Abstract
To analyze the coupling characteristics of system-level fuel supply and injection and the mechanism of multi-frequency pressure fluctuations affecting system stability, a prediction model of the high-pressure common rail system was established. The effects of common rail pressure, control pulse width and engine speed on pressure fluctuations were analyzed. Simultaneously, the influence of different hydraulic components such as pumps, rails, and injectors on pressure fluctuations was analyzed by employing hydraulic decoupling method. The influence of pressure fluctuations caused by fuel supply characteristics of pump, filtering effect of rail and fuel injection characteristics of injector on the entire system was studied. The result demonstrates that adjusting target rail pressure and control pulse width alters the fuel supply ability and fuel injection level respectively. During the fluctuation process, the pressure fluctuation overshoot is about 7.7%, and the steady state fluctuation is about ± 1.5%. The adjustment of engine speed influences the overall trend of pressure fluctuations apparently. Additionally, the pressure fluctuations in the system are mainly induced by the coupling of high and low frequency pressure waves. Among them, low-frequency fluctuations everywhere are highly consistent, whereas high-frequency fluctuations are affected significantly by working properties of hydraulic components. Through decoupling analysis, it is illustrated that the fuel pump fluctuations affect the entire fluctuation trend to a great extent. The volume of common rail pipe has an effect on the fluctuation degree and filtering capability. The transient motions of fuel inlet valve, fuel delivery valve and needle valve are the main source of high-frequency fluctuations.
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