Pool Flames Research Articles

Flame behavior and temperature distribution of coupled fire induced by the interaction of hydrogen jet flame and pool flame

Once fires occur unexpectedly at the oil-hydrogen integrated refueling stations, there is a high likelihood that they will escalate into a coupled fire, resulting in unpredictable casualties and property losses. In this work, experiments on coupled fire induced by hydrogen jet flame and a heptane pool flame were conducted with different nozzle diameters and release pressures. It has been found that there is a critical diameter above which the hydrogen jet can be ignited instantly. This critical diameter is determined by the release pressure and the location of the pool flame. The heat release rate is greater than that of the single pool flame, and it reaches its highest point at 0.2 MPa. Compared to a single fire, the height of the flame decreases while the length of the flame increases, a prediction model is proposed for the dimensionless flame length and width, taking into account the ratio of the heat release rate of the hydrogen jet flame to the heat release rate of the pool flame. The temperature of the coupled fire reaches its highest point at 0.2 MPa and increases as the nozzle diameter. And it decreases with the increase in the distance when Y= 0 m. However, it increases with the increase of the distance when Y= 0.05 m due to the inclination of the flame.

Experimental study of dynamics of flames from discrete methanol fuel wicks in ullages

The paper presents an experimental study of the burning characteristics of discrete methanol wicks in ullages, where the burning occurs at distances much lower than the lip of the burner. Burning configurations consisting of two methanol wicks burning in varying ullages (from zero to 24 cm at intervals of 6 cm) have been considered in the experiments. At zero and 6 cm ullages, flame shapes resemble that of a general buoyant pool flame. As the ullage is increased to 12 cm or higher, a plume-induced instability triggers in the ullage and the flame bends towards one side over the wicks, resembling a boundary layer type of flame. The transition from a pool flame to a boundary layer-type flame has been illustrated with direct flame photographs. At deeper ullages, as the flame leans over the fuel wicks, the mass burning rates are enhanced from 9% to 35% for different ullages. The resulting air flow inside the ullage and flame shape affects the mass burning rate and has been visualized using smoke flow in the ullage. This study opens further research on the coupling effect of burning of heterogeneous materials in ullages with the flow field induced by the buoyant plume.

A compact Scheimpflug lidar imaging instrument for industrial diagnostics of flames

Scheimpflug lidar is a compact alternative to traditional lidar setups. With Scheimpflug lidar it is possible to make continuous range-resolved measurements. In this study we investigate the feasibility of a Scheimpflug lidar instrument for remote sensing in pool flames, which are characterized by strong particle scattering, large temperature gradients, and substantial fluctuations in particle distribution due to turbulence. An extinction coefficient can be extracted using the information about the transmitted laser power and the spatial extent of the flame. The transmitted laser power is manifested by the intensity of the ‘echo’ from a hard-target termination of the beam located behind the flame, while the information of the spatial extent of the flame along the laser beam is provided by the range-resolved scattering signal. Measurements were performed in heptane and diesel flames, respectively.

Hydrophilic and hydrophobic selective measurement of PM exhausted from pool flame using QCM

Hydrophilic and hydrophobic selective measurement of PM exhausted from pool flame using QCM

The effect of lubricating oil addition in fuel on PM and combustion gas emitted from unsteady pool flame

The effect of lubricating oil addition in fuel on PM and combustion gas emitted from unsteady pool flame

Estimation of Radiation Heat Flux in Open Pool Flames for Application of Fire Protection Walls

Petrochemical plants are characterized by various flammable substances and complicated processes. Moreover, flammable fluids are transported through high-temperature and high-pressure pipes. To reduce the potential damage inflicted on adjacent facilities owing to the risk of fire and explosion, it is necessary to consider installing a fire protection wall, which is a physical space partitioning method. Currently, in Korea, the Dangerous Substances Safety Control Act and High-Pressure Gas Safety Act define the technical specifications of fire protection walls. However, there is no performance standard for fire protection walls considering the many possible fire hazards of petrochemical plants. Therefore, the heat release rate based on the size of open pool flames, radiation heat flux, and temperature per distance were measured through an open pool fire test using n-heptane, which is commonly used as a solvent in the production processes at petrochemical plants. The experimental results were evaluated by comparing them with values calculated according to ISO 24678-7, which is the standard for the numerical analysis of radiation heat flux in an open pool fire.

Soot volume fraction and size measurements over laminar pool flames and pre-vaporised non-premixed flames of biofuels, methyl esters and blends with diesel

Previous studies have demonstrated that methyl ester-based biodiesels produce significantly less soot compared to petroleum diesel in standard diffusion flames. However, the roles of the oxygen content and the degrees of unsaturation (DoU) of the biodiesels on their sooting propensity have not been independently analysed. In the present study, the relationship between soot yield of biodiesels and the DoU of the fuel is systematically analysed in laminar pool flames and pre-vaporised diffusion flames. The spatial distribution of soot volume fraction of the flames fuelled with four biodiesel fuels, two methyl esters and their blends with diesel are quantitatively measured using laser induced incandescence. All six biofuels have different DoU but similar oxygen mass fractions, so that the effect of the DoU on soot formation could be separately considered. The soot yield using biodiesels was measured to be lower than that of diesel fuel by a factor up to 7.5 in pool flames and by a factor of 4.0 in vapour flames. In both flame setups, the soot reduction effect of biodiesels ranks in order of DoU. The more saturated the fuel molecule is, the lower the soot yield. The soot reduction effect of the blending ratio with biodiesel was found to be non-linear, and different in pool and vapour flames. The morphology, size, and number density of soot particles were analysed using scanning electronic microscopy. The results suggest that the shape of primary soot particles is close to spherical and the structure of the point-contact aggregates is similar in all cases. Biofuels not only produce smaller particle sizes, but also fewer particles compared to diesel. Chemical kinetic simulations suggest that blending of biodiesels reduces the soot yield primarily by slowing the soot surface growth process, and secondarily by prohibiting the soot nucleation and inception. Both the nucleation (C3H3 and benzene) and growth species (C2H2) for soot formation take place more quickly and intensely for the combustion of more unsaturated fuels, which results in the correspondingly larger soot yield.

Arbitrary position 3D tomography for practical application in combustion diagnostics

This work aims to make three-dimensional (3D) tomographic techniques more flexible and accessible to in-situ measurements in practical apparatus by allowing arbitrary camera placements that benefit applications with more restrictive optical access. A highly customizable, in-house developed tomographic method is presented, applying smoothness priors through Laplacian matrices and hull constraints based on 3D space carving. The goal of this paper is to showcase a reconstruction method with full user control that can be adopted to various 3D field reconstructions. Simulations and experimental measurements of unsteady premixed CH4/air and ethanol (C2H5OH) diffusion pool flames were evaluated, comparing arbitrarily placed cameras around the probed domain to the more commonly used in-plane-half-circle camera arrangement. Reconstructions reproduced expected topological field features for both flame types. Results showed slight decrease in reconstruction quality for arbitrarily placed cameras compared to in-plane-half-circle arrangement. However, at lower numbers of camera views (N q ⩽ 6) arbitrary placement showed better results. The introduced methodology will be useful for optically limited setups in terms of handling a priori information, camera placement and 3D field evaluation.

Measurements of soot and response optimisation of laminar pool and prevaporised jet flames for various oxygenated biofuels

In this study, the generation of soot from the combustion of biodiesels and their blend with fossil diesel are investigated under laminar pool flame and prevaporised diffusion jet flame conditions. Neat biodiesels from eight feedstocks including carotene palm, palm, soy, coconut, rice bran, waste vegetable oil, duck, and goose, alongside two methyl esters of methyl laureate and methyl myristate are blended with fossil diesel at 20% volumetric intervals to form 51 different blends. The soot volume fractions for the combustion of all blends are determined using continuous-wave laser cavity extinction (CW-LCE) calibrated 2D laser-induced incandescence (2D-LII) technique. Results show that biodiesels with higher degree of saturation produce less soot, as reflected in both laminar pool and prevaroprised diffusion jet flames. The experimental data is further analysed using design of experiments (DOE) methodology. The mixture design model (MDM) following the simplex design is used to focus on the soot generating effects arising from the chemical compositions by classifying the chemical components into hydrocarbons and saturated, monounsaturated and polyunsaturated fatty acid methyl esters (FAME). The results from the Cox response trace plot associated with DOE elucidate the effects of the individual chemical group within the fuels. Both laminar flame types for the all 51 biodiesel-diesel blends exhibit the same trends with differing magnitudes. Saturated FAME has the largest singular effect on soot generation followed by hydrocarbons. However, when only neat biodiesels are considered, the laminar pool flame and laminar diffusion jet flames show differing trends for all the chemical groups. Monounsaturated FAME and saturated FAME have the greatest influence on neat biodiesel-generated soot for laminar pool flame and laminar diffusion jet flame, respectively. From the mixture design model, an optimum synthetic biodiesel mixture containing 16.1%, 34.6% and 49.3% of saturated, monounsaturated and polyunsaturated methyl esters is recommended for the lowest soot generation.

The effect of initial furnace temperature on combustion gas and PM exhausted from unsteady pool flame

In this study, PM exhausted from unsteady pool flame of iso-octane on a shallow dish under various furnace temperature conditions (25 – 700 °C) was investigated as fundamental study of fuel film combustion. Flame appearance during from ignition to combustion end under various furnace temperature conditions was observed. And relationship between maximum flame length and furnace temperature was obtained. Moreover, total masses of CO, CO₂ and PM emitted during flame formation period were measured. As the result, it was also found that total mass of PM exhausted during flame formation period increased with furnace temperature raise.

Real-time selective measurement of combustion origin hydrophobic PM using QCM

Combustion origin particulate matter (PM) has different characteristics such as hydrophilicity and hydrophobicity depending on the combustion method, however it is difficult to separate each PM characteristics. In this study, to develop real-time selective PM sensing system using a quartz crystal microbalance (QCM), PM adsorption characteristics on the QCM surface was investigated. PM emitted from a pool flame of hydrocarbon fuel such as cyclohexane and toluene was supplied to the QCM, and the frequency shift of the QCM was measured. In addition, polystyrene coated QCM with hydrophobic and acetylcellulose coated QCM with hydrophilic characteristics were also investigated.

The response of an ethanol pool fire to transverse acoustic waves

To investigate the response of a pool fire perturbed by acoustic waves to guide the technology for fire extinguishing by acoustic waves, combustion tests on an ethanol pool fire perturbed by acoustic waves were conducted at acoustic frequencies of 20–100 Hz and acoustic pressures of up to 1.2585 Pa. Firstly, acoustic parameters at the position of the pool flame perturbed by acoustic waves were tested. Secondly, the mass loss rate of the fuel, shape characteristics and oscillation characteristics of the area and height of the pool flames under acoustic perturbance were studied. A modified model of the flame height of the pool fire correlated with mass loss and acoustic parameters was established. The results indicate that, in comparison with situations without acoustic perturbance, the acoustic perturbance suppresses and promotes the dimensionless consumption rate of fuel for the pool fire, while the shape of flames is in stable or disordered state. The dimensionless combustion rate of fuel for the pool fire increases quasi-linearly with the amplitude of sound–induced local periodic displacement. The instability of the pool fire perturbed by acoustic waves is mainly caused by suppressing the dominant frequency and promoting the secondary frequency of flame pulsation.

Burning characteristics and soot formation in laminar methyl methacrylate pool flames

This study presents careful measurements from lab-scale experiments and predictions from comprehensive numerical model for the burning characteristics of laminar flames over MMA pools of different diameters with varying ullages or lip heights. Lab-scale experiments for steady burning of MMA pool are conducted, and temperature and concentrations of major species, have been measured for 3 mm ullage case for pool diameters of 25 and 30 mm. A compact kinetic mechanism with 49 species and 376 reactions, and a soot model are used for numerical simulations. Steady burning of laminar flame over an MMA pool is modelled using coupling heterogeneous interface conditions. Variable thermo-physical properties and multi-component diffusion are used. Results from grid-independent numerical simulations compare with reasonable accuracy against experimental measurements. For 25 mm MMA pool, the mass burning rate decreases rapidly from zero to 2 mm ullage and drops relatively gradually with further increase in the ullage. The ratio of mass of soot in the domain to mass of fuel burnt, decreases rapidly with an increase in ullage from zero to 3 mm, remains in same order till 5 mm ullage and then decreases with increasing ullage. Increased flame stand-off from the pool interface and oxygen penetration into the ullage causing partial premixing, form the reasons for the reduction in mass burning rate and decrease in the production of soot. The effects of pool diameter on burning characteristics at three ullages have also been presented.

Quantification of carbon particulates produced under open liquid pool and prevaporised flame conditions: Waste cooking oil biodiesel and diesel blends

The soot volume fraction (SVF) of waste cooking oil (WCO) biodiesel and blends was quantified and compared under the same total carbon flow rate via two experimental setups, namely prevaporised diffusion jet flames and pool flames using extinction calibrated laser induced-incandescence (LII). The spatial SVF distribution shows that for diesel-rich fuels, soot formation peaks near the flame and is convected downstream, whereas biodiesel flames show a more evenly distributed SVF at the flame center region. An increase in biodiesel fraction in diesel results in a reduced propensity for soot, as evident in both pool and vapour flames. Comparison of the radial profiles of SVF along the centerline shows broader SVF profiles for pool flames, reflecting the longer residence times for soot diffusion and growth compared to vapour flames, which reflected the lower mass flux for the pool burner. The total soot produced from pool flames was found to be higher than vapour flame by a factor of two for the same fuel mass consumption rate. WCO biodiesel exhibited the lowest total SVF value regardless of flame type owing to the combined effects of lack of aromatic compounds and fuel chemistry. The soot primary particle sizes produced by WCO biodiesel show lower mean diameter values by a factor of approximately 1.5 compared to diesel-produced soot. The pool flames produced carbon particulates of larger mean diameter by around 22% and 8% for diesel and WCO biodiesel, respectively, relative to the counterpart vapour flames, as a result of extended soot surface growth period.

Exhaust characteristics of PM from unsteady pool flame

Exhaust characteristics of PM from unsteady pool flame

Multilayer reaction zones of a counterflow flame of gaseous Nitrogen Tetroxide and a liquid Monomethylhydrazine pool

An experimental study of a Monomethylhydrazine (MMH)/nitrogen tetroxide (NTO) counterflow pool flame was conducted to obtain data that contributes to proposed detailed chemical reaction mechanisms. The flames were imaged through high-speed imaging of chemiluminescence of broad band light emission with Band Pass Filters (BPF) centered at 310 nm ± 5 nm and 430 nm ± 5 nm. To help explain the flame structures observed in the experiment, one-dimensional numerical simulations with detailed chemical kinetics were also performed, considering, along with the proposed reaction mechanisms, the MMH evaporation environment at the boundary conditions. The experimental results show a multi-layered flame structure of an MMH/NTO non-premixed flame composed of two orange flames and one weak blue/white flame. Results obtained in numerical simulations indicate that MMH/NTO forms the multi-layered flame structures of two orange flames due to NH3 decomposition and NO2 recombination, and the blue/white flame was newly found in the region between the two orange flames.

A study of the effects of ullage during the burning of horizontal PMMA and MMA surfaces

SummaryExperimental and numerical investigations of burning of horizontal surfaces of poly methyl methacrylate and methyl methacrylate are presented. A burner used in this study allows for the fuel surface to be oriented horizontally at a given distance from the burner rim. One of the aims of this study is to understand the effects of ullage (distance between burner rim and fuel surface) on the burning rate of the fuel and the flame structure. In the case of poly methyl methacrylate, the surface at an initial ullage regresses during its burning, and in the case of methyl methacrylate, the pool level is maintained at the given ullage by supplying the fuel at the rate of its burning. Careful repeatable measurements of temperature and species fields are carried out. These reveal the structure of a small‐scale pool flame established over a polymeric fluid such as methyl methacrylate, and such data are scarce in literature. In order to complement the experimental results, fire dynamics simulator is employed to simulate the experimental cases. Flame structure and flow field in the gas phase have been presented and discussed. As the ullage increases, the burning rate decreases. This trend is explained using surface convective heat flux results.

Behavior of PM exhausted from unsteady pool flame

Behavior of PM exhausted from unsteady pool flame

A vortex-dynamical scaling theory for flickering buoyant diffusion flames

The flickering of buoyant diffusion flames is associated with the periodic shedding of toroidal vortices that are formed under gravity-induced shearing at the flame surface. Numerous experimental investigations have confirmed the scaling,$f\propto D^{-1/2}$, where$f$is the flickering frequency and$D$is the diameter of the fuel inlet. However, the connection between the toroidal vortex dynamics and the scaling has not been clearly understood. By incorporating the finding of Gharibet al.(J. Fluid Mech., vol. 360, 1998, pp. 121–140) that the detachment of a continuously growing vortex ring is inevitable and can be dictated by a universal constant that is essentially a non-dimensional circulation of the vortex, we theoretically established the connection between the periodicity of the toroidal vortices and the flickering of a buoyant diffusion flame with small Froude number. The scaling theory for flickering frequency was validated by the existing experimental data of pool flames and jet diffusion flames.

Soot volume fraction measurements over laminar pool flames of biofuels, diesel and blends

Biodiesel and blends with petroleum diesel have shown their potential as renewable alternative fuels for engines, with additional benefits of low particulate matter and low sulfate emissions. In this paper we measure the soot volume fraction produced by three different methyl esters processed biodiesels (extracted from palm (PME), soy (SME) and coconut (CME)), and their blends with petroleum diesel, in a series of co-flow stabilized laminar pool flames, using laser induced-incandescence (LII) and laser extinction optical methods. The soot volume fraction measurement results show that all neat biodiesels produce only up to 33% of the total soot volume compared to pure diesel, and that the total soot volume correlates directly with the degree of unsaturation of the biodiesels. Blending leads to approximately linear behaviour of total soot volume, with a shift in slope with smaller sensitivity towards neat diesel.