A rapid compression machine study of hydrogen effects on the ignition delay times of n-butane at low-to-intermediate temperatures

Hydrogen effects on the ignition delay of n-butane were investigated through a rapid compression machine (RCM) experiment and numerical analysis. The experiment was done by varying compression pressures (20 and 25 bar), equivalence ratios (0.5, 1.0, and 1.5), compression temperatures (722–987 K), and molar ratios of hydrogen in the fuel mixture (0, 25, 50, and 75%). Heat transfer model was developed based on adiabatic core assumption with volume expansion, and NUIG Aramco 2.0 mechanism was used for kinetic modeling. The experimental and numerical results of this study were in good agreement with those of previous studies. The negative temperature coefficient (NTC) trend of n-butane was identified, and the ignition delay decreased as the pressure or equivalence ratio increased. The ignition delay increased upon addition of hydrogen, attributable to both chemical and dilution effects. Sensitivity and reaction path analysis were performed at 750 K, 830 K, and 910 K. Most added hydrogen was consumed via the reaction H₂ + OH = H + H₂O, reducing the level of OH radicals and increasing that of H radicals. The change also affected the levels of other radicals such as HO₂; all changes eventually affect an ignition delay.