Study of the Impact on the Spray Shape Stability and the Combustion Process of Supply Pressure Fluctuations in CR-Diesel Injectors

The paper presents a study of the influence of fuel pressure supply fluctuations on the upstream side of the fuel injector atomizer. The study is performed over a wide range of pressures (70 to 130 Mpa) with two different common-rail (CR) high-pressure fuel injectors. The common atomizer is a VCO-type equipped with conically shaped atomizer bores.

With the injector tip (nozzle) mounted in a counter-pressure vessel the pressure fluctuations in the fuel-rail and in the injector body are recorded simultaneously with stroboscopic Schlieren-visualization of the time-resolved spray behavior. It is demonstrated that not only the instantaneous mass flow is affected. As a function of rail-pressure, pulse-width and injection strategy the pressure fluctuations change the spray hard-core structure and its break-up behavior.

In order to quantify the impact on the combustion process the spray behavior visualizations in the pressure vessel are completed with analytical considerations of the spatial and temporal spray behavior obtained by the use of the 3D-numerical simulation code NCF-3D. The predicted combustion data for the different injectors are correlated to measured data from a 1.3-liter turbo-charged passenger car diesel engine.