Differences Between Unit Pump and High-Pressure Common Rail
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Unit pump is a device that generates the injection pressure for the fuel injector (or nozzle). For engines equipped with a unit pump electronic fuel injection system, each cylinder has multiple unit pumps. The unit pump represents the second generation of electronic fuel injection systems. Depending on the high-pressure generating mechanism, fuel injection systems can be categorized into distributor pumps, inline pumps, nozzle systems, and unit pump electronic fuel injection systems. High-pressure common rail electronic injection technology is a fuel supply method where the generation of injection pressure and the injection process are completely separated within a closed-loop system consisting of a high-pressure fuel pump, pressure sensor, and electronic control unit (ECU). It utilizes the high-pressure fuel pump to deliver fuel to the common rail, achieving precise control through the fuel pressure in the common rail. This ensures that the pressure in the high-pressure fuel line is independent of engine speed, significantly reducing the variation in diesel engine fuel supply pressure with engine speed. Unit pump engines require minimal modifications, with only some adjustments made to the fuel system. Additionally, unit pumps exhibit much better tolerance to fuel quality compared to common rail systems. Due to the continued use of the former Soviet Union's oil refining model, Chinese diesel not only has high impurity levels but also contains elevated sulfur content. The advantages of unit pump systems in terms of cost and performance are particularly prominent in heavy-duty vehicles. It is recommended that customers opt for unit pump systems. From a cost perspective, upgrading domestic engines from Euro II to Euro III with unit pumps involves minimal changes to the engine. Moreover, the application of a dual-valve system allows achieving Euro IV emission levels without major adjustments to the overall engine structure. In terms of performance, the unit pumps currently used in China can achieve pressures of up to 2480 bar. When upgraded to Euro IV and Euro V standards in dual-valve systems, this pressure can reach 2580 bar.
