Small Flame Research Articles

The Dynamic Response of Turbulent Dihedral V Flames: An Amplification Mechanism of Swirling Flames

The authors analyze the dynamic response of swirl-stabilized flames submitted to upstream acoustic perturbation. Extensive measurements were performed in an optically accessible single-nozzle gas turbine combustor operating on natural gas-air at inlet temperatures of 200 and 300 °C over a range of equivalence ratios from 0.55 to 0.70, a range of inlet velocities from 60 to 100 m/s, and swirl angles of 30° and 45°. Temporal oscillations of inlet velocity and heat release rate in the whole flame were measured using the 2-microphone method and global OH*, CH*, and CO2* chemiluminescence emission intensities, respectively, whereas spatially resolved measurement of heat release rate was made using time-averaged CH* chemiluminescence flame images. For the dihedral V flames, amplification characteristic of the flame transfer function was observed. This effect is, unlike the amplification mechanism of a small laminar flame, controlled by the relative ratio of the two length scales, disturbance convective wavelength and flame length. The measured transfer functions show resonance-like behavior when a nondimensional number, the ratio of half the convective wavelength to flame length, approaches unity. It was found that the flame geometric properties, specifically flame angle, also play a crucial role in the flame transfer function. The frequency-dependent behavior of swirl-stabilized flames is closely related to eigenfrequency selection processes at limit cycle pressure oscillations.

The Solidarity Days: A short reminiscence

With the retrospect of two decades, the denouement of the Solidarity saga and the revolutionary tide that swept across the face of Central Europe now seem dusted by a deceptive sheen of inevitability. But for those plunged in the hurtling cascade of events that made up 1989, the memory is rather different. The participants, the witnesses and the manipulators behind the scenes did not know where history was going, or how the river flow of events would spill across the terrain of social life, until the landscape reached, at last, a new conformation of stability. How hard it is, in the early years of the twenty-first century, with our present knowledge of the vast consequences born of the slight shifts in the political balance at the outset of 1989, to recall the specific tone and quality of those days. They were uncertain, they were drenched in uncertainty; in the cities of the Warsaw Pact, mantled by their constant coat of brown coal fumes and industrial smog, slender hopes and fine ideals were all that kept the heart alive. What did we who were visitors from outside the system see? Can we recapture our feelings and convictions then? We did not know what was going to happen, or how, or how far things would go; but there was a sense in the air, at the outset of the year of transformations, that history, after a long slumber, was starting up again. This resumption had been prepared by the preceding decade: the Solidarity years in Poland, above all, which was a period of moral rebirth. My own experience of Poland in the late 1980s left me greatly changed; I had a sense, for the first time in my life, of the power of ideas and the reality of national convictions. I also had a new sense of the way different factors, even conflicting factors, fit together in the march of history, and produce, by their clash and by the negotiation of their various intertwining influences, outcomes quite distinct from those intended by the principals in the drama. If we glance back now at a thematic x-ray of 1989, it is plain that four central figures helped shape the climate. First was Ronald Reagan, a president with very clear-cut ideas about communism; his actions while in office brought the Soviet Union to the negotiating table; his military build-up precipitated the Moscow regime's financial crisis. Reagan's Vice-President and successor, the cautious, quietist George Bush, then through masterful inaction allowed the cavalcade of change in Europe's heart to rush ahead in its natural rhythm. The second key actor onstage was the Polish Pope, John Paul II, whose insistent message to his people, and to the people of all the shadowed half of Europe, led them to lift up their eyes and to preserve a small flame of hope in their hearts. Lech Walcsa, who by this stage had come to incarnate Poland's demands for profound reform, was the natural counter to the Warsaw government. But by sublime paradox, the worst enemy of the European status quo was the leader of the Eastern Bloc, Mikhail Gorbachev, who, at every key turn in the course of 1989, was on hand, insisting that the time for force and constraint to hold the Soviet satellite empire intact was gone. All of these actors were necessary figures in the transformation. None of them expected the year of revolutions to end as it did; all of them, in their respective ways, exerted their will to break the system. Each one of the four was a man on a grander scale than the times; their mutual interaction in the course of the whole decade leading up to 1989 did much to ensure that confrontation found release, and that a dark interval of stagnation in European history came to a startling end. It is this quality of surprise that seems most worth dwelling on today. Not one correspondent predicted in serious fashion the outcome of the chain of events we all witnessed. Not one politician knew the script. Not one commentator or pundit, with the exception, oddly, of Polish emigre Zbigniew Brzezinski, dared envision the collapse in that year of the Berlin Wall. …

Effects of the Burner Diameter on the Flame Structure and Extinction Limit of Counterflow Non-Premixed Flames

Experiments and numerical simulations were conducted to investigate the effects of the burner diameter on the flame structure and extinction limit of counterflow non-premixed methane flames in normal gravity and microgravity. Experiments were performed for counterflow flames with a large inner diameter ( d) of 50 mm in normal gravity to compare the extinction limits with those obtained by previous studies where a small burner ( d < 25 mm) was used. Two-dimensional (2D) simulations were performed to clarify the flame structure and extinction limits of counterflow non-premixed flame with a three-step global reaction mechanism. One-dimensional (1D) simulations were also performed with the same three-step global reaction mechanism to provide reference data for the 2D simulation and experiment. For microgravity, the effect of the burner diameter on the flame location at the centerline was negligible at both high ( ag = 50 s−1) and low ( ag = 10 s−1) strain rates. However, a small burner flame ( d = 15 mm) in microgravity showed large differences in the maximum flame temperature and the flame size in radial direction compared to a large burner flame ( d = 50 mm) at low strain rate. In addition, for normal gravity, a small burner flame ( d = 23.4 mm) showed differences in the flame thickness, flame location, local strain rate, and maximum heat release rate compared to a large burner flame ( d = 50 mm) at low strain rate. Counterflow non-premixed flames with low and high strain rates that were established in a large burner were approximated by 1D simulation for normal gravity and microgravity. However, a counterflow non-premixed flame with a low strain rate in a small burner could not be approximated by 1D simulation for normal gravity due to buoyancy effects. The 2D simulations of the extinction limits correlated well with experiments for small and large burner flames. For microgravity, the extinction limit of a small burner flame ( d = 15 mm) was much lower than that of a large burner flame when ag ≤ 20 s−1. For normal gravity, the extinction limit of a small burner flame ( d = 23.4 mm) was also much lower than that of the large burner flame when ag ≤ 35 s−1. The effects of the burner diameter on the flame structure and extinction limit of counterflow non-premixed methane flames were more important in normal gravity than in microgravity.

The importance of thermal radiation transfer in laminar diffusion flames at normal and microgravity

The importance of radiation heat loss in laminar and turbulent diffusion flames at normal gravity has been relatively well recognized in recent years. There is currently lack of quantitative understanding on the importance of radiation heat loss in relatively small scale laminar diffusion flames at microgravity. The effects of radiation heat transfer and radiation absorption on the structure and soot formation characteristics of a coflow laminar ethylene/air diffusion flame at normal- and microgravity were numerically investigated. Numerical calculations were conducted using GRI-Mech 3.0 combustion chemistry without the NO x mechanism and complex thermal and transport properties, an acetylene based soot formation model, and a statistical narrow-band correlated- k non-grey gas radiation model. Radiation heat transfer and radiation absorption in the microgravity flame were found to be much more important than their counterparts at normal gravity. It is important to calculate thermal radiation transfer accurately in diffusion flame modelling under microgravity conditions.

Review of soot measurement in hydrocarbon-air flames

Soot, which is produced in fuel-rich parts of flames as a result of incomplete combustion of hydrocarbons, is the No. 2 contributor to global warming after carbon dioxide. Developing soot measurement techniques is important to understand soot formation mechanism and control soot emission. The various soot measurement techniques, such as thermophoretic sampling particles diagnostics followed by electron microscopy analysis, thermocouple particle densitometry, light extinction, laser-induced incandescence, two-color method, and emission computed tomography, are reviewed in this paper. The measurement principle and application cases of these measurement methods are described in detail. The development trend of soot measurement is to realize the on-line measurement of multi-dimensional distributions of temperature, soot volume fraction, soot particle size and other parameters in hydrocarbon-air flames. Soot measurement techniques suitable for both small flames in laboratories and large-scale flames in industrial combustion devices should be developed. Besides, in some special situations, such as high-pressure, zero gravity and micro-gravity flames, soot measurement also should be provided.

Experimental study on tribrachial flames in narrow channels with small fuel concentration gradients

Edge flames have become a subject of interest as basic structures for lifted-flame stabilization and turbulent flame propagation. Recently, with the development of small diffusion flame devices as energy sources for various small mechanical systems, edge flames within narrow spaces have also been investigated. In this study, the structures and propagation characteristics of a tribrachial flame (or an edge flame) in a confined narrow channel, with very small fuel concentration gradients, were experimentally investigated. Tribrachial flames could be successfully stabilized in the narrow channels. The flame shapes and propagation velocities were compared by changing the four experimental parameters of the mean velocity, fuel concentration gradient, channel gap, and fuel dilution ratio. It was experimentally observed that the luminosity of the diffusion branch diminished when the channel gap decreased. It was also found that there is a critical condition in the channel gap for maximum propagation velocity. A flow redirection effect and a heat loss effect are thought to have played a key role in the variation of the PVTF in a narrow channel, and their competition with each other caused a peak value of the PVTF at the critical channel gap.

European classes for the reaction to fire performance of wood-based panels

The classification system for the reaction to fire performance of building products in Europe has been applied to wood-based panels as being ‘products with known and stable fire performance’. The European classification system includes two sub-systems, one main system for all construction products except floorings and the other for flooring products. Panel properties such as density, thickness, joints and types of end-use application including different substrates have been studied thoroughly and are included in the classification. Most wood-based panels fall in classes D-s2, d0 or Dfl-s1 (for floorings). Testing has been performed according to EN 13823 SBI-Single Burning Item test, EN ISO 9239-1 Radiant panel test, and EN ISO 11925-2 Small flame test. Clear relationships between the main Euroclass fire performance parameters and product parameters (such as density and thickness) have been demonstrated. Tables with reaction to fire classification of different wood-based panels and end-use applications have been developed in two steps, approved by the European Commission and published in their Official Journal. The table is also included in the harmonized product standard and may be used for CE-marking. Copyright © 2010 John Wiley & Sons, Ltd.

Results from a Full-Scale Smoke Alarm Sensitivity Study

A series of 24 full-scale experiments was conducted to examine the effects of alarm type (photoelectric, ionization, and dual sensor), alarm location, fabric type (100% cotton and 100% polyester), polyurethane foam density, ignition scenario, and room configuration, on smoke alarm performance. A two-level, fractional factorial design of eight experimental configurations was developed around the five factors: fabric type, foam density, fire location, ventilation, and ignition scenario. A structure, designed to represent a single-story home or apartment, was constructed inside the Large Fire Laboratory at the National Institute for Standards and Technology for the experiments. The fire source was a chair mockup consisting of a seat and back cushion of a specific cover fabric and foam density, weighing between 5.5 kg and 8.3 kg. It rested on a metal frame and was subjected to a small propane gas flame, or an electric cartridge heater to initiate smoldering. Each experimental configuration was replicated three times. Smoldering fires were allowed to progress until they naturally transitioned to flaming fires except for one test that was terminated early due to time constraints. The smoldering to flaming transition times ranged from (81 to 182) min. Each fire progressed for a time sufficient to produce multiple hazards (smoke, heat, and toxic gases). All alarms tested were purchased from retail outlets and activated at their preset levels. Photoelectric, ionization, and dual photoelectric/ionization alarms were co-located at multiple locations to facilitate comparisons of each alarm type, and different designs of the same type of alarm. For smoke alarms in the room of fire origin, it was observed that each of the five factors had an effect on the measured alarm times that was primarily a result of fire growth rate (fabric type, foam density, and ignition scenario), or smoke dilution and transport (fire location and ventilation). The photoelectric alarm responded quicker on average than ionization alarm in two of four smoldering fire configurations, responding before the ionization alarm in all 6 trials, while the ionization alarm responded before the photoelectric alarm in two of three trials for the other two configurations. The ionization alarm responded quicker on average than photoelectric alarm in all four flaming fire configurations, and responded before the photoelectric alarm in all 12 flaming fire trials. One dual alarm had the fastest average alarm time for all four smoldering fire configurations, and responded first in 11 of the 12 trials. It also yielded faster average alarm times than the other dual alarm in seven of eight configurations, and was the first dual alarm to respond in 22 out of 23 trials where dual alarms were present.

Simultaneous Measurement of Three-Dimensional Soot Temperature and Volume Fraction Fields in Axisymmetric or Asymmetric Small Unconfined Flames With CCD Cameras

Abstract A nonintrusive measurement technique is presented numerically for simultaneous measurement of three-dimensional (3D) soot temperature and volume fraction fields in the axisymmetric or asymmetric flames with charge-coupled device (CCD) cameras. CCD cameras were introduced to capture the flame images for obtaining the line-of-sight radiation intensities. The distributions of local emission source under two wavelengths can be deduced through solving the reconstruction matrix equation by the least-square QR decomposition method from the knowledge of the line-of-sight radiation intensities of the flames. The two-color distributions of the local emission source were used to retrieve the soot temperature and volume fraction distributions. The effects of the discrete ray number of CCD cameras, the number of CCD cameras, and the system signal-to-noise ratio (SNR) on the measurement were investigated. The results show that for accurate measurement of soot volume fraction field, the CCD cameras number should not be less than four and the system SNR can be as low as 54 dB. The proposed technique can be capable for reconstructing the 3D soot temperature and volume fraction fields in both axisymmetric and asymmetric flames well.

Assessment of Fire Performance of Typical Furniture Foams with and without Fire Retardants Using a Cone Calorimeter

Both thermal and smoke aspects on typical samples of furniture foams with and without fire retardants available in the market were tested with a cone calorimeter. To study their behaviour under big fires, high incident radiative heat fluxes up to 70 kWm-2 were adjusted. Transient curves on heat release rate, mass loss rate, carbon monoxide concentration, carbon dioxide concentration, smoke release rate and other key parameters were measured. Further, chemical constituents of the fire retardants were analyzed by X-ray fluorescence, Fourier Transform Infrared, Gas Chromatography/Mass Spectrometry and Pyrolysis Gas Chromatography Mass Spectrometry. It is observed that foam treated with fire retardant would not be ignited under an incident heat flux of 10 kWm-2. However, when burning under heat fluxes higher than 20 kWm-2, there is not much improvement in the thermal aspect for foam treated with fire retardants. Even more smoke and toxic gases such as carbon monoxide was emitted. Therefore, testing ignitibility of furniture foam materials under a small match flame is not adequate. Tests with high radiative heat flux encountered in big fires are suggested. Cone calorimeter tests proposed in this paper would give a better assessment on fire safety. Finally, three risk parameters are proposed to work out a combustibility database.

The Scalar Gradient Alignment Statistics of Flame Kernels and its Modelling Implications for Turbulent Premixed Combustion

The effects of mean flame curvature on reaction progress variable gradient, \(\nabla c\), alignment with local turbulent strain rate are studied based on three-dimensional Direct Numerical Simulation (DNS) data of turbulent premixed flame kernels with different initial radii under decaying turbulence. A statistically planar flame is also considered in order to compare the results obtained from the kernels with a flame of zero mean curvature. It is found that the dilatation rate effects diminish with decreasing kernel radius due to defocusing of heat in the positively curved regions. This gives rise to a decrease in the extent of reaction progress variable gradient alignment with most extensive principal strain rate with decreasing kernel radius. The modelling implications of the statistics of the alignment of \(\nabla c\) with local strain rate have been studied in terms of scalar dissipation rate transport. A new modelling methodology for the contribution of the scalar-turbulence interaction term in the transport equation for the mean scalar dissipation is suggested addressing the reduced effects of dilatation rate for flame kernels and the diminished value of turbulent straining at the small length scales at which turbulence interacts with small flame kernels. The performance of the new models is found to be satisfactory while comparing to DNS results. The existing models for the dilatation contribution and the combined chemical reaction and molecular dissipation contributions to the transport of mean scalar dissipation, which were originally proposed for statistically planar flames, are found to satisfactorily predict the corresponding quantities for turbulent flame kernels.

Excitation of thermoacoustic oscillations by small premixed flames

Abstract Experiments have been carried out in which very small lean premixed flames closely representative of those formed by modern multiport domestic gas burners have been subjected to controlled acoustic perturbation. PLIF from CH has been used to visualise the flame response and the heat-release-rate fluctuations have been evaluated directly from the flame images. It is shown that small laminar flames can amplify the effects of acoustic velocity fluctuations by mechanisms that do not involve resonant heat loss to the burner and that the fluctuations in flame-front area are not adequately characterised by a Strouhal number alone. The measured transfer function is compared with the predictions of various analytical formulations and a new model of the flame oscillation is proposed which applies specifically to situations in which the design of the burner renders the flame base immobile.

Role of compressibility in moderating flame acceleration in tubes

The effect of gas compression on spontaneous flame acceleration leading to deflagration-to-detonation transition is studied theoretically for small Reynolds number flame propagation from the closed end of a tube. The theory assumes weak compressibility through expansion in small Mach number. Results show that the flame front accelerates exponentially during the initial stage of propagation when the Mach number is negligible. With continuous increase in the flame velocity with respect to the tube wall, the flame-generated compression waves subsequently moderate the acceleration process by affecting the flame shape and velocity, as well as the flow driven by the flame.

Case study on prevention of fire hazards in coating epoxy-based FRP work with illumination

In this study, we investigated and analyzed the causes of fire hazards on the basis of actual accidents that occurred during epoxy resin fiberglass-coating operations. Results of this study showed that during this process, two major factors could cause a fire. One factor was related to the heat produced during the mixing of the epoxy resin and a polyamide curing agent. From the results of thermal analysis, it was found that the T onset of the epoxy resin and the polyamide curing agent was 52.8 °C by DSC and T d 10 was 58.9 °C by DT/TGA, causing an exothermic hazard. Further, the results of a pseudo-adiabatic analysis performed in a Dewar vessel showed that the temperature increased from 23.5 °C to 177 °C. The other factor that could increase fire hazard was the illumination source used during the coating operation. Depending on the type of illumination source used, the temperature could increase above 350 °C. The decomposition temperature (T d 10) of PVC was 276.3 °C. The experiments involving epoxy resin fiberglass coating using an illumination source showed serious burn marks, and the polyvinyl chloride (PVC) electrical cable emitted small flames. Therefore, it can be concluded that fire was caused by the combination of two factors—the exothermic reaction between epoxy resin and the polyamide curing agent and the effect of prolonged illumination, both of which caused an increase in temperature leading to auto-ignition of the PVC electric cable.

Quenching-Resistant Multiple Micro-Flame Photometric Detector for Gas Chromatography

A multiple flame photometric detector (mFPD) based on many flames operated in series is introduced for the detection of sulfur and phosphorus compounds. The method employs attributes of a previously developed micro counter-current flame technique to readily establish any number of very small compact flames inside a narrow quartz tube. Results show for the first time that a five flame mFPD mode can improve hydrocarbon quenching resistance nearly 20-fold relative to a single flame (i.e., conventional FPD) mode, and nearly 10-fold relative to a two flame (i.e., dual FPD) mode. Under these conditions, the five flame mFPD mode is shown to maintain about 60% of its original analyte chemiluminescence even in the presence of over 100 mL/min of methane flow into the detector. In contrast to a conventional dual FPD device, the five flame mFPD mode also provides analyte sensitivity that is similar to a conventional FPD. Of note, the mFPD yields minimum detectable limits for sulfur and phosphorus of 4 x 10(-11) g S/s and 3 x 10(-12) g P/s respectively. Analyte selectivity over hydrocarbons, signal reproducibility, and response equimolarity are also improved in the mFPD, making it a potentially useful detector for applications in gas chromatography.

Measurement of infrared radiation emitted by the flame of a vegetation fire

An experimental study has been carried out on the radiation emitted in the infrared by a flame produced by the combustion of vegetation (vine branches) in a square tray of size 50 × 50 cm. Measurements have been performed with an FTIR spectrometer and an IR camera on the corresponding flame with characteristic height between 50 cm and 1 m. A specific device has been built in order to allow the simultaneous acquisition of spectra in the range between [1000–6000 cm −1] and pictures in selected bands of the infrared. Pictures with a camera in the visible range have been taken at the same time. A preliminary calibration using a reference emitter has been done in order to evaluate the emitted radiation quantitatively. By comparing the emission by flames with the one of this reference surface, the radiation emitted by a vegetation flame has been observed and analysed as a function of the wavenumber. The emission is observed to be predominant in a range around 2300 cm −1, due to CO 2 production, and strong emission bands related to H 2O are also observed. The experimental tools, FTIR spectrometer and IR camera, both in good agreement, show a weak emission due to soots, at least at this scale of relatively small flames.

Sample introduction in gas chromatography using a coiled wire filament

A simple device for field sampling and concentration of analytes for subsequent introduction into an injection port for gas chromatographic (GC) analysis has been developed. It consists of a tiny, coiled platinum wire filament (CWF) that is attached to a retractable plunger wire, which fits inside a syringe needle housing. Sampling is accomplished by dipping the end of the CWF in a liquid sample, which is drawn into the wire coil by capillary action, and introducing it into the injection port either before or after allowing the solvent to evaporate. The CWF can be used with or without a nonvolatile chemical coating. A major advantage of this sampling device is that nonvolatile sample matrix components remain on the wire coil, reducing the required injection port and liner cleaning frequency and contamination of the head of the chromatographic column. The coil itself can be easily cleaned between analyses by rinsing and/or burning off residual material in a small flame. The sampling coil facilitates specifically designed chemical reactions in the injection port, such as thermochemolysis and methylation. Applications demonstrated in this work include: (1) direct introduction of samples with little or no pre-treatment, (2) simultaneous thermochemolysis and methylation of lipid-containing samples such as bacteria and bacterial endospores for analysis of biomarkers, and (3) solid phase micro-extraction (SPME) using temporary wire coatings. The CWF allowed for significant reduction in sample preparation time, in most cases to less than a few minutes. The peak shapes examined for polycyclic aromatic hydrocarbon analytes (PAHs) were significantly better (asymmetry factors <1.3) when using the CWF sampling technique compared to splitless and on-column injection techniques (asymmetry factors >1.3). Extraction efficiencies for SPME (especially for high boiling point components such as PAHs) improved by an average of 2.5 times when using the CWF compared to the performance of commercially available SPME fibers. Coiled wire filaments and GC injection port liners were used for more than 100 Bacillus endospore thermochemolysis methylation analyses without the need for cleaning or replacement.

Generalized flame balls

We consider generalized flame balls which correspond to stationary spherical flames with a flow of hot inert gas, either a source or a sink, at the origin. Depending on the flow, these flames can have positive, zero, or negative burning speeds, with zero speeds characterizing the Zeldovich flame balls. A full analytical description of these structures and their stability to radial perturbations is provided, using a large activation energy asymptotic approach and a thermo-diffusive approximation. The results are also complemented by a numerical study. The number and stability of the generalized flame balls are identified in various regions of the l-M-h 0 space, where l is the (reduced) Lewis number, and M and h 0 the flow rate and its enthalpy at the origin, respectively. It is typically found that, when the flow is a source, there is a maximum value of the flow rate M ax depending on l and h 0, above which no stationary solutions exist, and below which there are two solutions characterizing a small stable flame ball and a large unstable flame ball; the implications of these results to the problem of ignition by a hot inert gas stream are discussed. When the flow is a sink, however, there is typically a single unstable solution, except for sufficiently large values of the Lewis number and large negative values of M, where three flame balls exist, the medium one being stable. Finally, the relation between the flame speed, positive or negative, and the flame curvature, small or large, is discussed.

Experimental Studies on Water Mist Suppression of Liquid Fires with and without Additives

The purpose of this article is to examine the effect of additives on the extinguishment of liquid pool fires with water mist. Tests are conducted using gasoline, diesel, and ethanol pool fires in a 3.0 × 3.0 × 3.0 m well ventilation compartment. The additives included representative kinds of metal compound, NaHCO3, film-forming agent, AFFF, and a multi-component agent, MC additive. Results showed that the suppression performance varied greatly depending on fuel type, additive type, and concentration. The higher the fire point, the easier it is to extinguish the hydrocarbon liquid pool fires with water mist. But for the polar fuel, small fractal flames existing around the pool edge after the fire is suppressed increased the suppression difficulty. The benefit of adding film-forming additives is observed in the suppression of hydrocarbon fires when forming a thin film layer by fluorinated surfactant on the surface. However, too much film-forming additive decreased the marginal fire extinguishing effectiveness due to the saturation effects of surfactants. Addition of a small quantity of film-forming additives did not improve the performance of water mist for ethanol fires, which is considered to be eroded by the fuel. Addition of metal compounds increased the effectiveness of water mist gradually both for ethanol and hydrocarbon fires, but there also existed upper agent limit because of the associated limiting vapor pressure of the active metal compound. The multi-component additive showed a combined suppression effect of film-forming agent and metal chemicals. It effectively extinguished both ethanol and hydrocarbon fires though coupling the physical and chemical fire suppression mechanisms and seems worth further exploration.

Numerical prediction of ion current from a small methane jet flame

This paper compares numerical simulations with experiments to describe the underlying mechanisms responsible for the voltage–current characteristic (VCC) response of a capillary-fed methane diffusion flame in an electric field. The numerical simulations, which include both combustion and electric phenomena, show good agreement with previously published experimental results, though computed flame temperatures were higher than those experimentally measured. Sub-saturated, saturated and super-saturated ion current regions are shown in the range of applied potentials: 0–2.5 kV, 2.5–3.4 kV and over 3.4 kV, respectively. The transition between the sub-saturated and saturated region is explored by predicting an evolution of the H 3O + ion profile. Furthermore, the transition between the saturated and super-saturated current region is considered by following the rate of ion production. The simulations show an enhancement of ion production at high voltages suggesting that the main factor behind the increased ion production is the entrainment of air by the ion-driven wind into the fuel jet before the reaction zone, producing a partially premixed flame. Additionally, the change in chemical reaction pathways as a result of air entrainment is discussed.