Study on the Mechanism of Soot Inhibition in Methanol-Ethylene Mixed Combustion under High-Pressure Conditions

Abstract

Soot particles emitted during the combustion of hydrocarbon fuels in power equipment are a major contributor to urban smog, which poses serious risks to human health. Therefore, reducing soot emissions is a key focus in combustion research. This study employs the Laser-Induced Incandescence (LII) flame diagnostics to measure soot volume fraction (SVF) and investigates the effects of methanol addition on flame morphology and SVF in a co-flow diffusion flame of ethylene under high-pressure conditions. Kinetic simulations are used to study the mechanisms by which methanol inhibits soot formation and the effects of reaction pressure on soot formation. The results show that as the methanol blending ratio increases, the blue region of the flame becomes more pronounced, and the flame brightness decreases. As pressure increases, the flame becomes taller and narrower, the bright yellow region expands, and the flame becomes brighter. At the same pressure, the SVF in the flame decreases linearly with increasing methanol blending ratio. At the same methanol blending ratio, the SVF increases quadratically with increasing pressure, the soot distribution area expands, and soot appears earlier. Numerical analysis reveals that adding methanol to the ethylene flame reduces the mole fraction of H radical during the reaction, lowers the reaction rates of elementary reactions in the pathway converting ethylene to benzene (A1), which reduces the mole fractions of key soot-forming substances such as C₂H₂, C₃H₃, and A1, and hinders the dehydrogenation of A1. This suppresses the formation of large molecular soot precursors from A1, leading to a reduction in soot formation. Reaction pressure has a minor effect on the primary reaction pathways for soot formation during ethylene combustion, but increasing the reaction pressure raises the concentration of reactants, significantly enhancing the reaction rates of key elementary reactions. This increases the mole fractions of key soot-forming substances, ultimately resulting in an increase in soot formation.