A shock tube and modeling study on the auto-ignition properties of pyrrole in O2/CO2 atmosphere at elevated pressures

Understanding the details of pyrrole combustion chemistry in the O2/CO2 atmosphere contributes to developing the strategies for nitrogen oxides (NOx) control during the pressurized oxy-coal combustion (POCC). However, the existing kinetic models for pyrrole oxidation lack multi-dimensional validation, and the ignition delay times (IDTs) of pyrrole in the O2/CO2 atmosphere are still scarce. This study measured the IDTs of pyrrole in O2/CO2 atmospheres at an elevated pressure of 5.2 bar, temperatures from 1271 to 1645 K, and equivalence ratios Φ = 0.5, 1.0, and 2.0 in a shock tube. The results demonstrate that the pyrrole IDTs decrease with decreasing equivalence ratio and the pyrrole mixtures in O2/CO2 atmospheres have longer IDTs than those in O2/Ar atmospheres. A pyrrole oxidation kinetic model (HUST pyrrole model) has been developed by updating 19 reactions in our previous model (HUST pyridine model). HUST pyrrole model gives a satisfactory prediction of the IDTs of pyrrole in the O2/Ar atmosphere (measured by MacNamara et al.) and O2/CO2 atmosphere (measured in this study) and the profiles of pyrrole, HCN, and NO (measured by Yamamoto et al.). The comparison of the HUST pyrrole model with the Lumbreras model (2001) was conducted by the pyrrole IDTs and profiles of HCN using the sensitivity and flux analysis. The addition of HNCPROP and modification of R665 (C3H3 + O2 = CH2CO + HCO), R1273 (AC3H4CN + H2 => ALLYLCN + H), R1251 (PYRLNE = ALLYLCN), R1238 (PYRROLE + H = PYRLYL + H2), and R1240 (PYRROLE + OH = PYRLYL + H2O) in HUST pyrrole model significantly improve the prediction performance for the pyrrole oxidation. The effects of the equivalence ratio and CO2 on the IDTs for pyrrole oxidation have been analyzed.