In a four-stroke internal combustion engine, what is the purpose of the intake stroke?

In a four-stroke internal combustion engine, what is the purpose of the intake stroke?

• A. Power the piston
• B. Compress the air
• C. Exhaust waste gases
• D. Draw in air-fuel mixture

Answer: (D)

The intake stroke’s purpose is to admit the charge into the cylinder. As the piston moves down and the intake valve opens, the rising volume creates a low pressure that draws in air—and, in most engines, fuel is mixed with that air in the intake tract to form the air-fuel mixture. This filling sets up the next step, compression, where the mixture is pressed for efficient combustion. The other strokes have different roles: compression strengthens and heats the mixture, the power stroke uses the combustion to push the piston, and the exhaust stroke expels burnt gases. So drawing in the air-fuel mixture is what the intake stroke accomplishes.

The intake stroke’s purpose is to admit the charge into the cylinder. As the piston moves down and the intake valve opens, the rising volume creates a low pressure that draws in air—and, in most engines, fuel is mixed with that air in the intake tract to form the air-fuel mixture. This filling sets up the next step, compression, where the mixture is pressed for efficient combustion. The other strokes have different roles: compression strengthens and heats the mixture, the power stroke uses the combustion to push the piston, and the exhaust stroke expels burnt gases. So drawing in the air-fuel mixture is what the intake stroke accomplishes.