Investigation on the combined influence mechanism of port water injection timing, injection pressure and ignition timing on natural gas engine performance based on the Taguchi method

For the engine with port water injection, the control parameters including injection timing, injection pressure and ignition timing are critical to balance engine performance. To maximize the advantages of water injection, a series of experiments and simulations were conducted to investigate the separate effects of the control param-eters on the combustion and emission. Then, the Taguchi method with an L16 orthogonal array was used to study the combined effects of the control parameters. In addition, the engine performance was considered to evaluate the influence degree of the control parameters using the signal-to-noise ratio and the analysis of variance. The result showed that injection timing and injection pressure played an important role in the spark ignition engine. The three-body effect outweighed the thermal effect with the delay of water injection timing, which accelerated the combustion progress and increased the NOx emission. Secondly, ignition advance eliminated combustion deterioration caused by port water injection. Thirdly, the combination of the control parameter of the optimum combustion characteristic and the lowest emission was acquired. The optimum combustion characteristic was acquired at 310 degrees CA injection timing, 5.0 MPa injection pressure and 44 degrees CA ignition timing. The lowest emission was acquired at 350 degrees CA injection timing, 10.6 MPa injection pressure, and 44 degrees CA ignition timing. Injection timing affects the combustion and emission more than injection pressure.