Experimental study of the soot formation of RP-3 behind reflected shock waves

Soot formation from RP-3 jet fuel has been investigated in a heated shock tube. Experiments were carried out at pressures of 2 and 5 atm, temperatures of 1670-2200 K, for pyrolysis and for equivalence ratios of 20, 10 and 5 highly diluted in argon. Soot induction delay time and soot yield were studied by measuring the soot-induced laser extinction signal at 632.8 nm. The effects of temperature, pressure and equivalence ratio on soot induction time and soot yield were investigated. A decrease in soot induction time can be observed as the temperature rises. The addition of oxygen or the increasing of pressure leads to a decrease in soot induction time. Bell-shaped evolution of the soot yield versus the temperature was obtained and a modified Gaussian expression was derived. The decrease of pressure or equivalence ratio reduces soot yield significantly. A noticeable shift of optimal temperature toward lower temperatures was observed as the equivalence ratio decreases. A soot particle model coupled with a gas-phase jet fuel mechanism was used to simulate the soot formation under the experimental conditions. The predicted soot yields are in approximate agreement with the experimental data under most conditions. The model underestimates the soot yield at 2 atm for pyrolysis, as well as at 4 atm for equivalence ratio of 5. The major reaction pathways for the formation of soot precursors were obtained and discussed by time-integrated element flux analysis.