to the wheels. If the fuel has a heating value of 44,000 kJ/kg and a density of 0.8 g/cm3, determine the efficiency of this engine.

Answer 1

The efficiency of the engine is 39.53%

Step-by-step explanation:

data given by the exercise

HV = heating value = 44000 kJ/kg

Vfuel = volume flow rate of fuel = 22 L/h = 0.0061 L/s

W = power output = 55 kW

p = density = 0.8 g/cm³

the mass flow rate of fuel is equal to

`m_(fuel) =V*p=0.0061*0.8=4.89x10^(-3) kg/s`

the rate of heat supplied is

`Q_(in) =m_(fuel) *HV=4.89x10^(-3) *44000=215kW`

the efficiency is equal to

`n=(W)/(Q_(in) ) *100=(85)/(215) *100=39.53`%

Answer 2

Efficiency of the engine is 39.51 %

Step-by-step explanation:

Mass of fuel consumed per hour = 22 L/h * 0.08 Kg/L = 17.6 Kg/h

Total Energy Consumed per hour = Mass of fuel consumed per hour * Heating value of fuel

Total Energy Consumed per hour = 17.6 Kg/h * 44,000 KJ/Kg = 774,400 KJ/h

since, 1 KW = 3600 KJ/h

774,400KJ/h = 774,400/3600 kW = 215.1 kW

`Efficiency of the engine = (Power to the wheels)/(Total Power)`

Efficiency = 85/215.1 = 39.51 %