Four Stroke Engine

ENGINE An Engine is a device or motor that coverts thermal energy to mechanical energy, or an engine is a mechanical device that produces some form of output from a given input. In an engine the linear motion of the pistons is converted into rotational motion by the crankshaft There are two types of engines; Two stroke engines (petrol engine) and Four stroke engines (petrol and diesel engines). Two stroke engines are built for high speed and performance while Four stroke engines are fuel efficient. Four stroke engines are more preferred than Two stroke engines.

STROKE A stroke is a single action of certain engines, or A Stroke is a half revolution of an engine during which the piston travels from one extreme of its range to the other.

TYPES OF ENGINES Four Stroke engine An internal combustion engine (type of engine in which burning of fuel takes place within the engine) in which the entire engine cycle is completed in four piston strokes. In this type of engine with a single intake of fuel the engine can run four strokes [3+1(fuel intake)]. Four stroke engine includes the following strokes; 1. Intake or Suction Stroke 2. Compression Stroke 3. Power or Combustion Stroke

4. Exhaust stroke Four stroke engine can be further divided on the bases of fuel, i.e. Four Stroke Diesel engine and Four Stroke Petrol engine. a)

Four stroke Petrol engine

The four stroke internal combustion engine which uses petrol as the burning fuel is known as four stroke petrol engine. The fuel actually used in the engine is the mixture of petrol and air (oxygen, used to ignite petrol). WORKING The cycle begins at top dead center (TDC), when the piston is farthest away from the axis of the crankshaft. 1. Intake or Suction Stroke

The piston starts at TDC, the intake valve opens and the piston moves down to let the engine to take in a cylinder-full of fuel (mixture of air and petrol). This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work. The piston is connected to crankshaft with the help of connecting rod. This crankshaft is further transforms the mechanical work into desired output.

2. Compression Stroke

Then in the compression stroke the piston moves back up to the extreme top position which compress the fuel (air + petrol mixture). The use or benefit of compression is to make the explosion more powerful. This stroke increases the temperature of fuel which produces large amount of heat during ignition.

3. Power or Combustion Stroke

Then in the Power stroke,

the fuel is then ignited near the end of

the

compression stroke, with the help of

spark

plug. The spark plug ignites the spark

right

before the power stroke which burns the

fuel.

The resulting pressure of burning fuel

pushes

the piston back to the extreme end or

down position.

4. Exhaust stroke In the exhaust stroke, once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out through the exhaust pipe which is attached to exhaust valve.

Now the engine is ready for the next cycle, so it intakes another charge of fuel and repeats the entire process.

b)

Four stroke Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression. This is in contrast to a petrol engine, which uses the Otto cycle, in which a petrol and air mixture is ignited by a spark plug. The major difference between the petrol and diesel engine is that diesel engines do not have spark plugs.

WORKING Like in the petrol engine, cycle begins at top dead center (TDC), when the piston is farthest away from the axis of the crankshaft. 1. Intake or Suction Stroke

The piston starts from TDC, the intake valve opens pushing air into the chamber and the piston moves down. The piston is connected to crankshaft with the help of connecting rod. This crankshaft further transforms the mechanical work into desired output.

2. Compression Stroke

Then in the compression stroke the piston moves back up to the extreme top position ,which compress the air which results in increase in pressure and temperature. The use or benefit of compression is to make the explosion more powerful.

3. Power or Combustion Stroke

Then in the Power stroke, the compressed air with very high temperature is brought in contact with the diesel, which is injected through the ignition pipe called as fuel injector. After this blast occurs in the chamber which builds up huge pressure. The resulting pressure of burning fuel pushes the piston back to the extreme end or down position.

4. Exhaust stroke In the exhaust stroke, once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out through the exhaust pipe which is attached to exhaust valve. Now the engine is ready for the next cycle, so it intakes another charge of air and repeats the entire process.

COMPONENTS OF A FOUR-STROKE ENGINE

A) Intake Valve, Rocker arm & Spring. Intake valve- A valve in the cylinder head of an internal-combustion engine that opens at the proper moment during the cycle to allow the fuel-air mixture to be drawn into the cylinder. Rocker arm- A rocking or oscillating arm or lever rotating with a moving shaft or pivoted on a stationary shaft. This is used to make the valves work on desired and regular intervals. B) Valve cover A long metal lid located on the top of the cylinder head on vehicles with overhead camshafts. The valve cover is removed when the valves need adjusting

C) Intake port The name given to the passage in the cylinder head which connects the intake manifold to the intake valve through which the fuel-air mixture proceeds on its way to the cylinder. D) Cylinder head

It is a detachable plate that covers the closed end of a cylinder chamber in a reciprocating engine or pump. The cylinder head is the main body of the engine wherein direct combustion of fuel takes place. E) Coolant A fluid agent (gas or liquid) that produces cooling is known as coolant. Here it is used to cool the external system or body of the engine in which heat is produced because of friction. F) Engine block The name given to the metal casting containing where the cylinders and cooling ducts of an engine are located. It is very important because if it cracks the whole of the engine had to be replaced. G) Oil pan

It is the removable chamber situated at the bottom of the crankcase which stores oil. The oil drain plug is found at the bottom of this pan and can be removed to allow the old oil to flow out of the vehicle during an oil change.

I) Camshaft A metal shaft with two or more cams (oval “lobes”) that rotates to operate inlet and/or exhaust valves in a four-stroke engine. J) Exhaust valve A valve in the cylinder head of an internal-combustion engine that opens at the proper moment during the cycle to send exhaust gases out of the chamber at repeated intervals. K) Spark plug These are the devices used for creating sparks and further to ignite gases using the same spark. One cylinder has one spark plug in it. L) Exhaust port The passage in the cylinder head which connects the exhaust valve and the exhaust manifold. The exhaust gases pass through the port to the exhaust manifold or header and moves out of the engine. M) Piston It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft. N) Connecting Rod The connecting rod connects the piston with the crankshaft. This shaft actually converts the energy from up and down motion of piston to rotational motion of crankshaft. O) Rod bearing

the bearing which are used to connect connecting rod with crankshaft. These should be friction less so as to provide maximum energy transfer.

P) Crankshaft It is that part of an engine which translates reciprocating linear piston motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rods from each cylinder attach.