Investigation about temperature effects on soot mechanisms using a phenomenological soot model of real biodiesel

A phenomenological soot model of real biodiesel was proposed to investigate the effects of initial ambient temperatures on combustion and soot emission characteristics of soybean biodiesel. Validation experiments were conducted in an optically accessible constant volume chamber under four difference initial ambient temperatures: 1000, 900, 800, and 700 K. Good agreement was observed in the comparison of time-related soot measurement and prediction. Results indicated that ignition delay prolonged with the decrease of the initial ambient temperature. The heat release rate demonstrated the transition from mixing controlled combustion at a high ambient temperature to premixed dominate combustion mode at a low ambient temperature. Although the soot formation and oxidation mechanisms were both suppressed, biodiesel showed less soot tendency at a lower ambient temperature. Temporal and spatial distribution pictures indicated that the drop in ambient temperature did not cool the combustion temperature. The reduction of the soot mass concentration with the decrease of the initial temperature was caused by the shrinked total area of a local high equivalence ratio, in which soot usually generated fast. At 700 K initial ambient temperature, soot emissions were almost negligible; therefore, clean combustion might be achieved at super low initial temperature operation conditions.