Turbulent Combustion Parameters in Gas Explosions with Two Obstacles with Variable Separation Distance

Most of the congested gas explosions studies have focused on quantifying global flame acceleration and maximum overpressure through obstacle groupings rather than detailed analysis of the flame propagation through the individual elements of the congested region. Fundamental data of the turbulent flow and combustion parameters would aid better understanding of gas explosion phenomena and mechanisms in the presence of obstacles in addition to the traditional flame speeds and overpressures that are usually reported. In this work we report near stoichiometric methane/air explosion tests in an elongated vented cylindrical vessel 162 mm internal diameter with an overall length-to-diameter, L/D of 27.7. Single and double obstacles (both hole and flat-bar types) of 20-40% blockage ratios, BR with variable obstacle scale were used. The spacing between the obstacles was systematically varied from 0.5 m to 2.75 m. Turbulence parameters were estimated from pressure differential measurements and geometrical obstacle dimensions. This enabled the calculation of the explosions induced gas velocities, rms turbulent velocity, turbulent Reynolds number and Karlovitz number. This allowed the current data to be plotted on a premixed turbulent combustion regimes diagram. The bulk of the data fell in the thickened-wrinkled flames regime. The influence of the calculated Karlovitz number on the measured overpressures was analysed and was related to obstacle separation distance and obstacle scale characteristics.