Working of 2 stroke engine

Before starting 2 stroke engine let us discuss what is a stroke. A stroke is a reciprocating motion. It can be either upward and downward and hence a reciprocating cycle consist of two opposite motion.

2 Stroke Engine is a type of internal combustion engine which attain power stroke after every one crank rotation i.e when the piston complete 2 separate upward and downward stroke.

   

Main components of 2 stroke engine :-

1. Crank case - It act as outer cover for engine i.e protect it from external damage and crank shaft is present inside this.
2. Crank shaft - It convert reciprocating motion into rotatory motion and transfer rotary motion to flywheel.
3. Crank - It helps to turn the crankshaft.
4. Connecting rod - It connect piston and crank shaft.
5. Gudgeon pin - It connect piston with connecting rod.
6. Piston - It reciprocates inside cylinder  and the reciprocating motion is further transferred to crank shaft.
7. Cylinder - In this part of engine the combustion takes place.
8. Transfer port - This transfer the fresh air into cylinder.
9. Inlet port - From this port fresh air enters into crank case.
10. Exhaust port - The burnt gases get removed from this port.
11. Spark plug/Injectors - This is used to ignite the combustion process inside cylinder.

Working of 2 stroke engine :-

2 Stroke Engine (working)

First of all the fresh air fuel mixture from the carburetor is transferred to inlet port of engine (blue air in diagram). During this process the piston is approaching downward (BDC) . This slightly compress the air fuel mixture and when the piston is  at downward position it opens the transfer port which transfer the fuel mixture to the combustion chamber. Now the piston start moving upward and compress the air fuel mixture. When the piston is at upward position (TDC) the spark plug ignites the compressed air fuel mixture and combustion take place. Due to sudden rise in pressure the piston is forced downward and again the fresh air fuel mixture get enter inside combustion chamber. Due to pressure difference of fresh and burnt mixture (exhaust gases, grey air in diagram) the fresh mixture push the exhaust gases outside the combustion chamber through exhaust port and the cycles repeats.

Whats is scavenging in 2 stroke engine?

The process of removal of exhaust gases from the combustion chamber is known as scavenging.

Basically scavenging is of 3 types :-

1. Cross flow :- It take place with the help of movement of piston. The piston is designed so that it pushes the exhaust gases out from the exhaust port.

Cross flow scavenging

2. Loop scavenging :- It is similar to cross flow scavenging but the inlet and exhaust ports are on the same side of engine.

Loop flow scavenging

3. Uni-flow scavenging :- In this type of scavenging the both inlet and outlet ports are same which is generally on the top of the engine.

Uni-flow scavenging 

Advantages of 2 Stroke engine :-

• It develops more power as compare to 4 stroke engine.
• It needs a small and light flywheel.
• Its construction is simple.
• It is light weight.
• Very less cost of maintenance.

Disadvantages of 2 Stroke engine :-

• Fresh mixture get wasted in exhaust stroke.
• Less efficiency.
• Produces harmful gases.
• Required more lubrication.

Uses of 2 strokes engine :-

• Scooters
• Bikes
• Ships
• Go kart
• Jet ski
• Snowmobiles