Towards a kinetic understanding of the NOx promoting-effect on ignition of coalbed methane: A case study of methane/nitrogen dioxide mixtures

•New ignition data of NO2/CH4/O2/Ar mixtures were provided.•Literature models are inapplicability in predicting reactivity for CH4/NO2 mixtures.•A modified model capturing well the new data and literature data was supposed.•Free radical pool during induced time is strongly perturbed by NO2 addition.•This study is valuable to develop the combustors and organize recycling of NOx.