Abnormal promotion effect of nitromethane on ethane ignition

Abstract

The promotion effect of nitromethane (NM) on ethane ignition is studied in a heated shock tube. An unusual promotion effect of NM is observed: the ignition delay time of blends first decreases and then increases with increasing NM blending ratio, and the promotion effect peaks at blending ratio of 0.5. A model from our recent study [Fuel, 2019, 256: 115956] can reproduce the measurements and the abnormal promotion effect of NM. The kinetic analyses indicate that the radical pool establishment is slow for ethane, but much faster for NM due to the weak C–N bond. After the first-stage ignition of NM, most radicals are consumed and the radical pool needs to be re-established. In the ethane/NM blends, ethyl radicals, produced from the H-atom abstraction from ethane, can accelerate the re-establishment of the radical pool and then lead to a faster ignition delay time in comparison to neat ethane and NM, thus resulting in an abnormal promotion effect.