Vented combustion of hydrogen/air mixtures in large volumes: Effects of vessel size and shape

A large (120-m3) rectangular heated vented combustion test facility was constructed, instrumented and commissioned at the AECL Whiteshell Laboratories to study the effects of scale on the vented combustion behavior of hydrogen/air/steam mixtures and to generate a database for validating the combustion codes. This facility is versatile: it has removable steel panels that enable a selection of vent ratios over a wide range and has extensive instrumentation and data acquisition capabilities for performing a variety of combustion experiments. On-line gas sampling and analysis can be done to a precision of 0.1 vol% using a 32-channel mass spectrometer. Combustion experiments performed over a range of hydrogen concentrations and vent areas indicate that pressure oscillations occur for hydrogen concentration above 10% hydrogen. Over the range of vent areas and hydrogen concentrations investigated, the burn-rate enhancement factor, indicative of the development of flame-front instabilities, does not appear to depend on the vent size. Comparison with experiments performed in the 6.3 m3 spherical vessel indicates that the burn-rate enhancement (ratio of the actual to laminar burning rates) caused by the flame front instabilities in both 120 m3 and 6.3 m3 facilities is about the same. However, more investigations over a wider range of hydrogen concentrations, volume geometries, vent areas and igniter locations are required to establish the effects of scale