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.
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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 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.
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
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.
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 –
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
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 –
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 –
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 –