# Farm Machinery Questions and Answers – I.C Engine – Working of 2-stroke Engine

This set of Farm Machinery Question Bank focuses on “I.C Engine – Working of 2-stroke Engine”.

1. What is molar heat capacity (C)?
a) C = Specific heat * Molecular weight of gas
b) C = Specific heat + Molecular weight of gas
c) C = Specific heat – Molecular weight of gas
d) C = $$\frac{Specific\, heat}{Molecular\, weight\, of\, gas}$$

Explanation: Molar heat capacity is defined as the amount of heat required to raise temperature of 1 mole of gas through 1°C. For gases, there are two values of molar heats, i.e., molar heat at constant pressure (Cp) and molar heat at constant volume (Cv).

2. The amount of heat required to raise the temperature of 1 gram of substance through 1°C is known as ________
a) Internal energy
b) Molar heat capacity
c) Specific heat
d) Heat enthalpy

Explanation: The relationship between heat and temperature change is usually expressed in the form
Q=cm∆T
Where c is the specific heat. The relationship does not apply if a phase change is encountered, because the heat added or removed during a phase change does not change temperature.

3. The lower part of a crankcase is commonly known as _______
a) Oil pan
b) Dry liner
c) Wet liner
d) Skirt

Explanation: The crankcase is that part of the engine which supports and encloses the crankshaft and camshaft. It provides a reservoir for the lubricating oil of the engine. It also serves as a mounting unit for such accessories as the oil pump, oil filter, generator, starting motor and ignition components. The upper portion of the crankcase is usually integral with cylinder block. The lower part is commonly known as oil pan and usually made of cast iron or cast aluminium.

4. What is the range of angles made between common face and seat angle of valve?
a) 50°-60°
b) 30°-45°
c) 70°-85°
d) 10°-20°

Explanation: Each valve (inlet and exhaust) is opened or closed once during each cycle. A strong spring with the help of retainer and a key holds the valve tightly against the seat and thus prevents leakage on the compression and power stroke. The common face and seat angle of valve is 45° but 30° angle is also used for intake valves.

5. How many kilopascals are there in 1 kg/cm2?
a) 89 kPa
b) 76 kPa
c) 98 kPa
d) 69 kPa

Explanation: 1 kg = 9.8 N
1 N.m. = 1 Joule
1 N. m/s = 1 Joule/s = 1 Watt
1 kg/cm2 = 9.8 * 104 N/m2 = 9.8 * 104 Pa = 98 kPa
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6. What is the stroke-bore ratio for tractor engines?
a) 1
b) 1.45
c) 0.25
d) 1.25

Explanation: The ratio of length (L) and diameter of bore (D) of the cylinder is called stroke-bore ratio (L/D). This ratio varies between 1 to 1.45 and for tractor engines, this ratio is about 1.25.

7. What is the compression ratio of an engine whose dimensions are 100*120 mm and length of clearance space at the top dead centre being 8 mm?
a) 16:1
b) 32:1
c) 1:16
d) 1:32

Explanation: Total length of cylinder L = 12+0.8=12.8 cm
Height of clearance space = 0.8 cm
Clearance volume= area * height = $$\frac{π}{4}$$*102*0.8
= 62.8 cm3
Total volume = $$\frac{π}{4}$$*D2*L
= $$\frac{π}{4}$$*102*12.8 = 1004.8 cm3
Compression ratio = $$\frac{Total \, volume}{Clearance \, volume}$$
= $$\frac{1004.8}{62.8}$$ = 16/1
= 16:1

8. A fuel contains 84% carbon and 16% hydrogen by mass. The necessary air- fuel ratio for chemically correct combustion is _______
a) 10.42: 1
b) 15.30: 1
c) 20.36: 1
d) 31.08: 1

Explanation: Let CxHy be the fuel
Molecular weight of CxHy = 12x+y
According to question: $$\frac{12x}{12x+y}$$*100 = 84
And $$\frac{y}{12x+y}$$*100 = 16
By solving the above equations, we get; x=7 and y=16
Thus, formula for fuel is C7H16
C7H16 (12*7 + 1*16=100) + 11O2(11*16*2=352) = 7CO2 + 8H20
$$\frac{Air}{Fuel} = \frac{352}{100*0.23}$$ = 15.3:1

9. Which component of I.C. engine is also known as ‘half time gear’?
a) Timing gear
b) Crankcase
c) Flywheel
d) Tappet

Explanation: Timing gear is a combination of multiple gears where in one gear is mounted at one end of the camshaft and the other gear is mounted at the end of the crankshaft. In terms of size, Camshaft gear is bigger than the crankshaft gear and has twice as many teeth than crankshaft gear. For this reason, this gear is commonly called half time gear.

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