Which of the following are cycles of the four-stroke engine?

The correct answer is based on the operational stages of a four-stroke engine, which are sequentially designed to efficiently convert fuel into mechanical energy. In a four-stroke engine, the cycle consists of four distinct phases: intake, compression, expansion, and exhaust.

During the intake phase, the engine draws in a mixture of air and fuel. Next, in the compression phase, this mixture is compressed to increase its temperature and pressure, which prepares it for ignition. Following this, the expansion phase occurs, where the compressed fuel-air mixture is ignited, causing a rapid expansion of gases that pushes the piston down, creating work. Finally, in the exhaust phase, the spent gases are expelled from the cylinder, making way for fresh air-fuel mixture to enter for the next cycle.

The other options do not accurately represent the defined cycles of a four-stroke engine. For instance, the inclusion of "Reaction" or "Cooling" phases in option A does not belong to the standard nomenclature of the four-stroke cycle. Option C introduces "Ignition" as a cycle, which is part of the compression phase rather than a separate cycle. Similarly, option D mentions "Combustion" and "Cooling," which describe processes but do not