Numerical study on combustion process of hydrogenated catalytical biodiesel sprays under methanol-air premixed atmosphere

Methanol's low reactivity impedes its application as a renewable fuel in compression-ignition (CI) engines. This study investigates the viability of methanol as a low-reactivity fuel (LRF) in hydrogenated catalytic biodiesel (HCB)-assisted dual-fuel (DF) combustion under reactivity-controlled compression ignition (RCCI) conditions. Using Reynolds-Averaged Navier–Stokes (RANS) simulations, the effects of varying methanol concentrations on ignition characteristics and flame structure are quantified. The results reveal that both single-fuel (SF) and DF spray combustion exhibit a two-stage ignition process, though this phenomenon is weaker in SF combustion. Moreover, ambient methanol and temperature variations significantly influence both low- and high-temperature combustion. The sensitivity of low-temperature combustion decreases once the premixed methanol equivalence ratio (${\phi }_m$) reaches 0.5, whereas the induction time continues to increase with higher methanol content. Additionally, the flame kernel location and peak heat-release rate are closely linked to regions of maximal formaldehyde (CH₂O) consumption. Following HCB injection cessation, high-temperature combustion, characterized by rapid CH₂O depletion, dominates the spray interior. In DF operation, substantial premixed methanol combustion occurs, with OH and C₂H₂ diffusing into fuel-lean zones. These insights into HCB-methanol RCCI interactions inform optimization of operational parameters for controlled ignition and efficient energy release, advancing methanol's viability as a clean CI engine fuel.