Classification of Engines

External Combustion Engine:

In an External Combustion Engine, the fuel combustion occurs outside the engine. The heat generated from the combustion process is transferred to a working fluid, such as steam, which then moves through the engine to produce mechanical work.

Key Features:

• Combustion Location: Outside the engine.

• Working Fluid: Commonly steam, but other fluids can be used.

• Components: Typically includes a boiler (to generate steam), a turbine or piston (to convert steam pressure into mechanical energy), and a condenser (to recycle the working fluid).

• Fuel Types: Can use a variety of fuels, including coal, wood, oil, or nuclear energy.

• Examples:

  • Steam Engine: Used in early trains and ships. The boiler heats water to create steam, which then drives pistons or turbines.

  • Stirling Engine: Uses the expansion and contraction of gas to drive pistons, often powered by an external heat source.

Advantages:

• Fuel Flexibility: Can use different types of fuel.

• Efficiency at Large Scales: Often more efficient when used in large power plants, like those generating electricity.

• Lower Emissions: Can be designed to have cleaner combustion with better emission control.

Disadvantages:

• Size and Weight: Typically larger and heavier due to the need for a boiler and other components.

• Slower Response Time: Takes time to start up as it needs to generate steam first.

• Complexity: More complex due to the need for multiple components like boilers, turbines, and condensers.

Internal Combustion Engine:

In an Internal Combustion Engine, the fuel combustion occurs inside the engine. The expansion of the combustion gases directly applies force to the engine components, such as pistons or rotors, producing mechanical work.

Key Features:

• Combustion Location: Inside the engine, typically in a cylinder.

• Working Fluid: The combustion gases themselves act as the working fluid.

• Components: Includes cylinders, pistons, crankshaft, and fuel injection or carburetor systems.

• Fuel Types: Commonly uses petrol (gasoline), diesel, or natural gas.

• Examples:

  • Petrol Engine: Found in most cars, motorcycles, and small machines. Operates on the Otto cycle.

  • Diesel Engine: Used in trucks, buses, and some cars. Operates on the Diesel cycle.

  • Rotary (Wankel) Engine: Uses a rotary design rather than pistons to convert combustion into mechanical work.

Advantages:

• Compact and Lightweight: More compact compared to ECEs, making them suitable for mobile applications.

• High Power-to-Weight Ratio: Can generate significant power for their size, ideal for vehicles.

• Quick Response: Starts and responds quickly to changes in demand for power.

Disadvantages:

• Fuel Specificity: Usually designed to run on specific fuels like petrol or diesel.

• Higher Emissions: Produces more pollutants, such as CO2, NOx, and particulates, though modern engines have improved emission controls.

• Heat Management: Requires complex cooling systems to manage the heat generated during combustion.

1. Based on Fuel Type

• Petrol (Gasoline) Engine: Uses petrol as fuel and operates on the Otto cycle. Common in passenger cars and motorcycles.

• Diesel Engine: Uses diesel fuel and operates on the Diesel cycle. Often found in trucks, buses, and some cars.

• Electric Engine: Powered by electricity, using electric motors instead of combustion. Found in electric vehicles (EVs).

• Hybrid Engine: Combines a petrol or diesel engine with an electric motor, offering both fuel efficiency and reduced emissions.

• Natural Gas Engine: Runs on compressed natural gas (CNG) or liquefied natural gas (LNG), used in some commercial vehicles.

2. Based on Configuration

• Inline Engine (Straight Engine): Cylinders are arranged in a single line. Common in smaller vehicles.

• V-Type Engine: Cylinders are arranged in two banks forming a "V" shape. Used in many high-performance cars.

• Flat (Boxer) Engine: Cylinders are horizontally opposed, used in some sports cars and motorcycles.

• Rotary (Wankel) Engine: Uses a rotor instead of pistons. Found in some Mazda vehicles.

• Radial Engine: Cylinders are arranged in a circular pattern around a central crankshaft. Common in older aircraft.

3. Based on Operating Cycle

• Two-Stroke Engine: Completes a power cycle in two strokes of the piston. Used in some motorcycles, lawnmowers, and outboard motors.

• Four-Stroke Engine: Completes a power cycle in four strokes of the piston. Most common in cars and motorcycles.

• Six-Stroke Engine: A more complex design aiming for greater efficiency, combining elements of the two- and four-stroke engines.

4. Based on Ignition System

• Spark Ignition (SI) Engine: Uses a spark plug to ignite the air-fuel mixture. Typically found in petrol engines.

• Compression Ignition (CI) Engine: The air-fuel mixture ignites due to high compression, typical in diesel engines.

5. Based on Cooling System

• Air-Cooled Engine: Relies on air flow to cool the engine. Used in some motorcycles and older cars.

• Liquid-Cooled Engine: Uses a coolant (usually water mixed with antifreeze) to dissipate heat. Common in modern vehicles.

6. Based on the Number of Cylinders

• Single-Cylinder Engine: Has one cylinder. Common in small motorcycles and lawnmowers.

• Multi-Cylinder Engine: Can have multiple cylinders (e.g., 2, 3, 4, 6, 8, 10, 12). The number of cylinders generally correlates with power and smoothness of operation.

7. Based on the Engine's Position

• Front-Engine: The engine is located at the front of the vehicle. Most common configuration.

• Mid-Engine: Positioned near the center of the vehicle, usually behind the front seats. Used in some sports cars.

• Rear-Engine: Located at the rear of the vehicle, common in some sports cars and older models.

8. Based on Valve Arrangement

• Overhead Valve (OHV) Engine: Valves are located in the cylinder head, and the camshaft is in the engine block.

• Overhead Cam (OHC) Engine: Valves and camshaft are located in the cylinder head. It can be single (SOHC) or double (DOHC).

9. Based on Application

• Automobile Engines: Used in cars, trucks, and buses.

• Aircraft Engines: Designed specifically for use in airplanes, often requiring high power-to-weight ratios.

• Marine Engines: Used in boats and ships, often designed to withstand corrosive environments.

• Stationary Engines: Used in generators, pumps, and industrial machinery.