ME-501 Internal Combustion Engines - Nov 2023 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
   aDifferentiate between 4-Stroke and 2-Stroke Engine.
   How to answer

   • Define 4-stroke cycle operations (suction, compression, power, exhaust) vs 2-stroke (combined scavenging and power).
   • Compare on number of revolutions per power stroke, valves vs ports, flywheel size.
   • Compare on power output, fuel consumption, thermal efficiency, lubrication and emissions.
   • Summarize applications with table.
2. 7 Marks
   bWhat are the requirements for spark plug?
   How to answer

   • State function of spark plug to produce spark for ignition.
   • List electrical, thermal and mechanical requirements.
   • Mention voltage withstand, heat range, fouling resistance and durability.
   • Mention electrode gap, sealing and size requirements.
3. 7 Marks
   aExplain stages of combustion in CI engines.
   How to answer

   • Define combustion in CI engine and p-theta diagram.
   • Explain ignition delay, uncontrolled/premixed combustion, controlled diffusion combustion, afterburning.
   • Explain factors affecting each stage.
   • Sketch pressure-crank angle diagram.
4. 7 Marks
   bExplain any one type of cooling system in engine with its advantages.
   How to answer

   • Name types of cooling systems (air, water).
   • Explain working of one type with components and flow path.
   • List advantages such as temperature control, efficiency, noise.
   • Give neat sketch of system.
5. 7 Marks
   aWhat are the functions of lubrication? State required properties of lubricating oil.
   How to answer

   • Define lubrication and its functions: friction reduction, cooling, sealing, cleaning, corrosion protection.
   • List required oil properties: viscosity, viscosity index, flash/fire point, pour point, etc.
   • Relate properties to engine operating conditions.
   • Conclude with selection criteria.
6. 7 Marks
   bIn a Trial of single cylinder diesel engine the following observations were made: Calorific value of fuel $= 43890$ kJ/kg. Oil consumption $= 10.2$ kg/h, Speed $= 1900$ rpm, Air consumption $= 3.8$ kg/min, compression ratio $= 15$, Torque $= 186$ Nm. Quantity of cooling water used $= 15.5$ kg/min, Temp, rise $= 36^{\circ}C$, Exhaust gas temp $= 410^{\circ}C$, Room Temp $= 20^{\circ}C$, Cp of exhaust gases $= 1.17$ KJ/kg K Calculate: i) B.P. ii) BSFC iii) Heat Balance sheet on minute basis
   How to answer

   • Calculate brake power from $BP = 2\pi N T/60$.
   • Calculate BSFC = fuel consumption / BP.
   • Compute heat supplied per minute from fuel CV.
   • Prepare heat balance: BP, cooling water, exhaust gas, unaccounted losses.
7. 7 Marks
   aExplain with sketch working of battery ignition system with its advantages and disadvantages.
   How to answer

   • Draw circuit: battery, ignition switch, primary winding, contact breaker, condenser, secondary winding, distributor, spark plugs.
   • Explain working during points closed/open and high voltage generation.
   • List advantages: good starting, low speed performance, simplicity.
   • List disadvantages: maintenance, dwell limitations at high speed.
8. 7 Marks
   bA perfect gas at 1 bar and 290 K undergoes ideal diesel cycle. The maximum pressure of the cycle is 50 bar. The volume at the beginning of compression is $1m^3$ and after constant pressure heating is $0.1m^3$. Determine the temperature at all salient points of the cycle and find out the efficiency of the cycle. Take $\gamma = 1.4$ for the gas.
   How to answer

   • Identify diesel cycle points: isentropic compression, constant pressure heat addition, isentropic expansion, constant volume heat rejection.
   • Use $pV^{\gamma}=$ const and $pV=mRT$ to find $T_2, T_3, T_4$.
   • Calculate cut-off ratio and efficiency $\eta = 1 - (1/\gamma r^{\gamma-1})[(\rho^{\gamma}-1)/(\rho-1)]$.
   • Present temperatures and efficiency with units.
9. 7 Marks
   aWhat is super charging and turbo charging? Describe in brief the methods of turbo charging.
   How to answer

   • Define supercharging vs turbocharging and purpose of increasing air density.
   • Describe exhaust turbocharging methods: constant pressure, pulse, etc.
   • Explain components: turbocharger, intercooler, waste gate.
   • Mention effects on power and efficiency.
10. 7 Marks
    bThe dimensions of carburetor are as follows. Venturi throat diameter is 20 mm with coefficient of discharge of 0.85, Fuel orifice diameter is 1.25 mm with coefficient of fuel flow of 0.66, the fuel surface is 5mm below the throat. Compute i) Air fuel ratio for depression of 0.07 bar when nozzle lip is neglected. ii) Air-fuel ratio when nozzle lip is considered.
    How to answer

    • Calculate air mass flow through venturi using $\dot{m}_a = C_{da}A_t\sqrt{2\rho_a\Delta p}$.
    • Calculate fuel flow with/without nozzle lip correction $h$ for hydrostatic head.
    • Compute AFR = $\dot{m}_a/\dot{m}_f$ for both cases.
    • Comment on effect of nozzle lip.
11. 7 Marks
    aWhat are the advantages of microprocessor-based control system for automobile? What is the disadvantage of microprocessor controlled devices?
    How to answer

    • Define microprocessor-based control for ignition, fuel injection, emissions.
    • List advantages: accuracy, adaptability, fuel economy, diagnostics.
    • List disadvantages: cost, complexity, failure sensitivity, maintenance skill.
    • Give automotive examples.
12. 7 Marks
    bWhat is Scavenging? Explain various types of scavenging.
    How to answer

    • Define scavenging in 2-stroke engines.
    • Explain cross, loop and uniflow scavenging with diagrams.
    • Compare efficiency, short-circuiting and complexity.
    • Mention scavenging efficiency and applications.
13. 7 Marks
    aExplain Wankel engine with neat sketch.
    How to answer

    • Describe Wankel rotary construction: epitrochoid housing, triangular rotor.
    • Explain working phases with rotation.
    • Give advantages and applications.
    • Provide neat labelled sketch.
14. 7 Marks
    bWrite the short note on Alternate fuels in IC engines.
    How to answer

    • Define alternate fuels need due to emissions and depletion.
    • List CNG, LPG, hydrogen, ethanol, biodiesel, etc.
    • Mention properties and suitability for SI/CI engines.
    • Conclude with merits and challenges.
15. 7 Marks
    aExhaust gas re-circulation advantage and limitations, with neat sketch.
    How to answer

    • Define EGR principle of recirculating part of exhaust.
    • Explain sketch with EGR valve and connections.
    • List advantages: NOx reduction, efficiency.
    • List limitations: deposits, power loss, control complexity.
16. 7 Marks
    bDifferent types of nozzles in Diesel fuel injection systems.
    How to answer

    • List nozzle types: single hole, multi-hole, pintle, pintaux, delay nozzle.
    • Describe construction and spray characteristics of each.
    • Mention applications in DI/IDI diesel engines.
    • Give sketches of nozzle tips.