In a two-stroke petrol engine, the primary function of the crankcase is to:

Explanation:

Crankcase in a Two-Stroke Petrol Engine:

• In a two-stroke petrol engine, the crankcase serves a critical function in the engine's operation. Unlike in four-stroke engines, where the crankcase primarily stores lubricating oil, in two-stroke engines, it plays a more active role in the engine's air-fuel mixture management.
• In a two-stroke engine, the engine completes a power cycle in two strokes of the piston (one revolution of the crankshaft). The crankcase in such an engine is used as a primary pumping chamber for the air-fuel mixture. This process is facilitated through the movement of the piston, which helps to draw the mixture into the crankcase and then transfer it to the combustion chamber.

In a two-stroke engine, the cycle is divided into two strokes: the compression stroke and the power stroke. During these strokes, the crankcase is used to manage the air-fuel mixture, which is crucial for the engine's operation. The following steps outline the process:

• As the piston moves upwards during the compression stroke, it creates a vacuum in the crankcase. This vacuum helps to draw the air-fuel mixture from the carburetor into the crankcase through the intake port.
• When the piston reaches the top of the compression stroke, the air-fuel mixture in the combustion chamber is compressed and ignited by the spark plug, causing a rapid expansion of gases and forcing the piston downwards during the power stroke.
• As the piston moves downwards, it compresses the air-fuel mixture in the crankcase, which is now ready to be transferred to the combustion chamber. This mixture is pushed through the transfer port into the combustion chamber as the piston uncovers the port towards the end of the power stroke.