A STUDY OF FUEL TEMPERATURE DYNAMIC CHARACTERISTICS FOR DIESEL ENGINE COMBINATION ELECTRONIC UNIT PUMP SYSTEM

The combination electronic unit pump (CEUP) is a type of electronic unit pump fuel injection system specially designed for meeting the requirements on emission and fuel efficiency of diesel engines. It is a fairly complex product which is assembled together by mechanical, hydraulic and electrical magnetic systems. The fuel temperature dynamic characteristics of CEUP which reflects heat load characteristics of the whole system are investigated both by bench test in the laboratory and numerical simulations. The research on dynamic characteristics of high-pressure fuel injection temperature (FIT) reveals the effects of fuel tank temperature and injection pulse width on FIT. The results show that FIT goes up with the increase of fuel injection pulse width when the cam rotational speed is kept constant. A maximum FIT of 118 degrees C is recorded at 10 degrees CaA pulse width, 1400 rpm cam rotational speed and 50 degrees C fuel tank temperature. It is concluded from research that increasing the pulse width by 4-6 degrees CaA and 6-10 degrees CaA results in FIT variation rate of 0-4 degrees C/degrees CaA and 4-5 degrees C/degrees CaA respectively. The research on the low-pressure fuel supply temperature (FST) dynamic characteristic illustrates that the increase of FST in low-pressure system is the result of thermal transmittance of the fuel flowing back from the high-pressure system to the low-pressure system after the end of fuel injection. Moreover, FST in the low-pressure system tends to climb up with the increase of cam rotational speed and injection pulse width. In addition, the deviation between entrance fuel temperature and exit fuel temperature in low-pressure system ranges between -0.7 degrees C and 3.4 degrees C, and the same tendency has been observed when the numbers of unit pumps in CEUP are increased. It is also concluded that the variation of FST in high/low pressure system is due to the transient coupling process of the fuel.