mechanical Engine MCQ with Answers

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mechanical Engine MCQ with Answers (100% free pdf download)

1. The working cycle in case of four stroke engine is completed in following number of revolutions of crankshaft
(a) 1/2
(b) 1
(c) 2
(d) 4
(e) 8.
Ans: c

2. In a diesel engine, the fuel is ignited by
(a) spark
(b) injected fuel
(c) heat resulting from compressing air that is supplied for combustion
(d) ignition
(e) combustion chamber.
Ans: c

3. Scavenging air in diesel engine means
(a) air used for combustion sent under pres-sure
(b) forced air for cooling cylinder
(c) burnt air containing products of combustion
(d) air used for forcing burnt gases out of engine’s cylinder during the exhaust period
(e) air fuel mixture.
Ans: d

4. Supercharging is the process of
(a) supplying the intake of an engine with air at a density greater than the density ofthe surrounding atmosphere
(b) providing forced cooling air
(c) injecting excess fuel for raising more load
(d) supplying compressed air to remove combustion products fully
(e) raising exhaust pressure.
Ans: a

5. Does the supply of scavenging air at a density greater than that of atmosphere mean engine is supercharged ?
(a) yes
(b) no
(c) to some extent
(d) unpredictable
(e) depends on other factors.
Ans: b

6. The ratio of indicated thermal efficiency to the corresponding air standard cycle efficiencyis called
(a) net efficiency
(b) efficiency ratio
(c) relative efficiency
(d) overall efficiency
(e) cycle efficiency.
Ans: c

7. Compression ratio of IC. engines is
(a) the ratio of volumes of air in cylinder before compression stroke and after compression stroke
(b) volume displaced by piston per stroke and clearance volume in cylinder
(c) ratio of pressure after compression and before compression
(d) swept volume/cylinder volume
(e) cylinder volume/swept volume.
Ans: a

8. The air standard efficiency of an Otto cycle compared to diesel cycle for the given compression ratio is
(a) same
(b) less
(c) more
(d) more or less depending on power rating
(e) unpredictable.
Ans: c

9. The calorific value of gaseous fuels is expressed in terms of
(a) kcal
(b) kcal/kg
(c) kcal/m2
(d) kcal/n?
(e) all of the above.
Ans: d

10. If the intake air temperature of I.C. engine increases, its efficiency will
(a) increase
(b) decrease
(c) remain same
(d) unpredictable
(e) depend on other factors.
Ans: b

12. All heat engines utilize
(a) low heat value of oil
(b) high heat value of oil
(c) net claorific value of oil
(d) calorific value of fuel
(e) all of the above.
Ans: a

13. An engine indicator is used to determine the following
(a) speed
(b) temperature
(c) volume of cylinder
(d) m.e.p. and I.H.P.
(e) BHP.
Ans: d

14. Fuel oil consumption guarantees for I .C. engine are usually based on
(a) low heat value of oil
(b) high heat value of oil
(c) net calorific value of oil
(d) calorific value of fuel
(e) all of the above.
Ans: b

17. If the compression ratio of an engine working on Otto cycle is increased from 5 to 7, the %age increase in efficiency will be
(a) 2%
(b) 4%
(c) 8%
(d) 14%
(e) 27%.
Ans: d

18. In a typical medium speed 4-stroke cycle diesel engine the inlet valve
(a) opens at 20° before top dead center and closes at 35° after the bottom dead center
(b) opens at top dead center and closes at bottom dead center
(c) opens at 10° after top dead center and closes 20° before the bottom dead center
(d) may open or close anywhere
(e) remains open for 200°.
Ans: a

19. The pressure and temperature at the end of compression stroke in a petrol engine
are of the order of
(a) 4 – 6 kg/cm2 and 200 – 250°C
(b) 6 – 12 kg/cm2 and 250 – 350°C
(c) 12 – 20 kg/cm2 and 350 – 450°C
(d) 20 – 30 kg/cm2 and 450 – 500°C
(e) 30 – 40 kg/cm2 and 500 – 700°C.
Ans: b

20. The pressure at the end of compression in the case of diesel engine is of the order of
(a) 6 kg/cm
(b) 12kg/cm2
(c) 20 kg/cm2
(d) 27.5 kg/cm2
(e) 35 kg/cm2
Ans: e

21. The maximum temperature in the I.C. engine cylinder is of the order of (a) 500- 1000°C
(b) 1000- 1500°C
(c) 1500-2000°C
(d) 2000-2500°C
(e) 2500-3000°C
Ans: d

22. The thermal efficiecny of a diesel cycle having fixed compression ratio, with increase in cut- off ratio will
(a) increase
(b) decrease
(c) be independent
(d) may increase or decrease depending on other factors
(e) none of the
above.
Ans: b

23. Pick up the wrong statement
(a) 2-stroke engine can run in any direction
(b) In 4-stroke engine, a power stroke is obtained in 4-strokes
(c) thermal efficiency of 4-stroke engine is more due to positive scavenging
(d) petrol engines work on otto cycle
(e) petrol engines occupy more space than diesel engines for same power output.
Ans: e

24. Combustion in compression ignition engines is
(a) homogeneous
(b) heterogeneous
(c) both (a) and (b)
(d) laminar
(e) turbulent.
Ans: b

25. The fuel in diesel engine is normally injected at pressure of
(a) 5-10 kg/cm2
(b) 20-25 kg/cm2
(c) 60-80 kg/cm2
(d) 90-130 kg/cm2
(e) 150-250 kg/cm2
Ans: d

26. The temperature of interior surface of cylinder wall in normal operation is not allowedto exceed
(a) 80°C
(b) 120°C
(c) 180°C
(d) 240°C
(e) 320°C.
Ans: c

30. Compression loss in I.C engines occurs duto
(a) leaking piston rings
(b) use of thick head gasket
(c) clogged air-inlet slots
(d) increase in clearance volume caused b bearing-bushing wear
(e) all of the above.
Ans: e

31. The air requirement of a petrol engine during starting compared to theoretical air required for complete combustion is
(a) more
(b) less
(c) same
(d) may be more or less depending on engine capacity
(e) unpredictable.
Ans: b