QUESTION 1
A test was done on a single cylinder, four-stroke internal combustion
engine with a swept volume of 8 140 cm3.
The cooling water with a flow rate of 4,5 kg/min enters the water
jackets at 18 °C and leaves at 58 °C
The indicated mean effective pressure was 567 kPa at a speed of 6,5 r/s.
The net brake load was 511 N measured at an effective brake radius of
575 mm.
The clearance volume is 6,25% of the cylinder volume.
The engine consumes fuel with a calorific value of 40 MJ/kg at a rate of
0,06 kg/min.
The exhaust gases carried 32% of the energy supplied by the fuel away to
the atmosphere.
The specific heat capacity of the water is 4,2 kJ/kg.K
Take the value of gamma as 1.4
Calculate:
1.1 The brake power in kW, the indicated power in kW and the mechanical
efficiency.
1.2 The volumetric compression ratio, the air standard efficiency, the
indicated thermal efficiency and the indicated efficiency ratio.
1.3 Draw up a heat balance in kJ/min and as a percentage to determine
the percentage of heat unaccounted for. Assume that the heat lost
to friction is taken up by the cooling water.
QUESTION 2
The following results were noted during a test on a two-cylinder, four-
stroke cycle, oil engine over a period of one hour:
Fuel consumption 2,5 kg
Rotational frequency 16,5 r/s
Calorific value of fuel 45,12 MJ/kg
Brake torque 90,67 N.m
Cylinder diameter 110,5 mm
Stroke length 132,6 mm
Mechanical efficiency 80%
Specific heat capacity of water 4,2 kJ/kg.K
The exhaust gases, on leaving the cylinder were passed through an
exhaust gas calorimeter and it raised the temperature of 216 kg of water
from 16 °C to 61 °C.
Calculate:
2.1 The brake power in kW and the brake thermal efficiency
2.2 The energy carried by the flue gases in kW, the energy carried away
by the combined effects of the jacket cooling water, friction and
radiation in kW and the percentage heat supplied, carried away by
this combined effects.
2.3 The indicated power in kW, the indicated mean effective pressure in
kPa and the indicated specific fuel consumption in kg/kW.h
2.4 The brake mean effective pressure in kPa
QUESTION 3
A six-cylinder, four-stroke petrol engine was tested on a Prony brake.
The effective length of the brake arm was 999 mm and the scale reading
on the arm was 32,48 kg net at 3600 r/min.
The diameter of a piston was 115,285 mm and the stroke length was
129,81 mm.
The fuel released 45 MJ energy for every kg burnt.
The indicated specific fuel consumption was 0,2 kg/kW.h
The indicated mean effective pressure was 615 kPa per cylinder.
The mass of cooling water flowing was 30 kg/min.
The change in the temperature of the cooling water was 60 °C.
The specific heat capacity of the water was 4,2 kJ/kg.K.
The change in the temperature of the exhaust gases was 450 °C
The specific heat capacity for the exhaust gases was 1,05 kJ/kg.K.
The air-fuel ratio was 24:1
Take gravitational acceleration as 9,81 m2/s.
Calculate the following:
3.1 The brake power in kW
3.2 The indicated power in kW and the mechanical efficiency
3.3 The mass of fuel used in kg/min
3.4 The indicated thermal efficiency
3.5 Draw up a heat balance in KJ/min as well as a percentage to
determine the percentage of heat lost to radiation. Assume that the
heat lost to friction is absorbed by the cooling water.
