A petrol engine with compression ratio of 5 develops \(20 \mathrm{~kW}\) indicated power and consumes 8 litres of fuel per hour. The specific gravity of fuel is 0.78 and its calorific value is \(44 \mathrm{MJ} / \mathrm{kg}\). Calculate the indicated thermal efficiency and relative efficiency. Take \(\gamma=1.4\).