At what point does the fuel mix with the air in a fuel injection engine?

• A. At the inlet port to the cylinder
• B. In the intake manifold
• C. At the throttle plate
• D. In the fuel rail

Answer: (A)

In port fuel injection, the fuel is sprayed into the intake port just ahead of the cylinder intake valve. As the incoming air rushes in, it atomizes and carries the fuel with it, so the air–fuel mixture forms in the intake port (and the runners) before the mixture enters the combustion chamber. This arrangement allows precise metering, good atomization, and consistent charging of the cylinder, which improves combustion control. The fuel rail simply stores and feeds pressurized fuel; the throttle plate controls air flow, not mixing. Mixing here, right at the inlet port to the cylinder, is why this option is the best choice.