Farm Machinery Questions and Answers – I.C Engine – Types of Heat Engine

This set of Farm Machinery Multiple Choice Questions & Answers (MCQs) focuses on “Types of Heat Engine”.

1. Which of the following describes the displacement or swept volume?
a) Vs=$$\frac{Π}{4}$$∗d2l
b) Vs=$$\frac{Π}{16}$$∗d2l
c) Vs=$$\frac{Π}{32}$$∗d2l
d) Vs=$$\frac{Π}{4}$$∗d3l

Explanation: Vs=$$\frac{Π}{4}$$∗d2l describes Swept volume or the displacement. Volume is swept when the piston moves between top dead centre and bottom dead centre during the movement of piston.

2. Which of these is not an external combustion engine?
a) Beam engines
b) Steam engines
c) Stirling engines
d) Diesel engines

Explanation: In the 19th century, a German engineer Rudolf Diesel realized he could make a powerful engine that could run off all kinds of different fuels (unlike Gasoline engines). Diesel engine compress fuel so that it spontaneously bursts into flames and releases the heat energy locked inside it.

3. Relative efficiency is the ratio of _________
a) $$\frac{actual \, thermal \, efficiency}{mechanical \, efficiency}$$
b) $$\frac{actual \, thermal \, efficiency}{air-standard \, efficiency}$$
c) $$\frac{air-standard \, efficiency}{actual \, thermal \, efficiency}$$
d) $$\frac{mechanical \, efficiency}{actual \, thermal \, efficiency}$$

Explanation: Relative efficiency is the ratio of actual thermal efficiency to the air-standard efficiency.
Relative efficiency = $$\frac{actual \, thermal \, efficiency}{air-standard \, efficiency}$$

4. What is the basic reaction in the battery of the ignition system?
a) PbO5 + Pb + 4H2SO4 = 4PbSO2 + 4H20
b) 2PbO2 + 2H2SO4 = 2PbO + 2SO4 + 2H2O + O2
c) PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O
d) PbO2 + 2H2SO4 = 2PbSO4 + 2H2O

Explanation: Sulphuric acid is used as an electrolyte, which contains about 35% sulphuric acid and 65% water. The specific gravity at full charge is about 1.270, while at complete discharge it is about 1.10.

5. Which of the following is not a feature of the spark plug?
a) Varies from 0.5 to 0.85 mm
b) Used in cold engines
c) Dissipates the heat very quickly, it used for hot engine
d) Ratio of turns in primary and secondary is 1:100

Explanation: The last option is a feature of the ignition coil in which 6 or 12-volt current is fed in the primary winding and from the secondary winding voltage to the tune of 2000 volt is tapped.
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6. What is the co-efficient of friction for lubricant?
a) Cf = $$\frac{ZN}{P}$$
b) Cf = $$\frac{PN}{Z}$$
c) Cf = $$\frac{ZP}{N}$$
d) Cf = ZPN

Explanation: The lubricated friction depends on the operating conditions such as the sliding speed, lubricant viscosity, temperature etc. In the formula, Z is the viscosity or oil thickness, N is the surface speed and P is the pressure caused by the weight.

7. What is the Carnot Cycle Efficiency?
a) η = 1- QC/QH
b) η = QC/QH
c) η = QC/QH -1
d) η = QH/QC

Explanation: Since energy is conserved according to the first law of thermodynamics and energy cannot be converted to work completely, the heat input, QH, must be equal to the work done, W, plus the heat that must be dissipated as waste heat QC, into the environment.

8. What is the Carnot efficiency for a coal–fired power plant?
a) 65%
b) 74%
c) 56%
d) 90%

Explanation: In modern day coal fire power plant, the temperature of high pressure steam (Thot) would be about 400° C and Tcold = 20° C.
η = 1−$$\frac{293}{673}$$
η = 56%.

Sanfoundry Global Education & Learning Series – Farm Machinery.