Objective of Ic engines

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IC Engines 01.Basic of IC Engines Objectives by:- Prakash shakti 1. Advantages of reciprocating IC engines over steam turbine is – Mechanical simplicity, improved plant efficiency & Lower average temperature. 2. The intake charge in a diesel engine consists of – Air alone. 3. Engine of different cylinder dimensions, power & speed can be compared on the basis of – Mean effective pressure. 4. Disadvantages of reciprocating IC engine are – Vibration, Use of fossils fuels & Balancing problems. 5. Gudgeon pin forms the link between – Piston & small end of connecting rod. 6. An IC engine gives an output of 3 kW when the input is 10,000 J/s. The thermal efficiency of the engine is – 30% 7. In a 4-stroke IC engine cam shaft rotates at – Half the speed of crankshaft. 8. Thermal efficiency of CI engine is higher than that of SI engine due to – Higher compression Ratio. 9. SI engines are of – Light weight, High speed & Homogeneous change of fuel & oil. 10. Compression ratio in diesel engines is of the order of – 14-20 11. In a reciprocating engine with a cylinder diameter of D and Stroke of L, the cylinder volume is – π/4 D 2 L + clearance volume. 12. Main advantages of a 2-stroke engine over 4-stroke engine is – More uniform torque on the crankshaft, amore power O/P for the cylinder of same dimension & Absence of valves. 13. Engines used for ships are normally – 2-stroke CI engines of very high power.

Transcript of Objective of Ic engines

Page 1: Objective of Ic engines

IC Engines

01. Basic of IC Engines

Objectives by:- Prakash shakti

1. Advantages of reciprocating IC engines over steam turbine is –

Mechanical simplicity, improved plant efficiency & Lower average temperature.

2. The intake charge in a diesel engine consists of –

Air alone.

3. Engine of different cylinder dimensions, power & speed can be compared on the basis of –

Mean effective pressure.

4. Disadvantages of reciprocating IC engine are – Vibration, Use of fossils fuels & Balancing problems.

5. Gudgeon pin forms the link between –

Piston & small end of connecting rod.

6. An IC engine gives an output of 3 kW when the input is 10,000 J/s. The thermal efficiency of the engine is –

30%

7. In a 4-stroke IC engine cam shaft rotates at –

Half the speed of crankshaft.

8. Thermal efficiency of CI engine is higher than that of SI engine due to –

Higher compression Ratio.

9. SI engines are of –

Light weight, High speed & Homogeneous change of fuel & oil.

10. Compression ratio in diesel engines is of the order of –

14-20

11. In a reciprocating engine with a cylinder diameter of D and Stroke of L, the cylinder volume is –

π/4 D2L + clearance volume.

12. Main advantages of a 2-stroke engine over 4-stroke engine is –

More uniform torque on the crankshaft, amore power O/P for the cylinder of same dimension & Absence of

valves.

13. Engines used for ships are normally –

2-stroke CI engines of very high power.

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14. If L is the stroke & N is the rpm, mean piston speed of 2-stroke engine is -

2LN

15. Equivalence ratio is –

Stoichiometric fuel – air ratio / actual fuel – air ratio

16. The volumetric efficiency of the SI engine is comparatively –

Lower than CI engine.

17. The range of volumetric efficiency of a –

85 – 90%

18. Relative efficiency is the ratio of –

Actual thermal efficiency / air – standard efficiency.

19. Brake specific fuel consumption is defined as –

Fuel consumption per brake power hour.

20. Engine can be fired with –

Solid fuel, liquid fuel or gaseous fuel.

21. The unit of force in SI units is –

Newton.

22. First law of thermodynamics define a property called –

Energy.

23. Specific value of any property is its value –

Per unit mass.

24. Second law of thermodynamics define the property called –

Entropy.

25. Unit of universal gas constant is –

KJ / kmol K

26. A constant volume process –

Heat supplied = change in internal energy.

27. A constant pressure process –

Heat transfer = change in enthalpy.

28. In an isothermal process –

Heat transfer = work done

29. In a reversible adiabatic process –

Entropy = constant

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30. At critical point the latent heat of vaporization is –

Zero

31. The internal energy of an ideal gas is –

A function of its temperature alone.

32. Property of system –

Pressure, temperature & entropy.

33. An isochoric process is a –

Constant volume process

34. An isobaric process is a –

Constant pressure process.

35. An isothermal process is a –

Constant temperature process.

36. An isentropic process is a –

Constant entropy process.

02. Air-Standard Cycles

37. Efficiency of strilling cycle is same as –

Carnot cycle.

38. The air standard Otto cycle consists of –

2 constant volume & 2 isentropic processes.

39. Mean effective pressure of Otto cycle is –

Directly proportional to pressure ratio.

40. For a given compression ratio the work )/P of Otto cycle is –

Increases with increase in r.

41. For a given value of r, efficiency of Otto cycle is –

Increases with compression ratio.

42. For dual combustion cycle for fixed value of heat addition & compression ratio –

mep will be greater with increase in rp & decrease in re.

43. The normal range of compression ratio for Otto cycle is –

6 to 10

44. The normal range of compression ratio for Diesel cycle is –

15 to 20

45. Lenoir cycle is used in –

Pulse jet engines.

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46. A brayton cycle consists of – 1 constant pressure, 1 constant volume & 2 isentropic processes.

47. Brayton cycle is used in –

Gas turbines.

03. Fuel-Air cycles & Actual cycles 48. The actual efficiency of a good engine is about –

85%

49. With dissociation peak temperature is obtained –

When the mixture is slightly lean.

50. With dissociation the exhaust gas temperature –

Decreases.

51. Fuel-air ratio affects maximum power O/P of the engine due to –

Higher specific heats & Chemical equilibrium losses.

52. Mean effective pressure at a given compression ratio is maximum when the air-fuel ratio is –

Lower than stoichiometric.

53. For a compressure process with variable specific heat the peak temperature & pressure are –

Lower.

54. Dissociation can be considered as –

Disintegration of combustion products at high temperature, reverse process of combustion or heat absorption

process.

55. When the mixture is lean –

Power O/P is less.

56. For a given compression ratio, as the mixture is made progressively rich from lean the mean effective pressure –

Initially increases & then decreases.

57. Time loss factor in actual cycle is due to –

Progressive combustion.

58. If the spark timing is at TDC, the work is less as –

The peak pressure is low.

59. When the spark is advanced, work O/P is less as –

Addition work is required to compress the burning gas.

60. Optimum spark timing gives –

Higher mean effective pressure & higher efficiency.

61. The major loss in a SI engine is due to –

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Variation in specific heat & chemical equilibrium.

62. Fuel-air cycle efficiency is less than air-standard cycle efficiency by an amount equal to –

Loss due to specific heat variation & chemical equilibrium.

63. The major loss in CI engine is –

Loss due to incomplete combustion.

64. The ratio of the actual efficiency & the fuel-air cycle efficiency for CI engines is about –

0.6-0.8

65. In actual SI engine the pumping loss with respect to speed –

Increases.

66. The volumetric efficiency is affected by –

The exhaust gas in the clearance volume, the design of intake & exhaust valve or valve timing.

04. Fuels

67. Advantages of gaseous fuel is that –

It can mix easily with air.

68. Paraffin’s are in general represented by –

CnH2n+2

69. paraffin’s have molecular structure of –

Chain saturated.

70. Olefins are represented by the formula –

CnH2n

71. Hydrocarbons are decomposed into smaller hydrocarbons by –

Cracking.

72. The molecular structure of the straight run gasoline is changed by –

Reforming.

73. For SI engines fuels most preferred are –

Aromatics.

74. For CI engines fuels most preferred are –

Paraffins

75. Octane number of iso-octane is –

100

76. Ignition quality of diesel fuel is indicated by its –

Cetane number.

05. Alternate Fuels

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77. Gasohol is a mixture of –

10% ethanol + 90% gasoline

78. Stoichiometric air-fuel ratio of alcohol when compared to gasoline is –

Lower.

79. Small amount of gasoline is often added to alcohol to –

To improve cold weather starting.

80. Methanol by itself is not a good CI engine fuel because –

Its octane number is high & its cetane number is low.

81. Anti-knock characteristics of alcohol when compared to gasoline is –

Higher.

82. Alcohols alone cannot be used in CI engines as –

Their self-ignition temperature is high & latent heat of vaporization is high.

83. Advantage of hydrogen as an IC engine fuel –

No HC & CO emissions.

84. Disadvantage of hydrogen as a fuel in IC engine –

Detonating tendency.

85. Major constituent of natural gas is –

Methane

86. Octane number of natural gas is –

>100

87. Major disadvantage of LPG as a fuel in automobile is –

Reduction in life of the engine & less power compared to a gasoline.

88. Advantage of LPG as fuel in automobiles –

Engine has longer life when running on LPG.

89. Compared to diesel, biomass fuels have the advantages of –

Lower emission & easy availability.

90. Biomass fuels suffer from the disadvantage of –

Low energy content & high specific fuel consumption.

06. Carburetion 91. Stoichiometric air-fuel ratio of petrol is roughly –

15:1

92. Venturi in the carburetor results in –

Increase of air velocity.

93. The choke is closed when the engine is –

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Cold

94. Lean air mixture is required during –

Cruising

95. The limits of air-fuel for SI engine are

8/1 to 18/1

96. In a SI engine for maximum power, the relative fuel-air ratio is –

1.2

97. For maximum thermal efficiency, the fuel-air mixture in SI engines should be –

Lean

98. During starting petrol engine require –

Rich mixture

99. For petrol engine the method of governing is –

Quantity governing.

00. Economizer is used to provide enriched mixture during –

Full throttle opening.

01. When the throttle is suddenly opened, the mixture from the simple carburetor tends to become –

Lean.

02. Precise petrol injection system is –

Throttle body injection.

03. The choke in an automobile meant for supplying –

Rich mixture.

04. Modern carburetors provide the correct quality of air-fuel mixture during –

Starting, idling & cruising.

05. A simple carburetors supplies rich mixture during –

Accelerating.

06.Mechanical Injection Systems 07. Fuel injector is used for –

CI engines

08. Advantage of air injection system is –

Cheaper fuels can be used, mep is high & fine atomization and distribution of the fuel.

09. Commonly used injection system in automobiles is –

Solid injection.

10. Fuel injection pressure in solid injection system is around –

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200-250 bar

11. Fuel filters do not use generally –

Paper

12. Fuel is injected in a 4-stroke CI engine –

At the end of compression stroke.

13. Injection system in which the pump and the injector nozzle is combined in one housing is known as –

Unit injector system.

14. Main advantage of pintaux nozzle is –

Better cold starting performance.

15. The most accurate gasoline injection system is –

Port injection.

16. Advantage of fuel injection in SI engine is –

Increased volumetric efficiency.

07. Electronic Injection System 17. Multi-point fuel injection system uses –

Port injection & throttle body injection.

18. L-MPFI system uses –

Port injection.

19. D-MPFI system use –

Manifold injection.

20. Common rail injection system uses injection pressures of the order –

1500 bar

21. Continuous injection system usually has –

Rotary pump.

22. The cold start injector –

Gives rich air-fuel ratio.

23. ECU is an electronic injection system used for –

Calculating the appropriate injection timing.

24. With EFI of diesel engines –

Very high injection pressure can be obtained.

25. EFI system can achieve –

Proper injection timing, Proper injection quantity & Proper injection pressure.

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08. Ignition 26. The secondary winding of ignition coil consists of –

Many turns of fine wire.

27. Dwell is the time –

For which the points remain closed.

28. Dwell period –

Is inversely proportional to engine speed.

29. If the contact breaker gap is small, it results in –

Rapid burning of the pointer gaps.

30. For a four cylinder engine operation at N rpm, the conytact breaker must make and break the circuit.

2N times.

31. Contact breaker should be set –

After adjustment of dwell angle.

32. Dwell meter is used for –

Contact breaker gap.

33. For a four cylinder vertical engine, the commonly used firing order is –

1-3-4-2

34. For engine operating with rich mixture the optimum spark timing.

Must be advanced.

35. For peak lead operation. The spark advance –

Must be increased.

36. Ignition timing is adjusted by –

Stroboscopic light.

37. Vacuum advance mechanism shifts the ignition point under –

Part load operation.

38. Battery ignition system –

Occupies more space, has more maintenance problem & is commonly employed in 4-Wheeler.

09. Combustion & Combustion Chamber

39. In SI engines maximum flame speed is obtained when the equivalent ratio is between –

1.1 and 1.2

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40. In SI engine flame speed increases –

With turbulence & with fuel-air ratio.

41. With increase in compression ratio flame speed –

Increases.

42. With increase in speed the crank angle required for flame propagation –

Not affected.

43. Increasing the compression ratio in SI engines the knocking tendency –

Increases.

44. Decreasing the cooling water temperature in SI engines the knocking tendency –

Decreases.

45. Detonation in SI engines occur due to –

Auto ignition of the charge after the spark in struck.

46. Desirable characteristics of the combustion chamber for SI engines to avoid knock is –

Small bore, short ratio of flame path to bore & absence of hot surface in the last region of the charge.

47. In CI engines with increase in compression ratio the delay period –

Decreases.

48. Knocking takes place in CI engines –

At the start of combustion.

49. In CI engines knocking tendency increases with –

Decrease in compression ratio.

50. In CI engines by increasing inlet air pressure the knocking tendency –

Decreases.

51. Open combustion chambers in CI engines require –

High injection pressures & accurate metering of fuel by the injection system.

52. The advantages of the indirect injection combustion chambers are –

Low injection pressure & direction of spray is not critical.

53. In CI engines the delay period is affected by –

Compression ratio, engine speed & output.

10. Engine Friction & Lubrication 54. Mechanical efficiency is the ratio of –

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Brake power to indicated power.

55. Most commonly used lubrication system in automobiles is the –

Pressure system.

56. Friction that occurs between the layers of oil film is called –

Viscous friction.

57. Crankcase ventilation is provided –

To remove blow by.

58. The most important property of lubricant is –

Viscosity.

59. The maximum pressure in the lubrication system is controlled by –

Valve relief.

60. The lubricants commonly used in the automobiles are –

Mineral oils.

61. Detergents are oil additives used to –

Prevent sludge formation.

62. Oil pressure in the dry sump lubrication system is around –

3bar – 8 bar.

63. F mep decreases when using –

Larger number of smaller cylinders.

64. With increase in compression ratio, mechanical efficiency –

Increases.

65. Blow by losses are –

Proportional to the square root of inlet pressure.

66. Most lubrication system is mainly used in –

Two-stroke petrol engine.

67. Additives are added in lubricant to have –

Detergent-dispersant characteristics, pour point depression & antifoam characteristics.

11. Heat Rejection & Cooling 68. The heat given to cooling medium in IC engine is about –

30 – 40%

69. Radiator is provided to –

Cool the jacket water.

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70. Thermostat is used in radiators to –

Control the water temperature.

71. As the compression ratio increases, there is a –

Marginal reduction in heat rejection.

72. Spark timing other than minimum spark advance for heat torque (MBT) results in –

More heat rejection.

73. Direct system of cooling air is one which –

Hot water is simply discharged.

74. In evaporate cooling systems, heat absorbed per kg of coolant air is equal to –

Latent heat of the coolant.

75. Pump used in the forced cooling system in normally –

Centrifugal pump.

76. Advantage of liquid cooling system is –

Even cooling.

77. Limitation of air cooling system are –

Higher working temperature compared to water cooling.

78. The main purpose of a thermostat in an engine cooling system is to –

Allow engine to warm-up quickly.

79. The radiator cooling tubes are generally made of –

Copper.

80. Water circulation in a thermo syphon cooling system is due to –

Conduction currents.

81. The main purpose of fan in a liquid cooling system is to –

Pump cold air over the hot water.

82. Engine overheating may be due to –

Broken fan belt.

12. Engine Emissions & Their Controls 83. Strictest emission norms are initiated in the world first in –

California.

84. One of the major exhaust emissions from CI engines compared to SI engine is –

Particulates.

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85. Decrease In air-fuel ratio in SI engines results in –

Increase of CO and UBHC.

86. NOx emission is maximum in SI engines when the air-fuel ratio is –

Nearly stoichiometric.

87. NOx emission in SI engines will be lowest during –

Idling.

88. Photochemical smog is mainly due to –

NOx and HC

89. Alcohol is the major source for the emission of –

Aldehydes.

90. Fumigation technique is used to control –

Smoke.

91. Blue smoke in diesel engine indicates –

Unburnt oil.

92. Thermal converters cannot reduce emission of –

NOx

93. Three way catalytic converters reduce emission of –

CO, NOx and HC

94. Platinum and Rhodium promote the oxidation of –

CO, HC

95. Rhodium promotes the reduction of –

NOx

96. Efficient operation of catalytic converters require maintenance of –

Temperature and equivalence ratio.

97. EGR is the most effective way of reducing emission of –

NOx

98. EGR has disadvantage of –

Decreasing thermal efficiency & increasing HC emission.

99. Evaporative emission in SI engines account for emission of –

25% HC

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00. Chemiluminescene technique is used to measure –

NOx

01. Lead compounds were added in gasoline to –

Reduce knocking.

13. Measurements & Testing

02. The range of mechanical efficiency for automobile engines is –

70-80%

03. The measurement of frictional power by willans line is applicable only to –

CI engines at a particular speed.

04. Morse test is applicable only to –

Multicylinder CI engines.

05. The most accurate method of determining f p is by –

Measurement of brake & indicated power.

06. In the air box method of measuring air flow, the air box is provided to –

Damp out the pulsations.

07. The air box/swept volume ratio should be in the range for angle cylinder engine –

500-600%

08. The best method of measuring speed is by –

Magnetic pickup.

09. Flame ionization detector is used for measuring –

HC

10. Non-dispersive infra-red analyzer is widely accepted instrument for measuring –

CO

14. Performance Parameters & Characteristics

11. Thermal efficiency varies –

Inversely as s f e.

12. Mechanical efficiency is ratio of –

Bp to ip

13. The spark timing & combustion rate should be such that –

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One half of the total pressure occurs at TDC.

14. Volumetric efficiency is a measure of –

Breathing capacity of the engine.

15. Indicated power is directly proportional to –

Air consumption.

16. Brake thermal efficiency of SI engine is in the range –

25% to 35%

17. Sankey diagram represents –

Heat balance of the engine.

18. The volumetric efficiency of a well-designed engine is in the range –

75 to 90%

15. Engine Electronics 19. Hall effect pickup use –

Semiconductors

20. LVDT is used to measure –

Large displacement.

21. The disadvantage of the piezoelectric pressure pickup is that –

It can only give pressure difference.

22. Thermistors are desirable because of –

Large temperature coefficient.

23. Seebeck effect is used in –

Thermocouples.

24. Hot-wire sensors are used for measurement of –

Mass flow rate.

25. Knock sensors use –

Piezoelectric pickup.

26. Catalytic converters use lambda sensors to keep –

Excess air ratio within a range.

27. Strain gauges are mainly used to measure –

Pressure.

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28. Electro-optical sensors are used for –

Position and speed measurement.

16. Supercharger & turbocharger 29. Turbocharger engines are those in which charge density is increased by –

Compressors driven by exhaust gas turbine.

30. Supercharger increases the power output of engine by –

Increasing the charge pressure.

31. The centrifugal type supercharger is preferable only for –

Low speed.

32. Advantage of Root’s supercharger is –

Minimum maintenance.

33. Supercharger air compressor is driven by –

Engine itself.

34. Turbocharger compressor is driven by –

Exhaust gas turbine.

35. Cooling after compression is necessary to –

Increase the density of air & reduce engine operating temperature.

36. Volumetric efficiency of supercharger engine is –

Between 100-110%

37. Compared to engine driven supercharger the exhaust driven supercharger is –

Utilizes the exhaust energy of the engine.

38. Types of supercharger are –

Centrifugal, Root’s & vane.

17. Two-Stroke Engines 39. A two-stroke engine is identified by –

Absence of valves.

40. Advantages of two-stroke engine is –

More uniform torque, lighter flywheel & no valves.

41. Charge pressure at the inlet port if a two-stroke engine is –

Higher than atmospheric.

42. The most perfect method of scavenging is –

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Uniflow scavenging.

43. Two-stroke engine suffer from –

Fuel loss.

44. At the same speed two-stroke engine of the same size as a four-stroke engine will develop.

Twice the power.

45. Two wheelers without deflector type piston use –

Cross scavenging.

46. Crankcase scavenged engine have delivery ratio of –

Equal to 1

47. Short-circuiting in the case of two-stroke engines is equal to –

1 – ηtrap

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