Shock tube measurement of NO time-histories in nitromethane pyrolysis using a quantum cascade laser at 5.26 μm

The pyrolysis of nitromethane, CH3NO2, was studied at similar to 3.5 atm and 1013 K-1418 K in a heated shock tube by measuring the key product nitric oxide (NO) using mid-infrared laser absorption spectroscopy. We used a quantum cascade laser (QCL) at 5.26 mu m to exploit the strong NO absorption at 1900.08 cm(-1). With the NO absorption cross-section data characterized at 1006 K-1789 K and 2.7 atm-3.5 atm behind reflected shock waves, we measured the NO concentration time-histories during the pyrolysis of nitromethane at two different concentrations (1.05% and 0.6%). The absorption interference from other major products such as CO and H2O was analyzed to be negligible, leading to an interference-free NO diagnostic in nitromethane pyrolysis. A recent kinetic model of Shang et al. (2019) was adopted to interpret the shock tube data. All the NO time-histories measured over the entire temperature range 1013 K-1418 K were well-predicted by this model in terms of the initial NO formation rate and the final plateau level. The rate-of-production, sensitivity, and reaction flux analyses were performed to identify four important reactions (CH3NO2 = CH3 + NO2, CH3NO2 <-> CH3ONO = CH3O + NO, CH3 + NO2 = CH3O + NO, and NO2 + H = NO + OH) that determine the NO formation during CH 3NO 2 pyrolysis. The satisfactory agreement between the simulation and shock tube/laser absorption measurement further validated the kinetic mechanism of nitromethane decom-position. The developed mid-infrared NO absorption sensor provides a promising diagnostic tool for studying fuel-nitrogen chemical kinetics in the shock tube experiments. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The pyrolysis of nitromethane was studied using mid-infrared laser absorption spectroscopy to measure the NO concentration time-histories. The results indicated that the NO formation during nitromethane pyrolysis is influenced by four important reactions, and the kinetic mechanism of nitromethane decomposition was validated through comparison of simulation and experimental data.