Spray-induced temperature stratification dynamics in a gasoline direct-injection engine

Simultaneous applications of high-speed toluene-LIF thermometry and PIV at kHz rates were utilized to investigate the evolution of gas temperature stratification imposed from direct-injection of liquid fuel within a motored SIDI engine. Temperature imaging was based on the two-color detection method that measures the LIF signal ratio from two separated wavelength ranges to enable LIF temperature imaging within inhomogeneously mixed systems. It was observed that cold gases associated with evaporative cooling exist within the regions of dense liquid fuel droplet clouds. As droplets disperse, the cold-gas regions expand and relative temperatures as low as −50 K exist. Average temperature gradients between cold- and bulk-gases are up to 30 K/mm and gradients persist but drop in magnitude throughout compression as cold- and bulk-gases mix. Temperature stratification is greatest as the fuel disperses within the field-of-view producing large areas of cold-gases with relative temperatures as low as −50 K. Individual temperature images and 2D PDFs of identified cold-gas regions reveal that local regions of cold-gas imposed from evaporative cooling can last up to 30 CAD after fuel injection for the given operating conditions. The time-resolved imaging study show the mechanics of localized evaporative cooling and bulk-flow motion-driven mixing that over time reduces temperature gradients but does not completely homogenize the temperature fields.