Effects of ambient temperature and pressure on the spray and combustion characteristics of diesel and Fischer–Tropsch diesel

To investigate the effects of ambient temperature and pressure on spray and combustion characteristics, this study employed high-speed imaging technology in a constant-volume combustion chamber (CVCC) to systematically compare the spray tip penetration (STP), spray projected area (SPA), spray cone angle (SCA), flame lift-off length (FLL), light-based ignition delay (LID), flame area (FA), and flame luminosity (FL) of conventional diesel (D100) and Fischer–Tropsch diesel (FT100) under different operating conditions. The results indicate that as ambient temperature increased from 300 to 773 K, the atomization parameters of both fuels decreased significantly, but the decrease was more pronounced for FT100: its STP and SPA decreased by 48.5% and 87.2%, respectively, while those of D100 decreased by only 28.3% and 72.7%. Although both increased ambient temperature and pressure shortened the LID and enhanced flame characteristics, the increase in FL for FT100 was significantly lower than that for D100: when the temperature rose from 800 to 850 K, the peak FL of FT100 increased by only 52.4%, whereas that of D100 increased by 87.1%. Further analysis indicates that FT100 exhibits significant asymmetry in its sensitivity to temperature and pressure: its evaporation-dominated effect responds extremely strongly at high temperatures, while the positive feedback of the soot formation pathway to high-pressure environments is relatively limited. This difference in sensitivity reveals that FT100 possesses superior adaptive combustion potential across a wide range of operating conditions, providing a theoretical basis for the spray and combustion design of clean alternative fuels under varying temperature and pressure conditions.