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IC Engines
0

IC Engines Practice Set-1

September 5, 2021

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Page 1 of 4

1. Pick up the false statement

Thermal efficiency of diesel engine is about 34%

High speed compression engines operate on dual combustion cycle

S.I. engines are quality governed engines

Theoretically correct mixture of air and petrol is approximately 15:1

2. A stoichiometric air-fuel ratio is

Chemically correct mixture

Lean mixture

Rich mixture for over loads

Rich mixture for idling

3. The loud pulsating noise heard within the cylinder of an internal combustion engine is known as

Detonation

Pre-ignition

Turbulence

Supercharging

4. In the opposed piston diesel engine, the combustion chamber is located

Below the piston

Above the piston

There is no such criterion

Between the pistons

5. The maximum temperature in the I.C. engine cylinder is of the order of

500-1000°C

2000-2500°C

1000-1500°C

1500-2000°C

6. If the temperature of intake air in internal combustion engine increases, then its efficiency will

None of these

Remain same

Decrease

Increase

7. The firing order in an I.C. engine depends upon

Design of crankshaft

Arrangement of the cylinders

All of these

Number of cylinders

8. The knocking in spark ignition engines can be reduced by

(A) Retarding the spark

(D) None of these

(B) Increasing the engine speed

(C) Both (A) and (B)

9. If the temperature of intake air in IC engines is lowered, then its efficiency will

Remain same

Increase up to certain limit and then decrease

Increase

Decrease

10. The ignition of the charge by some hot surface within the engine before the passage of spark is called

Ignition delay

Auto-ignition

Pre-ignition

Detonation

Page 2 of 4

11. The air requirement of a petrol engine during starting compared to theoretical air required for complete combustion is

May be more or less depending on engine capacity

Same

Less

More

12. Crankcase explosion in I.C. engines usually occurs as

First a big explosion followed by a mil explosion

First a mild explosion followed by a bi explosion

Both mild and big explosions occurs simultaneously

Never occurs

13. The working pressure and temperature inside the cylinder of an internal combustion engine is _________ as compared to a steam engine.

Very high

Low

High

Very low

14. In a four stroke cycle diesel engine, the compression

Starts at 40° after bottom dead center and ends at 10° before top dead center

May start and end anywhere

Starts at top dead center and ends at 40° before bottom dead center

Starts at 40° before top dead center and ends at 40° after top dead center

15. The operation of forcing additional air under pressure in the engine cylinder is known as

Pre-ignition

Turbulence

Scavenging

Supercharging

16. Which one of the following engines will have heavier flywheel than the remaining ones?

30 kW four-stroke petrol engine running at 1500 r.p.m.

30 kW two-stroke petrol engine running at 1500 r.p.m.

30 kW two-stroke diesel engine running at 750 r.p.m.

30 kW four-stroke diesel engine running at 750 r.p.m.

17. The pressure at the end of compression in the case of diesel engine is of the order of

20 kg/cm

12 kg/cm

35 kg/cm

6 kg/cm

18. Pick up the wrong statement about supercharging

There can be limited supercharging in petrol engines because of detonation

Supercharging at high altitudes is essential

Supercharging reduces knocking in diesel engines

Supercharging results in fuel economy

19. Pour point of fuel oil is the

Indicated by 90% distillation temperature i.e., when 90% of sample oil has distilled off

Temperature at which it solidifies or congeals

It catches fire without external aid

Minimum temperature to which oil is heated in order to give off inflammable vapours in sufficient quantity to ignite momentarily when brought in contact with a flame

20. Supercharging is the process of

Providing forced cooling air

Supplying the intake of an engine with air at a density greater than the density of the surrounding atmosphere

Injecting excess fuel for raising more loads

Supplying compressed air to remove combustion products fully

Page 3 of 4

21. The fuels in order of decreasing knock tendency for spark ignition engines are

Napthene, paraffin, aromatic

Napthene, aromatics, paraffin

Paraffin, napthene, aromatic

Paraffin, aromatic, napthene

22. In an internal combustion engine, the process of removing the burnt gases from the combustion chamber of the engine cylinder is known as

Scavenging

Detonation

Polymerisation

Supercharging

23. The probability of knocking in diesel engines is increased by

All of these

High self ignition temperature

Low volatility

Higher viscosity

24. The air standard efficiency of an I.C. engine is given by (where r = Compression ratio, and γ = Ratio of specific heats)

1+ r^{γ - 1}

None of these

1 - (1/r^{γ - 1})

1- r^{γ - 1}

25. The ignition quality of petrol is expressed by

Cetane number

All of these

Calorific value

Octane number

26. The operation of forcing additional air under pressure into the engine cylinder is known as

Supercharging

Carburetion

Delay period

Turbulence

27. Detonation is harmful due to

High intensity of knock causes crankshaft vibration and the engine runs rough

Increase in the rate of heat transfer, there is a reduction in the power output and efficiency of the engine

Excessive turbulence which removes most of the insulating gas boundary layer from the cylinder walls

None of the above

28. Number of working strokes per min. for a four stroke cycle engine are _________ the speed of the engine in r.p.m.

Equal to

One-half

Four-times

Twice

29. An engine indicator is used to determine the following

Temperature

Speed

Volume of cylinder

m.e.p. and I.H.P.

30. Which of the following is the lightest and most volatile liquid fuel?

Fuel oil

Kerosene

Diesel

Gasoline

Page 4 of 4

31. In a four stroke cycle petrol engine, the compression

May start and end anywhere

Starts at 40° before bottom dead centre and ends at 30° after bottom dead centre

Starts at 40° after bottom dead centre and ends at 30° before top dead centre

Starts at bottom dead centre and ends at top dead centre

32. In a typical medium speed 4-stroke cycle diesel engine the inlet valve

May open or close anywhere

Opens at top dead center and closes at bottom dead center

Opens at 20° before top dead center and closes at 35° after the bottom dead center

Opens at 10° after top dead center and closes 20° before the bottom dead center

33. Which of the following medium is compressed in a Diesel engine cylinder?

Fuel alone

Air and lub oil

Air and fuel

Air alone

34. In compression ignition engines, swirl denotes a

None of the above

Haphazard motion of the gases in the chamber

Radial motion of the gases in the chamber

Rotary motion of the gases in the chamber

35. In a typical medium speed, 4-stroke cycle diesel engine

Fuel injection starts at top dead center and ends at 20° after top dead center

May start and end anywhere

Fuel injection starts at 10° before top dead center and ends at 20° after top dead center

Fuel injection starts at just before top dead center and ends just after top dead center

36. The rating of a diesel engine, with increase in air inlet temperature, will

Increase parabolically

Increase linearly

Decrease linearly

Decrease parabolically

37. The mean effective pressure obtained from engine indicator indicates the

Average pressure

Instantaneous pressure at any instant

Minimum pressure

Maximum pressure developed

38. Compression ratio of I.C. Engines is

The ratio of volumes of air in cylinder before compression stroke and after compression stroke

Volume displaced by piston per stroke and clearance volume in cylinder

Ratio of pressure after compression and before compression

Swept volume/cylinder volume

39. The theoretically correct air fuel ratio for petrol engine is of the order of

12: 1

6: 1

15: 1

9: 1

40. In a four stroke cycle diesel engine, the exhaust valve

Opens at 30° after bottom dead centre and closes at 10° before top dead centre

Opens at bottom dead centre and closes at top dead centre

Opens at 30° before bottom dead centre and closes at 10° after top dead centre

May open and close anywhere

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

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