In a test on a four cylinder spark ignition engine the following power and fuel consumption measurements were made
With all cylinders firing 30.00 kW
With cylinder 1 only not firing 20.75 kW
With cylinder 2 only not firing 20.50 kW
With cylinder 3 only not firing 20.50 kW
With cylinder 4 only not firing 20.75 kW
The time taken to consume 250ml of fuel is 85 seconds. Specific gravity of fuel = 0.85. Calorific value of fuel is 40 MJ/kg. Determine the mechanical efficiency and brake thermal efficiency of the engine