Internal Combustion Engines - Comprehensive Notes

Introduction to Internal Combustion Engines (ICE)

• An internal combustion engine (ICE) is a heat engine where the combustion of fuel occurs with an oxidizer in a combustion chamber.
• Converts chemical energy of fuel into mechanical energy.
• Common in vehicles, generators, and machinery.

Engine - How it Works (Overview)

• Combustion (burning) releases energy from a fuel-air mixture.
• In an ICE, ignition and combustion occur inside the engine itself.
• The engine consists of a fixed cylinder and a moving piston.
• Expanding combustion gases push the piston, which rotates the crankshaft.
• Through a system of gears in the powertrain, this motion drives the vehicle's wheels.

Spark Ignition vs Compression Ignition

• Two main kinds in production:
  • Spark ignition gasoline engine (petrol)
  • Compression ignition diesel engine
• Most are four-stroke cycle engines (four piston strokes per cycle):
  • Intake, compression, combustion/power, exhaust
• In a spark ignition engine, fuel-air is mixed and inducted into the cylinder during intake; compression followed by spark ignition causes combustion.
• In a diesel engine, only air is inducted, compressed, and then fuel is sprayed into the hot compressed air to ignite.

4 Stroke Petrol (Gasoline) Engine

• Four-stroke gasoline engines are the most prevalent internal combustion engines on the market today.
• Used in automobiles, light-duty trucks, motorcycles, and other equipment.
• Convert chemical energy from gasoline into mechanical energy.
• Advantages: more fuel-efficient and cleaner than some alternatives, provide more torque, and are suitable for passenger vehicles.
• Compared to similar-sized two-stroke engines, petrol four-strokes are typically more expensive and less powerful per size but offer better fuel efficiency and smoother operation.

1) Intake Stroke (Suction Stroke)

• The inlet valve opens, and the piston moves downward.
• A mixture of air and petrol (gasoline) is drawn into the cylinder from the carburetor or fuel injector.
• The mixture enters the combustion chamber as the piston descends.

2) Compression Stroke

• The inlet valve closes, and the piston moves upward, compressing the air-fuel mixture.
• This compression increases the mixture's pressure and temperature, preparing it for combustion.
• Valves closed during compression.

3) Power Stroke (Combustion Stroke)

• At the end of compression, a spark plug ignites the compressed mixture.
• The explosion forces the piston downward, producing power that turns the crankshaft.
• This is the only stroke that generates power.

4) Exhaust Stroke

• The exhaust valve opens, and the piston moves upward again.
• Burnt gases are expelled out of the cylinder through the exhaust pipe.
• Exhaust gases are pushed out while the intake cycle begins again.

4 Stroke Diesel Engine

• A 4-stroke diesel engine is widely used in heavy vehicles, buses, trucks, trains, ships, and industrial machines.
• Diesel engines use compression ignition (no spark plug).
• The working principle is similar to a petrol engine but with key differences in how the fuel is ignited.

1) Intake Stroke (Suction Stroke)

• The inlet valve opens, and the piston moves downward.
• Only air (not fuel) is drawn into the cylinder.

2) Compression Stroke

• The inlet valve closes, and the piston moves upward, compressing the air.
• The air gets highly compressed and hot due to high pressure (around a 25:1 compression ratio).
• Near the end of this stroke, diesel fuel is injected into the hot compressed air.

3) Power Stroke (Combustion Stroke)

• The injected fuel auto-ignites due to the high temperature and pressure.
• This explosion forces the piston downward, generating power.
• This is the only stroke that produces mechanical work.

4) Exhaust Stroke

• The exhaust valve opens, and the piston moves upward again.
• The burnt gases are pushed out of the cylinder through the exhaust.

2-Stroke Petrol Engine

• A 2-stroke petrol engine completes a power cycle in just two strokes of the piston (one revolution of the crankshaft).
• Power is produced every revolution, giving a higher power-to-weight ratio.
• Key features:
  • Simple design with no valves; uses ports (intake, transfer, exhaust).
  • Lubrication oil is mixed with petrol (premix) or injected separately.
  • Lightweight and compact; used in motorcycles, scooters, motors, chainsaws, etc.
  • Transfer port is covered and then uncovered during the cycle to move charge.

1st Stroke - Compression & Combustion

• Piston moves upward; fuel-air mixture is compressed in the combustion chamber.
• Fresh charge enters the crankcase through the intake port.
• Near the end of the upward stroke, a spark plug ignites the compressed mixture, forcing the piston downward (power).

2nd Stroke - Power & Exhaust

• Piston moves downward; burning gases expand, producing power.
• Exhaust port opens, allowing burnt gases to escape.
• Downward motion compresses the fresh charge in the crankcase.
• As the piston uncovers the transfer port, the compressed fresh charge flows into the cylinder, pushing out remaining exhaust gases.

Key Features

• Power every revolution → higher power-to-weight ratio.
• Simple design → no valves; uses ports.
• Lubrication oil mixed with fuel (premix) or oil injection.
• Lightweight and compact → used in motorcycles, scooters, mopeds, outboard motors, chainsaws, dirt bikes, etc.

Power Cycle Comparison (Summary)

• 4-Stroke Engine:
  • Requires 4 strokes of the piston (2 revolutions of the crankshaft).
  • Produces one power stroke every two revolutions → lower power for same size.
  • Torque: Higher torque at lower RPM.
  • Efficiency: More fuel-efficient due to complete combustion.
  • Durability: Longer life due to less wear (lower RPM and better lubrication).
  • Lubrication: Separate lubrication system (engine oil in crankcase).
  • Size & Weight: Larger and heavier for same power output.
  • Complexity: More parts (valves, camshaft, etc.) → more complex design.
  • Maintenance: Less frequent maintenance required.
  • Applications: Cars, trucks, larger motorcycles, generators.
• 2-Stroke Engine:
  • Requires 2 strokes of the piston (1 revolution).
  • Produces one power stroke every revolution → higher power for same size.
  • Torque: Higher torque at higher RPM.
  • Efficiency: Less fuel-efficient; some fresh charge escapes with exhaust.
  • Durability: Shorter life due to higher wear and heat.
  • Lubrication: Lubrication by mixing oil with fuel (premix) or oil injection.
  • Size & Weight: Smaller and lighter for same power output.
  • Complexity: Simpler design (ports instead of valves).
  • Maintenance: Requires more frequent maintenance.
  • Applications: Scooters, mopeds, outboard motors, chainsaws, dirt bikes.

Key Parts of an Internal Combustion Engine

• Engine Block: main structure; houses cylinders and components; made of cast iron or aluminum.
• Cylinder: round hole in the engine block where the piston moves; can be single or multiple (e.g., 4-cylinder).
• Piston: cylindrical component moving up and down inside the cylinder; compresses/expands gases; transfers force to the crankshaft.
• Connecting Rod: connects piston to the crankshaft; transfers reciprocating motion to rotary motion; big end and small end with wrist pin bearing.
• Crankshaft: converts up-down motion to rotary motion to power the vehicle.
• Cylinder Head: top part of the engine; closes the cylinder; contains the combustion chamber, valves, and spark plugs or injectors.
• Spark Plug (Petrol engines): produces spark to ignite the air-fuel mixture; not used in diesel engines.
• Fuel Injector / Carburetor: injects fuel into the engine (fuel injector in modern engines; carburetor in older petrol engines).
• Valves (Inlet & Exhaust): allow air/fuel in and exhaust out; operated by the camshaft.
• Camshaft: controls the timing of valve openings and closings; driven by timing belt or chain.
• Timing Belt / Chain: connects camshaft to crankshaft; ensures proper timing between valves and pistons.
• Flywheel: heavy wheel attached to the crankshaft; helps maintain engine speed and smooth operation.
• Lubrication System: circulates oil to reduce friction and cool engine parts; includes oil pump, filter, oil passages, oil pan, etc.
• Cooling System: prevents overheating using coolant, radiator, water pump, and fan; maintains engine temperature.
• Exhaust System: removes exhaust gases after combustion; includes exhaust manifold, catalytic converter, muffler, tailpipe, etc.
• Intake System: supplies air to the engine; includes air filter, intake manifold, throttle body, EGR valve, throttle valve, bypass.
• Combustion Chamber: area where the fuel-air mix is ignited and combustion occurs.
• Glow Plug (Diesel engines): heats up the combustion chamber during cold starts (diesel engines only).
• Engine Parts (summary): a visual list of major components (block, head, pistons, crank, valves, etc.).

Basic Fuel Types Used in Vehicles

• Petrol (Gasoline):
  • Light, volatile fuel derived from crude oil via fractional distillation and refining.
  • Used in spark ignition engines found in cars, motorcycles, and small vehicles.
• Diesel:
  • Heavier, less volatile fuel obtained from middle distillates during crude oil refining.
  • Used in compression ignition engines without spark plugs.

Chemical Composition and Properties

• Petrol: -Primarily hydrocarbons in the C4 to C12 range (alkanes, cycloalkanes, and aromatics).
  • Often blended with additives (anti-knock agents, detergents, antioxidants).
  • Octane number: commonly 87, 91, 95 (indicates resistance to knocking).
• Diesel:
  • Hydrocarbons in the C12 to C20 range (primarily alkanes and cycloalkanes).
  • Cetane number: typically 40–55 (indicates ignition quality).
  • May contain small amounts of sulfur (low-sulfur diesel common today).

Properties of Petrol vs Diesel

• Petrol:
  • Density: about
    
    ho_{ ext{petrol}} \n \approx 0.71\text{--}0.77\ \frac{g}{cm^3}
  • Calorific value: $Q_{ ext{petrol}} \approx 44\text{--}46\ \frac{MJ}{kg}$
  • Volatility: high; ignites easily; flammability range: narrow but easy ignition.
• Diesel:
  • Density: about
    $\rho_{ ext{diesel}} \approx 0.82\text{--}0.85\ \frac{g}{cm^3}$
  • Calorific value: $Q_{ ext{diesel}} \approx 45\text{--}48\ \frac{MJ}{kg}$
  • Less volatile; requires high compression to ignite; more lubricating properties.

Advantages and Disadvantages of Each Fuel

• Petrol advantages:
  • Quieter operation; smoother acceleration; higher RPM capability; easier cold starts.
• Petrol disadvantages:
  • Lower fuel economy than diesel; higher CO emissions.
• Diesel advantages:
  • Better fuel economy (more energy per litre); more torque at low speeds; longer engine life due to robust design.
• Diesel disadvantages:
  • Louder engine noise and vibrations; higher NOx and particulates; slower acceleration.

Typical Applications

• Petrol: Cars, motorcycles, scooters, light commercial vehicles; small boats, lawn mowers, portable generators.
• Diesel: Trucks, buses, heavy commercial vehicles; agricultural machinery and construction equipment; some passenger cars (especially in Europe and India); marine engines and power generators.

Comparison of Petrol and Diesel (Key Features)

• Engine type: Petrol = Spark Ignition (SI); Diesel = Compression Ignition (CI)
• Hydrocarbon range: Petrol = C4–C12; Diesel = C12–C20
• Ignition method: Petrol = Spark plug; Diesel = Combustion ignition (no spark plug)
• Density: Petrol ≈ $0.71\text{--}0.77$ g/cm³; Diesel ≈ $0.82\text{--}0.85$ g/cm³
• Calorific value: Petrol ≈ $44\text{--}46\ \frac{MJ}{kg}$; Diesel ≈ $45\text{--}48\ \frac{MJ}{kg}$
• Fuel economy: Petrol = Lower; Diesel = Higher
• Torque: Petrol = Higher speed, less torque; Diesel = More torque at low speeds
• Emissions: Petrol = More CO; Diesel = More NOx and particulates
• Volatility: Petrol = High; Diesel = Higher density, lower volatility
• Noise and vibration: Petrol = Less noisy and smoother; Diesel = More noise and vibration
• Weight: Petrol engines generally lighter; Diesel engines heavier but more robust
• Applications: Petrol = Cars, bikes, lawn mowers; Diesel = Trucks, buses, tractors, generators

The Role of The Engine in The Movement of The Vehicle

• The engine is the heart of a vehicle; it converts stored chemical energy in fuel into mechanical power.
• This power moves the vehicle through several steps:
  1) Energy Conversion: The engine burns fuel inside its combustion chamber; chemical energy is released as heat energy; this heat pushes the pistons.
  2) Producing Mechanical Motion: The up-and-down (reciprocating) motion of the pistons is converted into rotary motion by the crankshaft; this rotary motion ultimately drives the wheels.
  3) Power Transmission: The engine's rotary power is sent to the transmission system (gearbox, clutch/torque converter); gears adjust torque and speed for driving conditions.
  4) Driving the Wheels: The transmission sends power to the drive shaft (in rear-wheel-drive) or directly to the axles (in front-wheel-drive); axles turn the wheels to move the vehicle.
  5) Supporting Functions: The engine also powers auxiliary systems (air conditioning, alternator for battery charging, power steering) and maintains sufficient torque for uphill driving and heavy loads.

Engine Notes and Diagrams (Key Concepts)

• The engine’s role can be summarized as:
  • Generate power by burning fuel.
  • Convert power into rotary motion.
  • Deliver motion through the transmission to the wheels.
  • Enable vehicle movement while powering other vehicle systems.

End of Notes