# Thermodynamics Questions and Answers – An Overview of Reciprocating Engines

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This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “An Overview of Reciprocating Engines”.

1. The top dead centre is the position of piston when it forms ____ volume in cylinder and bottom dead centre is the position of piston when it forms ____ volume in cylinder.
a) largest, smallest
b) smallest, largest
c) equal, equal
d) none of the mentioned

Explanation: This is the definition of TDC and BDC.

2. The distance between TDC and BDC is called ____
a) piston
b) bore
c) stroke
d) none of the mentioned

Explanation: It is the largest distance that piston can travel in one direction.

3. The diameter of piston is called ____
a) piston
b) bore
c) stroke
d) none of the mentioned

Explanation: This is what a bore means.
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4. The air or air-fuel mixture is ____ into cylinder through intake valve and ____ out of cylinder through exhaust valve.
a) drawn, expelled
b) taken, thrown
c) both of the mentioned
d) none of the mentioned

Explanation: This is what an intake valve and exhaust valve does.

5. The clearance volume is the ____ volume formed in cylinder when piston is at TDC.
a) minimum
b) maximum
c) average
d) none of the mentioned

Explanation: When the piston is at TDC, the volume is minimum.

6. The volume displaced by piston when it moves between TDC and BDC is called
a) swept volume
b) displacement volume
c) clearance volume
d) none of the mentioned

Explanation: Displacement volume is, how much the piston gets displaced when it moves from TDC to BDC and vice-versa.

7. The compression ratio is given by
a) Vmax / total volume
b) Vmin / Vmax
c) V(at TDC) / V(at BDC)
d) V(at BDC) / V(at TDC)

Explanation: The compression ratio of an engine is given by V(at BDC) / V(at TDC) which is also equal to Vmax / Vmin.

8. The net work produced during a cycle is given by
a) (mean effective pressure)*(piston area)*(stroke)
b) (mean effective pressure)*(displacement volume)
c) both of the mentioned
d) none of the mentioned

Explanation: The mean effective pressure is a fictitious pressure.

9. The compression ratio is a pressure ratio.
a) true
b) false

Explanation: The compression ratio is a volume ratio.

10. Which of the following is a classification of reciprocating engines?
a) spark-ignition engines
b) compression-ignition engines
c) both of the mentioned
d) none of the mentioned

Explanation: These two are classified based on how combustion process is initiated in the cylinder.

11. Which of the following statement is true?
a) in S.I. engines, combustion of air-fuel mixture is initiated by spark plug
b) in C.I. engines, combustion of air-fuel mixture is self-ignited
c) both of the mentioned
d) none of the mentioned

Explanation: In the C.I. engines,self-ignition takes place because of compression of mixture above self-ignition temperature.

12. A gasoline engine has a volumetric compression ratio of 10. Find the overall cycle efficiency.
a) 0.602
b) 0.302
c) 0.502
d) 0.702

Explanation: η = 1 − r^(1-k)
= 1 − 10^(-0.4)
= 0.602.

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