Oxidation of n-hexane in the vicinity of the auto-ignition temperature
The present study examines the possibility of inerting flammable mixtures (making the mixtures non-explosive/non-flammable) using a long duration thermal process close to but below the auto-ignition temperature. Experiments were performed in a stainless steel cell and a Pyrex cell. A Mid-IR FTIR spectrometer, a UV–vis spectrometer and several IR laserdiodes were employed to monitor the gas-phase composition. Experiments were performed for n-hexane-air mixtures with Φ = 0.67–1.35. The temperature and pressure were T = 420–500 K and P = 37–147 kPa. Experiments were performed over period of up to 7200 s. At temperatures close to 420 K, the chemical activity is characterized by a slow and constant reaction rate. At temperatures close to 500 K, the reaction proceeds in two-phases: 1) rapid production of CO_2, CO and carbonyls, identified as hydroperoxy-ketones, followed by 2) a period of slower production of CO_2 and H_2O and consumption of hydroperoxy-ketones. At the end of the thermal treatment, the possibility of igniting the mixtures using a large hot surface (representative of low-temperature ignition source) and a stationary concentrated hot surface (representative of high-temperature ignition source) was tested. The low-temperature flammability was verified by rapidly increasing the temperature of the test cell wall whereas the high-temperature flammability was verified by turning on a glow plug. The inerting strategy seems effective in preventing the low-temperature ignition but high-temperature ignition was always observed.
© 2018 Elsevier Ltd. Received 28 March 2018, Revised 1 September 2018, Accepted 5 September 2018, Available online 13 September 2018. The present work was mostly carried out in the Explosion Dynamics Laboratory of the California Institute of Technology. The authors are grateful to the Boeing Company for funding this research through a Strategic Research and Development Relationship Agreement CT-BA-GTA-1. RM was also supported by the 1000 Young Talent of China program and a start-up fund of the Center for Combustion Energy of Tsinghua University.
Accepted Version - Fuel_LowTemp_Final.pdf