The working principle of Cummins engines
The Cummins engine mainly adopts the four-stroke compression ignition working principle. Here is its core working process:
Intake Stroke
The piston moves downward, the intake valve opens, and the exhaust valve closes. Fresh air enters the cylinder through the pressurization system (such as exhaust turbocharging or pressurized intercooler technology), increasing the air density and providing sufficient oxygen for combustion.
Compression stroke
The intake valve closes, and the piston moves upward to compress the air in the cylinder, increasing the air pressure to 3000-5000 kPa and raising the temperature to 750-1000 K, far exceeding the auto-ignition temperature of diesel (about 520 K). The compression ratio of Cummins engines is usually 14.5-22, creating conditions for diesel ignition.
Power stroke
Near the end of the compression stroke, the high-pressure injector atomizes the diesel fuel and sprays it into the combustion chamber. The atomized diesel fuel mixes with the hot air and ignites spontaneously, generating explosive expansion force that pushes the piston downward. The piston’s movement is transmitted through the connecting rod to the crankshaft, thereby achieving power output. The combustion chamber typically adopts a direct injection “ω-shaped depression” design to optimize the efficiency of oil and air mixture.
Exhaust Stroke
The exhaust valve opens and the piston moves upward to expel the burned exhaust gas from the cylinder. The Cummins engine reduces pollutant emissions by controlling the exhaust temperature (700-900K) and employing modular after-treatment systems (such as SCR, DPF).
Furthermore, depending on the specific technology, Cummins engines may adopt either the PT fuel system or the electronically controlled high-pressure common rail fuel system:
PT fuel system: The fuel injection volume is controlled by pressure and time. The injector uses the pressure difference of high-pressure fuel to achieve precise fuel injection.
Electro-controlled high-pressure common rail system: The electronic control unit (ECU) adjusts the fuel injection volume, injection time and injection pressure in real time based on sensor data, achieving more precise combustion control, improving fuel economy and emission performance.
