Two stroke petrol engine with parts detail and difference between two stroke and four stroke petrol engine

          Two stroke petrol engine;                                         

Engine:

An internal combustion engine which completes  a power cycle in only one crankshaft revolution and with two strokes. or up and down movements, of the piston in comparison to a "four-stroke engine", which uses four strokes to do so. This is accomplished by the end of the combustion stroke and the beginning of the compression stroke happening simultaneously and performing the intake and exhaust functions at the same time

                                                                                                                          History:                                                       

Sir Dugald Clerk  was a Scottish engineer who designed the world's first successful two-stroke engine in 1878 and patented it in England in 1881. However it was not until the end of 1880 that he succeeded in producing the Clerk engine operating on the 2-stroke cycle, which became the commercial product.

Parts of engine:

                                                                                           

Piston;

A disk or a short cylinder fitted closely within a tube which moves up and down against the liquid or gas used in engine. It is the main part which transforms the gases into mechanical work.

                                               

 Piston ring:

It  is an expandable split ring used to provide a seal between the piston an the cylinder wall . Piston rings seal the combustion chamber, conduct heat from the piston to the cylinder wall. Piston ring size and configuration vary depending on engine design and cylinder material

Crank case:

Provides the casing for the crank shaft. The enclosure forms the largest cavity in the engine and is located below the cylinder. The area around the crankshaft is still usually called the crankcase. In two-stroke engines, the crankcase is sealed and is used as a pressurization chamber for the fuel/air mixture.

Crank shaft:

 Inside the crank case converts the reciprocating motion delivered by the connecting rod into piston. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins“ .It is typically connected to a flywheel.

 Crank pin;                                               

In a reciprocating engine, the crankpins, also known as crank journals are the journals of the big end bearings, at the ends of the connecting rods opposite to the pistons. If the engine has a crankshaft, then the crank pins are the journals of the off-centre bearings of the crankshaft.

                                                         

 Flywheel;

Is a rotating mechanical device that is used to store rotational energy. Common uses of a flywheel include:

1. Providing continuous energy when the energy source is discontinuous.
2. Delivering energy at rates beyond the ability of a continuous energy source.

                                       

Connecting rod:                                  

It connects the piston with the crankshaft. Together with the crank, they form a simple mechanism that converts reciprocating motion into rotating motion

                                                                                          

Spark plug:  

                                                                                                                                                                     Is a device for delivering electric current from an ignition system to the combustion chamber of a spark-     ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within the engine

                                                            

Cylinder:

Is the central working part of a reciprocating engine or pump, the space in which a piston travels The highly polished inner surface of the cylinder allows the piston to move with ease and prevent any gas from escaping

                                   

 Carburetor:

The air and fuel is mixed and travels into the cylinder through the intake port

                                  

                                            

  Working of  two stroke engine:

1.    Intake stroke:

The fuel/air mixture is first drawn into the crankcase by the vacuum that is created during the upward stroke of the piston.

2.     Compression stroke:

 The piston then rises, driven by flywheel momentum, and compresses the fuel mixture.

                                                

3.   Power stroke:

At the top of the stroke, the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle. (At the same time, another crankcase compression stroke is happening beneath the piston.

                                           

4.    Exhaust stroke;

Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port.

                                         

                                       

Advantage:

—  It can be operated at any orientation.

—  Two-stroke engines do not have valves, simplifying their construction.

—  Two-stroke engines fire once every revolution . This gives two-stroke engines a significant power boost.

—  Two-stroke engines are lighter, and cost less to manufacture.

       Two-stroke engines have the potential for about twice the power in the same size because there  

       are twice as many power strokes per revolution.

 Disadvantage:

—  The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster.

—  Two-stroke engines do not use fuel efficiently, yielding fewer miles per gallon.

—  Because it is inefficient gives a poorer mileage.

—  The combustion of the oil in the gas. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit more oily smoke.

—  Each time a new mix of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port

DIFFERENCE BETWEEN TWO AND FOUR STROKE ENGINES:

TWO STROKE ENGINE;

—  Two stroke means one stroke in each direction.

—  A two stroke will have a compression stroke followed by the ignition of compressed fuel.

—  Two stroke produces more power then four stroke.

—  Two stroke produces a power stroke every revolution.

—  Two stroke has fewer moving parts which makes its construction easy.

—  Two stroke is much lighter , louder, and pollutant.

 FOUR STROKE ENGINE ;

—   A four stroke has one compression stroke and one exhaust stroke followed by a return stroke.

—  A four stroke will get a better mileage because of its combustion process.

—  It produces less power then two stroke engine.

—  A four stroke produces a power stroke every other revolution of the crank shaft.

—  A four stroke has many parts which makes its construction complex.

—  A four stroke engine creates less noise and pollution then a two stroke.

—  In a four stroke engine the piston moves 720 degrees