I. PRINCIPLE OF OPERATION AND CLASSIFICATION OF INTERNAL COMBUSTION ENGINES

1. Principle of Operation

An Internal Combustion Engine (ICE) is a type of engine in which fuel is burned directly inside the combustion chamber. The heat generated from combustion produces high pressure that pushes the piston in a reciprocating motion. This linear motion is transmitted through the connecting rod to the crankshaft, converting it into rotary motion to drive machines or vehicles.

The Four-Stroke Cycle:

• Intake stroke: The piston moves downward, and the intake valve opens to draw in the air-fuel mixture (gasoline engine) or air (diesel engine).
• Compression stroke: The piston moves upward with both valves closed, compressing the mixture.
• Power stroke:
  • In gasoline engines, the spark plug ignites the compressed mixture.
  • In diesel engines, fuel is injected into the compressed hot air and self-ignites.
    The combustion produces high pressure, pushing the piston down.
• Exhaust stroke: The piston moves up again, and the exhaust valve opens to expel burnt gases.

Two-stroke engines combine intake–compression and power–exhaust strokes into one cycle per crankshaft revolution, making them more compact and powerful for their size but less fuel-efficient and more polluting.

2. Classification of Internal Combustion Engines

a) By fuel type:

• Gasoline Engine (Spark Ignition – SI)
• Diesel Engine (Compression Ignition – CI)
• Gas-Fueled Engine: CNG (Compressed Natural Gas), LPG (Liquefied Petroleum Gas)

b) By operating cycle:

• Four-stroke engine
• Two-stroke engine
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c) By application:

• Automotive engines (cars, motorcycles)
• Industrial engines (generators, construction machinery)
• Marine engines (ships, boats)

II. ENVIRONMENTAL REQUIREMENTS FOR INTERNAL COMBUSTION ENGINES

1. Reduction of Harmful Emissions:

• CO (Carbon Monoxide)
• NOx (Nitrogen Oxides)
• HC (Unburned Hydrocarbons)
• PM (Particulate Matter)

2. Compliance with Emission Standards:

• Euro 4–6 (Europe)
• EPA Tier levels (United States)
• TCVN (Vietnamese national standards)

3. Clean Technology Integration:

• EGR (Exhaust Gas Recirculation): Reduces NOx by recirculating part of the exhaust gas.
• Three-Way Catalytic Converter (TWC): Converts CO, HC, and NOx into CO₂, H₂O, and N₂.
• DPF (Diesel Particulate Filter): Captures fine particulates from diesel exhaust.
• SCR (Selective Catalytic Reduction): Uses urea (AdBlue) to convert NOx into nitrogen and water.

4. Use of Environmentally Friendly Lubricants:

• Low SAPS (Sulfated Ash, Phosphorus, Sulfur): Protects after-treatment devices (DPF, TWC).
• Compliant with standards such as API CK-4, FA-4 (USA), ACEA C1–C5 (Europe).