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Large hydrocarbon fuels are used for ground and air transportation and will be for the foreseeable future. A key parameter when burning these fuels is the turbulent consumption speed, which is the velocity at which fuel and air are consumed through a turbulent flame front. Such information can be useful as a model input parameter and for validation of modeled results. In this study, turbulent consumption speeds were measured for three jet-like fuels using a premixed turbulent Bunsen burner. The burner was used to independently control turbulence intensity, unburned temperature, and equivalence ratio. Each fuel had similar heat releases (within 2%), laminar flame speeds (within 5–15%), and adiabatic flame temperatures. Despite this similarity, for constant ReD and turbulence intensity, A2 fuel (i.e. jet-A) has the highest turbulent flame speeds and remains stable (i.e. without tip quenching) at lower ϕ than the other fuels. In contrast the C1 fuel, which consists of heavily-branched alkanes, contains no aromatics and has a relatively high average molecular weight, has the slowest turbulent flame speeds and is the most prone to tip quenching. The C1 fuel has the highest stretch sensitivity, in general, as indicated by calculated Markstein numbers. This work shows that turbulent flame speeds and tip stability of multi-component large hydrocarbon fuels can be sensitive to the chemical class of its components. [ABSTRACT FROM AUTHOR]

Abstract Alternative biofuels have the potential to reduce greenhouse gas emissions and particulate matter due to free of aromatics compared to traditional petroleum-based aviation fuel. The potential mitigating emission of hydrothermal-condensation-hydrotreating jet biofuel (HCHJ) derived from agriculture residue was investigated. The effects of aviation biofuel components, blend ratio and equivalent ratio on emission characteristics were conducted by Premixed Pre-evaporated Bunsen burner (PPBB) for laminar combustion and ZF850 jet engine for turbulent combustion. In compositions, HCHJ had a higher concentration of cycloparaffins (mostly in C8–C10) while petroleum-based aviation fuel (RP-3) had a higher concentration of alkylbenzenes (mostly in C8–C11). In laminar combustion, HCHJ and both 50% blend HCHJ appear no unburned hydrocarbon (UHC) due to low aromatics content and no sulfur in the biofuel. Moreover, there were no significant differences in NO and NO2 concentration for HCHJ and HCHJ blends. In turbulent combustion, HCHJ blends and RP-3 were compared engine emissions at various state points. Considering all complex effects of fuel and combustion environment, HCHJ blend had a noticeable reduction in PM2.5 emissions in comparison with RP-3 due to their lower aromatics and sulfur content. As HCHJ is similar to RP-3 in C/H ratio, density and heat value and the different aromatics contents have different tendencies to generate PM2.5 at different condition, PM2.5 emission is not only related with the total aromatic content and individual aromatic structure but also the combustion environment at thrust setting and coexisting pollutants including NOx and UHC emissions. CO and NOx emission indicated that both of turbulent state and fuel type influence emissions. HCHJ blend can be benefit for PM2.5 reduction and combustion efficiency growth. PM2.5 reduction can be obtained 77.5% at 10% HCHJ blend and 9.5% at 5% HCHJ blend while combustion efficiency can be obtained 0.05% at 5% HCHJ blend and 0.36% at 10% HCHJ blend through all thrust output.

Alternative biofuels have the potential to reduce greenhouse gas emissions and particulate matter due to free of aromatics compared to traditional petroleum-based aviation fuel. The potential mitigating emission of hydrothermal-condensation-hydrotreating jet biofuel (HCHJ) derived from agriculture residue was investigated. The effects of aviation biofuel components, blend ratio and equivalent ratio on emission characteristics were conducted by Premixed Pre-evaporated Bunsen burner (PPBB) for laminar combustion and ZF850 jet engine for turbulent combustion. In compositions, HCHJ had a higher concentration of cycloparaffins (mostly in C8–C10) while petroleum-based aviation fuel (RP-3) had a higher concentration of alkylbenzenes (mostly in C8–C11). In laminar combustion, HCHJ and both 50% blend HCHJ appear no unburned hydrocarbon (UHC) due to low aromatics content and no sulfur in the biofuel. Moreover, there were no significant differences in NO and NO2 concentration for HCHJ and HCHJ blends. In turbulent combustion, HCHJ blends and RP-3 were compared engine emissions at various state points. Considering all complex effects of fuel and combustion environment, HCHJ blend had a noticeable reduction in PM2.5 emissions in comparison with RP-3 due to their lower aromatics and sulfur content. As HCHJ is similar to RP-3 in C/H ratio, density and heat value and the different aromatics contents have different tendencies to generate PM2.5 at different condition, PM2.5 emission is not only related with the total aromatic content and individual aromatic structure but also the combustion environment at thrust setting and coexisting pollutants including NOx and UHC emissions. CO and NOx emission indicated that both of turbulent state and fuel type influence emissions. HCHJ blend can be benefit for PM2.5 reduction and combustion efficiency growth. PM2.5 reduction can be obtained 77.5% at 10% HCHJ blend and 9.5% at 5% HCHJ blend while combustion efficiency can be obtained 0.05% at 5% HCHJ blend and 0.36% at 10% HCHJ blend through all thrust output. [ABSTRACT FROM AUTHOR]

Nyamplung (Calophyllum Inophyllum) is an environmentally friendly alternative fuel that can be used to replace the consumption of fossil fuels. The purpose of this experiment was to analyze the effect of magnetic fields on the premixed flame of biodiesel from Calophyllum Inophyllum, the experiments were carried out on a bunsen burner. Fuel evaporation uses a temperature of 473 K and the equivalent ratio used is between ϕ 0.7; 0.8; 0.9; 1.0; 1.1 and 1.2. This experiment used a modified magnet that has magnetic force in 11.000 gausses with magnetic variations N-S, S-N, N-N, and S-S. Experiments revealed that magnetic fields have a significant effect to increase the value of laminar flame speed on magnetic variations point at S-S 3.8%; N-N 4.8%; S-N 17.09%, and the highest laminar flame speed were at point N-S 20.7%. The enhancement value of laminar flame speed indicated more optimum combustion processes. The magnetic fields can influence the O2, and H2O and change the orientation of the hydrocarbons which makes it easier for O2 and fuel to carry out the oxidation process, resulting in more optimal combustion.

Nyamplung (Calophyllum Inophyllum) is an environmentally friendly alternative fuel that can be used to replace the consumption of fossil fuels. The purpose of this experiment was to analyze the effect of magnetic fields on the premixed flame of biodiesel from Calophyllum Inophyllum, the experiments were carried out on a bunsen burner. Fuel evaporation uses a temperature of 473 K and the equivalent ratio used is between = 0.7; 0.8; 0.9; 1.0; 1.1 and 1.2. This experiment used a modified magnet that has magnetic force in 11.000 gausses with magnetic variations N-S, S-N, N-N, and S-S. Experiments revealed that magnetic fields have a significant effect to increase the value of laminar flame speed on magnetic variations point at S-S 3.8%; N-N 4.8%; S-N 17.09%, and the highest laminar flame speed were at point N-S 20.7%. The enhancement value of laminar flame speed indicated more optimum combustion processes. The magnetic fields can influence the O2, and H2O and change the orientation of the hydrocarbons which makes it easier for O2 and fuel to carry out the oxidation process, resulting in more optimal combustion. [ABSTRACT FROM AUTHOR]

AVGAS 100LL is an aviation fuel used in piston engine aircraft, particularly in training aircraft such as the Cessna 172S with Lycoming engines. The use of lead in this fuel can have various health-related concerns. Therefore, reducing the use of leaded fuel has become a solution to address these issues. This study aimed to investigate the combustion characteristics of AVGAS fuels, including AVGAS 100%, AVGAS 75% + PERTAMAX 25%, and AVGAS 50% + PERTAMAX 50%. The research involved conducting combustion tests using a Bunsen burner. The results showed that the addition of PERTAMAX to AVGAS significantly influenced the temperature, color, flame height, and flame area produced. The temperature values were higher for AVGAS 100% compared to AVGAS mixed with PERTAMAX. On the other hand, the flame height and flame area were lower for AVGAS 100% compared to the blended fuels. These findings indicate that the addition of PERTAMAX affects the combustion characteristics of AVGAS fuels. Further studies are recommended to explore and expand our understanding of the effects of blending AVGAS with alternative fuels. [ABSTRACT FROM AUTHOR]

The primary objective of this study is to measure the laminar burning velocity of perfectly premixed hydrogen-air, methane-air, ethane-air, ethylene-air, and propane-air flames, at near-cryogenic temperatures and atmospheric pressure. Initial fuel-air mixture temperatures as low as 160 K were investigated. The experimental methodology was validated by comparing the results obtained with those from previous studies available in the literature and with numerical simulations using five different chemical mechanisms. First, for all fuels, the laminar burning velocity evolution as a function of the equivalence ratio followed the same trend at 295 K and 240 K. Regardless of the equivalence ratio and mixture composition, the laminar burning velocity decreased by 22 to 44% for hydrogen, methane, ethane, ethylene, and propane flames when the temperature was decreased from 295 K to 240 K. Second, for stoichiometric conditions, the laminar burning velocity decreased by about 50% for all fuels, when the temperature was decreased by 100 K, from 295 to 195 K. These experimental results were in excellent agreement with laminar burning velocities calculated by a power law of the ratio of unburned gas temperature to ambient temperature, with exponent values from the literature, obtained for temperatures above the ambient. All five chemical mechanisms provided a very good agreement, within or near experimental uncertainties, for most of the fuels and conditions investigated, even at low temperatures. Overall, this study provides valuable information on the laminar burning velocities of various hydrocarbon and hydrogen fuels at near-cryogenic temperatures, which can be useful for the design of cryogenic storage systems and the validation of chemical kinetic models for conditions below ambient temperatures.

The Bunsen burner was designed by Robert W. E. Bunsen in Germany more than 150 years back. By controlling the mixing of aerial oxygen with the fuel (hydrocarbons, nitrogen oxide, biogas, etc.) or fuel mixture, Bunsen burners can produce either oxidizing or reducing flames. The temperature of the Bunsen burner flame is different in different zones. This burner is mandatory for qualitatively detecting various inorganic and organic samples through the flame test and Lassaigne's test, respectively. Application of the Bunsen burner extends to atomic absorption spectroscopy and atomic emission spectrometry. [ABSTRACT FROM AUTHOR]

The use of culture media and sterile technique involving flaming of equipment in order to maintain unialgal or aseptic conditions is standard laboratory practice. However, as a result, atmospheric CO2 concentrations, especially within laminar flow units but also in the laboratory as a whole, can become quite elevated. Media exposed in these conditions during routine work was observed to absorb this CO2 and become increasingly acidic with time. This has consequences for long-term culture maintenance and eco-physiological studies. The degree of this effect will vary between laboratories, as well as over time as global ambient CO2 concentrations continue to increase. Various ways of mitigating this are discussed. [ABSTRACT FROM AUTHOR]

The laminar flame speeds of CH4 /H2 /air mixtures were experimentally studied at elevated initial temperatures using the Bunsen burner method combined with the Schlieren technique, and the corresponding cases were computed using CHEMKIN-PRO. The effect of initial temperatures on the propagation characteristics of laminar premixed flames was discussed from the perspectives of thermodynamics and chemical kinetics. The results show that the laminar flame speeds of the mixtures at 293 - 500 K can be predicted well by GRI-3. 0 mechanism. The greater increments of laminar flame speeds of mixtures are presented at higher H1 fractions under all tested initial temperatures. The laminar flame speeds and adiabatic flame temperatures of mixtures almost linearly increase with a growth of initial temperatures with the same equivalence ratios. With the rise of initial temperatures, the dominant promotion of H + O2 = O + OH on the mass burning rates of mixtures can be enhanced by the great growth of the mole fractions of H radicals. Therefore, the laminar flame speed of CH4 /H2 / air mixtures significantly increases at elevated temperatures. [ABSTRACT FROM AUTHOR]

Nano γAl2O3 has been one of the nanometal oxides that has improved the characteristics of biodiesel. The effect of γAl2O3 nanoparticles addition on premixed flame combustion is investigated with an experiment on the laminar flame speed of Calophyllum inophyllum methyl ester 30% and 70% petrodiesel mixtures, at atmospheric pressure and preheated temperature T = 473K. The γAl2O3 nanoparticles added to CIME30 biodiesel were 0ppm, 100ppm, 200ppm, and 300ppm. Experiments were carried out on a bunsen burner. The equivalent ratio of the mixture between ϕ = 0.67 to 1.17. Experiments revealed that the addition of nanoparticles to CIME30 biodiesel expands the flammability limit and increases the laminar flame speed. CIME30 without nanoparticles, flame stable between ϕ = 0,76 -1,17. CIME30 with nanoparticles, flame stable between ϕ = 0,67 -1,17. Combustion of CIME30 required a lot of air. The highest laminar flame speed occurred at the equivalent ratio ϕ = 0.83. The highest laminar flame speed of CIME30 0, 100, 200, and 300 ppm were 30.77, 34.50, 35.90, 38.45 cm/s respectively. The higher the nano γAl2O3 concentration the higher the laminar flame speed. This occurs due to the catalytic effect of γAl2O3 on biodiesel and its mixtures.

The objective of this study is to investigate the impact of different fractions (0–0.05) of C 6 F 12 O addition on laminar flame speed of hydrocarbon syngas by varying the fuel/oxidizer equivalence ratio (0.6–1.2) using Bunsen burner method. The determination of the syngas composition comes from the venting gas of lithium-ion cell during thermal runaway. It is found that C 6 F 12 O is significantly more effective at stoichiometric and fuel-rich conditions compared to lean flames regardless of fuel species, which implies more suitable for syngas/air flame inhibition than CH 4. The laminar flame speeds of syngas/air increased with lower concentration (<0.01) of C 6 F 12 O when equivalence ratio less than 0.67, while it decreased with arbitrary concentration of C 6 F 12 O at the condition of equivalence ratio not less than 0.67 due to the increased heat release rate by exothermic reaction involving C 6 F 12 O. The laminar flame speed was more sensitive to C 6 F 12 O addition at stoichiometric and fuel-rich conditions due to the inhibitory effect of substances containing fluorine. Comparison between experimental and numerical results shows a better agreement under fuel-lean conditions with lower C 6 F 12 O additions using a modified mechanism derived from USC Mesh II. Thermodynamic equilibrium calculations and sensitivity analyses are showed separately that the variation of flame radical concentrations is consistent with laminar flame speeds and the lean flames are more sensitive to the reactions containing fluorine compared to rich for syngas/air flame with C 6 F 12 O addition. • Venting gases of Lithium-ion cells (LC) during thermal runaway is flammability. • Effectiveness of C 6 F 12 O in suppressing LC syngas/air flames is studied. • Kinetic mechanism of C 6 F 12 O/LC syngas (or CH 4)/air is verified by Bunsen flames. • C 6 F 12 O is more suitable for inhibiting LC syngas flames compared with CH 4. [ABSTRACT FROM AUTHOR]

Flame monitoring of industrial combustors with high-reliability sensors is essential to operation security and performance. An ion current flame sensor with a simple structure has great potential to be widely used, but a weak ion current is the critical defect to its reliability. In this study, parameters of the ion current sensor used for monitoring flames on a Bunsen burner are suggested, and a method of further improving the ion current is proposed. Effects of the parameters, including the excitation voltage, electrode area, and electrode radial and vertical positions on the ion current, were investigated. The ion current grew linearly with the excitation voltage. Given that the electrodes were in contact with the flame fronts, the ion current increased with the contact area of the cathode but independent of the contact area of the anode. The smaller electrode radial position resulted in a higher ion current. The ion current was insensitive to the anode vertical position but largely sensitive to the cathode vertical position. Based on the above ion current regularities, the sensor parameters were suggested as follows: The burner served as a cathode and the platinum wire acted as an anode. The excitation voltage, anode radial and vertical positions were 120 V, 0 mm, and 6 mm, respectively. The method of further improving the ion current by adding multiple sheet cathodes near the burner exit was proposed and verified. The results show that the ion current sensor with the suggested parameters could correctly identify the flame state, including the ignition, combustion, and extinction, and the proposed method could significantly improve the magnitude of the ion current.

Based on directed relation graph with error propagation methods, 39 species and 231 reactions skeletal mechanism were obtained from Mech_56.54 (113 species and 710 reactions) mechanism of methane. The ignition delay times, laminar flame propagation speed, and important species were calculated using the simplified mechanism at different pressures and equivalence ratios. The simulation results were in good agreement with that of detailed mechanisms and experimental data. The numerical simulation of the Bunsen burner jet flame was carried out using the simplified methane mechanism, and the simulation results well reproduced the temperature, flow fields and distribution of important species at flame zone. The compact methane reduced mechanism can not only correctly respond to its dynamic characteristics, but also can be well used for numerical simulation, which is of great significance in engineering applications. [ABSTRACT FROM AUTHOR]

Acoustic waves passing through a swirler generate inertial waves in rotating flow. In the present study, the response of a premixed flame to an inertial wave is scrutinized, with emphasis on the fundamental fluid-dynamic and flame-kinematic interaction mechanism. The analysis relies on linearized reactive flow equations, with a two-part solution strategy implemented in a finite element framework: Firstly, the steady state, low-Mach number, Navier–Stokes equations with Arrhenius type one-step reaction mechanism are solved by Newton's method. The flame impulse response is then computed by transient solution of the analytically linearized reactive flow equations in the time domain, with mean flow quantities provided by the steady-state solution. The corresponding flame transfer function is retrieved by fitting a finite impulse response model. This approach is validated against experiments for a perfectly premixed, lean, methane-air Bunsen flame, and then applied to a laminar swirling flame. This academic case serves to investigate in a generic manner the impact of an inertial wave on the flame response. The structure of the inertial wave is characterized by modal decomposition. It is shown that axial and radial velocity fluctuations related to the eigenmodes of the inertial wave dominate the flame front modulations. The dispersive nature of the eigenmodes plays an important role in the flame response. [ABSTRACT FROM AUTHOR]

The effect of wall thermal conditions, pre-heating of the inlet air–fuel mixture (Tin), and pore density of the porous medium (λ) on the stability limit and NO emission in a porous-free flame burner is numerically investigated. A reduced chemical mechanism and realizable k-ɛ turbulence model are used for the simulation. The numerical simulation is validated with the experimental data. The results show that the flame stability limit is extended with increasing the pore density while the maximum and minimum NO emissions are produced in pore densities of 8 ppc and 16 ppc, respectively. It is observed that the use of insulated wall condition causes the flame blow-off to occur at higher inlet velocities compared to that of the constant wall temperature condition. On the other hand, the use of constant wall temperature condition (cooled wall), causes flashback to occur in lower inlet velocities compared to that of the insulated wall. Constant wall temperature condition decreases NO emission in comparison with the insulated wall condition approximately by 18%. The flame stabilizes at higher inlet velocities and so stability limit is extended when inlet mixture temperature increases. This also causes NO emission to increase. [ABSTRACT FROM AUTHOR]

Highlights • PLIF measurements and DNS of methane/air Bunsen flames in high pressures are reported. • The accuracy of Bunsen burner rig for laminar flame speed measurement is evaluated. • The mid-height of the flame gives the most accurate flame speed data. • The flame-area and the flame-cone-angle experimental methods are compared. • An optimal inlet velocity is found for measurement of laminar flame speed. Abstract Laminar methane/air premixed flames at different pressures in a newly developed high-pressure Bunsen flame rig are studied using detailed numerical simulations and laser diagnostics. In the numerical simulations, one-dimensional and two-dimensional axisymmetric configurations were considered employing detailed transport properties and chemical kinetic mechanisms. In the measurements, OH PLIF was employed. The aims are to improved the understanding of the structures of the flames at varying pressures, to measure the laminar flame speed at different pressures, and to quantify the accuracy of the Bunsen flame method for measurement of laminar flame speed at different pressures. The stoichiometric and fuel-rich flames were found to exhibit a two-reaction-zone structure: an inner premixed flame in which the fuel was converted to CO and H 2 , and an outer diffusion flame in which CO and H 2 were oxidized further to form combustion products. With increasing pressure, the inner premixed flame becomes thinner and the flame as a whole has the tendency to become unstable. Using the numerical and the experimental data, the methods of f lame-cone-angle and flame-area were used to extract the laminar flame speed for different equivalence ratios and pressures. The flame-cone-angle method showed slightly better accuracy than the flame-area method did. The accuracy of both methods became lower under high pressure conditions. The inlet velocity of the burner was shown to affect the accuracy of the extracted laminar flame speed. For a stoichiometric atmospheric flame it was found that the most suitable inlet velocity for the fuel/air mixture was about 6 times the laminar flame speed, yielding a flame length about 7 times the radius of the burner. With appropriate flame length, the mid-height of the flame showed a rather low flame stretch rate, the laminar flame speed being in close agreement with the unstretched laminar flame speed, the error being less than 6% for the flames that were studied. [ABSTRACT FROM AUTHOR]

Epoxy-based intumescent coatings are widely used in oil and gas industries, shopping complexes and petrochemical plants to provide fire protection to the metallic substrates during the event of a fire. The present work shows how the incorporation of basalt fibers as filler material in an epoxy-based intumescent coating enhances its thermal insulation property. Dispersing agents (ethanol or glycidyl ether) were also added to the coating and their effects on the dispersion of the basalt fibers and the thermal performance of the coating were also discussed. Bunsen burner (ASTM E119) and expansion tests were performed to study the influence of basalt fibers’ dispersion on the thermal insulation property of the coating. Coatings and their chars were also analysed by Field Emission Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) analyses. Thermal stability was investigated using Thermogravimetric Analysis (TGA) in the pyrolysis conditions. Fire test results showed that the formulation containing ethanol as dispersing agent provided a higher fire protection, whereby the backside of the steel plate can reach a very stable plateau at 189 °C after 15 min exposure. It is also shown that the coating reached the highest expansion of 1087% with a very homogeneous char structure. The FESEM images also confirmed that basalt fibers were well dispersed when ethanol was used, whereas aggregates were formed when no dispersing agent was added. XRD and FTIR showed that the presence of boron oxide, boron phosphate, carbon and silica in the formulations which are thermally stable can improve the thermal performance of the intumescent coating. Finally, TGA confirmed that the thermal stability of formulations containing dispersing agents has been improved. [ABSTRACT FROM AUTHOR]

The simplification of the dynamic model of aviation kerosene oxidation is one of the important problems in numerical simulation of combustion chamber. It plays a decisive role in CFD numerical calculation and for reducing the stiffness of convergence, as well as for introducing chemical reactions to more complex turbulent combustion problems. This study aims to present a two-component surrogate fuel model for chemical reactions. Furthermore, the simplified mechanism of the optimization of the ignition delay time and experimental value is adopted using the direct relation graph method (DRG). As the primary originality for the paper, the eclectic simplified mechanisms with certain precision and fewer components and elementary reactions were concluded. And the simplified mechanism was introduced into FLUENT to simulate the precast evaporation flame of the Bunsen burner, which is a RP-3 fuel. Numerical results are in good agreement with the experimental results. The existing simplified mechanism for the two-component RP-3 aviation kerosene alternative fuel can be applied to the practical engineering problems of the numerical forecast. [ABSTRACT FROM AUTHOR]

Purpose This study aims to discuss the modification and/or improvement of intumescent coating system by incorporating waterborne resin with an appropriate combination of flame-retardant additives and four different fillers, namely, TiO2, Al(OH)3, Mg(OH)2 and CaCO3.Design/methodology/approach Coating mixtures are characterized using the Bunsen burner, thermogravimetric analysis, limiting oxygen index, scanning electron microscope, static immersion bath, Fourier transform infrared and adhesion tester.Findings Results show that the combination of coating with CaCO3 filler significantly improved fire protection performance because of its thick char layer and the equilibrium temperature being 264°C. Char layer showed a uniform dense foam structure on micrograph and this formulation had adhesion strength of 2.13 MPa, which indicates effectiveness of the interface adhesion on substrate. Conversely, the combination of coating with Al(OH)3 exhibited highest oxygen index of 35 per cent, which resulted in excellent flammability resistance.Research limitations/implications This paper discusses only the effect of mineral fillers on properties of intumescent coatings.Practical implications In the modern design of building infrastructure, fire safety is significant for the protection of human life and assets. The application of intumescent coating in buildings is currently practiced because of its effect on material flammability during a fire.Originality/value The analysis method to evaluate the performance of water-borne resin with different fillers is formulated, and it could be applied in all kinds of coatings and mixtures to be used as an effective fire protection system for steel constructions. [ABSTRACT FROM AUTHOR]

The characteristics of local extinction on the tip of syngas premixed Bunsen flames with different hydrogen fractions have been investigated experimentally with OH-PLIF technique and numerical simulation. Coupled effects of stretch and diffusion on the syngas Bunsen flame with highly negative curvature were studied. Local Karlovitz number was introduced to indicate the onset of local extinction at the Bunsen flame tip. Results showed that the onset equivelance ratio of local extinction at the syngas Bunsen flame tip does not change with the outlet velocity. The coupled effects of stretch and diffusion result in the decrease of flame reaction rate along the syngas Bunsen flame at fuel-lean condition. When the flame reaction rate decrease to a critical extent, local extinction of Bunsen flame tip occures. The local Karlovitz number can be considered as a parameter of the critical condition. The syngas Bunsen flame tip will extinguish when the local Karlovitz number reaches around 4, irrespective of hydrogen fractions and outlet velocity. This means that Bunsen flame tip starts to appear local extinction when the tangential flow time is comparable to normal chemical reaction time, which is the same as counterflow flames with positive stretch. Furthermore, results also showed that there is no H 2 leakage even the syngas Bunsen flame tip extinguishes at the numerical study conditions. [ABSTRACT FROM AUTHOR]

This work assesses two hypotheses that predict how turbulence properties vary within premixed turbulent flames that lie in the regime of Broadened Preheat-Thin Reaction layers. There have been few prior measurements describing flames in this regime. The authors previously found that very broad preheat layers were achieved for turbulence levels ( u ′/ S L ) up to 243. Surprisingly, the reaction layer thickness did not increase, despite having Kolmogorov scales smaller than the laminar reaction layer thickness. A first hypothesis is that the turbulence decays in the preheat layer (as the temperature rises and viscous forces increase), so that the reaction layer sees only a small fraction of the initial turbulence. It follows that this turbulence decay might be responsible for the observed non-linear bending of the curve of turbulent burning velocity versus turbulence level. A second hypothesis is that the total turbulent kinetic energy does not decrease significantly in the preheat zone; instead, the small eddies decay and cause the integral scale to increase. Conditional averages are required to assess these two hypotheses. Fluorescence imaging identified the reaction zone boundary and particle image velocimetry diagnostics were applied simultaneously. The velocity measurements were conditioned on η , the distance to the upstream boundary of the reaction zone in each image. Conditioned measurements of turbulent kinetic energy, average eddy rotational velocity, strain rate, enstrophy, and integral length scale were computed through the flame. Results indicate that the turbulence level does not decrease within the broad preheat layers, and therefore the first hypothesis is not valid. In fact, the turbulence level within the entire burner core does not vary appreciably. However, the second hypothesis was supported by the measurements, since the integral scale increased by 50% across the preheat layer. The total turbulent kinetic energy did not decrease significantly. One explanation for this result is that small eddies are dissipated in the preheat zone. [ABSTRACT FROM AUTHOR]