Theoretical and experimental investigation on soot and radiation in fires

Abstract

Fire growth is primarily controlled by luminous radiation from soot particles; there is therefore a lot of effort and need to model soot formation and its radiation in turbulent flames such as fires including enclosure fires and façade flames where experiments in this study were conducted. This work develops and validates a global soot formation model based on the laminar smoke point height that can be applied for any fuel in fires. This model is satisfactorily checked by using CFD laminar codes in gaseous laminar flames where detailed measurements of temperatures, velocities and soot concentrations are available. Subsequently, this soot model is inserted in a CFD turbulent code namely FDS (version 4.07) to allow predictions of soot and radiation in turbulent flames and fires. The agreement with the experiments in open fires is not as good, the main reason being that temperature is not well reproduced in the FDS code owing to its structure. The experiments in this work were conducted in a long corridor like enclosure (aspect ratio 6:1) being a continuation of experiments in shorter enclosures. The main results from these experiments were that the façade flames and the inflow of air for under ventilated conditions are not affected by the length of the corridor and that a new phenomenon of a moving and wandering flame front develops when a fire is at the close end of the corridor and the ventilation at the open end is restricted. The FDS code (version 4.07 and 5.3) was applied also for the enclosure cases with limited success. The application of FDS code has shown that the energy equation should be solved separately to improve more reliable prediction of temperatures that are essential together with the soot concentrations for calculating radiative heat fluxes.

Date of Award	Oct 2009
Original language	English
Supervisor	Michael Delichatsios (Supervisor) & Ali Nadjai (Supervisor)