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.