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.