Two Stroke Petrol Engine

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Two Stroke Petrol Engine

Two Stroke engine is a type internal combustion engine, which completes a power cycle in 'up and down' moments,it means two stroke of the piston during only one crankshaft revolution. 
This is in contrast to a four stroke engine, which required four stroke of the piston to completed a power cycle during two crankshaft revolution. 

In a two stroke engine the end of the combustion stroke and the begging of the compression stroke happen at together with the intake and exhaust function occurring at the same time.

Two stroke petrol engine are used when mechanical simplicity, light weight , and high power to weight ratio and design priorities, with the traditional lubrication technique of mixing oil into the fuel. They are also have an advantage of working in an any orientation , as there is no oil reservoir dependent on gravity, this is an essential property for hand held tool such as chainsaws.

Theoretically the power output of two stroke engine can be double from the same speed compared of the four stroke engine, Because in two stroke engine the cycle is completed in one revolution of the crank shaft on other hand four stroke engine the cycle is completed in two revolution of crankshaft.
The main difference between two stroke and four stroke engine is that the method of filling the fresh charge and removing the burnt gasses from the cylinder.

Applications

They are lighter in weight and it can also produce a higher power to weight ratio.
Two stroke engine are useful in applications such as-
Chainsaws,Weedeaters, outboards, lawnmowers and in motorcycles etc.
Two stroke engine are also easier to start in cold temp..

History

The first commercial two stroke engine involving in cylinder compression is attributed by Dugald clerk a Scottish Engineer who designed in 1881. However , unlike most later two stroke engines , his had a separate charging cylinder. The crankcase scavenged engine employing the area bellow the piston as a charging pump. It was generally created in 1879 by Englishman Joseph Day.
Two stroke gas engine produced by German inventor Karl Benz , for which he received a patent in Germany in 1880.

The first truly practical engine of two stroke is attributed to Alfred Angas Scott , who started producing twine cylinder water cooled motorcycles in 1908.

Spark ignition (Gasoline) versions are particularly use in light weight or portable applications such as chainsaws and motorcycles. However when weight and size are not issue , so for the cycle potential for high thermodynamics efficiency makes it ideal for diesel compression ignition engine.

Components of Two Stroke Petrol engine

There are the following components of the two stroke petrol engine.




 Piston
Piston is used to transfer the expending forces of gasses to mechanically rotation of crankshaft through a connecting rod. The piston is also able to do this because it is secured tightly within cylinder and piston rings to minimize the clearance between cylinder and piston.

Spark Plug
Spark plug is to delivered electric currents to the combustion chamber which ignites the air and fuel mixture leading to abrupt expansion of gas.

Crankshaft
A crankshaft is a part which is converted the reciprocation motion in to rotary motion. It is enclosed in the crankcase.

Connecting Rod
A connecting rod transfer motion from a piston to crankshaft, which acts as a lever arm.

Inlet and Outlet Port 
Inlet port allow to enter fresh air with fuel and the outlet port exit to spent air fuel mixture from the cylinder.


Working

The two stroke petrol engine cycle is completed in one revolution of crankshaft  of two stroke of the piston.
 This cycle consists of the following two stroke
Down Stroke
Up Stroke
Down Stroke

First the piston is moved downside from top dead center (T.D.C.) to bottom dead center (B.D.C.). In this time the fresh air fuel mixture enter by the outlet port into the combustion chamber. The fresh air fuel mixture get into the combustion chamber through crank case. during this stroke the crankshaft rotates 180 degree.


Up Stroke 

In this stroke the piston is pushed up from bottom dead center (B.D.C.) to top dead center (T.D.C.) . the air fuel mixture get compressed and spark plug ignites the mixture . As the mixture get expanded , the piston moves down. during the up stroke,the inlet port is opened. while this inlet port opened, the mixture of oil and air get shucked inside the crankcase. 
when the mixture is pushed up into the combustion chamber during the previous stroke , a partially vacuum is created as no mixture is left behind the crankcase. The mixture is ready to go into the combustion chamber during down stroke but remain the crankcase until the piston goes up till top dead center. Then the crankshaft rotates 360 degree after completion on one revolution of crankshaft.

From the second down stroke onwards the exhaust gasses get expelled out from one side while a fresh mixture enter into the combustion chamber simultaneously due to partially vacuum created in the combustion chamber after removal of exhaust gases. this is the beauty of this engine.















You should also read to know about 2-stroke diesel engine.

what is two stroke diesel engine and how it works?



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