Subtopic: Calculation of power, torque, fuel consumption, heat load and power losses
Question Statement:
In a Morse test on a 4-cylinder four-stroke petrol engine running at $1500\text{ rpm}$, the brake power with all cylinders firing was $32.0\text{ kW}$. When cylinders 1, 2, 3, and 4 were cut out successively, the measured brake powers were $22.5\text{ kW}$, $22.2\text{ kW}$, $22.6\text{ kW}$, and $22.3\text{ kW}$ respectively. Calculate the mechanical efficiency of the engine in percentage.
Answer Key:
83.33
Step-by-Step Solution & Explanation
Total Brake Power $BP = 32.0\text{ kW}$.
Indicated power of individual cylinders:
$IP_1 = BP - BP_1 = 32.0 - 22.5 = 9.5\text{ kW}$
$IP_2 = BP - BP_2 = 32.0 - 22.2 = 9.8\text{ kW}$
$IP_3 = BP - BP_3 = 32.0 - 22.6 = 9.4\text{ kW}$
$IP_4 = BP - BP_4 = 32.0 - 22.3 = 9.7\text{ kW}$
Total Indicated Power ($IP$):
$IP = IP_1 + IP_2 + IP_3 + IP_4 = 9.5 + 9.8 + 9.4 + 9.7 = 38.4\text{ kW}$
Mechanical efficiency:
$\eta_m = \frac{BP}{IP} \times 100 = \frac{32.0}{38.4} \times 100 = 83.33\%$