Question

An engineer claims to have made an engine delivering 10 kW power with fuel consumption of 1gm/sec. The calorific value of fuel is 2 kcal/gm.This claim is

• A. valid
• B. invalid
• C. depedent on engine design
• D. depedent on load

Answer 1

Answer: (B)

invalid

Efficiency of a Carnot engine is
$\eta =\frac{W}{Q_h}=1-\frac{T_c}{T_h}$
$W=Q_h(1-\frac{T_c}{T_h})=\left(1\right)\left(2\right)(1-\frac{T_c}{T_h})kcal/sec$
$10kW=2\left(4.2\right)(1-\frac{T_c}{T_h})kJ/s$
$\frac{10}{8.4}=1-\frac{T_c}{T_h}$
$\frac{T_c}{T_h}=1-1.19=-0.19$
Ratio of absolute temperatures can be not be negative. So, the claim by the engineer is invalid.