TIAN Songjie;REN Hao;XU Shunta;XI Liyang;TU Yaojie;LIU Hao;

• 1:State Key Laboratory of Coal Combustion
• 2:Huazhong University of Science and Technology

Abstract：

Moderate or intense low-oxygen dilution(MILD) combustion is an advanced low-oxygen diluted combustion technology capable of achieving simultaneous reductions in NOx and soot emissions. This study employs numerical simulations based on the counterflow flame model in the chemical kinetics analysis software CHEMKIN-PRO to investigate the soot formation pathways in propane MILD combustion and their distinctions from conventional combustion. Furthermore,the effects of strain rate(50–80 s~(-1)) and CO_2 dilution(volume fraction:0–60%) on soot formation pathways under MILD conditions are systematically analyzed. The results reveal that the dominant soot formation pathways in MILD combustion are: 2C_3H_3→A1, A_1~-+H(+M)?A1(+M), A_1~-+CH_4?A1+CH_3,A_1~-+C_2H_4?A1+C_2H_3, C_6H_5CH_3+H=A1+CH_3 and 2C_3H_3→A1 and A_1~-+ H(+M)? A1(+M) under MILD conditions are significantly reduced,leading to suppressed A1 formation and thus inhibiting soot nucleation. Consequently,the surface mass growth rate of soot decreases by 78.6%,and the peak soot volume fraction diminishes by 83.7%. Notably,the contribution of the 2C_3H_3→A1 pathway to soot formation decreases by 7.7% under MILD combustion,while the importance of the C_6H_5CH_3+H?A1+CH_3 and Additionally,the peak soot volume fraction under MILD conditions exhibits a nonlinear dependence on strain rate,initially increasing and subsequently decreasing with rising strain rates. This behavior stems from the competitive interplay between the non-monotonic variation in nucleation rates and the continuous increase in surface growth rates. Both the physical and chemical effects of CO_2 dilution intensify with higher dilution ratios. At CO_2 dilution levels of 0-40%,the physical effect of CO_2 exerts minimal influence on peak soot volume fraction. However,CO_2 chemically promotes H consumption via the CO+OH?CO_2+H reaction,thereby weakening the H-abstraction C_2H_2-addition(HACA) mechanism critical for polycyclic aromatic hydrocarbon(PAH) growth. This results in significant reductions in A1 and A4 concentrations. At 60% CO_2 dilution,the peak soot volume fraction further declines to 6.4×10~(-9),demonstrating enhanced suppression of soot formation in MILD combustion.

Key Words： MILD combustion;conventional combustion;propane;soot;strain rates;CO_2 dilution

Abstract:

Keywords:

Foundation: 国家自然科学基金面上资助项目（52376112）

Authors: TIAN Songjie;REN Hao;XU Shunta;XI Liyang;TU Yaojie;LIU Hao;

DOI: 10.13226/j.issn.1006-6772.23122801

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