The piston now moves upwards in the cylinder. The inlet valve is closed and the outlet valve remains closed even during this stroke. The air is now compressed, then the air also becomes warm from the high pressure. Just at the end of the compression stroke, the diesel is injected into the hot air and ignited by the high temperature. A Diesel engine always has the injection of diesel directly into the combustion chamber, never into the intake manifold as on most gasoline engines. During cold starts, the air must be heated, a so-called glow plug sits inside the combustion chamber, which then heats the air to the temperature required for the diesel to ignite.