In 1892, German engineer Rudolf Diesel invented the world’s first diesel engine and named the diesel engine after his Diesel. We all know that many characteristics of diesel are different from gasoline, such as viscosity (including dynamic viscosity, kinematic viscosity, and conditional viscosity). Intuitively, diesel is more viscous than gasoline; Compression ignition is used. These characteristics of diesel are destined to use high pressure to make it emit its due energy, so early diesel engines used high pressure gas cylinders to provide a certain pressure for the fuel supply system.
More than 30 years after that, the research of mechanical fuel pump was transformed into manufacturing, and gradually, the huge cylinder became history.
The traditional diesel injection system using a mechanical fuel pump is driven by a camshaft. The fuel injection pressure increases with the increase of the engine speed and the fuel injection quantity. This diesel system has problems such as unstable atomization effects, and difficult cold starts At the same time, it has been unable to meet the increasingly stringent emission standards and the desire to reduce fuel consumption.
A diesel supply technology that has been constrained by precision electronic control for decades. With the rapid development of electronic technology in the 1980s and 1990s, it has finally been completely applied to automotive diesel engines. This technology is an electronically controlled diesel high-pressure common rail system. It has higher fuel injection pressure, better atomization effect, lower fuel consumption and cleaner emissions.
What is a high pressure common rail system
The high-pressure common rail system refers to a fuel supply method that completely separates the generation of injection pressure and the injection process from each other in a closed-loop system composed of a high-pressure oil pump, a pressure sensor, and an electronic control unit (ECU). Diesel injection systems are completely different. It is a high-pressure fuel pump that delivers high-pressure fuel to the fuel rail. The oil pressure in the fuel rail is used to achieve precise control. The pressure of the high-pressure fuel pipe is independent of the engine speed.
Composition of high-pressure common rail system
The diesel high-pressure common rail injection system consists of a hydraulic system and an electronic control system. The hydraulic system is divided into a low-pressure hydraulic system and a high-pressure hydraulic system. Low-pressure hydraulic system includes fuel tank, fuel pump, fuel filter, and low-pressure oil pipe; high-pressure hydraulic system includes high-pressure pump, high-pressure rail, injector, and high-pressure oil pipe; Electronic Diesel Control (EDC) includes sensors , Electronic Control Unit (ECU), actuator (including fuel injector with solenoid valve, pressure control valve, glow plug control unit, boost pressure regulator, exhaust gas circulation regulator, throttle valve, etc. ) , and harness.
Among them, the injector, high-pressure pump, high-pressure oil rail, and electronic control unit are the four core components of the diesel common rail system.
An injector is a component that atomizes fuel and distributes it in the combustion chamber of an engine. The injection time and duration of the common rail injector are accurately calculated by the electronic control unit to give a signal, and then controlled by a solenoid valve.
The role of the high pressure pump is to compress the fuel from a low pressure state to a high pressure state through a plunger to meet the system and engine requirements for fuel injection pressure and fuel injection.
The role of the high-pressure fuel rail is to store fuel, while suppressing pressure fluctuations due to high-pressure pump oil supply and fuel injection from the injector, ensuring stable system pressure. The high-pressure oil rail is commonly owned by each cylinder, and it is the symbol of the common rail system.
The electronic control unit is like the brain of the engine. It collects the operating conditions of the engine, calculates them in combination with the stored characteristic map, and transmits the signals to the actuator to realize the functions of engine operation control and fault diagnosis.
Working principle of high pressure common rail system
The electronic control unit accurately calculates the current fuel injection amount based on various real-time parameters (vehicle speed, throttle opening, crankshaft speed, camshaft speed, rail pressure, etc.) (the amount of fuel injection depends on the rail pressure and The length of the solenoid valve opening time), and then control the opening and closing of the solenoid valve as an actuator, diesel is injected into the cylinder to achieve the best combustion under the current operating conditions.
The high-pressure common rail system enables stronger power, lower fuel consumption and cleaner emissions.
Talk about high pressure oil rails
The high-pressure fuel rail distributes the high-pressure fuel provided by the fuel supply pump to each injector, and functions as a pressure accumulator. Its volume should reduce the supply pressure fluctuation of the high-pressure oil pump and the pressure shock caused by the fuel injection process of each injector to control the pressure fluctuation in the high-pressure oil rail below 5MPa. However, its volume should not be too large to ensure that the common rail has sufficient pressure response speed to quickly track changes in diesel engine operating conditions.
Pressure sensors, fluid buffers (restrictors) and pressure limiters are also installed on the high-pressure rail. The pressure sensor provides the ECU with the pressure signal of the high-pressure fuel rail; the fluid flow buffer ensures that the fuel supply to the fuel injector is cut off when a fuel leak occurs in the fuel injector, and can reduce the pressure fluctuation in the common rail and the high-pressure fuel pipe; The limiter ensures that the pressure in the high-pressure rail is quickly released when the pressure of the high-pressure rail is abnormal.
Summary: The purpose of electronic control of high-pressure common rail diesel in diesel engines is to improve the fuel economy and emissions of diesel engines. At the same time, from the aspects of power performance, fuel consumption, and drivability, electronically controlled high-pressure common rail diesel systems are also increasing The more accepted by the market. Of course, in China, the use of diesel vehicles has been subject to many restrictions, for various reasons. I will not repeat them here, but I look forward to the day when technology and regulations will change all this. Thank you for your interest in testing with me!