PRESSURE EFFECTS OF HYDROGEN-AIR DEFLAGRATION AND DETONATION IN LARGE-SCALE SEMI-CONFINED GEOMETRY

Zbikowski M.1, Makarov D.1, Molkov V.1, Schneider H.2

1 University of Ulster, Newtownabbey, Co.Antrim, BT37 0QB, UK

2 Fraunhofer Institut Chemische Technologie, Joseph-von-Fraunhoferstr. 7, 76327 Pfinztal, Germany

SESSION: 01.3

Abstract

Pressure effects from hydrogen explosions are important in handling hydrogen, e.g. for calculation of safety distances. Release and ignition of hydrogen may lead to deflagration and/or detonation. Detonation is the worst case explosion scenario due to essentially higher pressures in area of combustion and in a blast wave. Detonation may be directly initiated or result from deflagration-to-detonation transition (DDT), e.g. initiated by a turbulent jet of combustion products.

The experiment [Pförtner et al., 1984] with the deflagration-to-detonation transition was simulated in this study to compare experimental and simulated pressures for both deflagration and detonation stages of the explosion. In the experiment the jet of hydrogen-air combustion products emerged from the driver section of sizes LxHxW=3x1.5x1.5 m through the vent into a “lane” of sizes LxHxW=12x3x3m, filled with the same 22.5% hydrogen-air mixture. The “lane” was confined by two rigid walls LxH=12x3m located 3 m from each other. The explosion started from deflagration and transition to detonation occurred outside the driver section.

The large eddy simulation (LES) model and results of numerical simulation of both deflagration and detonation stages are presented. There was no intention in this study to model DDT itself. The propagation of both deflagration and detonation was modeled by the progress variable equation similar to [Molkov et.al 2004]. The gradient method was applied for the source term in the progress variable equation to ensure the correct propagation velocity. The theoretical Chapman-Jouget detonation velocity DCJ was calculated using the model [Brown et al.] and the standard heat of combustion Hc was used.

Experimental pressures were compared as well to simulated pressures for an imaginary case of deflagration in the described geometry without transition to detonation. The safety distances for explosion with detonation and without are compared.

References

  1. Molkov V., Makarov D. and Grigorash A., Cellular structure of explosion flames: modelling and large eddy simulation. Combustion Science and Technology, 2004, V.176 (5-6), pp.851-865.
  2. H. Pförtner; Hemispherical Gas Detonations of H2-Air Mixtures; Report Fraunhofer Institut Chemische Technologie, Pfinztal, Germany, 1991
  3. H. Pförtner, H. Schneider; Tests with Jet Ignition of Partially Confined Hydrogen Air Mixtures in View of the Scaling of the Transition from Deflagration to Detonation; Report, Fraunhofer Institut Chemische Technologie, Pfinztal, Germany, 1984
  4. Brown, S., and Shepherd, J.E., Numerical Solution Methods for Shock and Detonation Jump Cpnditions, Galcit Report FM 2006.006 July 2004,