Which statement best defines the engine cycle?

• A. A random sequence of events.
• B. A series of events repeated regularly and constituting the principle of operation.
• C. A single event of operation.
• D. Only applicable to gasoline engines.

Answer: (B)

The engine cycle is the sequence of events that happen in a specific order during each operation of the engine, and this sequence repeats regularly to produce power. This repeating order—such as intake, compression, combustion/expansion, and exhaust in a typical piston engine (and the analogous steps in turbines for different cycles)—is what defines how the engine operates. Because the processes must occur in a precise order and repeat with each cycle to convert chemical energy into mechanical work, describing it as a series of events that repeats regularly and constitutes the engine’s operating principle is the most accurate explanation. It’s not a random sequence, not just a single event, and it applies beyond just gasoline engines (diesel and turbine engines rely on their own cycles but still operate via a defined cycle).