IC Engines Practice Set-1

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1. A stoichiometric air-fuel ratio is

Rich mixture for idling

Rich mixture for over loads

Chemically correct mixture

Lean mixture

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

Detonation

Polymerisation

Scavenging

Supercharging

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

High self ignition temperature

Higher viscosity

All of these

Low volatility

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

1 - (1/r^{γ - 1})

1+ r^{γ - 1}

None of these

1- r^{γ - 1}

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

15: 1

12: 1

6: 1

9: 1

6. 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

May open and close anywhere

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

7. Supercharging is the process of

Supplying compressed air to remove combustion products fully

Injecting excess fuel for raising more loads

Providing forced cooling air

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

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

Air and lub oil

Air and fuel

Air alone

Fuel alone

9. Compression ratio of I.C. Engines is

Volume displaced by piston per stroke and clearance volume in cylinder

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

Swept volume/cylinder volume

Ratio of pressure after compression and before compression

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

Increase

Increase up to certain limit and then decrease

Decrease

Remain same

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

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

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

May open or close anywhere

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

One-half

Twice

Equal to

Four-times

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

Detonation

Pre-ignition

Turbulence

Supercharging

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

There is no such criterion

Below the piston

Above the piston

Between the pistons

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

Decrease parabolically

Increase linearly

Decrease linearly

Increase parabolically

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

(C) Both (A) and (B)

(A) Retarding the spark

(B) Increasing the engine speed

(D) None of these

17. Pick up the wrong statement about supercharging

Supercharging results in fuel economy

Supercharging reduces knocking in diesel engines

Supercharging at high altitudes is essential

There can be limited supercharging in petrol engines because of detonation

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

Napthene, aromatics, paraffin

Paraffin, napthene, aromatic

Paraffin, aromatic, napthene

Napthene, paraffin, aromatic

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

500-1000°C

1500-2000°C

1000-1500°C

2000-2500°C

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

May start and end anywhere

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

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

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

Delay period

Carburetion

Supercharging

Turbulence

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

Scavenging

Turbulence

Pre-ignition

Supercharging

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

Maximum pressure developed

Average pressure

Instantaneous pressure at any instant

Minimum pressure

24. Pour point of fuel oil is the

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

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

It catches fire without external aid

Temperature at which it solidifies or congeals

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

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

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

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

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

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

High

Very high

Low

Very low

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

12 kg/cm

35 kg/cm

6 kg/cm

20 kg/cm

28. 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

29. The ignition quality of petrol is expressed by

Cetane number

All of these

Octane number

Calorific value

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

Starts at bottom dead centre and ends at top dead centre

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

May start and end anywhere

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

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

Gasoline

Diesel

Kerosene

Fuel oil

32. An engine indicator is used to determine the following

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

Speed

Temperature

Volume of cylinder

33. 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

34. In compression ignition engines, swirl denotes a

Haphazard motion of the gases in the chamber

Rotary motion of the gases in the chamber

None of the above

Radial motion of the gases in the chamber

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

None of these

Decrease

Increase

Remain same

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

More

Less

May be more or less depending on engine capacity

Same

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

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

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

Never occurs

Both mild and big explosions occurs simultaneously

First a big explosion followed by a mil explosion

First a mild explosion followed by a bi explosion

39. 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

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

All of these

Arrangement of the cylinders

Number of cylinders

Design of crankshaft

IC Engines Practice Set-1

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