Lesson 7.7: I.C. Engines (Fuels, Combustion, Performance, Emissions)

Internal Combustion (I.C.) engines are a core topic in Mechanical Engineering. GATE and PSU exams often test engine types, fuel properties, combustion, performance parameters, and emissions control.

🔹 1. Introduction

• Definition: I.C. engine is a heat engine in which combustion of fuel occurs inside the engine cylinder.

• Applications: Automobiles, power generators, marine engines, aerospace engines

• Types:

  1. Spark Ignition (SI) Engines – Petrol engines

  2. Compression Ignition (CI) Engines – Diesel engines

  3. Two-stroke & Four-stroke engines

🔹 2. Fuels for I.C. Engines

• Petrol / Gasoline: Used in SI engines, high volatility

• Diesel: Used in CI engines, high cetane number

• Alternative Fuels: CNG, LPG, Biofuels, Hydrogen

• Fuel Properties: Calorific value, flash point, fire point, octane/cetane number

🔹 3. Combustion in Engines

• SI Engines: Spark ignition, rapid combustion, premixed charge

• CI Engines: Compression ignition, diffusion combustion, fuel injected at high pressure

• Combustion Parameters: Flame speed, ignition delay, air-fuel ratio

• Knocking: Abnormal combustion affecting performance

🔹 4. Engine Performance Parameters

• Power Output: Brake Power (BP), Indicated Power (IP)

• Torque (T): Rotational force produced by engine

• Brake Mean Effective Pressure (BMEP): Indicator of engine efficiency

• Thermal Efficiency (η):

ηth=Work outputHeat input\eta_\text{th} = \frac{\text{Work output}}{\text{Heat input}}ηth​=Heat inputWork output​

• Volumetric Efficiency: Measure of cylinder filling with air-fuel mixture

🔹 5. Emissions & Environmental Impact

• Major Pollutants: CO, HC, NOx, Particulate matter, CO₂

• Causes: Incomplete combustion, excess fuel, high temperatures

• Control Methods: Catalytic converters, EGR (Exhaust Gas Recirculation), fuel additives, modern emission standards (BS VI, Euro norms)

🔹 6. Solved Examples (PYQ Style)

1. Calculate Brake Power and Indicated Power from cylinder pressure data

2. Determine Brake Thermal Efficiency and Mechanical Efficiency

3. Compute air-fuel ratio for given engine operating condition

4. Analyze emission levels for SI and CI engines

🔹 7. Practice Exercises

1. Identify engine type and fuel for specific applications

2. Solve problems on torque, power, and BMEP

3. Calculate thermal efficiency for given engine parameters

4. Analyze effects of fuel type and air-fuel ratio on emissions

5. Compare performance of SI vs CI engines

🔹 8. Summary

• I.C. Engines: Spark ignition (SI) and compression ignition (CI)

• Fuels: Petrol, Diesel, CNG, LPG, Biofuels

• Combustion: Premixed (SI) vs diffusion (CI)

• Performance: Torque, Power, Thermal Efficiency, BMEP

• Emissions: CO, HC, NOx, particulate matter; control methods essential

• Exam Tip: Focus on efficiency calculations, fuel properties, and emission analysis