AG Mechanics CDE Practice Exam

On the __________ stroke of an engine, the piston is going down, one valve is open and the other valve is closed and air and fuel are being drawn into the cylinder.

1. compression

2. exhaust

3. intake

4. power

The correct answer is: compression

During the compression stroke of an engine, the piston moves upward, compressing the air-fuel mixture in the cylinder. This is where both valves are closed, allowing the mixture to be compressed before ignition. The intake stroke is when the piston moves downward, drawing in the air-fuel mixture through the open intake valve. The exhaust stroke occurs when the piston moves upward again, pushing the exhaust gases out through the open exhaust valve. The power stroke is when the compressed air-fuel mixture ignites, driving the piston down with force. Therefore, the correct answer is the compression stroke because it is the only option that matches the description given in the question.