Göran Holmstedt

Single-pulse Laser-induced Oh Fluorescence In An Atmospheric Flame, Spatially Resolved With A Diode-array Detector

Laser-induced fluorescence measurements of OH have been performed in an atmospheric stoichiometric CH(4)/air flame and in a highly sooting propane flame. The measurements were realized with a single 6-nsec pulse from a frequency-doubled dye laser pumped by a Nd:YAG laser and with a spatial resolution of ~25 microm. This was achieved by imaging through a suitably chosen filter set a section of the laser beam onto a gated and intensified diode array.

CFD and experimental studies of room fire growth on wall lining materials

CFD simulation and experimental tests have been carried out to study the room corner fire growth on combustible wall-lining materials. In the CFD simulation, the turbulent mass and heat transfer, and combustion were considered. The discrete transfer (DT) method was employed to calculate the radiation with an absorptivity and emissivity model employed to predict the radiation property of combustion products including soot, CO2 and H2O, which are usually the primary radiating species in the combustion of hydrocarbon fuels. The temperature of the solid boundary was determined by numerical solution of the heat conduction equation. A simple and practical pyrolysis model was developed to describe the response of the solid fuel. This pyrolysis model was first tested against the Cone Calorimeter data for both charring and non-charring materials under different irradiance levels and then coupled to CFD calculations. Both full and one-third scale room corner fire growths on particle board were modelled with CFD. The calculation was tested with various numbers of rays and grid sizes, showing that the present choice gives practically grid- and ray number-independent predictions. The heat release rate, wall surface temperature, char depth, gas temperature and radiation flux are compared with experimental measurements. The results are reasonable and the comparison between prediction and experiment is fairly good and promising.

A two-equation turbulence model and its application to a buoyant diffusion flame

A modified k–e two-equation turbulence model was developed to improve the consideration of the important buoyancy effect on turbulence and turbulent transport, which is a serious deficiency of the standard buoyancy-modified k–e model. The present model was tested against both plane and axisymmetric thermal plumes and a buoyant diffusion flame. The model was found to be stable, computationally economic, promising and applicable to complex situations. The predicted plume spreading rates and velocity and temperature profiles agreed well with experimental measurements. When compared with the standard buoyancy-modified k–e turbulence model, this model gives significantly improved numerical results.

CFD Simulation Of Upward Flame Spread Over Fuel Surface

Two-dimensional upward flame spread and subsequent steady burning of a vertical PMMA surface was studied using CFD methodology. Both the turbulent combustion of the gas phase and the pyrolysis of the solid fuel were numerically simulated. The transpired wall function was used to calculate the convection heat transfer with the blowing effect considered. Radiation was considered by using the discrete transfer method. A fast narrowband computer model, FASTNB, which predicts the radiation properties of the combustion products in a general, non-isothermal and non-homogeneous combustion environment, was implemented for the solution of the radiation equation along every ray. An efficient, simple and practical pyrolysis model was adopted to describe the pyrolysis of the solid fuel. The sensitivity of the prediction to grid, time step interval and ray number was analysed. The calculated flame spread velocity, heat fluxes, and the steady burning rate, etc. were analysed and compared with experimental measurements. Good agreement was obtained.

Correlation Between Firefighting Operation and Fire Area: Analysis of Statistics

The aim of this study is to investigate whether current statistics can quantify the benefits of fire brigades. A detailed investigation by the London Fire Brigade of most fires in the greater London area has been underway since 1994. The present study concerns 307 fires in non-residential buildings between 1994 and 1997. Times to detection, to arrival of the fire brigade, and to extinguishment of the fire, as well as the process of extinguishing it, are compared to the final property damage caused by the fire. In half of the fires, the final fire area equals the area at detection, and in three-quarters of the fires, the final fire area equals the fire area when the fire brigade arrived. No support was obtained for the hypothesis that the period between ignition and the time the fire brigade intervened correlates with fire area. However, the hypothesis is supported for fires still spreading when the brigade arrives. Both water flow rate for extinguishing a fire and water application time are proportional to the square root of the fire area. Total water demand is proportional to the fire area.

FAST, NARROW-BAND COMPUTER MODEL FOR RADIATION CALCULATIONS

A fast, narrow-band computer model, FASTNB, which predicts the radiation intensity in a general nonisothermal and nonhomogeneous combustion environment, has been developed. The spectral absorption coefficients of the combustion products, including carbon dioxide, water vapor, and soot, are calculated based on the narrow-band model FASTNB provides an accurate calculation at reasonably high speed. Compared with Grosshandlers narrowband model, RADCAL, which has been verified quite extensively against experimental measurements, FASTNB is more than 20 times faster and gives almost exactly the same results.

Limitations of Water Mist as a Total Flooding Agent

The limitations of water mist in acting as a total flooding agent are discussed in this paper. The paper focuses on water mist consisting of droplets 1-100 µm in diameter. Water mists are very efficient as an extinguishing media if they are present in the flame. There are, however, several problems associated with introducing the water mist into the flame: the spray reaches only a short distance; small water droplets have a very short lifetime; droplets coagulate into larger droplets; large droplets hit obstacles such as walls and therefore have difficulties in being dispersed throughout the protected volume.

The upper limit of flammability of hydrogen in air, oxygen, and oxygen-inert mixtures at elevated pressures

The upper limit of flammability of hydrogen in air, oxygen, oxygen-helium, oxygen-neon, oxygen-argon and oxygen-carbon dioxide mixtures was measured at room temperature and pressures between 0.97 and 29 atm in two cylindrical bombs with volumes of 1.5 and 5.2 liters. The limit in ternary mixtures was determined in 20%, 40%, 60% and 80% helium, 20% neon and argon and 10% carbon dioxide concentrations. The maximum safe percentage of oxygen in a hydrogen-oxygen-helium mixture was calculated for pressures between 0.97 and 29 atm.

Sensitivity calculations of tunnel fires using CFD

Detailed numerical simulations of fires in road tunnels were carried out using the CFD code JASMINE. Fire tests performed in the Ofenegg tunnel have also been validated. A parametric study of fires in an arbitrary 300-m-long tunnel was made, in which the influence of fire size, tunnel width, ventilation and ground slope was investigated. The movement of hazardous temperature and smoke regions as a function of time was calculated to vestigate escape possibilities from the tunnel in case of fire.

Three-dimensional computation of heat transfer from flames between vertical parallel walls

The heat transfer from turbulent diffusion flames between vertical walls has been computed for different wall and burner configurations. The buoyancy-modified k- model was used to study the turbulent characteristics of the flow. The flamelet concept, coupled to a prescribed probability density function, was employed to model the nonpremixed combustion process. With the nucleation, surface growth, coagulation, and oxidation considered, sooting was modeled by solving the balance equations for mass fraction and number density. The radiation from the main radiating species - carbon dioxide, water vapor and soot - was calculated using the discrete transfer method. A recently developed fast, narrow-band model was adopted to provide the radiation properties of the radiating species. Computations were performed for different cases by varying the wall separation and burner output. The results were analyzed and compared with experimental measurements, with which they showed good agreement. The effects of wall separation and burner output on heat transfer were faithfully reproduced. (Less)