# 60+ Engine terms and definitions pdf

If you are a technical student or a technician, you should be familiar with the various engine terms that are used. This will make it easier for you to know very well about the engine. In this post, we have listed different engine terms and definitions as follows.

## Engine terms and definitions pdf

Terms related to the engine construction:

Following are various engine terms related to the construction of the engine:-

Crankshaft: The crankshaft is the shaft with one or more cranks for multiple cylinders that helps to convert the reciprocating motion of the piston into the rotary motion. The cranks are connected to the big end of the connecting rod.

Cylinder: The cylinder is the bore inside a cylinder block in which the piston is allowed to reciprocate. It also acts as a combustion chamber for the engine.

Engine Block: The engine block is the metal casting component on which the different components of the IC engine are mounted. The cylinders of the engine are bored into the engine block or separate cylinder liners are inserted into the bores of a cylinder block.

Head Gasket: It is the gasket fitted between the engine block and cylinder head. Its main job is to prevent the leakage of the combustion gases outside of the combustion chamber.

Spark Plug: It is the component of the spark-ignition engine that generates a spark to ignite the air-fuel mixture. It is mounted inside the combustion chamber on the cylinder head.

Fuel Injector: A fuel injector is a mechanically or electronically controlled device that is used to spray the fuel into compressed air. It is generally used in Compressed ignition (CI) engines.

Bore: For the internal combustion engines, the bore is the inner diameter of the engine cylinder.

Stroke: Stroke is the travel of the piston from the TDC to BDC or from the BDC to TDC. Stroke length is the distance between the TDC and BDC of the engine.

Crankcase: A crankcase is the housing or enclosure made for mounting of the crankshaft. The crankcase also helps to protect the crankshaft and other engine parts from dirt and other impacts.

Cylinder head: The cylinder head is mounted above the engine cylinder and it forms an upper enclosure to create a combustion chamber. It also acts as a housing for mounting intake and exhaust valves, spark plug/fuel injector, and glow plug.

Piston: Piston is a mechanical device that is reciprocated inside a cylinder and continuously changes the volume inside the cylinder. Thus it helps to perform different strokes and converts the pressure energy of the combustion gases into mechanical work.

Combustion Chamber: The combustion chamber is the portion of a cylinder where a mixture of air and fuel is burned to develop high pressure and temperature.

Block heater: It is an electric heater used to warm the engine components during cold weather. It preheats the engine and provides ease while starting the engine during the winter mornings.

Glow plug: Glow plug is the electric heater used in a diesel engine that increases the temperature of the air inside a combustion chamber thus it helps for starting the diesel engine during the cold season.

Inlet valve: The inlet valve is the component of a four-stroke engine that controls the opening between the engine cylinder and intake manifold. During the suction stroke, the intake valve opens to allow the flow of air-fuel mixture inside a cylinder and it remains closed during the compression stroke, expansion stroke and exhaust stroke.

Exhaust valve: The exhaust valve is the component of four-stroke engines that controls the opening between the engine cylinder and exhaust manifold. During the exhaust stroke, the exhaust valve opens to remove the exhaust gases outside of a cylinder and it remains closed during the suction stroke, compression stroke, and expansion stroke.

Inlet port: Inlet port is the opening inside of the crankcase of 2 stroke engine for entering fresh charge into the crankcase.

Exhaust Port: Exhaust port is the opening into the cylinder of the two-stroke engine for expelling the exhaust gases. The opening of the intake port and exhaust port is controlled by the movement of the piston.

Transfer port: In a two-stroke engine the transfer port connects the engine crankcase to the cylinder. Thus during the downward movement of the piston, the air-fuel mixture present in the crankcase is pushed into the engine cylinder through the transfer port.

Piston rings: Piston rings are mounted on the piston to seal the gap between the piston and cylinder. The piston rings are classified as a compression ring, wiper ring, and oil ring. The main function of the compression ring is to ensure the sealing of the combustion chamber. The wiper ring helps for sealing as well as for wiping the excessive oil from the cylinder walls. The oil ring controls the flow of the lubricating oil over the cylinder surface.

Cylinder liner: The cylinder liner is a thin-walled sleeve made up of hard material and fitted inside a bore made in the cylinder block. It acts as a smooth surface for the reciprocating of the piston and sustains the higher temperature stresses during combustion.

Intake manifold: Ii is a component of a multicylinder engine that supplies air-fuel mixture to all the cylinders. The intake manifold is consists of a plenum and runners. The plenum takes the air-fuel mixture from the throttle body and distributes the mixture to all the runners that are connected to the cylinders.

Exhaust manifold: The exhaust manifold is used to collect the exhaust gases from all the cylinders into the exhaust pipe.

Connecting rod: The connecting rod is the component of the engine that connects the piston to the engine crankshaft. The connecting rod along with the crankshaft helps to convert the reciprocating motion into the rotary motion.

Gudgeon pin (Wrist pin): The gudgeon pin is used to connect the piston to the small end of the connecting rod.

Piston skirt: A cylindrical surface of the piston below piston rings is known as a piston skirt.

Terms related to the engine performance:

Following are the different terms related to the performance of the engine:-

Brake power: In IC engines, brake power is the power obtained at the crankshaft of an engine.

Horsepower: It is a unit used to measure power and is abbreviated as HP. Where 1 HP = 745 watt

BHP: The BHP stands for the brake horse power and it is the unit used to measure power obtained at an engine crankshaft.

Specific fuel consumption: Specific fuel consumption is the mass of fuel supplied to produce the unit amount of power from the engine.

Indicated power: It is the power developed inside a combustion chamber of the engine because of the combustion of the air-fuel mixture.

Mean effective pressure: Mean effective pressure is an average value of pressure inside a cylinder that gives the same power output as that of actual pressure inside the cylinder.

Volumetric efficiency: Volumetric efficiency is the ratio of the actual volume of air taken by the piston to the swept volume of the engine cylinder.

Knocking/Detonation: Detonation/knocking is sudden combustion of the end gas which creates high-pressure waves inside the cylinder that leads to the pinging noise from engine cylinders.

Scavenging: Scavenging is the process of replacing the exhaust gases present inside the cylinder with a fresh charge.

Engine surging: Engine surging is the fluctuation of the engine speed caused due to the malfunctioning of the combustion process.

Terms related to the engine specification:

Following are various engine terms related to the engine specifications:-

Compression ratio: Compression ratio is the ratio of volume inside the cylinder when the piston is at BDC to the volume inside a cylinder when the piston is at TDC.
It is also defined as a ratio of maximum volume inside a cylinder to the minimum volume inside a cylinder.

Spark ignition: It is the combustion of the intake charge with the help of a spark generated by the spark plug. The engine that uses a spark plug for combustion is known as a spark ignition (SI) engine.

Compression ignition: It is the process of combustion in which the air is compressed to increase its temperature above the self-ignition temperature of the fuel and then the fuel is spread with the help of an injector to start the combustion. The engines that work on the principle of compression ignition are known as CI engines.

Engine displacement/ Swept volume: It is the volume covered by the piston while moving from TDC to BDC or from BDC to TDC. It is also known as the volume of the cylinder between TDC and BDC.

TDC: Top dead center or TDC is the position of the piston in the cylinder when the piston is very close to the cylinder head.

BDC: Bottom dead center or BDC is the position of the piston in the cylinder when the piston is very far from the cylinder head.

Bore-stroke ratio: It is the ratio of the bore diameter of the engine to the stroke length.

Two-stroke engine: It is the internal combustion engine that completes the single power cycle within two strokes of the piston or within one revolution of the crankshaft.

Four-stroke engine: It is the internal combustion engine that completes the single power cycle within four strokes of the piston or within two revolutions of the crankshaft.

Direct injection: Direct injection is the type of fuel injection system in which the fuel is directly injected into the main combustion chamber.

Indirect injection: Indirect injection is the type of fuel injection system in which the fuel is injected into the pre-combustion chamber. In this, the combustion process starts in the pre-combustion chamber, and then this mixture is spread into the main combustion chamber.

Terms related to the engine working:

Following are various engine terms related to the engine working:-

Idle speed: It is the speed of the engine when there is no load is acting on the engine.

Ignition timing: Ignition timing is the position of the crankshaft when the spark is generated into the combustion chamber of the engine.

Mean piston speed: It is the average speed of the piston while performing reciprocating motion into the engine cylinder

Air fuel ratio: Air fuel ratio is the ratio of a mass flow rate of air to the mass flow rate of fuel supplied to the engine for combustion.

Blow-by gases: Blow-by gases are the leakage of the combustion gases from the combustion chamber into the crankcase. These gases leak from the gap between piston rings and the cylinder walls.

Power stroke: In IC engines, power stroke is the movement of the piston from TDC to BDC due to the pressure applied by the combustion products during the expansion stroke.

Compression stroke: It is one of the strokes in the power cycle of an IC engine in which the piston moves from BDC to TDC to compress the fresh charge before combustion.

Suction stroke: In the IC engine cycle, suction stroke is one of the strokes in which the piston moves from TDC to BDC to take fresh charge into the cylinder.

Exhaust stroke: In the IC engine cycle, exhaust stroke is one of the strokes in which the piston moves from BDC to TDC to remove exhaust gases from the cylinder.

Idle stroke: In IC engines, the idle stroke is those strokes that don’t contribute to developing mechanical power but it consumes power for its completion.

Engine cycle: It is a sequence of processes that are performed repeatedly to convert the chemical energy of the fuel into mechanical energy.

Other terms related to the engine:

Engine control unit: The engine control unit also known as the engine control module, which controls the different actuators based on the input from different engine sensors to ensure the optimum working of the engine.

Naturally aspirated engine: These are the IC engines that use air at atmospheric pressure during suction stroke and don’t uses forced induction for charging air into the cylinder.

Supercharger: A supercharger is a compressor that is run by the crankshaft to feed compressed air into the engine cylinder to increase the power output.

Turbocharger: A turbocharger is a turbine-driven compressor unit that is run by the exhaust gases and forces extra compressed air into the engine cylinder to increase power output from the engine.

Crankcase ventilation: It is the process that removes the blow-by gases from the engine crankcase and feeds into the intake manifold of the engine.

Inline engine: It is the multi-cylinder internal combustion engine in which the cylinders are arranged in a single line.

V engine: V-engine is an IC engine that consists of two cylinder banks that make a V-shaped arrangement at the crankshaft.

Cylinder bank: In IC engines the cylinders are arranged in a line parallel to the engine and each of these lines is known as a cylinder bank.
Example: V-engine has two cylinder banks arranged parallel to the crankshaft.

IC engine: It is the heat engine in which the air-fuel mixture is combusted into the closed space and converts the heat and pressure energy developed into mechanical energy.

Thank you for reading, and I hope you liked today’s post 60+ Engine terms and definitions pdf. If you like this post, please share that piece with your mates since it is a fundamental portion that should be learned before beginning the study of automotive engineering or IC engines.

If you find that certain terms are missing from this post, please provide them in the comments area and we will add them along with definitions.