Four-stroke engine cycle — firing frequency In a four-cylinder inline, four-stroke engine, how many firing (power) strokes occur during one revolution of the crankshaft?

Introduction / Context:
Understanding the relationship between cylinder count and firing frequency helps diagnose vibration, misfire patterns, and gearbox input torque pulsations. In a four-stroke engine, each cylinder completes the full cycle (intake, compression, power, exhaust) over two crankshaft revolutions.

Given Data / Assumptions:

• Four-stroke operating principle: one power stroke per cylinder every 2 revolutions.
• Four cylinders in-line, evenly phased for smoothness.
• Constant speed steady operation without misfire.

Concept / Approach:
Number of power strokes per revolution equals total cylinders divided by 2 (for four-stroke engines). For a 4-cylinder: 4 / 2 = 2 power strokes per single crank revolution, evenly spaced.

Step-by-Step Solution:
Each cylinder fires once every 720 degrees of crank rotation.During 360 degrees (one revolution), only half of the cylinders fire.With 4 cylinders, half is 2; hence 2 firing strokes per revolution.

Verification / Alternative check:
Typical firing orders (e.g., 1-3-4-2) show two firings per revolution when plotted over 720 degrees; strobing at the crank confirms 2 pulses per rev at the flywheel.

Why Other Options Are Wrong:
1 and 3 do not match the 4/2 rule.

4 would imply every cylinder fires each revolution, which is two-stroke behavior.

0 is incorrect because in any given single revolution there are indeed power events.

Common Pitfalls:
Confusing two-stroke and four-stroke firing frequencies; overlooking that multi-cylinder phasing spreads torque pulses to reduce vibration.

Final Answer:
2