Worksheet.docx - ADDIS ABABA SCIENCE AND TECHNOLOGY...

ADDIS ABABA SCIENCE AND TECHNOLOGY UNIVERSITY
IC Engines and Reciprocating Machines
Worksheet-I
1. A 42.5 kW engine has a mechanical efficiency of 85%. Find the indicated power and
frictional power. If the frictional power is assumed to be constant with load, what will be
the mechanical efficiency at 60% of the load?
2. A four stroke, four cylinder diesel engine running at 2000 rpm develops 60 kW. Brake
thermal efficiency is 30% and calorific value of fuel is 42MJ/kg. Engine has a bore of
120 mm and stroke of 100 mm. Take ρ
a
= 1.15 kg/m 3 , air-fuel ratio is 15:1, mechanical
efficiency is 80%. Calculate (i) fuel consumption (kg/s) (ii) air consumption (m
3
/s) (iii)
indicated thermal efficiency (iv) volumetric efficiency (v) brake mean effective pressure
(vi) mean piston speed.
3. A single cylinder, four stroke hydrogen fuelled spark-ignition engine delivers a brake
power of 20 kW at 6000 r.p.m. The air-gas ratio is 8:1 and the calorific value of fuel is
11000 kJ/m
3
. The compression ratio is 8. If volumetric efficiency is 70%, indicated
thermal efficiency is 33% and the mechanical efficiency is 90%. Calculate the cubic
capacity of the engine.
4. A four stroke petrol engine at full load delivers 50 kW. It requires 8.5 kW to rotate it
without load at the same speed. Find its mechanical efficiency at full load, half load and
quarter load. Also find out the volume of the fuel consumed per second at full load if
brake thermal efficiency is 25%, given that the calorific value of the fuel = 42 MJ/kg and
specific gravity of petrol is 0.75. Estimate the indicated thermal efficiency.
5. Find out the speed at which a four cylinder engine using natural gas can develop a brake
power of 50 kW working under the following conditions. Air-gas ratio 9:1, calorific value