ME-501 Internal Combustion Engines - Nov 2022 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. OR Choice

   14 Marks
   In an Otto cycle, air at 1 bar and 300 K is compressed isentropically until the pressure is 17 bar. Heat is added at constant volume until the pressure rises to 40 bar. Calculate the compression ratio, air standard efficiency, work done per cycle and mean effective pressure for the cycle. Take $C_V = 0.717$ kJ/kg K and $\bar R = 8.314$ kJ/kg mol.K
   How to answer

   • Find compression ratio from isentropic p1 to p2
   • Find T2, heat added at constant volume to 40 bar
   • Calculate air-standard efficiency
   • Calculate work per cycle and mean effective pressure
2. 7 Marks
   aCalculate the changes in efficiency of gas engine working on Otto cycle, when its compression ratio is changed from 4 to 5. Take $\gamma = 1.4$.
   How to answer

   • Define Otto cycle air-standard efficiency formula
   • Calculate efficiency at r=4 with gamma=1.4
   • Calculate efficiency at r=5
   • Find change / increase in efficiency
3. 7 Marks
   bWith the help of a p-v diagram, explain the loss that occurs due to variation of specific heats in an Otto cycle.
   How to answer

   • Draw p-v diagram of Otto cycle
   • Show effect of increasing specific heats with temperature
   • Explain loss in heat addition and efficiency
   • Compare ideal vs actual cycle work
4. OR Choice

   14 Marks
   In the Morse test with a four cylinder four stroke petrol engine, the following data were obtained for a particular setting and speed. B.P with all cylinders working = 32 kW. B.P with No.1 cylinder cut out = 21.6 kW. B.P with No.2 cylinder cut out = 22.3 kW. B.P with No.3 cylinder cut out = 22.5 kW. B.P with No.4 cylinder cut out = 23 kW. Estimate the I.P of the engine and its mechanical efficiency. What are the assumption made in Morse test?
   How to answer

   • Compute I.P. per cylinder as difference in B.P.
   • Sum to get total I.P. and mechanical efficiency = B.P./I.P.
   • State Morse test assumptions on friction and speed
   • Conclude results
5. 7 Marks
   aWhy theoretical valve timing diagrams are different from actual valve timing diagrams. Draw actual valve timing diagram for a 4-stroke S.I. engine.
   How to answer

   • Explain need for valve lead, lag and overlap
   • Contrast theoretical instantaneous opening at dead centres
   • List actual timing angles for 4-stroke S.I. engine
   • Draw neat actual valve timing diagram
6. 7 Marks
   bDefine the following terms:

   1. i)Indicated power
   2. ii)Break power
   3. iii)Volumetric efficiency
   4. iv)Specific fuel consumption
   5. v)Indicated thermal efficiency
   How to answer

   • Define indicated power, brake power, volumetric efficiency
   • Define specific fuel consumption and indicated thermal efficiency
   • Give formulas and units
   • State significance for engine performance
7. 7 Marks
   aDescribe the stages of combustion in S.I. engine with the help of pressure-crank angle diagram.
   How to answer

   • Define three stages: ignition lag, flame propagation, afterburning
   • Draw pressure-crank angle diagram
   • Explain pressure rise in each stage
   • State factors affecting stages
8. OR Choice

   7 Marks
   aDescribe the phenomenon of detonation or knocking in S.I. engines. On what factors does detonation depend?
   How to answer

   • Define detonation/knocking and auto-ignition of end gas
   • Explain pressure waves and noise
   • List factors: compression ratio, fuel, spark timing
   • Suggest prevention
9. 7 Marks
   bWhat is Ignition lag? Discuss the effect of engine variables on ignition lag.
   How to answer

   • Define ignition lag
   • List engine variables: compression ratio, speed, mixture, temperature
   • Discuss effect of each on lag
   • Conclude control measures
10. OR Choice

    7 Marks
    bWhat do you understand by "pre-ignition" in S.I. engine? What are its causes and remedy?
    How to answer

    • Define pre-ignition before spark
    • Differentiate from detonation
    • List causes: hot spots, deposits, overheated plug
    • Give remedies
11. 7 Marks
    aExplain the basic requirements of a good combustion chamber of S.I. engine.
    How to answer

    • List requirements: compact shape, turbulence, cooling, knock resistance
    • Explain flame travel and surface-volume ratio
    • Discuss spark plug location
    • Summarize efficiency and emissions
12. OR Choice

    7 Marks
    aWhat are different rates of pressure rise and rate of combustion? How are these influenced by the crank angle?
    How to answer

    • Define rate of pressure rise and rate of combustion
    • Show variation with crank angle
    • Explain peak pressure and roughness
    • Discuss influencing factors
13. 7 Marks
    bExplain different types of combustion chambers being used in S.I. engines.
    How to answer

    • List types: bath-tub, wedge, hemispherical, bowl-in-piston
    • Sketch each layout
    • Compare turbulence and knock tendency
    • State applications
14. OR Choice

    7 Marks
    bDistinguish between normal and abnormal combustion, and explain as to how the abnormal combustion can be controlled?
    How to answer

    • Define normal vs abnormal combustion
    • Give characteristics of knock and pre-ignition
    • Compare pressure traces
    • Explain control by design and operating parameters
15. 7 Marks
    aWhat are the advantages and disadvantages of Compression-Swirl?
    How to answer

    • Define compression-swirl
    • List advantages: mixing, combustion efficiency
    • List disadvantages: heat loss, complexity
    • Conclude applications
16. OR Choice

    7 Marks
    aSketch and explain the construction and working of a fuel injector. Describe various kinds of nozzles used on it.
    How to answer

    • Sketch fuel injector assembly
    • Explain working and injection pressure
    • Describe nozzle types: pintle, hole, pintaux
    • State selection criteria
17. 7 Marks
    bDefine the following:

    1. i)Cetane number
    2. ii)Knock inhibitors
    3. iii)Diesel knock
    How to answer

    • Define cetane number and ignition quality
    • Define knock inhibitors and diesel knock
    • Give rating method
    • State effects on engine
18. OR Choice

    7 Marks
    bDescribe the air cell type of combustion chamber with the help of a diagram.
    How to answer

    • Draw air cell chamber layout
    • Explain working during compression and combustion
    • State advantages for diesel engines
    • Mention applications
19. OR Choice

    14 Marks
    A simple carburetor has to supply 5 kg of air per minute at a pressure of 1.013 bar and temperature of $27^{\circ}C$. Calculate the throat diameter of the choke for air flow velocity of 90m/s. Take discharge coefficient to be 0.8, assume isentropic flow and the flow to be compressible.
    How to answer

    • Calculate air density from p and T
    • Use compressible isentropic flow with discharge coefficient
    • Find throat area for 90 m/s velocity
    • Convert to throat diameter
20. 7 Marks
    aDescribe the construction and working of a simple carburetor. Why is the float chamber vented to the atmosphere?
    How to answer

    • Draw simple carburetor with float, venturi, jet
    • Explain air-fuel mixing and metering
    • Explain atmospheric vent for constant fuel level
    • State limitations
21. 7 Marks
    bWhat do you mean by MPFI in S.I. engines? What are the merits and demerits of this system as compared to carburetor system?
    How to answer

    • Define MPFI system
    • Explain multi-point injection working
    • Compare merits: efficiency, emissions, response
    • List demerits: cost, complexity
22. 7 Marks
    aList various qualities desired in the fuels for S.I. engines and discuss their importance.
    How to answer

    • List qualities: volatility, knock resistance, gum content
    • Explain starting, warm-up and economy
    • Discuss octane and additives
    • Link to S.I. performance
23. OR Choice

    7 Marks
    aEnumerate various gaseous fuels and discuss CNG, explaining their suitability as I.C. engine fuels
    How to answer

    • List gaseous fuels: CNG, LPG, hydrogen, biogas
    • Discuss properties and storage
    • Explain suitability as I.C. engine fuel
    • Focus on CNG merits and issues
24. 7 Marks
    bWhat is necessity of rating a fuel? Enumerate the various ways of fuel ratings for the fuels of (i) S.I. engines (ii) C.I. engines
    How to answer

    • Explain need for rating to compare knock behaviour
    • Describe octane rating for S.I. fuels
    • Describe cetane rating for C.I. fuels
    • Compare test methods
25. OR Choice

    7 Marks
    bWhat are Dopes? Why are they mixed with fuels? Write the requirements of good additives.
    How to answer

    • Define dopes/additives
    • Explain purpose: octane, anti-knock, anti-oxidant
    • List requirements of good additives
    • Give examples
26. 7 Marks
    aWhat do you mean by supercharging of I.C. engines? Explain why supercharging is essential for the aircraft engines?
    How to answer

    • Define supercharging and increased air density
    • Explain power increase and altitude compensation
    • Discuss aircraft engine need at high altitude
    • Mention types of superchargers
27. OR Choice

    7 Marks
    aExplain the thermodynamic cycle of a supercharged internal combustion engine.
    How to answer

    • Draw supercharged cycle on p-v/T-s
    • Explain compressor and intercooler addition
    • Show increased mean effective pressure
    • Discuss efficiency effects
28. 7 Marks
    bExplain the factors that limit the extent of super-charging of S.I. and C.I. engines.
    How to answer

    • List limits: detonation, thermal stress, mechanical loading
    • Compare S.I. vs C.I. constraints
    • Explain fuel and cooling limits
    • Conclude extent of supercharging
29. OR Choice

    7 Marks
    bWhat are the different methods of supercharging? Discuss them briefly.
    How to answer

    • List methods: mechanically driven, turbocharging, ram effect
    • Explain each arrangement briefly
    • Compare power source and efficiency
    • State applications