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subject: IC ENGINES

Terminology of IC Engine:


They correspond to the positions occupied by the piston at the end of its stroke where the center lines of the connecting rod and crank are in the same straight line. These conditions arise at two specific positions of the piston. At the start of the journey of stroke and at the end of the stroke are these two specific conditions, which are named as Top Dead Center (TDC) and Bottom Dead Center or BDC for vertical engines and IDC or Inner Dead Center and ODC or Outer Dead Center for horizontal engines.

TDC: The top most position of the piston towards the cover end side of the cylinder of a vertical engine is called Top Dead Center or TDC.

BDC: The lowest position of the piston towards the crank end side of the cylinder of a vertical engine is known as BDC.


The distance between the center of main shaft and center of crank pin is known as Crank Throw or Crank Radius. This distance will be equal to half the stroke length.


It is the volume through which the piston sweeps for its one stroke. Swept Volume is represented by Vs and it is equal to cross-sectional area of the piston x stroke length
Vs = {(π x d²)/4} x stroke length (L)


It is the volume included between the piston and the cylinder head when it is at TDC (for vertical engines) or IDC (for horizonal engine). The piston can never enters this portion of the cylinder during its travel. Clearence volume (Vc) is generally expressed as percentage of the swept volume and is denoted by Vc.


It is the ratio of the total cylinder volume to the clearence volume. If swept volume is (Vs) and clearence volume is (Vc) then total volume of the cylinder

V = Vs + Vc

and Compression Ratio will be equals to
(Vs + Vc)/Vc

For petrol engine it varies from 5:1 to 9:1 and for diesel engines from 14:1 to 22:1.


It is the distance travelled by piston in one minute. If rpm of engine shaft is (N) and length of stroke is (L), then piston speed will be 2LN m/min.


Direct injection is basically fuel injection into the main combustion chamber of an engine. Engines either have one main combustion chamber (open chamber) or a divided combustion chamber made up of a main chamber and a smaller connected secondary chamber.


Indirect injection is the fuel injection into the secondary chamber of an engine with a divided combustion chamber.

Bore: Diameter of the cylinder or diameter of the piston face, which is the same minus a very small clearance.

Displacement volume: Volume displaced by the piston as it travels through one stroke. Displacement can be given for one cylinder or for the entire engine (one cylinder time’s number of cylinders). Some literature calls this swept volume.


Gasoline Direct Injection (GDI) is spark ignition engine with fuel injectors mounted in combustion chambers. Gasoline fuel is injected directly into cylinders during compression stroke.


Homogeneous Charge Compression Ignition (HCCI) occurs in Compression-Ignition engine operating with a homogeneous airfuel charge instead of the diffusion combustion mixture normally used in CI engines.

Smart Engine: either computer controls that regulate operating characteristics such as air fuel ratio, ignition timing, valve timing, exhaust control, intake tuning etc. Computer inputs come from electronic, mechanical, thermal and chemical sensors located throughout the engine. Computers in some automobiles are even programmed to adjust engine operation for things like valve water and combustion chamber deposit build up as the engine ages. In automobiles, the same computers are used to make smart cars by controlling the steering, brakes, exhaust system, suspension, seats, anti-theft systems, sound-endear analysis navigation entertainment systems, shifting, doors, noise, suppression, environment, comfort etc.

Engine Management System: Computer and electronics used to control smart engines.

Wide- Open throttle (WOT): Engine operated with throttle valve fully open when maximum power and/or speed is desired.

Ignition Delay (ID): Time interval between ignition initiation and the actual start of combustion.

Air Fuel Ratio: Ratio of mass air to mass of fuel input into engine.

Fuel-Air ratio: Ratio of mass of fuel to mass of air input into engine.

Brake Maximum torque: (BMT): Speed at which maximum torque occurs.

Overhead Valve (OHV): Valves mounted in engine head.

Overhead Cam (OHC): Camshaft mounted in engine head, giving more direct control of valves which are also mounted in engine head.

Fuel Injection (FI)


The following is the list of major components found in most reciprocating internal combustion engines.

Block: Body of engine containing the cylinders made of cast iron or aluminum. In many older engines the valves and the valve ports were contained in the block. The block of water cooled engines includes a water jacket cast around the cylinders. On air cooled engines the exterior surface of the block has cooling fins. Camshaft: Rotating shaft used to push open valves at the proper time in the engine cycle either directly or through mechanical or hydraulic linkage (push rods, rocker arms, and tappets). Most modern automobile engines have one or more camshafts mounted in the engine head (Overhead cam). Older engines had camshafts in the crank case.

Crankshafts are generally made of forget steel or cast iron and driven off the crankshaft by means of a belt or chain (Timing chain). To reduce weight, some cams are made from a hollow shaft with the cam lobes press-fit on. In four stroke cycle engines the camshaft rotates at half engine speed.

Carburetor: Venturi flow device that meters the proper amount of fuel into the air flow by means of pressure differential. For many decades it was the basic fuel metering system on all automobile (and other) engines. It is still used on low cost small engines like lawn mowers but is uncommon on new automobiles.

Catalytic converter: Chamber mounted in exhaust flow containing catalytical material that promotes reduction of emission by chemical reaction.

Choke: Butterfly valve at carburetor intake, used to create rich fuel-air mixture in intake system for cold weather starting.

Combustion chamber: The end of the cylinder between the head and the piston face where the combustion occurs. The size of the combustion chamber continuously changes from a minimum volume when the piston is at TDC to a maximum when the piston is at BDC. The term cylinder is sometimes synonymous with combustion chamber (e.g., the engine was firing on all cylinders). Some engines have open combustion chambers which consist of one chamber for each cylinder. Other engines have divided chambers which consist of dual chambers on each cylinder connected by an orifice passage.

Connecting rod: Linkage connecting piston with rotating crankshaft usually made of steel alloy forging or aluminum.

Connecting rod bearing: Bearing where connecting rod fastens to crankshaft.

Cooling fins: Metal fins on the outside surfaces of cylinders and head of an air cooled engine. These extended surfaces cool the cylinders by conduction and convection.

Crankcase: Part of the engine block surrounding the rotating crankshaft in many engines the oil pan makes up part of the crankcase housing. In some high performance engines the crankcase is designed with windows between the piston bays to allow free airflow between bays. This is to reduce air pressure build up on the backside of the pistons during power and intake strokes.

Crankshaft: Rotating shaft through which engine work output is supplied to external systems. The crankshaft is connected to the engine block with the main bearings. It is rotated by the reciprocating pistons through connecting rods connected to the crankshaft, offset from the axis of rotation. This offset is sometimes called Crankthrow or crank radius. Most crankshafts are made of forged steel, while some are made of cast iron.

Cylinders: The circular cylinders in the engine block in which the pistons reciprocate back and forth. The walls of the cylinder have highly polished hard surfaces. Cylinders may be machined directly in the engine block or hard metal (drawn steel) sleeve may be pressed into the softer metal block. Sleeves may be dry sleeves, which do not contact the liquid in the water jacket or wet sleeves which form part of the water jacket. In a few engines, the cylinder valves are given knurled surface to help hold a lubricant film on the walls. In some very rare cases, the cross-section of the cylinder is not round.

Exhaust Manifold: Piping systems that carries exhaust gases away from the engine cylinders, usually made of cast iron.

Exhaust system: Flow systems for removing exhaust gases from the cylinders, treating them and exhausting them to the surroundings. It consists of an exhaust manifold that carries the exhaust gases away from the engine a thermal or catalytic converter to reduce emissions a muffler to reduce engine noise and a tail pipe to carry the exhaust gases away from the passenger compartment.

Fan: Most engines have an engine-driven fan to increase air flow through the radiator and through the engine compartment which increases waste heat removal from the engine. Fans can be driven mechanically or electrically, and can run continuously or be used only when needed.

Flywheel: Rotating mass with large moment of inertia connected to the crankshaft of the engine. The purpose of the flywheel is to store energy and furnish a large angular momentum that that keeps the engine rotating between power strokes and smoothes out engine operation. After the electrical systems of automobiles evolve from 12 volts to 42 volts in the next decades the engine starter and generator will be built as a part of multipurpose flywheel. On some aircraft engines the propeller serves as the flywheel as does the rotating blade on many lawn movers.

Fuel Injector: A pressurized nozzle that sprays fuel into the incoming Air on SI engines or into the cylinder on CI engines is known as fuel injector. On SI engines, fuel injectors are located at the intake valve ports on multipoint port injection systems, upstream at the intake manifold inlet on throttle body injection systems and in the combustion chambers in the direct injection systems.

Fuel pump: Electrically or mechanically driven pump to supply fuel from the fuel tank (reservoir) to the engine. Many modern automobiles have an electrical fuel pump mounted submerged in the fuel tank. Most small engines and some early automobiles had no fuel pump relying on gravity feed.

Historic –Fuel pumps: Lacking a fuel pump, it was necessary to back model T Fords (1909-1927) up steep hills because of the location of the fuel tank relative to the engine.

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