When does valve overlap occur in the operation of an aircraft reciprocating engine?

Valve overlap occurs at the end of the exhaust stroke and the beginning of the intake stroke in an aircraft reciprocating engine. This phenomenon is designed to improve engine efficiency and performance by allowing the exhaust gases to exit the cylinder while simultaneously starting to draw in the fresh intake charge.

During this overlap period, both the exhaust valve and the intake valve are open at the same time. This strategic timing ensures that the exiting exhaust gases can help draw in more air-fuel mixture into the combustion chamber, which enhances the scavenging effect. This not only helps clear out the spent exhaust gases but also prepares the cylinder for the next power cycle, ultimately contributing to better fuel combustion and engine performance.

The timing and duration of valve overlap are critical for optimizing engine power and can vary depending on the specific design and intended operation of the engine. Proper understanding of this concept is essential for effective engine tuning and performance enhancement.