1. High Pressure and Temperature: As the piston moves upward during the compression stroke, the air inside the cylinder is compressed, causing a significant increase in pressure and temperature. The pressure can reach several hundred atmospheres, while the temperature can rise well above the autoignition temperature of the fuel.
2. Fuel Injection: Just before the piston reaches the top of the compression stroke, a precise amount of diesel fuel is injected directly into the highly compressed and heated air within the cylinder. This is achieved using a high-pressure fuel injector.
3. Atomization and Vaporization: The fuel droplets injected into the cylinder undergo rapid atomization, meaning they break down into smaller droplets. These droplets quickly vaporize due to the high temperature and pressure inside the cylinder.
4. Autoignition: The combination of high pressure, high temperature, and vaporized fuel creates ideal conditions for autoignition, also known as spontaneous combustion. A small portion of the fuel reaches its autoignition temperature and ignites, initiating the combustion process. This process is different from spark-ignition engines, which rely on an electrical spark to ignite the fuel-air mixture.
5. Rapid Pressure Rise: The ignition of the fuel causes a rapid increase in pressure within the cylinder, known as the pressure rise. This pressure rise generates the force that drives the piston downward during the power stroke.
The precise timing of fuel injection and the control of pressure and temperature are crucial factors in achieving efficient and smooth operation of a compression ignition engine. These processes allow the engine to convert the chemical energy stored in the diesel fuel into mechanical energy that powers the vehicle or machinery.
