What is sucked into the cylinder of the diesel engine during the intake stroke?

During the intake stroke of a diesel engine, air is drawn into the cylinder. This process is crucial because diesel engines operate on the principle of compression ignition, where only air is inhaled initially. The intake stroke creates a vacuum in the cylinder, allowing atmospheric air to fill the space.

In a diesel engine, once the air is compressed to a very high pressure and temperature, fuel is injected into the cylinder towards the end of the compression stroke. It ignites due to the heat of the compressed air, driving the engine cycle forward. This distinguishes diesel engines from gasoline engines, which draw in a mixture of air and fuel during the intake phase. Thus, the presence of only air being sucked into the cylinder during this stroke is fundamental to the operation of a diesel engine.