Subject: Fuels and Combustion
Subject Code: KME058
Branch: Mechanical Engineering
Maximum Marks: 100 | Duration: 3 Hours
Section A – Short Answer Questions (10 × 2 = 20 Marks)
Students must attempt all questions briefly.
Topics included:
Meaning and classification of fuels. Properties of coal (calorific value, ash, moisture, volatile matter).
Definition of agro-fuels. Applications of oxygen-enriched combustion.
Working of pot-type burner (with diagram). Effects of air pollution caused by combustion.
Difference between primary and secondary pollutants.
Definition of laminar flame. Explanation of elementary reaction.
Difference between premixed laminar flame and premixed turbulent flame.
Section B – Descriptive / Medium-Length Questions (3 × 10 = 30 Marks)
Attempt any three questions:
Liquefaction of Coal — need, process, and comparison between direct and indirect methods.
Thermodynamic Functions of Combustion — enthalpy, internal energy, and Gibbs function with examples.
Air Pollution Control — devices and preventive steps used in industries.
Fuel Property Tests — viscosity, flash point, fire point, and pour point testing.
Adiabatic Flame Temperature — derivation under constant pressure with assumptions.
Section C – Long / Analytical Questions (5 × 10 = 50 Marks)
Attempt one part from each of the following questions (Q3–Q7):
Q3. Coal and Dew Point
a. Explain the formation of coal and classify it as Peat, Lignite, Bituminous, and Anthracite.
b. Define dew-point temperature and explain how it is determined for flue gases.
Q4. Petroleum and Refining
a. Explain cracking, reforming, polymerization, and alkylation processes in refining.
b. Discuss testing of liquid fuels such as viscosity, calorific value, and flash point.
Q5. Combustion Calculations
a. Explain types of combustion (complete, incomplete, spontaneous).
b. Numerical problem using Dulong’s formula:
Given: C = 76%, H = 5%, O = 8.5%, N = 2%, S = 1.5%, Ash = 7%.
Calculate HCV and LCV using:
- HCV=33800C+144000(H−O/8)+9300SHCV = 33800C + 144000(H - O/8) + 9300SHCV=33800C+144000(H−O/8)+9300S LCV=HCV−9H×2442LCV = HCV - 9H \times 2442LCV=HCV−9H×2442
Q6. Pollution Control
a. Explain working of Electrostatic Precipitator (ESP) — principle, construction, and advantages.
b. Problem on air-fuel ratio and excess air percentage for complete combustion of gasoline.
Q7. Industrial Applications
a. Explain the travelling grate stoker boiler — construction, working, and efficiency.
b. Explain Orsat’s apparatus — construction, working, and flue gas analysis steps.
Key Topics Covered
Fuel classification and coal analysis Coal liquefaction and refining
Combustion chemistry and thermodynamics Pollution control techniques (ESP, scrubbers)
Adiabatic flame temperature and dew point Calorific value calculations
Orsat’s gas analysis method
Frequently Asked Questions (FAQs)
Q1. What are agro-fuels?
Agro-fuels are biofuels made from crops, residues, or organic waste used as renewable alternatives to fossil fuels.
Q2. What is oxygen-enriched combustion?
It improves fuel efficiency and reduces emissions by increasing oxygen concentration in air.
Q3. What is the function of an Electrostatic Precipitator (ESP)?
It removes dust and ash particles from exhaust gases using high-voltage electrostatic fields.
Q4. What are primary and secondary pollutants?
Primary pollutants (e.g., CO, SO₂) are emitted directly; secondary pollutants (like smog) form due to chemical reactions in the atmosphere.
Q5. What is the dew point of flue gases?
It’s the temperature at which water vapor from combustion starts condensing, critical for avoiding corrosion in exhaust systems.
