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Electronic Unit Pump VS Common Rail Pump
With emission standard increased from EURO II to EURO III,unit pump and common rail pump is two main technology route,both of which realize the high efficiency of combustion through electrical control injection.Compared common rail system developed by top manufacturer like BOSCH,the unit pump lack of capital investment and research.Today we will compare them and you might find the difference and reasons.
high pressure pump
1.Control of injection pressure
The injection pressure of the electric unit pump is realized through the design of the pump CAM profile and is related to the bore diameter of the injector and the speed of the engine.That is, the smaller the nozzle bore diameter, the higher the maximum injection pressure.The lower the engine speed, the lower the injection pressure.The system is currently capable of achieving a maximum injection pressure of 180MPa.
The injection pressure of the common rail system can be completely independent of the engine speed which can improve the low speed performance of the engine.It is adjusted by the electro magnetic valve on the high-pressure pump, and flexibly controlled by the related MAP. Meanwhile, the injection pressure is also independent of the nozzle bore diameter.At present, the system can achieve a maximum injection pressure of 160MPa.
Therefore, in terms of fuel injection pressure control, the common rail system is superior to the electronic unit pump.It is more beneficial to meet stricter emission.
unit pump
2.Control amount of fuel injection
Both of them can achieve the flexible and accurate adjustment of the fuel injection quantity in each engine working condition.
The minimum amount of fuel injection achieved by the electronic unit pump is 3mm3/st, but the pre-injection cannot be achieved.
While the minimum amount of fuel injection that the common rail system can achieve is 2mm3/st, and the pre-injection and post-injection can be realized.The pre-injection can facilitate cold start and reduce noise.Post-injection, then, can be applied to post-treatment, providing a technical reserve to meet future stricter emission regulations such as euro IV.
3.Injection timing 
Both the unit pump and the common rail system can flexibly adjust the fuel injection timing according to the needs of the engine in each working condition, which is very beneficial to adjust and improve the fuel consumption, NOX and smoke of the engine.
4.Fuel-injection laws 
The injection law of the electronic unit pump is the same as that of the mechanical in-line pump which is beneficial for reducing NOX.
The fuel injection law of the common rail system is rectangular, with high explosion pressure and rough combustion, which is not conducive to reducing NOX.
Therefore, the injection law of the EUP is better than the common rail system.
5.Quick oil cutting capability
The electric unit pump relies on the needle valve spring of the injector to cut off oil. Because of the long high-pressure pipe from the high-pressure pump to the injector, the pressure wave of the high-pressure oil pipe will affect the quick oil cutting of the injector, which is adverse to the fuel consumption and smoke of the engine.
The common rail system controls the fuel pressure difference between the upper and lower cavity of the injector plunger through the electro magnetic valve, and the combined action of the needle valve spring makes the oil break quickly after the injector is finished, which is beneficial to the improvement of particle emission and smoke.
6.The absorption power of the pump
One injector for each unit pump and six unit pump are integrated by a pump their volume is larger, the drive mechanism is bulky, and the pump has higher absorption power.
HP0 high pressure pump of common rail system is driven by two triangular CAM, each CAM has three protrusions, compact structure, light weight, easy to install, and low absorption power of oil pump.
7.Fuel cleanliness requirements
The requirement of electric unit pump for fuel cleanliness is low, and the filter precision of fuel is equal to that of mechanical in-line pump.
The common rail system has higher requirements on fuel quality, and the filter accuracy of fuel is required to reach 5u, which is much higher than that of mechanical in-line pumps.Impurities in the fuel system can easily cause the common rail system to fail.
8.Localization level
The high pressure pump, electro magnetic valve, injector or ECU from unit pump can be fully produced with low price in China.
There are still some key components of common rail system need to be imported at high cost from overseas.Fortunately those components like CB18 pumps,common rail injectors,nozzle and valve sets can be supplied in genuine BASCOLIN in China with competitive price and outstanding performance.It has become the choice of most importers and manufacturers at home and abroad.