Farm Machinery Questions and Answers – Working Principles of I.C Engine

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

1. If a diesel engine has a compression ratio of 24 and the cut-off takes place at 5% of stroke, the air standard efficiency will be ___________
a) 60.66%
b) 64.50%
c) 66.60%
d) 65.40%

Explanation: Here, r = V1/V2 = 24
V1 = 24 V2
V3 = V2 + 0.05 (V1-V2)
V3 = V2 + 0.05(24 V2-V2)
V3/V2 = 2.15
Efficiency: 1 – (1/r)γ-1 * [rcγ – 1] / r [rc – 1]
= 1 – (1/24)1.4-1 [2.151.4 – 1] / 1.4 [2.15-1]
= 66.60%.

2. Whenever a system undergoes a cyclic change, the algebraic sum of work transfer is proportional to the algebraic sum of heat transfer as work and heat are mutually convertible. Which law of thermodynamics suggests this?
a) Zeroth law of thermodynamics
b) Second law of thermodynamics
c) Third law of thermodynamics
d) First law of thermodynamics

Explanation: For closed system, a change in the energy content is the algebraic difference between the heat supply, Q, and the work done, W, during any change of state. The energy may include many types of energies including kinetic, potential, electrical etc., but from thermodynamic point of view these energies are ignored and the energy due to rise in temperature is considered.

3. The end of the connecting rod which fits over the gudgeon pin is known as __________ connecting rod.
a) Small end
b) Big end
c) Piston
d) Cylinder block

Explanation: The end which fits over the crank pin is called the big end of the connecting rod. Piston a cylindrical part closed at one end which maintains a close sliding fit in the engine cylinder. Cylinder block is the solid casting which includes the cylinder and water jackets.

4. The ratio of the actual weight of air induced by the engine in the intake stroke to the theoretical weight of air that should have been induced due to piston displacement at intake temperature and pressure is known as ___________
a) Efficiency ratio
b) Volumetric efficiency
c) Mechanical efficiency
d) Indicated thermal efficiency

Explanation: Efficiency ratio is the degree by which the actual thermal efficiency approaches the ideal cyclic efficiency. Mechanical efficiency is the ratio of power delivered by the engine to the total power developed within the engine. An indicated thermal efficiency show what fraction of the heat is supplied is converted into indicated work.

5. A four-cylinder tractor engine develops 50 KW at 3000 engines when tested on a prony dynamometer on brake arm length of 96 cm. What is the torque?
a) 190.98 Nm
b) 159.15 Nm
c) 186.49 Nm
d) 155.28 Nm

Explanation: P = 2πNT/ 60000
T = 50*60000/ 2π*3000
T = 3000000/2*3.14*3000
T = 3000000/18840
T = 159.15 Nm.

6. Who found the working principle of compression ignition engine in 1982?
a) Rudolf Diesel
b) Johannes Gutenberg
c) Otto von Guericke
d) Edwin Beard Budding

Explanation: Rudolf Diesel invented working principle of compression ignition engine. Gutenberg invented the printing press. Von Guericke was the founder of Air pump or vacuum pump and Edwin beard budding was the inventor of lawn mower.

7. What is the correct sequence of strokes in four stroke cycle engines?
a) Compression, Suction, Exhaust, Power
b) Power, Suction, Exhaust, Compression
c) Suction, Compression, Power, Exhaust
d) Suction, Power, Compression, Exhaust

Explanation: The intake valves are open as a result of the cam lobe pressing down on the valve stem. The piston moves downward increasing the volume of the combustion chamber and allowing an air fuel mixture. This step is known as suction. The charge taken in the cylinder is compressed during the compression stroke. During power stroke, the high pressure developed due to combustion of fuel causes the piston to be forced forward or backward at regular intervals. Exhaust gases go out through exhaust valves during exhaust stroke.

8. Who created the first modern internal combustion engine in 1876?
a) Etienne Lenoir
b) Nikolaus Otto
c) John Barber
d) John Stevens

Explanation: The first commercially successful internal combustion engine was created by Etienne Lenoir around 1859. John Baber developed a turbine in 1791. In 1798, John Stevens designed the first American internal combustion engine. Nikolaus Otto created the first modern internal combustion engine in 1876.

9. What is the regulation of speed when speed at no load of engine is 1973 rpm and speed at load is 1873 rpm?
a) 5.20%
b) 4.80%
c) 5.12%
d) 4.56%

Explanation: N1 = 1973; N2 = 1873
∆N = N2-N1
∆N = 1973-1873 = 100rpm
N = N2-N1/2
N = 1973+1873/2
= 1923
Regulation of speed = ∆N/ N
= 100/ 1923
= 0.0520
= 5.20%.

10. What is the net-work for the following cyclic process?
+14.7 KJ, -25.2 KJ, -3.56 KJ, +31.5 KJ
a) 19.35 KJ
b) 12.09 KJ
c) 17.44 KJ
d) 10.35 KJ

Explanation: ∂Wnet = ∂Qnet
∂Qnet = (14.7 – 25.2 – 3.56 + 31.5)
∂Qnet = 17.44 KJ.

11. 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

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.

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