Simultaneous measurement and analysis of gas needle lift and injected rate for HPDI fuel injector

Abstract

Achieving a sufficient understanding of the transient fuel injection process is key to improving the efficiency of direct injection engines and reducing emissions. In this research, the momentum method and pressure–volume method are applied to measure the gas injected rate, the eddy current displacement sensor is installed underneath the open-type gas needle to measure the needle lift. The dynamic characteristic of the dual-fuel injector is studied by measuring the gas injected rate and the needle lift simultaneously. To simulate to the actual high-pressure environment of the engine, the influence of back pressure on the dynamic behavior of the injector is paid more attention in the experiment. In addition, the experiment of the main-after injection strategy is investigated to analyze the influence of the interval time on the after-injection. The experimental results are as follows: Firstly, the increase of back pressure will significantly promote the needle rising stage. That is, the maximum position that the needle can reach increases under the short energizing time, while the needle reaches the maximum limit faster under the long energizing time. When the injected pressure is 30 MPa while the energizing time is 0.7 ms, the gas injected mass increases by 33.92 mg (an increase of 86.8 % compared with the gas injected mass under atmospheric pressure), and the gas injected mass increased by 20.3 mg (an increase of 11.9 % compared to atmospheric pressure). Secondly, the reflected compression wave generated by the diesel supply system will inhibit the needle rising stage, resulting in the speed change of the needle lifting process. With the increase of back pressure, the affected proportion of the needle rising stage is sharply decreased even no longer influenced by the reflected compression wave. Finally, the gas injection rate develops from fusion to separation with the interval time increasing, resulting in two different trends during injected mass growth. The increase in back pressure leads to the delay of the main injection ending and the advance of the after injection starting, which facilitates the injection fusion.