Four-stroke engine kinematics — number of crankshaft revolutions per cycle: In a four-stroke internal combustion engine, the working cycle (intake, compression, power, and exhaust) is completed in how many revolutions of the crankshaft?

Introduction / Context:Understanding engine timing is fundamental for diagnostics, valve train design, and ignition scheduling. A four-stroke engine performs distinct piston strokes that together constitute one thermodynamic cycle with specific mechanical timing between the crankshaft and camshaft.

Given Data / Assumptions:

• Four strokes: intake (suction), compression, power (expansion), exhaust.
• One up-and-down piston movement equals two strokes (down + up).
• Camshaft typically rotates at half crankshaft speed to synchronize valve events with the four-stroke sequence.

Concept / Approach:Each piston stroke corresponds to 180 degrees of crankshaft rotation. Four strokes therefore require 4 * 180 degrees = 720 degrees, or two full revolutions of the crankshaft, to complete one cycle and deliver a single power stroke per cylinder per cycle.

Step-by-Step Solution:

Verification / Alternative check:Camshaft-to-crankshaft gear ratio of 1:2 in four-stroke engines corroborates the two-revolution-per-cycle fact, ensuring valve events occur once every two crank revolutions for each cylinder.

Why Other Options Are Wrong:

• One revolution: corresponds to two-stroke operation, not four-stroke.
• Three or four revolutions: would misalign valve and ignition timing and are inconsistent with standard four-stroke kinematics.

Common Pitfalls:Confusing firing frequency across multiple cylinders with per-cylinder cycle frequency; multi-cylinder engines achieve more frequent overall power strokes but each cylinder still completes one cycle in two revolutions.

Final Answer:two revolutions of the crankshaft