Impact of oxygenated biofuels dopant on soot and PAH formation in laminar flames: Experimental and theoretical insights

Combustion-derived soot is a hazardous contributor to air pollution and poses significant health risks. n- decane and methyl butanoate (MB) are key constituents of diesel and biodiesel fuels, respectively. This study examines how varying MB concentrations (0-80%) affect soot formation in n- decane laminar diffusion flames to explore ways to reduce these harmful emissions. The concentrations of soot, polycyclic aromatic hydrocarbons (PAHs), and hydroxyl radical (OH) were measured using laser-induced incandescence (LII) and laser-induced fluorescence (LIF) techniques. Results show that increasing MB concentration decreases OH, PAHs and soot concentrations, indicating that MB weakens combustion intensity and inhibits PAH and soot formation. A chemical reaction mechanism comprising 225 species and 1,321 reactions was developed and validated for n- decane, MB, and PAHs against literature data on ignition delay times, laminar flame velocities, and major specises. Chemical kinetic analysis revealed that increasing MB reduces aromatic hydrocarbon mole fractions. Rate of production (ROP) and sensitivity analyses for A1 (benzene), a key PAH precursor for soot formation, indicate that A1 is primarily formed through the sequential combination of C3 and smaller chain radicals produced during fuel pyrolysis. However, the addition of MB results in the generation of significant amounts of CO and CO₂, which reduces the formation of key soot precursor radicals (e.g., C₂H₂, C₂H₄, C₃H₃), thereby reducing soot formation. These findings provide insights into the impact of oxygenated fuel additives on soot formation, offering potential applications for optimizing fuel formulations to reduce soot emissions.