Hydrogen effects on ignition delay time of methyl butanoate in a rapid compression machine

The effect of hydrogen addition on the ignition delay time of methyl butanoate was studied using a rapid compression machine experiment and ANSYS CHEMKIN-PRO 19.0 numerical analysis. The ignition delay was measured under engine-relevant conditions by varying equivalence ratios (0.5 and 1.0), compression pressures (15 and 30 bar), compression temperatures (860-1060 K), and hydrogen mole fractions in the methyl butanoate/hydrogen mixture (0%, 25%, 50%, and 75%). The kinetic mechanism was modified by adding the methyl butanoate mechanism to the NUIG Aramco 3.0 mechanism and modifying the rate parameters of the H-atom abstraction reactions of methyl butanoate. The numerical results obtained using the modified mechanism were in good agreement with the experimental results. The methyl butanoate/hydrogen mixture did not show a negative temperature coefficient characteristic. With hydrogen addition, the ignition delay increased at low temperatures but decreased at high temperatures. The results of the chemical and dilution effect analysis using the imaginary inert H₂ showed that the chemical effects differ depending on the temperature. Most added hydrogen molecules participate in the chain propagation reactions to produce H radicals and consume OH by the reaction H₂ + OH → H + H₂O. This, in turn, changes the reactions of other species, such as HO₂ and H₂O₂. The results of the reaction path analysis for the related species showed that the addition of hydrogen reduced radical reactions at low temperatures, while increasing them at high temperatures.