Experimental and Kinetic Study of the Effect of Nitrogen Dioxide on Ethanol Autoignition

The contribution of NO₂ to the ethanol ignition delay time was investigated behind reflected shock waves. The experiments were performed at a pressure of 0.20 MPa, temperature range of 1050-1650 K, equivalence ratio of 0.5/1.0/1.5, and ethanol/NO₂ mixing ratios of 100/0, 90/10, and 50/50. The experimental results showed that the addition of NO₂ decreased the ignition delay time and promoted the reactivity of ethanol under all equivalence ratios. With an increase in NO₂ blending, the effect of equivalence ratio on the ethanol ignition delay time decreased, and with an increase in temperature, the effect of NO₂ in promoting ethanol ignition weakened. An updated mechanism was proposed to quantify NO₂-promoted ethanol ignition. The mechanism was validated based on available experimental data, and the results were in line with the experimental trends under all conditions. Chemical kinetic analyses were performed to interpret the interactions between NO₂ and ethanol for fuel ignition. The numerical analysis indicated that the promotion effect of NO₂ is primarily due to an increase of the rate of production and concentration of the radical pool, especially the OH radical pool. The reaction NO + HO₂ ⇔ NO₂ + OH is key to generating chain-initiating OH radicals.