Gas Jet Flames Research Articles

The study of solid flame model of diffusion jet flame for the ammonia and propane mixed gas under the inclined ceiling

In order to solve the environmental pollution and energy dilemma, the ammonia has been considered as a new fuel and a carbon-free hydrogen carrier, which can be blended into the traditional hydrocarbon fuels. In this study, the evolution of flame emissivity, view factor and radiative heat flux have been investigated under different mass flow rates of ammonia and propane, and inclined angle of ceiling. A radiation prediction model of ammonia-propane mixed gas jet flame under inclined ceiling with different inclined angles has been developed. This prediction model can accurately describe the flame morphology and simplify the calculations, and consider the influence of mixing ratio on combustion reaction. The experimental results indicated that the flame emissivity, view factor, and radiative heat flux decrease with the increase of ammonia concentration. The prediction error of the traditional model will be enlarged with the increase in the inclined angle of ceiling. The modified model added the undersurface of ceiling jet flame, which reduces the prediction error from 25 % to 14 %. These prediction models are helpful in predicting the thermal radiation of jet flame under inclined ceiling.

Experimental study on hydrogen-enriched natural gas jet fire hazards: Assessment of the flame geometrical parameters

In the future, hydrogen will be more frequently injected into natural gas networks for storage and transportation purposes. A diffusion jet flame forms when gaseous fuel leakage occurs during the transportation or utilization of hydrogen-enriched natural gas, and the fuel is ignited by an ignition source in still air. In the study, methane was chosen to simulate natural gas. Experiments with the hydrogen addition fraction reaching up to 20% were performed to study the effects of the initial flame angle (θ = 90°, 60°, 30°, 0°, and −30°), variable nozzle diameter (de = 3.15, 4, 4.94, 5.65, and 6 mm) and a multitude of fuel flow rates (10, 20, 30, 40, 50, and 60 L/min) on the morphological parameters of the gas jet flames. The geometrical features of the jet flame were determined via video processing for each experiment. The geometrical parameters of hydrogen-enriched natural gas were quantified under different conditions. The experimental results indicate that a dimensionless prediction model was established for the flame height of hydrogen-enriched natural gas by modifying the flame Froude number (Frf) for vertical jet flames. For upward jet flames, the normalized flame horizontal projection length (Lx) of hydrogen-enriched natural gas is well correlated with Q∗. A global prediction model for inclination angles of 0° ≤ θ ≤ 60° and 2000 < Q∗<20,000 was proposed based on the experimental data. For downward jet flames, the normalized horizontal projection length and downward extension length (Ld) of the hydrogen-enriched natural gas jet flame are correlated with Q∗, with powers of 2/5 and 3/5, respectively. Dimensionless prediction models for the horizontal projection length and downward extension length are given by modifying the flame Froude number. Quantitative results were proposed in order to gain insight into the development of the key parameters and the effects on the environment, from which extinguishing concepts and safety areas can be directly derived.

Comparing the risk of third-party excavation damage between natural gas and hydrogen pipelines

Existing natural gas pipelines can facilitate low-cost, large-scale hydrogen transportation and storage, but hydrogen may entail safety challenges. These challenges stem from hydrogen’s different properties compared to natural gas, such as higher ignition probability, different flame behavior, and potential for hydrogen embrittlement. Although risk assessments for hydrogen pipelines are increasing, the impact of hydrogen on the risk of third-party excavation damage (TPD), the major cause of pipeline incidents in the U.S., has received little attention. This work presents the SHyTERP model for Safe Hydrogen Transportation and Excavation Risk Prevention for Pipelines. The model incorporates causal models, excavation damage and pipeline failure statistics, and validated physical models of hydrogen and natural gas release and jet flame behavior. Through four case studies, the model compares the TPD risks of hydrogen and natural gas pipelines, offering insights and recommendations for the safe implementation of hydrogen in existing pipelines.

Understanding the influence of the confined cabinet on thermal runaway of large format batteries with different chemistries: A comparison and safety assessment study

With the increasing development of large format lithium-ion batteries (LIBs) in automotive sectors, thermal runaway (TR) and fire hazards have become crucial challenges. A series of overheating experiments were performed on four large format LIBs with various chemistries under two conditions. To simulate the electric vehicle applications, the cabinet was employed in the confined space tests. The results showed that under the condition of stopping heating at safety venting (SV), all LiNixCoyMnzO2 (NCM) cells caught fire and TR, while no TR occurred for LiFePO4 (LFP) cells. The LFP cells cannot ignite spontaneously but only spray the electrolyte during TR. The triggering temperatures of TR for NCM cells are similar and close to the temperature of SV for LFP cells. For NCM LIBs, with the ratio of nickel increasing, the TR hazards increase, including the thermal and toxic hazards, larger than that of LFP cells. From the aspects of the TR risks and TR hazards, a safety assessment method was established to grade the fire hazards. Compared with open space tests, the LIBs with different chemistries in confined space tests have the same TR risks but lower TR hazards. The fire-induced toxicity was quantitatively evaluated by determining the fractional effective concentration and fractional effective dose. Moreover, the fire of LIBs is compared to the gas jet flame and pool fire of several typical fuels. Such a comparison analysis on large-scale LIBs with different chemistries can contribute to the selection of cells and safety design for automotive sectors.

The Safety of Hydrogen Jet-flame Suppression Training

The purpose of this study was to reproduce hydrogen gas leakage and jet flame accidents that can occur in hydrogen gas storage facilities to obtain basic data and apply the gained knowledge to firefighter training facilities, thereby improving safety and the response to accidents. A total of 11 scenarios were explored. In scenarios 1∼5, the hydrogen leakage and jet flame types for high (70 MPa), medium (55 MPa), and low pressures (40 MPa) were visualized with the Schlieren system. With the aid of a high-speed camera, it was confirmed that the spraying angle and length were 18∼20° and approximately 10∼12 m, respectively. In addition, in scenarios 4 and 5, the damage caused by the radiant heat was recorded to be slightly higher in the arm/hand and thigh/leg regions. The noise of jet flames was measured in scenarios 6∼11 using a sound level meter, indicating a 10 dB louder flame at medium pressure (52 MPa, 130 dB) than at low pressure (17 MPa, 120 dB) Therefore, long-term exposure is may damage hearing.

Experimental Study on the Thermal Effect according to the Distance around a Hydrogen Jet Flame

In this study, the safe distance in the case of a hydrogen vehicle fire was analyzed according to the temperature distribution around a hydrogen gas jet flame formed by the thermally activated pressure relief device operation of a hydrogen storage container. The experiment was conducted while 70 MPa hydrogen gas was released from a 1.8-mm-diameter nozzle to a 1.8- × 1.8 m fire-resistant structure wall for distances of 2 and 4 m between the nozzle output and the wall. To analyze the temperature around the hydrogen gas jet flame, five fire-fighting heat-protective hood test samples, certified by the Korea Fire Institute, and temperature sensors were installed every 1 m from the center of the jet flame in the vertical direction to the direction of the flame. In the experiment, the temperature around the jet flame was measured to observe the safe distance for firefighters. The results show that the safe distances at 70°C or less, which is harmless to firefighters, were 5 m without a heat-protective hood and 3 m with a heat-protective hood. In addition, it was confirmed that the direction of the jet flame and blocking by obstacles affect the safe distance during fire-fighting and rescue activities by firefighters.

Numerical and experimental analysis of jet release and jet flame length for qualitative risk analysis at hydrogen refueling station

The advent of eco-friendly hydrogen vehicles has prompted attempts to increase the installation of hydrogen refueling stations in urban areas; however, sufficient safety measures have yet to be established. Gas plume dispersion, jet flame, and heat flux were investigated using HyRAM software by considering accidents at hydrogen refueling stations in reports published by Sandia National Laboratories. Hydrogen release and jet flame length were measured using the Schlieren imaging system and a thermal imaging camera. The HyRAM simulation analysis results were more conservative than the experimental results. These showed that the pressure and leak diameter greatly influenced the safety of hydrogen facilities. Individual and societal risks were analyzed through RISKCURVES, and the risks were found to be highest in the sidewalk and dispenser. An F-N (Frequency- Number of fatalities) curve to verify the risk of installing a hydrogen refueling station in urban areas was derived, and the safety distance from residents was proposed.

Conversion of natural gas jet flame burners to hydrogen

In a study of conversion from CH4 to H2, jet flame characteristics of these gases and their blends are compared on a burner diameter scale of mm. Low velocity H2 and CH4 jets, burned on pipes of different diameters, indicate higher blow-off limits for H2, but lower heat release rates, a consequence of its lower specific energy. Compensation for this might be obtained through increased H2 flow velocity, or a small increase in pipe diameter. Blended CH4/H2 flames have lower heat release rates than CH4 alone, yet small proportions of H2, with CH4 might still be burned, on a CH4 burner. Throughout, fundamental understanding is enhanced through two dimensionless groups: laminar flame thickness normalised by burner diameter, δk/D, and the dimensionless flow number, U∗. These suggest an optimal role for H2 combustion, utilizing its high acoustic and blow-off velocities, in high intensity, subsonic, combustors, at low δk/D, and high U∗.

Effects of Hydrogen-Enrichment on Flame-Holding of Natural Gas Jet Flames in Crossflow at Elevated Temperature and Pressure

The effect of hydrogen (mathrm {H}_{mathrm {2}}) enrichment on the flame-holding characteristics of two natural gas jet flames in crossflow is investigated here, experimentally. The flame and flowfield measurements are analyzed using simultaneously acquired high-speed (10 kHz) stereoscopic particle image velocimetry, planar laser-induced fluorescence of the hydroxyl radical, and OH* chemiluminescence. The flames, enriched with 20% and 40% mathrm {H}_{mathrm {2}}, by volume, are studied at conditions typical of the mixing duct of a modern gas turbine engine; specifically in confinement, at 10 bars, and with a crossflow preheat of 530 K. Consistent with previous findings, the 40% mathrm {H}_{mathrm {2}} flame was found to be stabilized on the windward and leeward side of the jet, while the 20% mathrm {H}_{mathrm {2}} flame was stabilized only on the leeward side. Analysis of mean and instantaneous velocity fields showed no major differences in the trajectories and principal compressive strain fields of the two flames. The presence of the windward stabilized flame in the 40% mathrm {H}_{mathrm {2}} case was, however, found to decrease the centerline velocity decay and greatly reduce or eliminate large scale vortices along the windward shear layer. The difference in the flame-holding here was attributed to the difference in the extinction strain rate from the addition of hydrogen, which would impact the local and global extinction of the flame along the high shear windward region of the flame.

Effect of Pressure on Hydrogen Enriched Natural Gas Jet Flames in Crossflow

The effect of pressure on hydrogen (H2) enriched natural gas jet flames in crossflow is experimentally investigated here. Simultaneously acquired high speed OH* chemiluminescence, OH planar laser induced fluorescence (PLIF), and stereoscopic particle image velocimetry are used to study flames at conditions typical of a gas turbine premixer, i.e. at elevated pressure, preheated crossflow, and in confinement. Two different H2 enrichment levels (40% and 20%, by volume) and pressures (10 bar and 15 bar) were studied here.Flames at the higher H2 enrichment level were found to be stabilized on the windward side, while the flames at the lower H2 enrichment were found to be stabilized only on the leeward side. Increased H2 enrichment was also associated with greater sootiness in the measured region. Jet centerline trajectories showed greater penetration for the higher H2 enrichment flames, which is in agreement with existing theories on the effect of heat release from a flame on crossflow entrainment. There were no significant changes observed in the mean OH* chemiluminescence, OH-PLIF, velocity fields, and velocity fluctuation fields with changes in pressure.

A Novel In Situ Flamelet Tabulation Methodology for the Representative Interactive Flamelet Model

ABSTRACTA priori flamelet tabulation methods have been used extensively to model premixed and non-premixed combustion in Reynolds-averaged Navier–Stokes (RANS) and large Eddy simulations (LES). Pre-tabulation of flamelet libraries have led to significant cost reduction of Computational Fluid Dynamics (CFD) simulations. However, these tabulation methods rely on certain simplifying assumptions. The dimensionality of the flamelet manifolds and size of flamelet libraries are also constrained due to memory and computational limitations. This limits the applicability and predictive capability of flamelet models. The traditional representative interactive flamelet (RIF) approach with multiple flamelets on the other hand involves online solution of flamelet equations and presumed probability density function (PDF) integration at each computational cell, making it attractive but computationally expensive and not suitable for LES with large cell counts. The current work discusses the development of a novel methodology that combines the advantages of an online flamelet solver along with the computational efficacy of tabulated models. The novel in situ tabulation approach consists of creating a flamelet table at each computational time step using the unsteady flamelet equations. The flamelets are then integrated in real time based on their respective scalar dissipation rate histories. This approach is capable of including history effects and unsteady chemical kinetic effects as it involves the online solution of unsteady flamelets. Implementation and comprehensive validation of the new framework is carried out against gas-jet flames as well as spray flames at high pressures. The approach is first validated for a partially premixed methane gas-jet flame in a RANS framework. The temperature and species mass fractions are compared against experimental results at different locations of a lifted flame. The approach is able to capture the transient flame characteristics. The model is then validated against an n-dodecane spray flame at high pressures in an LES framework with a 103-species n-dodecane chemistry mechanism. The model is able to capture ignition delays and flame liftoff of the n-dodecane spray over varying ambient temperature conditions. Due to the offsetting of presumed PDF integration cost, the proposed framework is shown to be faster than the traditional RIF approach, and the speedup over RIF increases with an increase in the cell count. This framework enables use of the RIF model for large cell count LES simulations.

Self-excited transverse combustion instabilities in a high pressure lean premixed jet flame

An experimental investigation of self-excited combustion instabilities in a high pressure, lean premixed natural gas jet flame is presented. The combustor is designed with optical access and is instrumented with high frequency pressure transducers at multiple axial and circumferential locations. OH*-chemiluminescence measurements performed at a frequency of 50 kHz were temporally synchronized with the acoustic measurements recorded from the pressure transducer array during the test. Two representative test conditions are analyzed in detail: Flame 1 (F1) that presents longitudinal mode dynamics (p′/pc=3%) and Flame 2 (F2) that presents high amplitude transverse instabilities (p′/pc=15%). Singular Spectrum Analysis (SSA) and Dynamic Mode Decomposition (DMD) analysis indicate a strong correlation of both instabilities to flame-vortex interactions. Longitudinal mode instabilities are correlated with axisymmetric vortex shedding about the combustor axis that result in periodic axial variations in heat release at the 1L frequency. Transverse mode instabilities correspond to asymmetric vortex shedding pattern that drive transverse variations in heat release at the fundamental 1T frequency of the combustion chamber. The phase relationship of the flame emission intensity and the chamber head-end pressure measurement at the 1T frequency indicates presence of a non-stationary transverse mode that rotates about the chamber axis at 55 Hz.

Dilution effects on laminar jet diffusion flame lengths

Many studies have examined the stoichiometric lengths of laminar gas jet diffusion flames. However, these have emphasized normal flames of undiluted fuel burning in air. Many questions remain about the effects of fuel dilution, oxygen-enhanced combustion, and inverse flames. Thus, the stoichiometric lengths of 287 normal and inverse gas jet flames are measured for a broad range of nitrogen dilution. The fuels are methane and propane and the ambient pressure is atmospheric. Nitrogen addition to the fuel and/or oxidizer is found to increase the stoichiometric lengths of both normal and inverse diffusion flames, but this effect is small at high reactant mole fraction. This counters previous assertions that inert addition to the fuel stream has a negligible effect on the lengths of normal diffusion flames. The analytical model of Roper is extended to these conditions by specifying the characteristic diffusivity to be the mean diffusivity of the fuel and oxidizer into stoichiometric products and a characteristic temperature that scales with the adiabatic flame temperature and the ambient temperature. The extended model correlates the measured lengths of normal and inverse flames with coefficients of determination of 0.87 for methane and 0.97 for propane.

Effects of combustion models on soot formation and evolution in turbulent nonpremixed flames

Due to the complex multiscale turbulence–chemistry-soot (TCS) interactions in sooting flames, developing predictive models remains a formidable challenge even with the improved accuracy of the large eddy simulation (LES) approach. LES-based soot models have three main components: a) models for gas-phase chemistry and precursor evolution, b) models for soot particle dynamics, and c) models for subfilter scale TCS interactions. The focus of this work is this latter aspect, for several recent studies have shown that subfilter correlations between the gas-phase and the soot particles are of primary importance in affecting predictability. To this end, a consistent LES/probability density function (PDF) approach with detailed chemistry (denoted as full transport and chemistry (FTC)) and state-of-the-art soot models is used to accurately characterize subfilter TCS interactions. The statistical soot model is based on the Hybrid Method of Moments (HMOM), considering detailed nucleation, condensation, coagulation, surface growth, oxidation, and fragmentation processes. To study the sensitivity of soot predictions to combustion model, tabulated chemistry based on the radiation flamelet/progress variable (RFPV) approach is accounted for in the LES/PDF framework. The Delft-Adelaide natural gas jet flame is simulated to investigate the effects of combustion models on soot predictions. It is found that the location of inception and soot evolution are rather sensitive to the combustion model. Compared to the PDF/RFPV model, the PDF/FTC model improves the simulation results and predicts lower soot volume fraction with soot formation and growth further downstream. Accounting for detailed subfilter TCS interactions through the PDF/FTC model suppresses the contributions of aromatic-based soot growth (nucleation and condensation), while the contribution of acetylene-based surface growth is significantly enhanced and even dominates over condensation at downstream locations. These results imply that the choice of combustion model has a significant impact on the characterization of subfilter TCS interactions due to the strong coupling between turbulence, soot, and chemistry. The tabulated chemistry approach probably cannot capture the high sensitivity of soot formation and growth phases to the history of turbulent gas-phase compositions encountered.

Modeling of the gas-phase combustion of a grate-firing biomass furnace using an extended approach of Eddy Dissipation Concept

The ability of the standard Eddy Dissipation Concept (EDC) approach to account for the chemical kinetic rates during the interaction between chemistry and turbulent flow field made it a suitable scheme for simulating gas-phase combustion. However, its application poses a challenge for modeling weakly turbulent reacting flow conditions, as well as reacting flows with comparable flow and chemical time scales. A modified version of EDC (referred to here as extended EDC) has recently been developed for predominantly non-premixed turbulent flames. This led to significant improvement in the predictions of species and temperature fields of biomass-derived gas jet flames over a wide range of turbulence conditions (from weakly to highly turbulent flow conditions). The present study examines the application of this extended EDC approach for the simulation of a small-scale updraft biomass combustor. The predictions of the model are compared with those of the standard EDC and their counterparts’ experimental temperature and species concentrations. In addition, the pathway of formation/destruction of gas-fuel species and pollutants (e.g., NOx) is investigated. The findings of the present study reveal a significant improvement in the predictions of temperature field and species of the gas-phase of grate-firing biomass combustion.

Attaching Characteristics of the Natural Gas Jet Flame in Air-Coflow at Various Conditions

AbstractFor better understanding of the thermodynamic characteristics of natural gas, this paper experimentally investigated the attaching characteristics of the natural gas jet flame on a partially premixed coflow burner, and the effects of velocities and equivalence ratios are considered. Based on the experiment results, the instantaneous height and attaching velocity of the tribrachial flame base obviously vary for different jet velocities at a small (approximately 7) fuel equivalence ratio. With the increase in fuel equivalence ratio, a critical velocity exists and the attaching characteristics become significantly different. For the tip of the tribrachial flame, due to the Kelvin-Helmholtz instability, oscillation is observed and its level is quantified. According to the quantified results, the attaching characteristics of the flame tip can be divided into two regimes: stable and oscillation. Furthermore, the increase in jet velocity and/or fuel equivalence ratio induces the flicker phenomenon and/or...

Pool Fires Of Biofuels And Their Blends With Petroleum Diesel

The combustion characteristics of pool fires of biofuels, canola methyl ester (CME), soy methyl ester (SME), and their blends with a petroleum fuel (No. 2 diesel) were studied. The fuels were burned in cups of two sizes (0.042 m and 0.057 m in diameter and 0.038 m height) that simulated convection-dominated small pool fires of liquids. Blends of CME and SME with diesel fuel were tested with biofuel concentrations of 25, 50, and 75% by volume. The mass burn rate, the fuel surface regression rate, the radiation emission from the flames, the flame temperature field, and the emission indices of CO and NOx were recorded. The fuel surface regression rate in both containers was comparable. Both the fuel mass burning rate and surface regression rate varied non-monotonically with the volume concentration of biofuel in the blend. The radiation fraction of heat release and the temperature profiles were similar for all the flames. The CO emission index decreased with the biofuel content in the fuel. The NOx emission index did not show a systematic and significant dependence on the fuel blend; however, it was smaller than that measured in the turbulent gas jet and liquid spray flames of the corresponding fuels.

An Experimental and Computational Study of Interaction between Water Mist and Gas Jet Flame

The experiment on gas jet flame extinguishing with water mist in open space was conducted in this paper. On the basis of experimental result, the process of the flame extinguishment can be classified into two categories:1) when fuel flow rate is small, the gas jet flame can be suppressed and extinguished quickly; 2) When fuel flow is large, the flame lifts from the attached position at the burner exit after suppressed by the water mist. FLUENT is used to simulate the interaction of water mist with gas jet flame. The Eddy-dissipation model (EDM) is used for combustion of flame. the water mist is simulated by Discrete Phase Model (DPM).The simulated results agree well with the experimental results. To some extent, EDM is suitable for simulating the interaction of water mist with a turbulent gas jet flame.

Laminar smoke points of coflowing flames in microgravity

Laminar smoke points were measured in nonbuoyant laminar jet diffusion flames in coflowing air. Microgravity was obtained on board the International Space Station. A total of 55 smoke points were found for ethylene, propane, propylene, and propylene/nitrogen mixtures. Burner diameters were 0.41, 0.76, and 1.6 mm, and coflow velocities varied from 5.4 to 65 cm/s. These flames allow extensive control over residence time via variations in dilution, burner diameter, and coflow velocity. The measured smoke-point lengths scaled with d −0.91 u air 0.41, where d is burner diameter and u air is coflow velocity. The measurements yielded estimates of sooting propensities of the present fuels in microgravity diffusion flames. Analytical models of residence times in gas jet flames are presented, and although residence time helps explain many of the observed trends it does not correlate the measured smoke points.

Investigation of the trajectories and length of combustible gas jet flames in a sweeping air stream

The trajectories of round gas jets and jet flames introduced into a sweeping air stream are studied. The influence of various initial conditions and of the physical properties of gases on the trajectory is considered. Experimental verification of the available approximation relations for the trajectories of flames in a wide range of the values of the blowing ratio has been carried out. It is shown that the newly obtained experimental approximation of the trajectory shape differs from the existing ones by about 20%. At small values of the blowing ratio (smaller than ~4.5) the flame trajectories cease to depend on it.