Internal Combustion Engine: Definition, Types and Working of Engine

 

Internal Combustion Engine

Usually, Internal Combustion Engine is the type of Heat Engine. A heat engine is a Mechanical Device that converts the chemical energy of the fuel into Heat energy and then converts the heat energy to obtain mechanical work by employing the pressure and temperature of gases.

An Internal Combustion Engine (ICE) is a type of heat engine in which fuel combustion occurs inside a combustion chamber, producing high-pressure gases that expand and perform mechanical work. This contrasts with external combustion engines, where the combustion process occurs outside the engine, as in steam engines. Internal combustion engines are commonly used in automobiles, motorcycles, aircraft, and power generation.

Classification of Internal Combustion Engine

The classification of internal combustion engines (ICEs) can be done based on various parameters such as fuel type, ignition method, working cycle, number of cylinders, engine configuration, and application. Below is a detailed classification of internal combustion engines:

• According to Fuel Used
• Gasoline Engine
• Diesel Engine
• According to Ignition Method
• Spark Ignition (S.I.) Engine
• Compression Ignition (C. I.) Engine
• According to Number of Strokes in a Cycle
• Two-Stroke Engine
• Four-Stroke Engine
• According to Number of Cylinders
• Single Cylinder Engine
• Multiple Cylinder Engine
• According to Cylinder Arrangement
• Inline Engine
• V-Type Engine
• Flat / Boxer Engine
• Radial Engine
• According to Cooling Method
• Air Cooled Engine
• Liquid Cooled Engine
• According to Valve / Port Configuration
• Overhead Valve Engine
• Overhead Camshaft Engine
• Pushrod Engine
• According to Working Cycle
• Otto Cycle Engine
• Diesel Cycle Engine
• Dual Cycle Engine
• According to Application
• Automotive Engine
• Aircraft Engine
• Marine Engine
• Stationary Engine
• According to Speed of Engine
• High-Speed Engine
• Medium-Speed Engine
• Low-Speed Engine

    Internal combustion engines can be classified into many categories depending on their design, fuel type, and application. The choice of engine type is determined by the specific requirements of the application, such as fuel efficiency, power output, size, and environmental concerns. This classification provides insight into the vast range of engines used in transportation, industrial, and power generation sectors.

Basic Terminology of I. C. Engine

Fig.1: Basic Terminology of IC Engine

• Cylinder: A cylindrical chamber in which the piston moves up and down. Combustion occurs inside the cylinder, producing the force that moves the piston.
• Piston: A movable component inside the cylinder that transmits the force of expanding gases from combustion to the crankshaft via the connecting rod. The piston moves in a reciprocating (up-and-down) motion.
• Crankshaft: A rotating shaft that converts the linear motion of the piston into rotational motion, which powers the vehicle or machinery.
• Connecting Rod: The link between the piston and the crankshaft, transferring the piston’s linear motion to the crankshaft’s rotational motion.
• Combustion Chamber: The space in the cylinder where fuel combustion occurs. The air-fuel mixture is ignited here, creating the explosion that drives the piston.
• Inlet Valve: Opens to allow the air-fuel mixture into the cylinder during the intake or suction stroke.
• Exhaust Valve: Opens to allow exhaust gases to exit the cylinder after combustion during the exhaust stroke.
• Spark Plug: A component used in spark-ignition engines (e.g., gasoline i.e. Petrol engines) to ignite the air-fuel mixture by producing an electrical spark.
• Fuel Injector: A device that sprays fuel into the combustion chamber. Modern engines use fuel injectors for more precise fuel delivery, replacing older carburetors.
• Camshaft: A rotating shaft that controls the opening and closing of the engine's inlet and exhaust valves in synchronization with the motion of the piston.
• Stroke: The movement of the piston from one end of the cylinder to the other.
• Stroke Length: The distance the piston travels between the top dead center (TDC) and bottom dead center (BDC) of the cylinder. Longer stroke lengths generally provide more torque, while shorter strokes allow higher RPMs.
• Bore: The diameter of the cylinder. The bore, along with the stroke, determines the engine’s displacement or capacity.
• Top Dead Center (TDC): The highest point the piston reaches during its stroke inside the cylinder.
• Bottom Dead Center (BDC): The lowest point the piston reaches during its stroke inside the cylinder.
• Displacement (Engine Capacity): The total volume swept by all the pistons in all cylinders of an engine, typically expressed in litters or cubic centimeters (cc). It gives an idea of the engine size and power potential.
• Indicated Power: The total power produced by combustion inside the engine’s cylinders, calculated without considering losses like friction.
• Brake Power (BHP - Brake Horsepower): The usable power available at the engine’s output shaft, after accounting for losses like friction and auxiliary components.
• Mechanical Efficiency: The ratio of brake power to indicated power. It measures how efficiently the engine converts the power from combustion into usable mechanical work.
• Volumetric Efficiency: The efficiency with which the engine draws in the air-fuel mixture relative to the cylinder’s displacement. Higher volumetric efficiency indicates better engine breathing.

    These are some of the basic terms associated with internal combustion engines. Understanding these terms is essential for anyone working in automotive or mechanical engineering, as they define the key components and processes that determine engine performance, efficiency, and operation.

Working of Four Stroke Petrol Engine

The four-stroke petrol engine (also called a spark-ignition engine) operates on the Otto cycle and is commonly used in cars, motorcycles, and other vehicles. The engine completes a power cycle in four strokes of the piston, during which it converts chemical energy from fuel into mechanical work. Each cycle consists of suction, compression, power, and exhaust strokes.

Let us understand the strokes and their working with the help of graphical representation,

Fig.2: Working of Four-Stroke Engine

Let us have a look on each stroke separately,

Suction Stroke

Objective: Draw an air-fuel mixture into the combustion chamber.

• The intake valve opens, and the piston moves down from the Top Dead Centre (TDC) to the Bottom Dead Centre (BDC).
• As the piston moves downward, it creates a vacuum inside the cylinder, causing the air-fuel mixture (petrol and air) to be drawn into the combustion chamber through the intake valve.
• The intake valve remains open until the piston reaches BDC, and the cylinder is filled with the air-fuel mixture.

Result: The cylinder is filled with the air-fuel mixture, and the piston is at BDC.

Compression Stroke

Objective: Compress the air-fuel mixture to increase its temperature and pressure for efficient combustion.

• The intake valve closes, and the piston moves upward from BDC to TDC, compressing the air-fuel mixture inside the combustion chamber.
• The compression of the air-fuel mixture increases its pressure and temperature, making it more reactive to the ignition spark.
• Compression Ratio: The degree to which the air-fuel mixture is compressed. A higher compression ratio improves engine efficiency.

Result: The air-fuel mixture is highly compressed, and the piston is at TDC, ready for ignition.

Expansion Stroke (Power Stroke)

Objective: Ignite the compressed air-fuel mixture to generate power.

• At the end of the compression stroke, a spark plug generates an electric spark that ignites the compressed air-fuel mixture.
• The combustion of the air-fuel mixture causes a rapid expansion of hot gases, creating high pressure inside the cylinder.
• This high pressure pushes the piston downward with significant force, from TDC to BDC, which turns the crankshaft, converting the chemical energy from combustion into mechanical work (rotational energy).

Result: The expansion of gases drives the piston downwards, producing the power that drives the vehicle or machinery.

Exhaust Stroke

Objective: Remove the burnt exhaust gases from the cylinder.

• After the power stroke, the exhaust valve opens, and the piston moves upwards from BDC to TDC.
• As the piston moves up, it pushes the exhaust gases (produced by the combustion) out of the cylinder through the open exhaust valve.
• Once the piston reaches TDC, the exhaust valve closes, and the cycle is ready to repeat

Result: The exhaust gases are expelled from the cylinder, and the piston is at TDC, ready for the next intake stroke.

Let us have a look at Summary of Working of Four-Stroke Engine,

Stroke in Operation	Movement of Piston	Position of Inlet Valve	Position of Exhaust Valve
Suction	TDC to BDC	Open	Close
Compression	BDC to TDC	Close	Close
Expansion	TDC to BDC	Close	Close
Exhaust	BDC to TDC	Close	Open

The internal combustion engine has shaped modern transportation and industrial progress. While challenges related to emissions and sustainability persist, ongoing advancements in ICE technology continue to improve efficiency and reduce environmental impact. With a move towards hybrid and alternative-fuel systems, the internal combustion engine will likely remain a key player in global industries for years to come.

Advantages of Four-Stroke Petrol Engines

1. Higher Efficiency: Compared to two-stroke engines, four-stroke engines are more fuel-efficient due to complete combustion.
2. Less Pollution: Four-stroke engines produce fewer emissions as they burn fuel more completely and have dedicated exhaust strokes.
3. Better Torque Distribution: The power is more evenly distributed over the engine’s cycle, leading to smoother operation.

Applications of Four Stroke Petrol Engine

1. Automobiles (cars, trucks, SUVs)
2. Motorcycles
3. Power generators
4. Small aircraft
5. Boats (outboard motors)

While both four-stroke petrol and diesel engines share the same basic operating cycle (intake, compression, power, exhaust), their methods of ignition, fuel injection, compression, and thermal efficiency are different. Diesel engines rely on higher compression ratios and compression ignition, making them more efficient but also more robust. Petrol engines use spark ignition and typically operate with lower compression ratios, providing smoother operation but lower fuel efficiency. Each type of engine is suited for different applications based on performance, efficiency, and cost considerations.

This concludes our discussion for this blog. We'll dive deeper into the terminology and working of the two-stroke engine in the next post. Don't forget to subscribe and comment your favorite topics you'd like to see covered in future blogs!

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