1. The clearance between rocker arm and valve stem that enables the valves to sit properly is known as _____________
a) Valve lifter guide
b) Valve stem guide
c) Cam gear
d) Tappet clearance
Discussion
Explanation: Valve lifter guide is used in guiding the tappet in motion. Valve stem guide fits into the cylinder block. Cam gear is fixed at the end of the camshaft to mesh with the crankshaft gear.
2. What is the degree of crank rotation during the completion of a four-stroke cycle?
a) 90°
b) 279°
c) 180°
d) 360°
Discussion
Explanation: In a four-stroke engine, the cycle of operations is completed in four strokes of the piston or two revolutions of crankshaft. Each stroke consists of 180° of crankshaft rotation and hence a four-stroke cycle is completed through 720° of crank rotation.
3. What is the compression ratio in SI engine?
a) 6 – 10
b) 3 – 5
c) 1 – 2
d) 11 – 15
Discussion
Explanation: Gasoline, a highly volatile fuel is used in SI engines and upper limit is fixed by antiknock quality of fuel. Compression ratio in SI engine is 6 – 10.
4. What is the firing order of a four cylinder engines?
a) 1-3-4-2
b) 1-4-3-2
c) 1-2-3-4
d) 4-3-2-1
Discussion
Explanation: The firing order of a four cylinder engines is 1-3-4-2. The sequence in which the power stroke in each cylinder of an engine occurs is called firing order. The arrangement of the crank pin on the crankshaft a design of the camshaft both determines the firing order.
5. Which of the following describes the firing interval in a four-stroke engine?
a) F.I. = 720°/Number of cylinders
b) F.I. = 360°/Number of cylinders
c) F.I. = 270°/Number of cylinders
d) F.I. = 180°/Number of cylinders
Discussion
Explanation: The interval between successive power strokes in different cylinders of the engine is called firing intervals. During the first 180° rotation of crankshaft, the cylinder 1 gets the power stroke, cylinder 2 gets the compression stroke and cylinder 3 & 4 gets the exhaust and suction stroke respectively.
6. What is the efficiency of compressed charge engine?
a) 40%
b) 20%
c) 30%
d) 10%
Discussion
Explanation: As engine RPM rises, the speed of the flame front does not change so the spark point is advanced earlier in the cycle to allow greater proportions of the cycle for the charge to combust before the power stroke commences. Efficiency of compressed charge engine is 30%.
7. Diameter and stroke length of the piston of a 4 stroke-4-cylinder diesel engine are 10 cm and 12 cm respectively and speed of crank shaft is 2000 rpm. Calculate brake power.
a) 18.90 KW
b) 12.89 KW
c) 12.98 KW
d) 18.98 KW
Discussion
Explanation: Integrated power = \((\frac{pLAN}{60,000})\)*n/2
= \(\frac{7*105*0.12*\frac{π}{4}*(0.1)2*2000*4}{60000*2}\)
= 43.98 KW
Brake power = Integrated power – Frictional power
= 43.98-25
= 18.98 KW.
8. A six-cylinder engine has 130 mm stroke and 109.4 mm bore. The displacement of the engine at a compression ratio is 17:1 is equal to _________
a) 5.4 litres
b) 7.32 litres
c) 8.27 litres
d) 6.96 litres
Discussion
Explanation: Vd=\(\frac{π}{4}\)D2Ln
=\(\frac{π}{4}\)*(109.4)2*130*6
=7.32 litres.
9. What per cent of supplied energy is converted into mechanical work by an IC engine?
a) 10%-20%
b) 30%-40%
c) 50%-60%
d) 70%-80%
Discussion
Explanation: An IC engine on average is capable of converting just 30-40% of the supplied energy into mechanical work because a large part of the waste energy is in the form of heat that is released to the environment through coolant, fins etc.
10. Which engine is designed to convert chemical energy of heavier fuel oil into mechanical energy?
a) Diesel engine
b) Petrol engine
c) Injector
d) Tappet clearance
Discussion
Explanation: The injected fuel is ignited by the heat of the air which compressed by the piston within the cylinder head. In diesel engine, only air is sucked during suction stroke.