In a two-stroke petrol engine, which of the following best describes the sequence of events during an exhaust stroke?

Explanation:

In a two-stroke petrol engine, the exhaust and transfer ports play a crucial role in completing the cycle efficiently. Here’s the sequence during the exhaust stroke (which in a two-stroke engine coincides with the second half of the power stroke):

Exhaust Port Opens First:

• As the piston moves downward after the combustion, it first uncovers the exhaust port. This allows the high-pressure burnt gases to escape from the combustion chamber to the exhaust system. This early opening helps reduce the pressure inside the cylinder.

Transfer Port Opens Later:

• As the piston continues to move down, it then uncovers the transfer port. At this point, the fresh charge (air-fuel mixture) enters the cylinder from the crankcase. This process is called scavenging, and it helps push out the remaining exhaust gases while filling the cylinder with a fresh charge.

This sequential timing ensures that the combustion chamber is properly cleared of exhaust gases before the fresh charge enters, thus avoiding excessive mixing and improving engine efficiency.