How does the injection system of a common rail diesel engine control the injection time and injection quantity?

The common rail diesel injection system is a key technology for modern diesel engines, which can accurately control the injection time and quantity, greatly improving engine performance and emission levels. It mainly achieves this precise control through a complex set of hardware and software working together.

From a hardware perspective, the common rail system mainly consists of high-pressure oil pumps, common rail pipes, fuel injectors, and various sensors. The high-pressure oil pump is responsible for pressurizing low-pressure diesel to extremely high pressure, usually up to 1600-2000 bar or even higher, and delivering high-pressure diesel to the common rail. The common rail serves as an accumulator, maintaining a stable pressure for high-pressure diesel fuel and providing a stable fuel source for each cylinder injection.

The fuel injector is a key executing component for achieving precise fuel injection. Each injector is equipped with a high-speed solenoid valve, and the opening and closing of the solenoid valve is precisely controlled by the engine electronic control unit (ECU). When the solenoid valve is opened, high-pressure diesel flows from the common rail into the fuel injector and is injected into the engine cylinder through the fuel injector.

In terms of fuel injection time control, the ECU accurately calculates the optimal fuel injection time under the current engine operating conditions based on feedback signals from the engine speed sensor, crankshaft position sensor, and camshaft position sensor. For example, when the engine starts, due to the low speed, an earlier injection time is required to ensure a smooth start; When driving at high speeds, the fuel injection time needs to be adjusted according to the engine load and speed to ensure power output and fuel economy. Once the injection timing is determined, the ECU will issue commands to the solenoid valve of the injector to control the opening timing of the solenoid valve, thereby achieving precise control of the injection timing.

In terms of fuel injection control, the ECU not only refers to the signals from the above-mentioned sensors, but also considers the information provided by the intake pressure sensor, air flow sensor, etc., to comprehensively calculate the fuel injection amount currently required by the engine. The size of the fuel injection quantity is mainly achieved by controlling the opening time of the solenoid valve. When the ECU determines that more fuel is needed, it will extend the opening time of the solenoid valve, allowing more high-pressure diesel to be injected into the cylinder; On the contrary, shorten the opening time of the solenoid valve and reduce the fuel injection quantity. At the same time, the precise design inside the fuel injector also ensures uniform and stable fuel injection at different injection durations, ensuring that the fuel is fully burned in the cylinder.

In summary, the common rail diesel injection system achieves precise control of injection time and quantity through precise hardware design and intelligent software control, providing strong guarantees for the efficient and clean operation of diesel engines.