1. A four cylinder two- stroke cycle engine with a swept volume of 750 cm3 per cylinder gives a specific fuel consumption of 0.25 kg KW-1 h-1. When developing a brake mean effective mean pressure 650 kPa at 1500 rpm. What is the brake thermal efficiency, if the calorific value is 40 MJ kg-1?
a) 9%
b) 18%
c) 32%
d) 36%
Discussion
Explanation:
Brake power = \(\frac{pLAN*n}{60000} \)
B.P. = \(\frac{650∗750∗10^{−6}∗1500∗ 4∗10^3}{60000} \)
B.P. = 48.75 KW
Brake thermal efficiency = \(\frac{B.P.*60}{Wf*Cf} \)
B.T.E. = \(\frac{48.75∗60}{0.203∗40∗10^3} \)
B.T.E. = 36%.
2. Which of the following is not a type of transmission dynamometer?
a) Epicyclic train dynamometer
b) Belt transmission dynamometer
c) Rope break dynamometer
d) Torsion dynamometer
Discussion
Explanation: In rope break dynamometer, the power is expressed by
P = \(\frac{[(W-S)π(D+d)N]}{60000} \)
Where, W is the dead load
S is the spring balanced
D is the diameter of the wheel
‘d’ is the diameter of the rope.
3. Engines of different cylinder dimensions, power and speed can be compared on the basis of __________
a) maximum pressure
b) fuel consumption
c) mean effective pressure
d) unit power
Discussion
Explanation: Basically, it is unit measurement of the output that the engine gives out. The development of the steam engine provided a reason to compare the output of horses with that of the engines that could replace them.
4. The measure of knock characteristics of a fuel is known as ______
a) Cetane number
b) Octane number
c) Calorific value
d) Volatility
Discussion
Explanation: The percentage of iso-octane (C8H18) in the reference fuel consisting of a mixture of iso-octane and normal heptane (C7H16), when produces the same knocking effect as the fuel under test, is called Octane number of the fuel.
5. What is the formula for A.P.I. degrees used in gravity tests for fuels?
a) A.P.I. degrees = \(\frac{141.5}{specific \, gravity \, of \, oil \, at \, 60°F} \)-131.5
b) A.P.I. degrees = \(\frac{131.5}{specific \, gravity \, of \, oil \, at \, 60°F} \)-141.5
c) A.P.I. degrees = \(\frac{Specific \, gravity \, of \, oil \, at \, 60°F}{141.5} \)-131.5
d) A.P.I. degrees = \(\frac{Specific \, gravity \, of \, oil \, at \, 60°F}{131.5} \)-141.5
Discussion
Explanation: The gravity of a fuel or an oil may be expressed as specific gravity or as an API gravity, a scale devised by American Petroleum Institute. The specific gravity of a liquid is the ratio of its weight to the weight of an equal volume of water at 60°F.
6. Which component of the carburettor is used to produce low pressure in the throat of the carburettor?
a) Throttle
b) Main jet
c) Choke
d) Venturi tube
Discussion
Explanation: Venturi tube is provided to produce low pressure in the throat of the carburettor. The suction force causes the fuel to rise in the jet. The fuel is discharged at a rate proportional to the air velocity, available at that point.
7. What is the range of pressure created at fuel injection pump?
a) 120 kg/cm2-300 kg/cm2
b) 106 kg/cm2-120 kg/cm2
c) 106 kg/cm2-300 kg/cm2
d) 120 kg/cm2-248 kg/cm2
Discussion
Explanation: Fuel injection pump is a high-pressure pump, which supplies fuel to the injectors according to the firing order of the engine. It is used to create pressure varying from 120 kg/cm2 to 300 kg/cm2. It supplies metered quantity of fuel to each cylinder at appropriate time.
8. Which component of the carburettor is used to maintain a constant level of fuel in the carburettor?
a) Main jet
b) Compensating jet
c) Float chamber
d) Economiser
Discussion
Explanation: Float chamber is a reservoir to maintain a constant level of fuel in the carburettor. Fuel comes from the tank to the float chamber. There is a hollow float provided with a needle. With the level of the fuel going down, the float with the needle also goes down allowing the fuel to come into the float chamber from the fuel tank. As the fuel level goes up, the needle closes the passage and hence a constant level in float chamber is always maintained.
9. Which component is used to supply air under pressure to the cylinders of the engine?
a) Turbocharger
b) Fuel filter
c) Fuel injector
d) Combustion chamber
Discussion
Explanation: Turbocharger is a turbo-compressor driven by the exhaust gases of the engines to supply air under pressure to the cylinders of the engine. Turbocharger is useful because the power output of a diesel engine can be increased by supplying compressed air to the engine cylinders.
10. An I.C. engine consumes high speed diesel oil at the rate of 0.5 kg/h. What is the power of the engine?
a) 6.51 KW
b) 6.48 KW
c) 6.10 KW
d) 6.15 KW
Discussion
Explanation: Heat value = quantity * calorific value
= 0.5 * 10550 (calorific value of high speed diesel = 10550 kcal/kg)
1 calorie = 4.2 joules
1 joule/sec = 1 watt
5275 kcal/h = 5275 * 4.2 k joules/h
= \(\frac{5275*4.2*1000}{60*60}\) joules/sec = \(\frac{5275*4.2*1000}{60*60} \)watts
= \(\frac{5275*4.2*1000}{60*60*1000} \) KW
Power of engine = 6.15 KW