Subject Code: KAU051
Subject Name: Automobile Engines & Combustion
Course: B.Tech (Semester V)
Maximum Marks: 100
Duration: 3 Hours
Exam Year: 2023–24
Sections: A, B, and C
SECTION A – Short Answer Questions (2 × 10 = 20 Marks)
Attempt all questions briefly.
a. Explain the term Internal Combustion Engine.
b. Discuss the term Mechanical Efficiency.
c. Discuss the concept of Flame Propagation and Flame Stability.
d. What is Adiabatic Flame Temperature?
e. Discuss Lean and Rich Mixture.
f. List factors affecting combustion in CI engines.
g. Explain Physical delay and Chemical delay in CI Engines.
h. When does an engine need Supercharging and how is it done?
i. Discuss NOx Emissions.
j. What is the purpose of a Catalytic Converter in IC Engines?
SECTION B – Medium-Length Questions (10 × 3 = 30 Marks)
Attempt any three of the following:
Derive the efficiency expression for Otto Cycle and discuss the effect of compression ratio and specific heat ratio using a suitable graph.
Explain flame temperature and burning velocity of fuels.
Describe combustion in CI engines with detailed explanation of the stages of combustion.
Explain the operation of two modern fuel injection systems with neat sketches. Discuss pintle and pintaux nozzles.
Illustrate particulate emissions and explain methods of controlling emissions.
SECTION C – Long / Analytical Questions (10 × 5 = 50 Marks)
Q3. Thermodynamics & Efficiency
a. For an ideal dual-combustion cycle, given:
T1=100°C,P1=1 bar,r=13,Pmax=80 barT_1 = 100°C, P_1 = 1 \, bar, r = 13, P_{max} = 80 \, barT1=100°C,P1=1bar,r=13,Pmax=80bar,
qs=1700 kJ/kgq_s = 1700 \, kJ/kgqs=1700kJ/kg, γ=1.4,Cp=1.01,Cv=0.72γ = 1.4, C_p = 1.01, C_v = 0.72γ=1.4,Cp=1.01,Cv=0.72.
Find temperatures at key points and ideal thermal efficiency.
OR
b. Briefly explain:
(i) Burning time loss factor
(ii) Heat loss factor
(iii) Exhaust blowdown factor
(iv) Pumping loss factor.
Q4. Combustion Analysis
a. One kg of octane (C₈H₁₈) is supplied with 13 kg of air.
Find the % of CO₂ by volume in dry exhaust gas (CO₂, CO, N₂).
OR
b. Discuss Flue Gas Analysis and Theoretical Air Requirement for complete combustion.
Q5. SI Engine Design & Ignition
a. Explain types of combustion chambers used in SI engines and the phenomenon of knock.
OR
b. Describe two conventional ignition systems used in automobiles with neat diagrams.
Q6. Fuel Supply Systems
a. A simple jet carburetor supplies 5 kg air/min and 0.5 kg fuel/min.
Fuel specific gravity = 0.75, P=1bar,T=300KP = 1 bar, T = 300 KP=1bar,T=300K, velocity coefficient = 0.8.
Find choke throat diameter for 100 m/s flow and fuel orifice diameter (Cd = 0.60).
OR
b. Derive an expression for exact air-fuel ratio:
(i) Neglecting compressibility
(ii) Including compressibility.
Q7. Lubrication & Fuels
a. Compare wet sump and dry sump lubrication systems and explain crankcase ventilation.
OR
b. Discuss alternative fuels for IC engines and fuel rating for CI engines.
Key Topics to Study
IC Engine Basics: Working principle, efficiency, and performance parameters.
Combustion: Flame propagation, burning velocity, adiabatic flame temperature.
CI Engines: Stages of combustion, ignition delay, fuel injection systems.
Emissions: NOx, CO, HC, and particulate control (EGR, catalytic converters).
Thermodynamic Cycles: Otto, Diesel, Dual cycles — efficiency relations.
Carburetion: Jet carburetor design, air-fuel ratio, mixture strength.
Lubrication: Types, comparison, crankcase ventilation.
Alternative Fuels: LPG, CNG, biodiesel, alcohol fuels, hydrogen.
Study Tips
Revise cycle derivations — Otto, Diesel, and Dual (with graphs).
Practice numerical problems — air-fuel ratio, efficiency, temperature, emissions.
Draw diagrams — carburetor, injection systems, nozzles, combustion chambers.
Understand real-world relevance — emissions control, fuel quality, and efficiency improvements.
Focus on short definitions — for Section A, be concise (2–3 lines per question).
