Experimental and modeling study of NO₂ addition effects on autoignition behavior of propylene

Abstract

Autoignition behaviors of NO2/C3H6/O2/Ar mixtures with the blending ratio of [NO2]/[C3H6] ranging from 0 % to 100 % were measured at pressure of 2.03E+5 - 1.01E+6 Pa, temperature of 950 – 1820 K, and equivalence ratio of 0.5 – 2.0 in a high-pressure shock tube. NO2 blending effects are characterized through changes in ignition delay times. Experiments indicate the strong promoting effect of NO2 on the reactivity of propane, with greater impacts observed at elevated pressures, lower temperatures, and fuel-leaner conditions. A chemical kinetic model is also proposed, with incorporating the unique and direct interactions between NOx and propylene and its primary derivatives. Comparison against available experiments and across different models highlight the commendable performance of the updated model, where the updated model out-performs the existing models, both quantitatively and qualitatively, in replicating the propylene autoignition behaviors and oxidation species profiles. Sensitivity and flux analyses are further conducted with the updated model, which reveals the unique NOx interacting chemistry that leads to the diverse NO2 blending effects. Particularly, NO2 addition leads to a clear shift in the consumption of C3H6 and its primary derivatives (e.g., C3H5-A (CH2=CH-ĊH2), C3H5-T (CH2=Ċ-CH3) and IC3H7 (CH3-ĊH-CH3)) toward the direct interacting channels R+NO2=RO+NO, which considerably promotes the system's reactivity. This paper highlights the importance of the unique interactions between NOx and unsaturated hydrocarbons, which need to be sufficiently represented in chemistry models in order to accurately predict the complicated effects of EGR.