The effect of fuel additives on the autoignition dynamics of rich methanol/air mixtures

The use of H2O2, CH2O, H2O, CH4, C2H5OH, CHOCHO and CH3CHO as additives in rich methanol/air mixtures is investigated for the control of ignition delay and of the super adiabatic temperature phenomenon (SAT) during autoignition. Since H2O2 acts as an oxidizer, effectively it shifts the process to smaller equivalence ratios, which none of the other additives can do and decreases drastically ignition delay and suppresses SAT. CH2O is the second most influential additive, resulting in a milder decrease of ignition delay and an even milder suppression of SAT. Of the remaining additives considered, only those containing the methyl group are shown to influence ignition delay. The effect of additives on SAT is shown to depend on the amount of oxygen in the additive molecule. A detailed investigation of the influence of H2O2 and CH2O additives leads to the conclusion that, for the cases of pure fuel and CH2O addition, a chemical runaway develops that is supported by the reactions of methanol and CH2O with HO2 that form H2O2, which then dissociates to OH. H2O2 addition, though, obviates the need for a chemical runaway because it provides the system with H2O2 readily, thus leading to a much shorter ignition delay. In the post-ignition regime, CH2O does not alter the dominance of the endothermic dissociation reactions that cause the SAT, while H2O2 reinforces exothermic reactions, thus suppressing SAT. •Rich methanol/air mixtures are considered.•Super adiabatic temperature phenomenon is controlled by additives.•Best such additive is H2O2, having a relatively large mass of oxygen.•H2O2 can act as oxidizer.