# Farm Machinery Questions and Answers – Diesel Engine Vs. Petrol Engine – 1

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This set of Farm Machinery Multiple Choice Questions & Answers (MCQs) focuses on “Diesel Engine Vs. Petrol Engine – 1”.

1. 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

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.

2. The process of removal of burnt or exhaust gases from the engine cylinder is known as ___________
a) Tappet
b) Skirt
c) Scavenging
d) Suction

Explanation: Entire burnt gases do not out in normal stroke, hence some type of blower or compressor is used to remove the exhaust gases which are known as scavenging.

3. The device in which air-fuel mixture is prepared away from the cylinder of an engine is known as __________
a) Lubricant
b) Delivery valve
c) Nozzle holder
d) Carburettor

Explanation: The process of preparing an air-fuel mixture away from the cylinders of an engine is called carburetion. Lubricant is a substance capable of reducing friction by making surface smooth. Delivery valve is a high-pressure pump for feeding fuel to the engine. Nozzle holder accelerates the flow of fuel to generate thrust.
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4. The correct way of representing the compression ratio is __________
a) C.R.=$$\frac{Total \, cylinder \, volume}{Clearance \, Volume}$$
b) C.R.=$$\frac{Clearance \, Volume}{Total \, Clearance \, Volume}$$
c) C.R.=$$\frac{Total \, clearance \, volume}{Cylinder \, Volume}$$
d) C.R.=$$\frac{Clearance \, volume}{Total \, cylinder \, volume}$$

Explanation: Compression ratio is the ratio of the volume of the charge at the beginning of the compression stroke to that at the end of the compression stroke, i.e., ratio of total cylinder to clearance volume or $$\frac{Swept \, volume+Clearance \, volume}{Clearance \, Volume}.$$

5. Which of the following is not an example of drawbar dynamometer?
a) Spring dynamometer
b) Hydraulic dynamometer
c) Electrical dynamometer
d) Strain gauge dynamometer

Explanation: The electrical dynamometer is an example of brake dynamometer. It consists of a generating unit, a resistance unit and a control board. The engine to be tested is mounted by the side of the generator and its crankshaft is connected directly to the armature. It is very accurate and precise instrument but its installation cost is high.

6. A high-speed diesel engine operating at 2000 rev/min has a single cylinder. During the compression stroke, the fuel injection starts 20° before TDC and ends at TDC. Determine the duration the fuel injection takes place.
a) 1/600 seconds
b) 2/248 seconds
c) 1/60 seconds
d) 2/319 seconds

Explanation: Revolution/sec = 2000/3 = 100/3
Crankshaft angle/sec = $$\frac{100}{3}*\frac{360}{1}$$
Injection time for 20° rotation = 1*$$\frac{20}{12000}$$
= 1/600 seconds.

7. A six-cylinder 4-stroke engine has bore diameter 11 cm and stroke length 12.2 cm running at 2800 rev/min consumes 455m2 of air per hour. What would be the volumetric efficiency of the engine?
a) 75%
b) 78.7%
c) 77.8%
d) 76%

Explanation: Swept volume per hour = $$\frac{π}{4}$$*D2*Number of cycles per hour*Number of cylinder
= $$\frac{π}{4}$$[11/100]2*[12.2/100]*2800/2*60*6
= 584.33 m2
Volumetric efficiency = $$\frac{Actual \,volume \,of \,air \,taken}{Swept \,Volume}$$*100
= $$\frac{455}{584.33}$$*100
= 77.8%.

8. A diesel engine transmits 25 KW at the end of the crankshaft, moving at 1650 rev/min, find the torque exerted by the piston.
a) 148.90 Newton-metre
b) 144.75 Newton-metre
c) 150.75 Newton-metre
d) 120.10 Newton-metre

Explanation: Power(W) = $$\frac{2πnT}{60}$$
25*1000=$$\frac{2π*1650*T}{60}$$
T=144.75 Newton-metre.

9. Which of the following is not a function of a flywheel?
a) It stores energy during power stroke and returns back the same energy during the idle strokes, providing a rotary motion
b) It carries ring gear that meshes with the pinion of starting motor
c) It is used to join the connecting rod to piston
d) It serves the purpose of a pulley for transmitting power

Explanation: Flywheel is a regulator consisting of heavy wheel that stores kinetic energy and smooth’s the operation of a reciprocating engine. The third option refers to the function of a piston pin which provides a flexible or hinge like connection between piston and the connecting rod.

10. The minimum temperature required for a liquid fuel to form a spontaneously combustible mixture is known as ____________
a) Flash point
b) Fluid coupling
c) Differential
d) Disc brake

Explanation: Petrol is a volatile fuel, readily evaporates, so it gets mixed with the air efficiently. As a result, just a spark is sufficient to produce smooth combustion in a well-mixed petrol engine. Petrol has a very low flash point which is opposite in the case of diesel.

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