doi:10.3850/978-981-08-7724-8_06-02

ABSTRACT

In this work, three major objectives have been pursued. First, an LES methodology to predict flame suppression by water sprays was developed. Its validation includes simulations of buoyant turbulent diffusion flames with and without sprays applied. In the latter case, time averaged fields are compared to appropriately scaled measured temperature and velocity profiles. Predictions of flame suppression are validated against published data in a large scale, 2 m diameter flame suppressed by narrow-angle coarse and fine sprays. In the cases considered, suppression outcome agrees with that reported in the experiments. Second, we demonstrate that spray refinement (droplet size reduction) facilitates flame extinguishment due to accumulation of total spray momentum in a narrowly focused turbulent vapour-rich jet. Necessary conditions for spray refinement to enhance flame suppression are (i) sufficiently high total spray momentum (compared to that of the rising plume) and (ii) jet orientation towards the fuel source. Third, in this paper we suggest a new criterion to distinguish coarse and fine sprays, namely the ratio of the droplet deceleration length to the distance to the fuel bed.

Keywords: Buoyant turbulent diffusion flame, Turbulent evaporating spray, Fire suppression.

© 2011 CPD Unit, University of Leeds