During the intake stroke of a four-stroke engine, what occurs?

• A. The piston compresses the air-fuel mixture.
• B. The piston draws in air-fuel mixture.
• C. The piston burns the air-fuel mixture.
• D. The exhaust gases exit the cylinder.

Answer: (B)

During the intake stroke, the piston moves downward inside the cylinder while the intake valve is open and the exhaust valve remains closed. This downward motion creates a partial vacuum, so the air-fuel mixture is drawn from the intake manifold into the cylinder. This fills the cylinder in preparation for the next step, where the mixture is compressed and then ignited to produce power. The other strokes describe different events: compressing the mixture occurs in the compression stroke, burning (combustion) happens during the power stroke, and exhaust gases exit the cylinder in the exhaust stroke.