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Working Principle Of Four Stroke Engine


  • Engine
    • An engine is motor which converts chemical energy into mechanical energy
  • History
    • Otto Cycle: Dr. Nicolaus Otto -1876
  • History One of the most important landmarks in engine design by Nicolaus August Otto in 1876 who is invented as effective four stroke engine.that's why it is also called as Otto cycle engine. In 1885,German mechanical engineer,Karl Benz designed and built the world's first practical automobile to be powered by an internal-combustion engine. On January 29,1886.
    • 2-Cycle Engine; Du gal Clerk -1878
    • Diesel Engine; Dr. Rudolph Diesel -1895
  • Four Stroke Engine Four stroke engine was first demonstrate by Nikolaus Otto in 1876,hence it is also known as Otto cycle. It consist of 4 stroke ,one cycle operation is completed in 4 stroke of the piston, That is one cycle is completed in every 2 revolutions of the crankshaft. Each stroke consist of 180,of crankshaft rotation and hence a cycle consist of 720,of crankshaft rotation.
  • Working principle of four Stroke Engine Following are the four strokes 1 Intake/Suction stroke 2 Compression stroke 3 Expansion stroke 4 Exhaust stroke
  • 1 Intake stroke In suction stroke piston starts at Top Dead Center (TDC) of the cylinder and moves to the Bottom Dead Center (BDC). Outlet valve will be closed and inlet valve will be open to allowing the fresh charge of mixed fuel & air into the cylinder.
  • 2 Compression stroke In compression stroke,Once piston reaches BDC & moves back TDC,inlet valve will be closed,As the piston moves towards TDC,It compress air fuel mixture inside the cylinder & compression takes place,Hence it is called compression stroke.
  • 3 Expansion stroke In expansion stroke,Both the valves are closed,When piston reaches top of its stroke the fuel mixture is ignited by spark plug due to spark high temperature & pressure generated inside the cylinder & push down the piston to BDC,Hence it is known as expansion stroke.
  • 4 Exhaust stroke In this stroke exhaust valve is opened,when piston reaches to BDC & moves to upward. Piston pushes out the burnt gases to the atmosphere through the exhaust valve. Hence called exhaust stroke & the engine is ready to begin the cycle again.
  • Parts of an engine
  • Various Parts of Engine
    • Crankshaft
    • Crankcase
    • Crank Pin
    • Camshaft
    • Spark plug
    • Fuel pump
    • Cylinder Block
    • Cylinder Head
    • Inlet valve &
    • Exhaust valve
    • Piston
    • Piston Rings
    • Connecting Rod
    • Gudgeon Pin
  • Cylinder Block The cylinder block, also called as engine block is the main bottom end structure. Usually it is made up of iron or aluminum. Function: In the bore of the cylinder the fresh charge of air-fuel mixture is ignited,compressed by piston.
  • Cylinder Head The cylinder head is flat plate of metal bolted to the top of cylinder block with head gasket in between;Top of head contains rocker arm & push rod to transfer rotational mechanic from the crankshaft to linear mechanic to operate the valves. It is the key to performance of the internal combustion chamber.
  • Inlet valve & Exhaust valve Inlet valve:Its function is to intake the fresh air-fuel mixture into the cylinder. Exhaust valve:Its function is to exhaust is the burnt gases by the force of piston.
  • Piston Piston is connected to the crankshaft through the connecting rod,when piston moves downward sucks fresh air-fuel mixture in suction stroke & ignited inside the cylinder due to this high temperature and pressure generated,thus expanded gas force down to piston.
  • Piston Rings A piston ring is an open ended ring that fits into a groove or outer diameter of the cylinder. Piston rings have three major functions which are to seal the expansion chamber,support heat transfer & finally,regulate the engine oil consumption.
  • Connecting Rod & Gudgeon Pin A small end of connecting rod is connected to the piston and other end is connected to the crankshaft. Its function is to transmit the reciprocating motion of piston to the to the rotary motion of crankshaft. Gudgeon pin is used to connect the piston & connecting rod.
  • Crankshaft Crankshaft is the part of an engine which translates the reciprocating linear motion of piston into rotation. To convert the reciprocating motion into rotation,the crankshaft has crank pin,it typically connects to flywheel,to reduce the pulsation characteristics four stroke cycle.
  • Crankshaft The crank-connecting rod is first fully developed by Arab inventor Al-Jazari in (1136-1206).Similar crankshaft late described by Conrad Keyser in 1405.The main function of crankshaft is receives the oscillating motion from connecting rod and gives rotary motion to main shaft. It also drives the camshaft which actuate the valves of the engine.
  • Camshaft Camshaft is a part which is used in piston engine to operate valves. It consists of cylindrical rod with cams. The camshaft were invented in Iraq (Mesopotamia), described by Al-Jazari in 1206.The relationship between camshaft rotation & crankshaft rotation is of critical importance.
  • Camshaft Since valves controls the flow of air-fuel mixture intake & exhaust burnt gases. Valves must be opened & closed at appropriate time during the stroke of piston,For this reason ,the camshaft is connected to the crankshaft either directly,via a gear mechanism, or indirectly via belt/chain called a timing belt or timing chain, the camshaft rotates at the same rate of crankshaft.
  • Spark Plug Spark plug is used in petrol engine only which is help to ignite the air-fuel mixture for combustion.
  • Two Stroke Engine Two stroke engine is first described by Du gal Clerk in 1878.In two stroke engine one cycle is completed in every revolution of crankshaft.
  • Working principle of two Stroke Engine Two stroke engine is widely used employed where small power required for motor cycle like auto rickshaw, scooter. This type of engine is compact in size,easy for manufacturing and simple in operation. In two stroke engine there are no inlet or exhaust valve as in four stroke engine.
  • Working principle of two Stroke Engine But only inlet & exhaust ports used ,Due to which suction & exhaust stroke is eliminated in two stroke cycle engine.
  • Compression Stroke When piston moves from BDC to TDC,it first closes the transfer port & then exhaust port,The charge of air-fuel mixture in the chamber is pressurised & creates high temperature. At the same time,
  • Compression Stroke a vacuum is developing in the crankcase,so the fresh charge of fuel mixture is being drawn into the crankcase from the carburettor. As the piston moves towards TDC ,a high voltage discharge from the spark plug & ignites the air-fuel mixture in the combustion chamber.
  • Combustion Stroke In this stroke both the ports still closed condition,the pressure of the expanding gases forces the piston towards BDC.the pressure in the crankcase is already rising. Later in down stroke exhaust port will be open & forced out the burnt gases,Very shortly after that the
  • Combustion Stroke Inlet / Transfer port will also open to intake the fresh charge of fuel mixture,and engine is ready to start of the cycle.
  • Advantages & Disadvantages of Two Stroke Engine
    • One cycle completed in every revolution of crankshaft.
    • It is more compact,required less space and lighter in weight than four stroke engine.
    • The design & construction is much simpler than four stroke engine.
    • Easy to manufacture & low cost.
    Advantages :
  • Advantages & D