Study on the mechanism of influence of cetane improver on methanol ignition

Abstract

Methanol has attracted much attention because it can realize carbon neutral cycle. Methanol is difficult to use in compression ignition engines because of its low cetane number and high latent heat of vaporization. 2-ethylhexyl nitrate (EHN) is a widely used cetane number improver, which can effectively promote the ignition of methanol. Therefore, a reduced mechanism of methanol and EHN containing 61 species and 479 reactions is proposed in this paper, and it has been verified to fit well with the original mechanism and experimental date. Then, chemical kinetic analysis is carried out using CHEMKIN PRO. Results show that after adding EHN, the ignition delay is significantly shortened. As the EHN ratio increases, the effect of EHN on shortening the ignition delay period does not increase nonlinearly, but shows a slowing trend. The reaction with higher positive temperature sensitivity changes from R133 (CH3OH + HO2 = CH2OH + H2O2) to R307 (CH2O + NO2 = HONO + HCO), and the reaction with higher negative temperature sensitivity changes from R18 (2HO2 = H2O2 + O2) to R305 (HCO + NO2 = HONO + CO). The reaction time of H, OH and HO2 is advanced and the peak values decrease. In the methanol dehydrogenation pathway, the proportions of reactions involving HO2 decrease significantly and the proportions of reactions involving NO2 and OH increase. The methanol consumption rate increases significantly after adding EHN. With the addition of 3% EHN, the reaction time of methanol was reduced by 99.8% compared to pure methanol.