Experimental study of injection characteristics under diesel's sub/trans/supercritical conditions with various nozzle diameters and injection pressures

The supercritical fluid combustion technology was expected to enhance fuel-gas mixing and heat exchange management both in the application of automobile and marine engines. Considering the challenge and shortage of relevant researches, the transcritical injection experiment is conducted in a constant volume chamber to obtain the detailed knowledge about the effect of key factors, such as nozzle diameters, injection pressures and critical conditions, on injection and critical characteristics. A total of 216 experimental cases were operated to analyze the effect of three different injector nozzle diameters (100, 300, 350 mu m), four injection pressures (60, 100, 140, 180 MPa) and nine ambient conditions, with two optical techniques (backlight illumination, schlieren imaging). The fuel injection characteristics are studied, where the spray structure is recorded, and the liquid length, R-parameter, spray volumes, cone angles as well as relevant empirical correlations are calculated to investigate the axial and radial dispersion. The results show that different critical conditions dominate the fuel spray to behave as different structures. The 350 mu m nozzle produces a higher fuel mass flow rate than other nozzles to expand the side periphery region, while the 100 mu m nozzle is prone to be dominated by ambient gas entrainment to strength the puffing process. The injection pressure has an insignificant effect on the liquid length, liquid volume and spray cone angles, but an increasing influence on the jet volume with higher pressures. Under supercritical condition, higher injection pressure can promote the fuel-gas mixing and hot gas entrainment in the downstream region.