Comparison Between Two and Four Stroke Engine

One Complete Cycle

Four stroke internal combustion engine executes four complete strokes within the Cylinder while the crankshaft completes two revolutions for each thermodynamic Cycle while Two stroke engine executes two complete strokes within the cylinder while the crankshaft completes One revolutions for each thermodynamic cycle.

Main Strokes

As the mane say fore stroke engine have four strokes Intake Stroke (Induction or Suction Stroke), Compression Stroke, Power Stroke (Combustion Stroke) and Exhaust Stroke while two stroke engine only two stroke First Stroke (Suction & Compression Stroke) and Second Stroke (Power & Exhaust Stroke)

Friction Losses

Because of absence of valve tappets and crank shafts, friction losses are minimum in 2-stroke petrol engine as compared to 4 stroke engine

Power Deliverance

As mention above 2 stroke engine has less friction as compared to 4 stroke engine that's why have more power deliverance an compared to 4 stroke 

Rate Of Power Production

In 2-stroke engine, one stroke is working and other is idle stroke and in 4-stroke engines, there is one working stroke and three idle strokes. So the rate of power production for 2-stroke engine is more.

Effects On Environment  

In two stroke there is a exhaust of unburnt gasses to the environment so it is harmful to the environment but in four stroke engine there is no exhaust of unburnt gasses to the environment so it is not harmful to the environment 

Lose of lubricating oil

As suction & compression stroke take place in a single stroke so there is a heavy combustion of lubricating oil where as in four stroke engine suction and compression stroke are separate so there is no loss of lubrication oil

Lose Of Fuel

Few amount of fresh fuel is exhausted as exhaust and suction takes place simultaneously.in two stroke engine but no fresh fuel is exhausted as exhaust and suction takes place separately

Four Stroke Engine

Petrol Engine uses petrol as a fuel for combustion inside the cylinder. The petrol engine consist of a spark plug which ignite the air-fuel mixture (Air + Petrol). In petrol engine the carburetor prepare the require air fuel mixture Send it into the combustion chamber (Cylinder). Distance travelled between top dead centre and bottom dead centre is known as stroke.

Four Stroke Internal Combustion Engine

Four stroke internal combustion engine executes four complete strokes within the Cylinder while the crankshaft completes two revolutions for each thermodynamic Cycle.Petrol Engine uses petrol as a fuel for combustion inside the cylinder. The petrol engine consist of a spark plug which ignite the air-fuel mixture (Air + Petrol). In petrol engine the carburetor prepare the require air fuel mixture Send it into the combustion chamber  (Cylinder). Distance travelled between top dead centre and bottom dead centre is known as stroke.

Intake Stroke (Induction or Suction Stroke):

During the intake stroke, the piston moves downward, drawing a fresh charge of Vaporized fuel/air mixture.  The illustrated engine features a 'poppet' intake valve which is drawn open by the vacuum produced by the intake stroke.  Some early engines worked this way, however most modern engines incorporate an extra cam/lifter arrangement as seen on the exhaust valve.  The exhaust valve is held shut by a spring

Compression Stroke:

It is the process in which the fuel that was introduced into the engine cylinder is Compressed. During Compression Stroke the Piston moves from Bottom Dead Centre to Top Dead Centre. The Flywheel momentum drives the piston upward, compressing the fuel/air mixture. After the top dead centre the volume left is known as clearance volume. During Compression Stroke Both Intake Valve and Exhaust Valve remains closed.

Power Stroke (Combustion Stroke):

At the top of the compression stroke the spark plug fires, igniting the compressed fuel.  As

the fuel burns it expands, driving the piston downward. It is the only process in which the engine does work onto the surroundings.

Exhaust Stroke:

At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism.  The upward stroke of the piston drives the exhausted fuel out of the Cylinder

Main PARTS of Four Stroke Petrol Engine

• Fly Wheel:Crank Shaft
• Connecting Rod
• Piston Rings
• Engine Chamber or Engine Cylinder
• Counter Weights
• Cooling Water Jackets
• Carburettor Inlet and Outlet Manifold Valve
• Tappets Rods
• Cam 
• Gears
• Spark Plug

          

Two Stroke Engine

Two stroke engine executes two complete strokes within the cylinder while the crankshaft completes One revolutions for each thermodynamic cycle.

First Stroke (Suction & Compression Stroke):-

In the first stroke the suction and compression processes take place simultaneously. The suction is done through port named inlet port and the movement of piston from bottom dead centre to the top dead centre causes the fuel to be compressed.

Second Stroke (Power & Exhaust Stroke):-

In the 2nd stroke the combustion and exhaust takes place. Due to combustion the piston moves downwards and the exhaust also takes place in the same stroke. During the exhaust the fresh charge also starts entering the engine cylinder. The designing of the top of the engine is such that the fresh charge does not combine with the expelling one. This is done by taking the term known as cross flow

Two Stroke Engine working

Starting from bottom the engine consists of a circular cylinder named as crank case. In crank case, counter weight is present that revolve to complete the cycles. It is connected to both fly wheel outside the engine and inside it is attached to the crank shaft that is further attached with the piston at gudgeon tube through connecting rod. The piston is movable with in the bottom dead centre and the top dead centre. Space named as engine chamber is the part above the piston. It is surrounded by some lined structures to keep the engine cool, these lines are called cooling fins. At the upper side of the engine a spark plug is present which is connected to the battery. The connection of spark plug to the battery is controlled by the movement of fly wheel. The piston is movable due to the presence of piston rings around the piston to avoid friction. The inlet and outlet ports are present on the same side of cylinder. However the fuel enters first into the crank case then by the creation of vacuum it is in turn sucked into the engine chamber with the help of fuel transport port.

Main Parts Of Two Stroke Engine

• Cylinder
• Cylinder head
• Piston
• Piston rings
• Gudgeon pin
• Connecting rod
• Crankshaft 
• Crank
• Engine bearing
• Crank case
• Flywheel
• Governor
• Valves and valve operating mechanism
•  Fuel pump

ADVANTAGES OF TWO STROKE  ENGINE

Following are some advantages of 2-stroke petrol engine.

•As there is only one idle stroke, horsepower developed in it is twice as that of 4-stroke.

•The work resumed during exhaust and suction stroke to overcome friction is same.

•There is more turning movement of crank shaft.

•In this engine there is no valve but ports, which one is closed by motion of piston itself.

•Easy manufacturing as compared to 4-stroke petrol engine and overcome.

DISADVANTAGES OF TWO STROKE 

Following are some disadvantages of 2-stroke petrol engine.

•It is high speed but less efficient.

•It takes heavy combustion of lubricating oil.

•Few amount of fresh fuel is exhausted as exhaust and suction takes place simultaneously.

•Due to the loss of unburnt gasses it is harmful to environment.