In this stroke the piston moves down into the cylinder. The inlet valve is open and air is sucked in by the negative pressure that occurs in the cylinder. In the inlet, can also be called intake stroke, duct is an injection valve which injects petrol at a specific time and mixes with the air. The outlet valve is closed. If the engine is so-called direct injection, only air is sucked in and the fuel is injected directly into the combustion chamber at the time that is considered optimal. If the engine is so-called supercharged using an exhaust compressor, turbo, or mechanical compressor driven by some kind of belt or chain, the mixture is pressed in using the overpressure created by it.