FAA Powerplant Written Practice Test

What happens to the position of the intake and exhaust valves during the intake stroke?

1. Both valves close

2. Both valves remain open

3. The intake valve opens and the exhaust valve closes

4. The exhaust valve opens and the intake valve closes

The correct answer is: The intake valve opens and the exhaust valve closes

During the intake stroke of a four-stroke engine cycle, the piston moves down the cylinder, creating a vacuum that draws air-fuel mixture into the combustion chamber. For this process to occur effectively, the intake valve must be open to allow the air-fuel mixture to enter, while the exhaust valve must be closed to prevent the mixture from escaping. The correct answer indicates that the intake valve opens at this time, facilitating the entry of the air-fuel mixture, while the exhaust valve remains closed to ensure that all the newly drawn in mixture is contained in the combustion chamber, allowing for the subsequent compression stroke to follow. This sequence is crucial for proper engine operation and efficiency, ensuring that the combustion process can occur without any loss of the critical air-fuel mixture. Understanding the positions of the valves during each stroke is essential for maintaining engine timing and function, which is why this answer is accurate in the context of the functioning of an engine during the intake stroke.