Question Bank • QB_EXP_FP_GEN_002 NAT • 2 Marks

Section 3: Farm Power

Engine Fuels, Lubricants & Viscosity

Subtopic: Diesel and petrol properties (calorific value, density, flash point)

Question Statement:

A diesel engine consumes $8.0\text{ kg/h}$ of diesel fuel with a lower heating value of $42000\text{ kJ/kg}$. If the engine delivers a brake power of $35.0\text{ kW}$, the brake thermal efficiency is ________ $\%$ (round off to two decimal places).

Answer Key:

37.50

Step-by-Step Solution & Explanation

1. Total heat energy input rate from fuel combustion: $Q_{in} = \frac{\dot{m}_f \times \text{CV}}{3600} = \frac{8.0 \times 42000}{3600} = 93.33\text{ kW}$ 2. Brake thermal efficiency: $\eta_{bth} = \frac{\text{BP}}{Q_{in}} \times 100 = \frac{35.0}{93.33} \times 100 = 37.50\%$
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