Combustion characteristics, soot precursors and soot particle characteristics of methanol/coal-to-liquid (CTL) in RCCI combustion mode

This study explores methanol/coal-to-liquid (CTL) dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion in a diesel engine. Combining experimental measurements and computational fluid dynamics simulations, the research evaluates combustion performance, soot precursor formation, and the physicochemical properties of emitted soot particles. Results indicate that methanol port injection significantly shortens ignition delay (5.1 °CA vs. 15.2–17.0 °CA for conventional modes) and increases peak in-cylinder pressure due to intensified premixed combustion. Although brake thermal efficiency decreased by 3.1% compared to diesel, soot precursors (A1–A7) were effectively suppressed, attributed to enhanced OH radical activity and shifted formation zones toward lower temperatures and higher equivalence ratios. Notably, methanol/CTL soot exhibited larger primary particle size, higher organic carbon fraction, elevated surface oxygen content, and more disordered nanostructure. These structural modifications contributed to markedly improved oxidation reactivity. The findings demonstrate that methanol/CTL RCCI combustion effectively reduces soot precursor generation and alters soot properties toward higher reactivity, facilitating more efficient oxidation in aftertreatment systems.