R. Mével

Induction Delay Times and Detonation Cell Size Prediction of Hydrogen-Nitrous Oxide-Diluent Mixtures

Silane-nitrous oxide mixtures are widely used in some industries such as semiconductor manufacturing. Since the decomposition of silane is faster than that of N2O and involves the formation of H2, the H2-N2O system might be an important sub-system of the silane oxidation mechanism. The induction delay times of this system have been widely studied in the low pressure range. Aim of the present study is to investigate the high-pressure behaviour of H2-N2O-Ar. Induction delays behind reflected shock waves have been measured between 1300–1860 K, at the pressure of 910±50 kPa for mixtures with equivalence ratios of 0.5, 1, and 2. It has been shown that equivalence ratio variations have no effect on induction delays. The modeling of delays has been improved by including an excited OH* kinetic sub-mechanism. Finally, various techniques of detonation cell size prediction have been evaluated in comparison with available experimental data.

Hot Surface Ignition of n-Hexane Mixtures Using Simplified Kinetics

ABSTRACT Hot surface ignition is relevant in the context of industrial safety. In the present work, two-dimensional simulations using simplified kinetics of the buoyancy-driven flow and ignition of a slightly lean n-hexane–air mixture by a rapidly heated surface (glowplug) are reported. Experimentally, ignition is most often observed to occur at the top of the glowplug; numerical results reproduce this trend and shed light on this behavior. The numerical predictions of the flow field and hot surface temperature at ignition are in quantitative agreement with experiments. The simulations suggest that flow separation plays a crucial role in creating zones where convective losses are minimized and heat diffusion is maximized, resulting in the critical conditions for ignition to take place.

Chemical Kinetics of n-Hexane-Air Atmospheres in the Boundary Layer of a Moving Hot Sphere

ABSTRACT The present article focuses on the chemical kinetics of the ignition of premixed n-hexane-air atmospheres by a moving hot sphere with emphasis on the role of low-temperature chemistry (T < 1000 K). Experiments were performed to measure the minimum surface temperature for ignition of a propagating flame and nonreactive two-dimensional simulations were performed to estimate the temperature a parcel of fluid experiences as it travels within the thermal boundary layer near the surface of the sphere. Reactive simulations using detailed reaction models and a one-step model were used to investigate the chemical reaction dynamics in a constant pressure reactor with a variable heat transfer coefficient, which reproduces the temperature history. It was found that, under the specific conditions studied, the chemistry is activated at T > 1000 K with no noticeable impact of the low-temperature chemical pathways.