Characterization and mechanism of soot formation in C4H10 combustion with H2-NH3 addition

•Adding H2-NH3 can reduce carbon emissions and soot formation in C4H10 flames.•ReaxFF MD is used to analyze A1 mechanism in H2-NH3 blended C4H10 combustion.•Adding H2 has opposite effects on PAHs formation in n-C4H10 and i-C4H10 flames.•Adding H2-NH3 reduces soot peak average primary particle diameter in C4H10 flames. This study employed extinction method and thermophoretic sampling techniques to explore the characteristics of soot formation in C4H10 combustion with H2-NH3 addition. The impact of H2-NH3 addition on the formation of PAHs and soot was analyzed using ReaxFF MD. It is found that the adding H2-NH3 leads to a decrease of fvmax, with the inhibitory effect on soot formation being stronger for i-C4H10 compared to n-C4H10. Adding H2-NH3 inhibits the growth of soot particles, reducing the peak average primary particle diameter of soot particles. The chemical effect of H2 promotes soot formation in n-C4H10 combustion but inhibits it in i-C4H10 combustion. However, both NH3 and H2-NH3 addition chemically inhibit soot formation in C4H10 combustion. The A1 pathways reveal that the C–C bond cleavage in n-C4H10 is significantly stronger than C–H bond cleavage, while it is exactly the opposite in i-C4H10. Adding H2 promotes the reaction equilibrium CH3+H2↔CH4+H towards the forward reaction, facilitating C–C bond cleavage and A1 formation in n-C4H10 but inhibiting C–H bond cleavage and A1 formation in i-C4H10. However, adding NH3 results in the cleavage of N–H bonds, producing a large amount of H. This shifts the reaction equilibrium CH3+H2↔CH4+H towards the reverse reaction, ultimately suppressing A1 formation.