working principle of two stroke petrol engine in Telugu lecture

WORKING PRINCIPLE OF TWO STROKE PETROL ENGINE
UPWARD STROKE: During upward stroke of the piston partial vacuum is created in crank case (i.e., pressure in crank case is less than atmospheric pressure). Inlet port is uncovered by the piston and a mixture of air and petrol vapour from the carburetor is sucked into the crank case. For this reason, the crank case of two stroke engine is made gas tight. The upward stroke of the piston causes compression of the previously available charge inside the cylinder. Thus, during upward stroke suction and compression of the charge take place simultaneously, and both transfer and exhaust ports remain closed.
At the end of the compression stroke the charge is ignited by a high voltage electric spark plug. After the ignition of charge, hot high pressure gases expands.
DOWNWARD STROKE: During the down ward stroke the piston goes downwards and compresses the charge drawn in the crank case. At the end of expansion stroke exhaust port which is slightly higher level than the transfer port, opens releasing the burnt gases from the cylinder to the atmosphere. Immediately the piston uncovers the transfer port and fresh charge from the crankcase rushes into the cylinder. The shape of piston head helps in scavenging the burnt gases out of the cylinder and prevents the fresh charge from mixing with burnt gases going out directly through the exhaust port.