Which statement best defines a four-stroke internal combustion engine?

Which statement best defines a four-stroke internal combustion engine?

• A. It completes four strokes per operating cycle, corresponding to intake, compression, power, and exhaust.
• B. It uses a two-stroke cycle with a single piston.
• C. It uses external combustion.
• D. It does not involve any piston movement.

Answer: (A)

Four-stroke operation means the engine completes four distinct piston actions in one operating cycle: intake, compression, power, and exhaust. During intake, the piston moves down to draw in air and fuel. During compression, it moves up to squeeze that mixture. In the power stroke, ignition occurs and the burning mixture pushes the piston downward, delivering work to the crankshaft. Finally, during exhaust, the piston moves up again to push out the burnt gases. This sequence typically requires two revolutions of the crankshaft. The statement is the best answer because it precisely describes these four strokes and their order, which defines a four-stroke internal combustion engine. It’s internal combustion because the fuel burns inside the cylinder to create the power. In contrast, a two-stroke cycle completes the cycle in only two strokes, external combustion engines burn fuel outside the cylinder, and engines with no piston movement don’t fit how a four-stroke engine actually converts combustion into useful work.

Four-stroke operation means the engine completes four distinct piston actions in one operating cycle: intake, compression, power, and exhaust. During intake, the piston moves down to draw in air and fuel. During compression, it moves up to squeeze that mixture. In the power stroke, ignition occurs and the burning mixture pushes the piston downward, delivering work to the crankshaft. Finally, during exhaust, the piston moves up again to push out the burnt gases. This sequence typically requires two revolutions of the crankshaft.

The statement is the best answer because it precisely describes these four strokes and their order, which defines a four-stroke internal combustion engine. It’s internal combustion because the fuel burns inside the cylinder to create the power. In contrast, a two-stroke cycle completes the cycle in only two strokes, external combustion engines burn fuel outside the cylinder, and engines with no piston movement don’t fit how a four-stroke engine actually converts combustion into useful work.