DIESEL POWER PLANT 265
4.In an engine working on the Otto cycle, the measured suction temperature was 100°C and the
temperature at the end of compression was 300°C. ‘Faking k for compression as 1.41, find the
ideal efficiency and the compression ratio. [Ans. 35%, 2.85]
5.A four stroke gas engine develops 4.2 kW at 180 r.p.m. and at full load. Assuming the follow-
ing data, calculate the relative efficiency based on indicated power and air-fuel ratio used.
Volumetric efficiency = 87%, mechanical efficiency = 74%, clearance volume = 2100 cm^3 ,
swept volume = 9000 cm” fuel consumption = 5 m^3 /h, calorific value of fuel = 16750 kJ/m^3
[Ans. 50.2%, 7.456: 1]
6.A four-stroke cycle gas engine has a bore of 15.24 cm and a stroke of 22.86 cm. The com-
pression ratio is 4 and the m.e.p. 3.43 bar. If the engine speed is 300 rev/min. and the thermal
efficiency is 30%. Calculate the fuel consumption in m^3 /kW hr. and the efficiency relative to
the air-standard cycle. Calorific value of gas is 18297.2 kJ/m^3 .[Ans. 0.49 m^3 , 69.7%]
7.A two-cylinder, Single acting Diesel engine with a compression ratio of 14 and a cut-off ratio
1.8, works in the four-stroke cycle and uses 13.8 kg of oil per hour when running at 200 rev/
min. If the relative efficiency is 0.6 (k = 1.4), find the LP. and the m.e.p. of the engine.
Cylinder diameter 30.48 cm, stroke 45.72 cm and the calorific value of oil 41870 kJ/kg.
[Ans. 78.3, 5.23 bar]
8.The following observations were recorded during a trial of a four-stroke engine with rope
brake dynamometer:
Engine speed = 650 r.p.m.,
Diameter of brake drum = 600 mm,
Diameter of rope = 50 mm,
Dead load on the brake drum = 32 kg,
Spring balance reading = 4.75 kg.
Calculate the brake power. [Ans. 5.9 kW]
9.The following data refer to a four-stroke petrol engine:
Engine speed = 2000 r.p.m.
Ideal thermal efficiency = 35%,
Relative efficiency = 80%,
Mechanical efficiency = 85%,
Volumetric efficiency = 70%.
If the engine develops 29.42 kW brake power. Calculate the cylinder swept volume.
[Ans. 0.00185 m^3 ]
10.Derive an expression in terms of volume ratio for the ideal efficiency of the Diesel engine
cycle, assuming constant specific heats. Calculate this ideal efficiency for an engine with a
compression ratio of 15 and cutting off fuel at 5% of the stroke. [Ans. 62%]
11.During a 60 minutes trial of a single cylinder four stroke engine the following observations
were recorded:
Bore = 0.3 m
Stroke = 0.45 m
Fuel consumption = 11.4 kg