1000+ Internal Combustion MCQ for LSAT [Solved]

1. The operation of forcing additional air under pressure in the engine cylinder is known as
A. Scavenging
B. Turbulence
C. Supercharging
D. Pre-ignition
Answer : C

2. In order to prevent knocking in spark ignition engines, the charge away from the spark plug should have
A. Low density
B. Low temperature
C. Long ignition delay
D. All of these
Answer : D

3. The knocking tendency in compression ignition engines for a given fuel will be
A. Enhanced by decreasing compression ratio
B. Enhanced by increasing compression ratio
C. Dependent on other factors
D. None of the above
Answer : A

4. The theoretically correct mixture of air and petrol is
A. 10 : 1
B. 15 : 1
C. 20 : 1
D. 25 : 1
Answer : B

5. Morse test is used to determine the I.P. of a
A. Single cylinder petrol engine
B. Four stroke engine
C. Single cylinder diesel engine
D. Multi cylinder engine
Answer : D

6. The reference fuels for knock rating of spark ignition engines would include
A. Iso-octane and alpha-methyl naphthalene
B. Normal octane and aniline
C. Isooctane and normal hexane
D. Normal heptane and isooctane
Answer : D

7. In a typical medium speed 4-stroke cycle diesel engines
A. Exhaust valve opens at 35° before bottom dead centre and closes at 20° after top dead centre
B. Exhaust valve opens at bottom dead centre and closes at top dead centre
C. Exhaust valve opens just after bottom dead centre and closes just before top dead centre
D. May open and close anywhere
Answer : A

8. A fuel of cetane number 40 has the same ignition quality as a mixture of
A. 40% cetane and 60% alpha methyl naphthalene
B. 40% alpha methyl naphthalene and 60% cetane
C. 40% petrol and 60% diesel
D. 40% diesel and 60% petrol
Answer : A

9. A supercharged engine as compared to an ordinary engine
A. Is lighter
B. Requires smaller foundations
C. Consumes less lubricating oil
D. All of these
Answer : D

10. The temperature of interior surface of cylinder wall in normal operation is not allowed to exceed
A. 80°C
B. 120°C
C. 180°C
D. 240°C
Answer : C

11. The higher combustion chamber wall temperature in compression ignition engines will _________ knocking tendency.
A. Increase
B. Reduce
C. Not effect
D. None of these
Answer : B

12. The normal heptane (C₇H₁₆) is given a rating of ________ octane number.
A. 0
B. 50
C. 100
D. 120
Answer : A

13. The size of inlet valve of an engine in comparison to exhaust valve is
A. More
B. Less
C. Same
D. More/less depending on capacity of engine
Answer : B

14. Solid fuel fabricated into various small shapes, which are assembled to form fuel elements, is in the form of
A. Plates
B. Pallets
C. Pins
D. All of these
Answer : D

15. The knocking tendency in spark ignition engines may be decreased by
A. Controlling the air-fuel mixture
B. Controlling the ignition timing
C. Controlling the exhaust temperature
D. Reducing the compression ratio
Answer : D

16. In petrol engines, advancing of the spark timing will _________ the knocking tendency.
A. Not effect
B. Decrease
C. Increase
D. None of these
Answer : C

17. A gas engine has a swept volume of 300 cm3 and clearance volume of 25 cm3. Its volumetric efficiency is 0.88 and mechanical efficiency is 0.90. The volume of the mixture taken in per stroke is
A. 248 cm³
B. 252 cm³
C. 264 cm³
D. 286 cm³
Answer : C

18. When crude oil is heated, then which of the following hydrocarbon is given off first?
A. Kerosene
B. Gasoline
C. Paraffin
D. Natural gas
Answer : D

19. The increase in intake temperature of internal combustion engines will _________ efficiency.
A. Have no effect on
B. Increase
C. Decrease
D. None of these
Answer : C

20. The thermal efficiency of a standard Otto cycle for a compression ratio of 5.5 will be
A. 25 %
B. 50 %
C. 70 %
D. 100 %
Answer : B

21. The power actually developed by the engine cylinder of an I.C. engine is known as
A. Theoretical power
B. Actual power
C. Indicated power
D. None of these
Answer : C

22. A diesel engine has compression ratio from
A. 6 to 10
B. 10 to 15
C. 15 to 25
D. 25 to 40
Answer : C

23. In a four stroke cycle petrol engine, the pressure inside the engine cylinder during the suction stroke is __________ the atmospheric pressure.
A. Equal to
B. Below
C. Above
D. None of these
Answer : B

24. The fuel air ratio in a petrol engine fitted with suction carburettor, operating with dirty air filter as compared to clean filter will be
A. Higher
B. Lower
C. Remain unaffected
D. None of the above
Answer : A

25. The term scavenging is generally associated with
A. 2-stroke cycle engines
B. 4-stroke cycle engines
C. Aeroplane engines
D. High efficiency engines
Answer : D

26. The rating of a diesel engine, with increase in air inlet temperature, will
A. Increase linearly
B. Decrease linearly
C. Increase parabolically
D. Decrease parabolically
Answer : B

27. In a naturally aspirated diesel engine, the air is supplied by
A. A supercharger
B. A centrifugal blower
C. A vacuum chamber
D. An injection tube
Answer : C

28. The firing order in an I.C. engine depends upon
A. Arrangement of the cylinders
B. Design of crankshaft
C. Number of cylinders
D. All of these
Answer : D

29. Which of the following does not relate to a compression ignition engine?
A. Fuel pump
B. Fuel injector
C. Governor
D. Carburettor
Answer : D

30. Supercharging is essential in
A. Diesel engines
B. Gas turbines
C. Petrol engines
D. Aircraft engines
Answer : D

31. The pressure at the end of compression, in diesel engines, is approximately
A. 10 bar
B. 20 bar
C. 25 bar
D. 35 bar
Answer : D

32. In loop scavenging, the top of the piston is
A. Flat
B. Contoured
C. Slanted
D. Depressed
Answer : B

33. 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 occupy more space than diesel engines for same power output
Answer : D

34. Which of the following statement is correct?
A. Compression ratio for petrol engines varies from 6 to 10
B. Higher compression ratio in diesel engines results in higher pressures
C. Petrol engines work on Otto cycle
D. All of the above
Answer : D

35. Diesel engine can work on very lean air fuel ratio of the order of 30: 1. A petrol engine can also work on such a lean ratio provided
A. It is properly designed
B. Best quality fuel is used
C. Cannot work as it is impossible
D. Flywheel size is proper
Answer : C

36. The air standard efficiency of an I.C. engine depends on
A. Fuel used
B. Speed of engine
C. Compression ratio
D. None of these
Answer : C

37. The object of supercharging the engine is
A. To reduce mass of the engine per brake power
B. To reduce space occupied by the engine
C. To increase the power output of an engine when greater power is required
D. All of the above
Answer : D

38. The voltage required to produce a spark across the gap, between the sparking points is
A. 2000 to 4000 volts
B. 4000 to 6000 volts
C. 6000 to 10,000 volts
D. 10,000 to 12,000 volts
Answer : C

39. As a result of detonation in an I.C. engine, following parameter attains very high value
A. Peak pressure
B. Rate of rise of pressure
C. Rate of rise of temperature
D. Peak temperature
Answer : B

40. Most high speed compression engines operate on
A. Diesel cycle
B. Otto cycle
C. Dual combustion cycle
D. Special type of air cycle
Answer : C

41. The advancing of spark timing in spark ignition engines will _________ knocking tendency.
A. Increase
B. Reduce
C. Not effect
D. None of these
Answer : A

42. In a four stroke cycle petrol engine, the compression
A. Starts at 40° after bottom dead centre and ends at 30° before top dead centre
B. Starts at 40° before bottom dead centre and ends at 30° after bottom dead centre
C. Starts at bottom dead centre and ends at top dead centre
D. May start and end anywhere
Answer : A

43. If one cylinder of a diesel engine receives more fuel than the others, then for that cylinder the
A. Exhaust will be smoky
B. Piston rings would stick into piston grooves
C. Engine starts overheating
D. Scavenging occurs
Answer : D

44. The volumetric efficiency of a well designed engine may be
A. 30 to 40 %
B. 40 to 60 %
C. 60 to 70 %
D. 75 to 90 %
Answer : D

45. In a four stroke cycle petrol engine, the expansion
A. Starts at top dead centre and ends at bottom dead centre
B. Starts at 30° before top dead centre and ends at 50° before bottom dead centre
C. Starts at 30° after top dead centre and ends at 50° after bottom dead centre
D. May start and end anywhere
Answer : B

46. Number of working strokes per min. for a two stroke cycle engine is _________ the speed of the engine in r.p.m.
A. Equal to
B. One-half
C. Twice
D. Four-times
Answer : A

47. The accumulation of carbon in a cylinder results in increase of
A. Clearance volume
B. Volumetric efficiency
C. Ignition time
D. Effective compression ratio
Answer : D

48. High speed compression engines operate on
A. Otto cycle
B. Diesel cycle
C. Dual combustion cycle
D. All of these
Answer : C

49. Scavenging is usually done to increase
A. Thermal efficiency
B. Speed
C. Power output
D. Fuel consumption
Answer : C

50. Polymerisation is a chemical process in which molecules of a compound become
A. Larger
B. Slowed down
C. Smaller
D. Liquid
Answer : A