Effects of n-butanol blending on soot and NO formation in biodiesel/air co-flow diffusion flame

Biodiesel can significantly reduce the emissions of soot and other pollutants. However, NOx emission from biodiesel combustion will increase significantly. N-butanol can reduce the flame temperature of biodiesel thus affecting NOx emission. The effects of soot and NO formation in the biodiesel/n-butanol co-flow diffusion flames with different blending ratios under the condition of carbon mass flow rate conservation were studied. The results showed that the n-butanol blending decreased the peak soot volume fraction (SVF) by 60.9 % and was mainly attributable to the decrease in Hydrogen Abstraction Carbon Addition (HACA) rates. The decrease of C₂H₂ concentration decreased the concentration of C₃H₃ and inhibited A1 formation. The decrease in benzo[a]styrene (BAPYR) concentration was caused by the decreases of C₂H₂ and A1 concentrations, through the reaction pathway A1/C₇H₇→INDENE→INDENYL→A2R5→A2R5-/A4→BAPYR. The OH and O₂ oxidation processes were inhibited in the biodiesel/n-butanol flames due to the reduction of SVF through the soot condensation process. The concentration of NO decreased by 62.0 %, the decrease of H and OH radicals inhibited the formation of NO, while the decrease of O radicals inhibited the consumption of NO. Overall, the main reason for the decrease of soot concentration was the decrease of C₂H₂ concentration and the inhibition of HACA process. The reason of inhibiting NO was the promoting effect of H and OH free radicals on NO formation was greater than the inhibiting effect of O free radicals.