# Farm Machinery Questions and Answers – I.C Engine – Working Principles of 4-stroke Engine

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This set of Farm Machinery Multiple Choice Questions & Answers (MCQs) focuses on “I.C Engine – Working Principles of 4-stroke Engine”.

1. What is the degree of crank rotation during the completion of a four-stroke cycle?
a) 90°
b) 279°
c) 180°
d) 360°

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.

2. What is the compression ratio in SI engine?
a) 6 – 10
b) 3 – 5
c) 1 – 2
d) 11 – 15

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.

3. 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

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.

4. 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

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.

5. What is the efficiency of compressed charge engine?
a) 40%
b) 20%
c) 30%
d) 10%

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%.

6. 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

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.

7. 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

Explanation: Vd=$$\frac{π}{4}$$D2Ln
=$$\frac{π}{4}$$*(109.4)2*130*6
=7.32 litres.

8. 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%

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.

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