In a Morse test on a 2-cylinder, 2-stroke SI engine, the brake power is 9 kW and the BHP of individual cylinders with spark cut-off are 4.25 kW and 3.75 kW, respectively. The mechanical efficiency of the engine is

Concept:

Morse Test for Mechanical Efficiency Calculation

In a Morse test on a 2-cylinder, 2-stroke SI engine, the brake power (BP) is 9 kW and the BHP of individual cylinders with spark cut-off are 4.25 kW and 3.75 kW, respectively. The mechanical efficiency of the engine is calculated as follows:

Step-by-Step Solution:

1. Calculate the Indicated Power (IP):

- The Indicated Power for each cylinder can be determined when its spark is cut off.

- For the first cylinder: IP₁ = Total BP - BP with first cylinder cut-off = 9 kW - 4.25 kW = 4.75 kW

- For the second cylinder: IP₂ = Total BP - BP with second cylinder cut-off = 9 kW - 3.75 kW = 5.25 kW

- Total Indicated Power (IP) is: IP = IP₁ + IP₂ = 4.75 kW + 5.25 kW = 10 kW

2. Calculate the Mechanical Efficiency (η_m):

- Mechanical efficiency is the ratio of Brake Power (BP) to Indicated Power (IP):

- η_m = (BP / IP) × 100 = (9 kW / 10 kW) × 100 = 90%

Therefore, the mechanical efficiency of the engine is 90%.

Answer: 1) 90%