IN THE NAME OF ALLAH THE MOST BENEFICIENT THE MOST MERCIFUL:

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Sohail Matloob 07-ME-11 Muhammad Nauman 07-ME-14 Junaid Kazmi 07-ME-18 Ammad Shabir 07-ME-115 Sardar M. Baber 07-ME-128

PRESENTED TO ENGR. NASIR Sb

Two Stroke engines Four stroke engines TOPIC Two Stroke engines Four stroke engines

Engine A device which convert heat energy in to mechanical energy to obtain some power is called an engine.

TYPES OF AN ENGINE There are two types of an engine. Internal Combustion Engine(I.C. Engines) External Combustion Engine(E.C. Engines)

Internal Combustion Engine(I.C. Engines) The engines in which combustion takes place inside the engine as in the cylinder are called as I. C. Engines e.g.; Petrol Engine, Diesel Engines.

External Combustion Engine(E.C. Engines) The engines in which combustion takes place outside the engine as in boilers are called as E.C. Engines e.g.; Steam Engines.

Internal Combustion Engine(I.C. Engines) Spark Ignition Engines Compression Ignition Engines

Spark Ignition Engines These are petrol engines in which the air and fuel are mixed before compression and the charge is ignited with the help of spark plug.

Compression Ignition Engines These are diesel engines in which the air only is compressed, and the fuel is injected into the air which is then at a sufficiently high temperature to initiate combustion.

Spark Ignition Engines Two Stroke Petrol Engines Four Stroke Petrol Engines

Two Stroke Petrol Engines The two stroke cycle is so called because it takes two strokes of the piston to complete the processes needed to convert the energy in the fuel into work.

Because the engine is reciprocating, this means that the piston must move up and down the cylinder, and therefore the crankshaft must revolve once. The air and fuel(Petrol or CNG) are mixed before compression.

PROCESSES Suction Compression Power Exhaust

Four Stroke Petrol Engines The four strokes refer to intake, compression, combustion (power), and exhaust strokes that occur during two crankshaft rotations to complete the processes needed to convert the energy in the fuel into work.

Working of Four Stroke Petrol Engines

Intake Stroke On the intake or induction stroke of the piston , the piston descends from the top of the cylinder to the bottom of the cylinder, reducing the pressure inside the cylinder. A mixture of fuel and air is forced by atmospheric (or greater) pressure into the cylinder through the intake port. The intake valve(s) then close.

Compression Stroke With both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the fuel-air mixture. This is known as the compression stroke.

Power Stroke While the piston is close to Top Dead Center, the compressed air–fuel mixture is ignited, usually by a spark plug (for a gasoline or Otto cycle engine) or by the heat and pressure of compression (for a diesel cycle or compression ignition engine).

The resulting massive pressure from the combustion of the compressed fuel-air mixture drives the piston back down toward bottom dead center with tremendous force. This is known as the power stroke, which is the main source of the engine's torque and power.

Exhaust Stroke During the exhaust stroke, the piston once again returns to top dead center while the exhaust valve is open. This action evacuates the products of combustion from the cylinder by pushing the spent fuel-air mixture through the exhaust valve(s).

Starting Position

Intake Stroke

COMPRESSION STROKE

Ignition of fuel

Power stroke

Exhaust stroke

Two stroke diesel engine The two stroke cycle is so called because it takes two strokes of the piston to complete the processes needed to convert the energy in the fuel into work.

Compression Ignition Engines Two Stroke diesel Engines Four Stroke diesel Engines

Two Stroke Diesel Engines The two stroke cycle is so called because it takes two strokes of the piston to complete the processes needed to convert the energy in the fuel into work.

Because the engine is reciprocating, this means that the piston must move up and down the cylinder, and therefore the crankshaft must revolve once. The air only is compressed, and the fuel is injected into the air which is then at a sufficiently high temperature to initiate combustion.

Working Of two stroke diesel engine

Intake stroke The crankshaft is revolving clockwise and the piston is moving up the cylinder, compressing the charge of air. Because energy is being transferred into the air, its pressure and temperature increase. By the time the piston is approaching the top of the cylinder (known as Top Dead Center or TDC) the pressure is over 100 bar and the temperature over 500°C

Compression Just before TDC fuel is injected into the cylinder by the fuel injector. The fuel is "atomized" into tiny droplets. Because they are very small these droplets heat up very quickly and start to burn as the piston passes over TDC. The expanding gas from the fuel burning in the oxygen forces the piston down the cylinder, turning the crankshaft. It is during this stroke that work energy is being put into the engine; during the upward stroke of the piston, the engine is having to do the work.

Power stroke As the piston moves down the cylinder, the useful energy from the burning fuel is expended. At about 110° after TDC the exhaust valve opens and the hot exhaust gas (consisting mostly of nitrogen, carbon dioxide, water vapour and unused oxygen) begin to leave the cylinder.

At about 140º after TDC the piston uncovers a set of ports known as scavenge ports. Pressurized air enters the cylinder via these ports and pushes the remaining exhaust gas from the cylinder in a process known as "scavenging". The piston now goes past Bottom Dead Centre and starts moving up the cylinder, closing off the scavenge ports. The exhaust valve then closes and compression begins.

Four Stroke Diesel Engines The four strokes refer to intake, compression, combustion (power), and exhaust strokes that occur during two crankshaft rotations to complete the processes needed to convert the energy in the fuel into work.

Working of four Stroke Diesel Engines

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