Two-Stroke Engines – Number of Crankshaft Revolutions per Working Cycle Evaluate the statement: “In a two-stroke engine, the working cycle is completed in two revolutions of the crankshaft.”

Introduction / Context:
The term “working cycle” in reciprocating engines refers to the sequence of events comprising intake, compression, combustion/expansion (power), and exhaust. Whether this requires one or two crankshaft revolutions distinguishes two-stroke from four-stroke engines and directly affects specific power and scavenging strategy.

Given Data / Assumptions:

• A conventional crankcase- or externally-scavenged two-stroke engine.
• Ports and/or valves time gas exchange within one revolution.
• Combustion occurs once per revolution for each cylinder in a two-stroke engine.

Concept / Approach:

In two-stroke operation, every revolution produces one power event (one expansion stroke), because intake and exhaust are combined with compression and power within a single crankshaft revolution, using ports and/or a blower to accomplish scavenging. In contrast, a four-stroke engine requires two revolutions for one power stroke.

Step-by-Step Solution:

Verification / Alternative check:

Timing diagrams show intake and exhaust port events near BDC within the same revolution; firing frequency equals engine speed (one firing per revolution per cylinder).

Why Other Options Are Wrong:

Conditions such as opposed-piston geometry, low speed, or supercharging do not change the fundamental one-revolution cycle property of two-stroke engines.

Common Pitfalls:

Confusing “cycle” with “number of strokes” and assuming two strokes must equal two revolutions; each revolution has two strokes (up and down), so a two-stroke cycle is indeed one crank revolution.

Final Answer:

Incorrect