Internal combustion engine (IC engine) is the heart and soul of countless machines that power our modern world. IC engines have revolutionised transportation and provided unprecedented mobility, from cars and motorcycles to ships and airplanes.
Combustion reaction within these engines involves a complex interplay of fuel, air, and ignition, releasing energy that propels vehicles forward.
What is an Internal Combustion Engine?
An internal combustion engine (IC engine) is a type of heat engine that converts the chemical energy stored in fuel into mechanical energy.
It is commonly used in vehicles, power generators, and various industrial applications.
Fuel and air are mixed, combusted, and burned in an IC engine within a combustion chamber. The resulting high-pressure gases exert force on a piston, which translates the pressure into rotational motion through a crankshaft. This mechanical energy is then used to power the vehicle or operate machinery.
IC engines come in different variations, such as gasoline engines and diesel engines, each with its own combustion process and characteristics.
The main Components of IC Engine are:
- Exhaust camshaft: A rotating shaft that controls the opening and closing of the exhaust valves.
- Exhaust valve bucket: A component that sits on top of the valve stem and transfers the motion from the camshaft to open and close the exhaust valve.
- Spark plug: A device that ignites the air-fuel mixture in the combustion chamber to initiate the combustion process.
- Intake valve bucket: Similar to the exhaust valve bucket, it transfers the motion from the camshaft to open and close the intake valve.
- Intake camshaft: A rotating shaft that controls the opening and closing of the intake valves.
- Exhaust valve: A valve that opens to allow the exhaust gases to exit the combustion chamber during the exhaust stroke.
- Intake valve: A valve that opens to allow the fresh air-fuel mixture to enter the combustion chamber during the intake stroke.
- Cylinder head: The topmost part of the engine that houses the combustion chambers, valves, and spark plugs.
- Piston: A cylindrical component that moves up and down inside the cylinder, driven by the force generated by the combustion process.
- Piston pin: Also known as a wrist pin, it connects the piston to the connecting rod, allowing the piston to pivot.
- Connecting rod: Connects the piston to the crankshaft and transfers the linear motion of the piston into rotational motion.
- Engine block: The main housing of the engine that contains the cylinders and provides support for various engine components.
- Crankshaft: Converts the reciprocating motion of the pistons into rotational motion, which drives the transmission and, ultimately, the wheels.
Classification of IC Engines
IC engines can be classified based on the number of strokes, type of fuel consumed and arrangement of engine cylinders. An insight into this classification of ic engine is enumerated below:
Based on Number of Strokes
Two-stroke engine
A two-stroke engine is an internal combustion engine that completes a power cycle with two strokes of the piston, making it simpler but less fuel-efficient compared to its counterpart, the four-stroke engine. Two-stroke engines are commonly found in small power tools, scooters, and some motorcycles. They have a simpler design compared to four-stroke engines and complete a power cycle in two strokes of the piston.
Four-stroke engine
A four-stroke engine is a type of internal combustion engine that completes four distinct phases in one complete cycle: intake, compression, power, and exhaust. It is commonly used in cars, motorcycles, and other vehicles. These engines have a more complicated design as compared to the Two-stroke engines.
Based on Fuel Type
Spark-ignition combustion engine
In a spark ignition engine, the fuel is mixed with air and introduced into the cylinder during the intake process. Following compression of the fuel-air mixture by the piston, ignition occurs via a spark, initiating combustion. The resulting expansion of the combustion gases pushes the piston during the power stroke. These are commonly used in passenger cars, motorcycles, and small vehicles.
Compression-ignition combustion engine
Diesel engines solely introduce air into the engine, which is then compressed. Subsequently, the fuel is injected into the hot compressed air at a carefully controlled rate, causing it to ignite. Diesel engines are commonly found in trucks, buses, and heavy machinery.
Based on Engine Configuration
Inline engines
An inline engine is characterised by its cylinders arranged in a straight line. This configuration is frequently employed in smaller cars and motorcycles.
V engines
A V-shaped engine features cylinders arranged in a V-shape, commonly employed in larger cars and trucks.
Flat engines
A flat engine, also known as a horizontally opposed engine, consists of cylinders arranged in a horizontally opposed configuration, with two banks of cylinders facing each other. This design is commonly found in aircraft and certain high-performance sports cars.
Radial engines
A radial engine features cylinders arranged in a circular pattern around the crankshaft. This particular setup is widely used in aircraft.
IC Engine Performance Parameters
The primary function of an internal combustion engine is to transform heat energy into mechanical energy. In practical terms, this means that any type of IC engine generates mechanical work in the form of a rotating shaft, delivering torque at specific RPMs through the continuous combustion of fuel. The performance of an IC engine refers to how effectively it accomplishes this task. Evaluating or comparing engine performance is possible only through specific parameters outlined in this chapter, which are commonly referred to as performance parameters.
Indicated Power (IP)
Indicated Power (IP) refers to the overall power generated through the combustion of fuel within the combustion chamber.
Brake Power (BP)
Brake Power refers to the power output available at the engine’s output shaft. It represents the power that can be effectively utilised to overcome resistance or counteract the braking forces in the specific application where the engine is employed.
Frictional power
The Friction Power of an engine is the power needed to overcome internal friction within the engine. It accounts for the total losses incurred from the indicated power, and it is the difference between the indicated power and the brake power.
Mechanical efficiency
The Mechanical Efficiency of an IC Engine is the ratio of the brake power to the indicated power.
Indicated Mean Effective Pressure
Mean Effective Pressure (MEP) is the theoretical pressure assumed to be exerted on the piston during the power stroke of an engine. It represents the average pressure that would produce the same amount of work as the actual mechanical work generated per engine cycle.
Brake mean efficiency pressure
Similar to the Indicated Mean Effective Pressure (IMEP) that is based on indicated power, the Brake Mean Effective Pressure (BMEP) is a hypothetical average pressure acting on the piston. BMEP is derived from the brake power of the engine, providing an estimation of the mean effective pressure that would produce the same amount of work as the actual brake power.
Specific output
Specific Power is a performance parameter defined as the brake power output per unit of piston displacement. It serves as a measure of the power-to-size ratio of an engine, making it a significant indicator of engine performance.
Volumetric efficiency
Volumetric Efficiency of an IC Engine is the ratio of the actual volume of the air or charge drawn into the cylinder during the suction stroke (adjusted to standard conditions) to the swept volume of the piston. It quantifies the effectiveness of an engine in utilising its maximum cylinder capacity for intake and is an important factor in evaluating engine performance.
Specific fuel consumption
Specific Fuel Consumption is the measure of the fuel consumption rate of an engine, expressed as the mass of fuel consumed in kilograms per hour per kilowatt (kW) of power produced. It provides insight into the efficiency of an engine in converting fuel into mechanical power output.
Thermal efficiency
Thermal Efficiency is the ratio of work done or power developed by an engine to the rate of chemical energy or heat supplied by the combustion of fuel in the engine. It quantifies the efficiency of an engine in converting the heat energy from fuel combustion into useful mechanical work.
Compression Ratio
The Compression ratio of an IC Engine is the ratio of the total volume of the combustion chamber with the piston at the bottom dead Center (BDC) position to the volume of the chamber when the piston is at the Top Dead Center (TDC) position. Its higher value represents an improvement in the engine efficiency and power output,
Air-to-Fuel Ratio
The air-to-fuel ratio (AFR) refers to the ratio of the mass of air to the mass of fuel in a combustion process. It plays a critical role in the combustion efficiency and performance of internal combustion engines. Here are some key points about the air-to-fuel ratio:
This ratio is typically expressed in terms of mass and connotes the ideal ratio at which all the fuel is completely combusted with the available oxygen. For gasoline, the stoichiometric ratio is approximately 14.7:1, meaning 14.7 parts of air to 1 part of fuel by mass. A lean air-to-fuel ratio refers to a fuel-lean mixture with more air relative to the available fuel. It is expressed as a higher value than the stoichiometric ratio, such as 16:1.
Cylinder Pressure in IC Engine
Cylinder pressure refers to the pressure exerted by the combustion process within the cylinders of an internal combustion engine. It is a key parameter that influences engine performance and efficiency. Cylinder pressure is the result of the combustion process that occurs when the fuel-air mixture ignites within the combustion chamber. The pressure within the cylinder increases rapidly during the combustion phase, reaching its peak value known as peak cylinder pressure (PCP) or peak firing pressure. Cylinder pressure is typically measured using pressure sensors or transducers installed within the combustion chamber or in the cylinder head.
Applications of IC Engines
Some of the notable applications of IC Engines are discussed below:
- Automotive Vehicles: The major application of IC Engine is in cars, motorcycles, trucks, buses, and other vehicles.
- Aircraft: Another application of IC Engine is to power various types of aircraft, including general aviation planes and some helicopters.
- Marine Vessels: IC engines are used in boats, ships, and other watercraft for propulsion.
- Power Generators: IC engines are used in generators to produce electricity for various applications, especially in remote areas and as backup power sources.
- Construction Equipment: IC engines are found in various construction machinery like excavators, bulldozers, and cranes.
- Agriculture: Tractors and other farming equipment often use IC engines to perform various tasks on farms.
- Industrial Machinery: IC engines are used in various industrial machines, including compressors, pumps, and generators.
- Lawn and Garden Equipment: Lawnmowers, chainsaws, and other gardening tools often use IC engines for power.
- Portable Equipment: Portable generators, pressure washers, and other equipment often rely on IC engines for mobility and power generation.
- Small Engine Applications: IC engines power a wide range of small-scale applications like motorised scooters, mopeds, and motorbikes.