ME-501 Internal Combustion Engines - Jun 2025 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. 7 Marks
   aAn ideal Otto cycle has compression ratio of 8 and initial conditions are 1bar and $15^{\circ}C$. Heat added during constant volume process is $1045 kJ/kg$. Find:

   1. i)Maximum cycle temperature.
   2. ii)Air standard efficiency.
   3. iii)Work done per kg of air.
   4. iv)Heat rejected.
   How to answer

   • Otto cycle relations: $T_2 = T_1 r^{\gamma-1}$, $Q_{added}=C_v(T_3-T_2)$
   • Calculate $T_2$, then $T_3$ = maximum cycle temperature
   • Air standard efficiency $\eta = 1-1/r^{\gamma-1}$
   • Work $W = \eta \cdot Q_{added}$ and heat rejected $Q_{rej}=Q_{added}-W$
2. 7 Marks
   bWhat are the various processes involved in Diesel cycle? Explain it with P-V and T-S diagrams.
   How to answer

   • List Diesel cycle processes: isentropic compression, constant pressure heat addition, isentropic expansion, constant volume heat rejection
   • Explain each process on P-V coordinates
   • Explain each process on T-S coordinates
   • Neat labelled P-V and T-S diagrams
3. 7 Marks
   aIn a SI engine working on ideal Otto cycle, the compression ratio is 11. The pressure and temperature at the beginning of compression are 2bar and $27^{\circ}C$ respectively. The peak pressure is 60 bar. Determine the pressure and temperatures at the salient points, the air standard efficiency and the mean effective pressure. Assume ratio of specific heats to be 1.4 for air.
   How to answer

   • Use $T_2=T_1 r^{\gamma-1}$, $p_2=p_1 r^{\gamma}$ for compression
   • Use $p_3/p_2 = T_3/T_2$ at constant volume to get peak temperature
   • Use expansion relations to get $p_4, T_4$
   • Calculate $\eta =1-1/r^{\gamma-1}$ and $mep = W/V_s$
4. 7 Marks
   bWhat is ignition lag in SI engine? Discuss the effect of engine variables on ignition lag.
   How to answer

   • Define ignition lag as time/angle between spark and start of combustion
   • Describe chemical and physical delay stages
   • Discuss effects of compression ratio, mixture, speed, temperature, fuel, spark timing
   • Summarize optimum conditions for short lag
5. 7 Marks
   aWrite shorts notes on the following:

   1. i)Fuel injection in C.I. engine.
   2. ii)Air injection in C.I. engine.
   How to answer

   • Define fuel injection purpose in CI engine
   • Explain solid/mechanical injection components
   • Define air injection system and its working
   • Compare applications and limitations
6. 7 Marks
   bExplain the factors affecting Delay period in C.I. Engine.
   How to answer

   • Define delay period in CI engine
   • List factors: compression ratio, fuel properties, intake conditions, speed, load
   • Explain effect of each factor on physical and chemical delay
   • Conclude with control measures
7. 7 Marks
   aGive the general chemical formula of the following fuels: Also state their molecular arrangements and mention. Whether they are saturated and unsaturated.

   1. i)Paraffin
   2. ii)Olefin
   3. iii)Naphthene
   4. iv)Aromatic
   How to answer

   • Give general formulae: paraffin $C_nH_{2n+2}$, olefin $C_nH_{2n}$, naphthene $C_nH_{2n}$, aromatic $C_nH_{2n-6}$
   • Sketch/describe chain, ring, unsaturated bond arrangements
   • Classify saturated vs unsaturated
   • Give examples like methane, ethylene, cyclohexane, benzene
8. 7 Marks
   bExplain why dopes/ additives are mixed with fuels? What are the requirements of a good additive?
   How to answer

   • Purpose of dopes/additives: improve octane, prevent knock, oxidation, icing
   • Types of additives with examples
   • Requirements: solubility, stability, no deposits, economical
   • Effect on performance and emissions
9. 7 Marks
   aWhat is the effect of supercharging on power output and fuel consumption?
   How to answer

   • Define supercharging and increased air mass
   • Effect on power output: increased mean effective pressure
   • Effect on fuel consumption: specific consumption trends
   • Limitations like mechanical stress and knocking
10. 7 Marks
    bWrite short notes on the following:

    1. i)Anti-freeze solutions.
    2. ii)Cooling fins.
    How to answer

    • Composition and function of anti-freeze solutions
    • Purpose of cooling fins and heat transfer enhancement
    • Materials and applications
    • Advantages in engine cooling
11. 7 Marks
    aExplain the construction and working of Forced Cooling system with neat sketch.
    How to answer

    • Components: radiator, pump, fan, thermostat, jackets
    • Coolant circulation path
    • Working during warm-up and normal running
    • Neat sketch with flow directions
12. 7 Marks
    bExplain about the various types of combustion chambers of S.I Engine with neat sketch.
    How to answer

    • List SI combustion chambers: bath-tub, wedge, hemispherical, bowl-in-piston
    • Sketch each chamber shape
    • Explain turbulence, squish and flame travel
    • Merits of each design
13. 7 Marks
    aWhat is the need of turbo charging? Explain anyone method of turbocharging giving its merits and demerits.
    How to answer

    • Need: compensate altitude loss, increase power density
    • Describe one method e.g., exhaust turbocharger layout
    • Working of turbine-compressor coupling
    • Merits: fuel economy, power; demerits: lag, cost, thermal load
14. 7 Marks
    bDefine carburetion. Explain the following Rich mixture, Stoichiometric mixture and lean mixture.
    How to answer

    • Define carburetion as air-fuel mixing process
    • Define rich, stoichiometric, lean with A/F ratios
    • Explain combustion characteristics of each
    • Applications and effect on power/emissions
15. 7 Marks
    aDiscuss the detonation theories of S.I. engine. Enlist variables affecting detonation in S.I. engine.
    How to answer

    • Define detonation/knock in SI engine
    • Explain theories: auto-ignition, detonation wave
    • List variables: compression ratio, spark advance, fuel, temperature
    • Control methods
16. 7 Marks
    bWhat is the use of Lubrication system in automobiles? Explain various types of lubrication systems with neat sketch.
    How to answer

    • Purpose of lubrication: reduce friction, cooling, sealing
    • Types: splash, pressure, dry sump, mist
    • Working of each with oil flow path
    • Neat sketches of systems