Investigation of Key Mechanisms for Liquid Length Fluctuations in Transient Vaporizing Diesel Sprays

Diesel combustion and emissions formation is spray and mixing controlled and understanding spray parameters is key to determining the impact of fuel injector operation and nozzle design on combustion and emissions. In this study, both spray visualization and computational fluid dynamics (CFD) modeling were undertaken to investigate key mechanisms for liquid length fluctuations. For the experimental portion of this study a common rail piezoelectric injector was tested in an optically accessible constant volume combustion vessel. Liquid penetration of the spray was determined via processing of images acquired from Mie back scattering under vaporizing conditions by injecting into a charge gas at elevated temperature with a 0% oxygen environment. Tests were undertaken at a gas density of 34.8 kg/m₃, 2000 bar injection pressure, and at ambient temperatures of 900, 1100, and 1300 K. Under these conditions there are noticeable fluctuations in liquid phase penetration once the steady state liquid length has been established, on the order of 10% of the mean liquid length. These fluctuations in penetration were seen in each plume. An analysis of the experimental data, along with CFD modeling of the liquid spray is undertaken to identify the key mechanisms for liquid length fluctuations. Results are presented comparing experimental and CFD results of the liquid spray and its fluctuations, including a quantification of fluctuation magnitude. Based on the experimental and CFD analysis, it is concluded that a key mechanism for liquid length fluctuations in a transient diesel spray is due to spray-induced turbulent eddies near the edge of spray plume.