# Thermodynamics Questions and Answers – Diesel Cycle and Dual Cycle

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Diesel Cycle and Dual Cycle”.

1. In SI engines,
a) air-fuel mixture is compressed
b) compression ratio is limited
c) both of the mentioned
d) none of the mentioned

Explanation: The onset of engine knock or auto-ignition limits the compression ratio in SI engines.

2. In CI engines,
a) during compression stroke, only air is compressed
b) compression ratios can be much higher
c) both of the mentioned
d) none of the mentioned

Explanation: This is an advantage of CI engine over SI engine.

3. The correct sequence of processes in CI engine is
a) intake->fuel injection and combustion->compression->expansion->exhaust
b) intake->compression->fuel injection and combustion->expansion->exhaust
c) intake->compression->expansion->fuel injection and combustion->exhaust
d) intake->compression->exhaust->fuel injection and combustion->expansion

Explanation: The correct sequence of processes in CI engine is intake->compression->fuel injection and combustion->expansion->exhaust.

4. The processes in CI engine cycle is completed in ____ strokes of piston and ____ revolutions of crankshaft.
a) four, four
b) two, two
c) two, four
d) four, two

Explanation: There are four strokes and number of revolutions of crankshaft required are two.

5. The Diesel cycle consists of
a) two reversible isotherms and two reversible isobars
b) one reversible isochore and two reversible adiabatics and one reversible isobar
c) one reversible isotherm and two reversible isochores and one reversible isobar
d) two reversible isobars and two reversible adiabatics

Explanation: These four processes comprises Diesel cycle.

6. Which of the following is the relation between compression ratio, expansion ratio and cut-off ratio?
a) rc=(rk)*(re)
b) re=(rk)*(rc)
c) rk=(re)*(rc)
d) none of the mentioned

Explanation: Here rk=compression ratio, re=expansion ratio and rc=cut-off ratio.

7. The efficiency of Diesel cycle is ____ the efficiency of Otto cycle.
a) less than
b) greater than
c) equal to
d) none of the mentioned

Explanation: This comes from the formula for the efficiency of Diesel cycle.

8. In Dual cycle,
a) all the heat is added at constant volume
b) all the heat is added at constant pressure
c) some heat is added at constant volume and remaining at constant pressure
d) none of the mentioned

Explanation: This is the reason why Dual cycle is also called Mixed cycle.

9. The constant volume pressure ratio is given by the ratio of pressures of constant volume heat addition.
a) true
b) false

Explanation: This ratio is used in Dual cycle.

10. Detonation in SI engine is
a) noisy and destructive combustion phenomenon
b) limits the compression ratio
c) it depends on engine design and fuel
d) all of the mentioned

Explanation: This is what detonation means and its causes.

11. The premature ignition of fuel is called ____
a) engine knock
b) auto-ignition
c) detonation
d) all of the mentioned

Explanation: Engine knock or detonation is the audible noise produces by auto-ignition.

12. The auto-ignition
a) reduces performance of engine
b) can cause damage to engine
c) sets upper limit to compression ratios used in SI engines
d) all of the mentioned

Explanation: Thus auto-ignition should always be avoided.

13. Many a times, tetraethyl ether is added to gasoline.
a) true
b) false

Explanation: This is done to raise the octane rating of fuel.

14. For a given compression raise, the highest efficiency can be obtained by using
a) triatomic gases
b) diatomic gases
c) monoatomic gases
d) all of the mentioned

Explanation: Monoatomic gases like helium and argon has highest value of ɣ.

15. ɣ ____ with temperature.
a) increases
b) decreases
c) remains constant
d) none of the mentioned

Explanation: This is a property of ɣ .

Sanfoundry Global Education & Learning Series – Thermodynamics.
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