Investigations of spray breakup Rayleigh-Taylor instability via multiphase lattice Boltzmann flux solver

Poor fuel-air mixing of the diesel spray in low ambient temperature and pressure or thin air leads to intricate fuel breakup mechanism near the nozzle, which still remains worth of study. In this study, a pressure-based modified multiphase lattice Boltzmann flux solver (MLBFS) is proposed to accommodate the fuel spray breakup characteristics of multiphase, multicomponent, and large density ratio, in which the source terms of governing equation are modified emphatically for high injection pressure. Therefore, the characteristics of microscopic diesel spray breakup induced by Rayleigh-Taylor instability are investigated, including spray penetration, spray area, and spray arc length. It is revealed that the spray penetration is increased exponentially with the fuel-air density ratio R rho. Influenced by air resistance and circulation interference, the roll-up vortex, droplet size, and spray area increase with the decreasing of R rho (corresponding to high ambient pressure). Affected by entrainment and Rayleigh-Taylor instability, the development of the spray arc length experienced three stages: rapid growth, peak, and violent fluctuation, in which the lower R rho facilitates development. It is concluded that Rayleigh-Taylor instability is favorable for stimulating the spray internal circulation of spray to enhance entrainment with surrounding air, while improving roll-up and breakup in the spray tail region. Such investigation is conductive to better understanding the micro-breakup mechanisms of fuel spray in the spray-induced internal combustion engine.