Engine Cycles — Where Are Ports Used Instead of Poppet Valves? Identify the engine type that typically uses inlet and exhaust ports rather than mechanically actuated valves.

Introduction / Context:
Gas exchange in engines can be managed by cam-operated poppet valves or by timing the piston’s uncovering of ports in the cylinder wall. Recognizing which cycle relies on ports is a basic engine design concept.

Given Data / Assumptions:

• Conventional piston engines considered.
• Focus on typical automotive and small engine practices.
• Special exceptions (e.g., sleeve valves) are out of scope.

Concept / Approach:
Two-stroke engines commonly employ scavenging and exhaust via ports cut in the cylinder wall. As the piston moves, it sequentially uncovers and covers transfer and exhaust ports, controlling flow without a valve train. Four-stroke engines almost universally use poppet valves operated by a camshaft to control intake and exhaust events every other revolution.

Step-by-Step Solution:
Identify engine cycle: two-stroke completes a power cycle every crank revolution.Note gas exchange: piston-controlled ports instead of valve gear.Therefore, the correct choice is the two-stroke engine.

Verification / Alternative check:
Common two-stroke small engines (mopeds, chainsaws) use ported cylinders with crankcase compression or external blowers.

Why Other Options Are Wrong:
Four-stroke engines rely on valves and a camshaft.“V-6” describes configuration, not cycle; many V-6 engines are four-stroke with valves.“None of these” is incorrect given the two-stroke option.

Common Pitfalls:
Assuming all engines use poppet valves; port-timed two-strokes are prevalent in small power applications.

Final Answer:
Two-stroke internal-combustion engines