Numerical investigation on the temporal and quasi-steady state soot characteristics of n-dodecane-n-butanol spray combustion

Recently, n-butanol has emerged as a potential biofuel candidate to reduce soot emission in diesel combustion while still able to maintain comparable engine performance. Herein, the temporal and quasi-steady state soot characteristics of pure n-dodecane (Bu0) and its blends with n-butanol at 20% blending ratio (Bu20) and 40% blending ratio (Bu40) at ambient temperatures of 800 K, 850 K and 900 K are numerically investigated using the Moss-Brookes soot model. Results show that the soot volume fraction (SVF) and soot particle size decrease as the n-butanol blending ratio increases and as the ambient temperature decreases. Comparing to the case of Bu0 (900 K), both peak SVF and soot particle size of Bu40 (900 K) decreases by 93.11% and 56.58%, respectively. Similarly, Bu20 (800 K) shows a decrease of 88% and 50.62% in the peak SVF and soot particle size when comparing to Bu20 (900 K). The mass fractions of benzene (A1), pyrene (A4), acetylene (C2H2) and hydroxyl radical (OH) also decrease as the n-butanol blending ratio increases and as the ambient temperature decreases. Both soot formation and oxidation mechanisms are suppressed at higher n-butanol blending ratio and at lower ambient temperature but the soot formation mechanism plays a more dominant role in the resulting SVF and soot particle size. Nevertheless, the high oxygen concentration in high n-butanol blending ratio could help maintain the performance of the soot oxidation mechanism while suppressing the soot formation mechanism simultaneously. Therefore, the SVF and soot particle size decrease more significantly with the increase in n-butanol blending ratio than the decrease in ambient temperature.