ANALYZING THE CYCLE-TO-CYCLE VARIATIONS OF PULSING SPRAY CHARACTERISTICS BY MEANS OF THE PROPER ORTHOGONAL DECOMPOSITION

This paper presents a novel approach to analyze the cycle-to-cycle variations of pulsing spray characteristics. The purpose is to quantify the cycle-to-cycle variations of the macroscopic characteristics of spark-ignition direct-injection (SIDI) fuel injector spray, so that improvements of air-fuel mixture formation can be made to enhance the combustion efficiency and reduce emissions of SIDI engines. The experiments were carried out using an eight-hole SIDI fuel injector under a controlled ambient environment with an extended range of test conditions. Using a strobe light as an illumination source, multiple cycles of macroscopic spray structure images at a fixed injection delay time were taken by a CCD camera. The proper orthogonal decomposition (POD) technique was implemented to analyze the cycle-to-cycle characteristics of spray variation. In addition, the effects of injection pressure, ambient pressure, and fuel type on spray variation were also investigated. POD analysis reveals that the mode 1 pattern captured the ensemble-averaged spray shape, the mode 2 pattern provided quantification of spatial fuel distribution variations of different cycles of spray, and higher mode patterns further quantified the finer details of the variations surrounding the well-atomized periphery of the spray structure. POD analysis also quantitatively confirms that better-atomized sprays led to slightly higher variations of finer structures along the spray boundary. Overall, this study demonstrates that POD analysis can be used as a novel approach to quantify the cycle-to-cycle variation of pulsing spray characteristics.