Average Flame Research Articles

Dynamic evolution of flame and overpressure of leakage and explosion of hydrogen-blended natural gas in utility tunnels

In order to ascertain the true characteristics of the leakage explosion loads of hydrogen-blended natural gas (HBNG) in utility tunnels, the influence of leakage location on the concentration field distribution of HBNG leakage in utility tunnels was studied through the CFD technique. Furthermore, the characteristics of explosion flame and overpressure load distribution of HBNG of inhomogeneous distribution under effect of different ignition delay times and ignition positions were also investigated. The results show that the greater the distance between the leakage location and the air outlet, the more readily HBNG can propagate throughout the utility tunnel. This, in turn, leads to more prominent downstream gas cloud stratification. The development of explosion flame is primarily seen in the direction of low resistance and ample space within the utility tunnel. With the increase in ignition delay time (tid) and the backward shift of the leakage location (Llk), the average flame velocity generally exhibits a decreasing trend. Overall, the peak overpressure exhibits a concave trend. Under circumstances where the leakage source is in the front or middle section of the tunnel, the average peak overpressure demonstrates a general tendency of increase followed by decline with the increase in tid. In comparison, in the case of a leakage source located at the back end, it decreases gradually as tid increases. The most severe explosion overpressure load is readily induced when the leakage source is located at the front end. In the case of a leakage source located in the front section of the tunnel, the overpressure load at each measuring point decreases continuously and then rises as the ignition position moves backward. However, in the case of a leakage source located in the rear section of the tunnel, the average value of peak overpressure induced by ignition in the middle of the tunnel is the greatest, while the average value of peak overpressure induced by ignition at the back end is the smallest. The maximum explosion overpressure load is found at the front-most leakage source under front-end ignition conditions. The findings of this study offer scientific substantiation for the structure of the utility tunnel, which is designed for explosion withstanding, prevention, and control as well as risk assessment.

Ignition Characteristics and Flame Behavior of Automotive Lubricating Oil on Hot Surfaces

Hot surfaces in industrial processes and automotive systems present a remarkable fire hazard. Lubricating oil is a widely used oil in these scenarios. Quantifying the ignition characteristics and flame behavior of lubricating oil on hot surfaces is critical for enhancing fire safety in energy-related applications. This paper utilizes a self-developed experimental platform for the hot surface ignition to systematically conduct combustion tests on lubricating oil with varying volumes at different surface temperatures. Through statistical analysis and image processing, the ignition temperature, flame height, flame propagation velocity, and flame temperature were examined to assess the fire risk of a hot surface ignition. The results demonstrate that the ignition and combustion process of lubricating oil on hot surfaces can be categorized into five stages. The ignition temperature decreases as the oil volume increases. The flame height and flame propagation velocity are positively correlated with the hot surface temperature. The maximum flame height increases with the increase in the oil volumes. When the flame height reaches the maximum value, the flame area is the largest, and the average flame temperature is 1540.30 °C, showing a greater fire risk. When the oil content is 0.2 mL, the flame propagation velocity is the fastest, reaching 3.81 m/s. Meanwhile, the flame is very close to the oil pipe, which may cause a secondary fire. Therefore, hot surface ignition of lubricating oil poses a direct threat to vehicle safety.

Study on gas explosion propagation law in excavation roadway with TBM

Gas explosion is one of the five major hazards in mines, with about 36% of such incidents occurring in the excavation working face. Therefore, to investigate the impact of gas explosion propagation laws within excavation roadways, we conducted a simulation analysis of parameters such as peak of explosion overpressure, peak rate of pressure rise, and flame propagation speed in the presence of a Tunnel Boring Machine (TBM). In the presence of the TBM, the explosion overpressure approximately doubles, and the flame propagation speed also greatly increases, exacerbating the explosion hazard. Thus, when investigating gas explosion laws within excavation roadways, the presence of a TBM emerges as a significant factor that cannot be overlooked. Furthermore, an analysis of the effects of methane concentration and gas accumulation length on explosion parameters was conducted. The results indicate that when the flame passes through the TBM baffle, the average flame propagation speed increases the most when the methane concentration is 9.5%, increasing by about 6 times. In addition, as the gas accumulation length increases, both explosion overpressure and flame propagation speed gradually increase. Additionally, TBM has a certain impact on flame propagation and methane dissipation.

Automated system for classifying images of video streams for timely detection of fires

ABSTRACT Early detection of a fire during its development stage is highly desired to minimize human and material losses. The improvement of the efficiency of these monitoring systems through the analysis of fire video data drawn from unmanned aerial vehicles is considered . Classification of video images when monitoring a fire event on the territory is used based on their segmentation into identical rectangular segments of a given size and then assigning them to one of three classes: Smoke, Flame, and Indifferent classes. The Walsh-Hadamard transform was used to form descriptors for the Weak classifiers. Descriptors were calculated for three Weak classifiers; first, the Walsh-Hadamard transform was calculated for the window of the entire segment, and its spectral coefficients were used for the first Weak classifier. Next, the descriptors were calculated in windows whose sizes were half and a quarter of the original window size. The classifier consisted of three independently-trained neural networks. A simple ensemble averaging block was used to combine the outputs of those networks. A special software code has been developed to classify video images. The code allows us to create a database of segments of the ‘Smoke’ and ‘Flame’ classes, determine the two-dimensional Walsh-Hadamard spectrum of video image segments, train fully connected neural networks, conduct exploratory analysis and evaluate the relevance of the calculated two-dimensional spectral coefficients. For validation we used real data from Сlosed Circuit Television cameras presented in open databases. The experimental studies on the classification of video data containing flames and smoke showed that the proposed method has an average smoke detection accuracy of 86% and an average flame detection accuracy of 89.5%. Errors II in smoke detection and flame detection had the averages of 13% and 4.5%, respectively.

Mechanisms of flame spread over convex polymethyl methacrylate building material

Polymethyl methacrylate (PMMA) is a widely used combustible building material in convex structures, such as highway sound barriers and building façades. However, most flame spread studies focus on flat surfaces. This study investigates flame spread along convex surfaces through a series of burning experiments with varying curvatures and widths. The average path flame spread rate increases along with a bigger curvature and width. By introducing a dimensionless average path flame spread rate, an empirical correlation linking the average path flame spread rate with sample width and curvature is proposed. In reality, flame spread over convex surface exhibits a distinct time-varying process. For a large curvature, the transition of the flame shape from a wall-fire regime to a pool-fire regime is observed during the process. Moreover, as curvature and width increase, the flame spread transitions from a two-stage process (regime I) to a three-stage process (regime II). In regime II, the transient flame spread rate initially decreases, then increases, and finally decreases again. This behavior is due to the shift from convection dominance to radiation dominance, although radiant heat transfer significantly influences regime I as well. During this transition, a two-peak phenomenon in radiant heat flux emerges, indicating the onset of regime II. Based on this phenomenon, a power-law correlation between curvature and sample width as the critical criterion for triggering regime II is determined. The results of this study have implications concerning the fire safety design of buildings.

Wall Follower Based Fire Extinguisher Wheeled Robot Prototype using 5 Channel Fire Sensor

Fires can occur anywhere, be it in schools, offices, and housing or other open spaces. Fire cannot be predicted when it will happen. In the modern era robots are one of the very special technologies, the benefits of these robots can facilitate human work. Robot cars in this era are attracting quite a lot of attention from experts to develop. Therefore, the author designed a "Wall Follower-based Fire Extinguishing Robot using a 5 Channel fire sensor" to reduce the risk of fire. This robot uses the HC-SR04 sensor to detect the barrier wall so that the extinguishing robot reaches the fire point. For the microcontroller tool used in this design system in the form of an Arduino Nano microcontroller which functions as part of the 5 Channel Flame Sensor controller to detect hotspots and a DC water pump to extinguish the fire. In this study using experimental research. This robot has successfully passed the track and put out the fire as the author has designed. The average flame sensor on this robot can read the fire point at a distance of 20 cm with angles of 90°, 60°, 120°, 150°, then the output voltage generated on the DC motor with a PWM value of 191 or 75% duty cycle produces an output of 8.77V measured using a multimeter, and this robot can extinguish the fire on the track with different distances with an average fire extinguishing time of 7.1 seconds.

Mathematical modeling and model predictive control research on coal powder burners for aggregate dryers

Aggregate drying is a crucial step in asphalt mixture production. Enhancing the model accuracy and controller performance of aggregate dryer burners is essential for consistent flame characteristics, reducing NOx emissions, and minimizing fuel consumption. This paper introduces a second-order nonlinear parametric model for coal powder burners that includes delay and noise. Model parameters were determined through experimental data using the Salp Swarm Algorithm, showing higher accuracy than models based on the least square method. A dual-layer model predictive control (MPC) based on this mathematical model was developed to improve the economic efficiency of the aggregate drying process. Simulation results showed that the dual-layer MPC saves 1.08 tons of coal every 10 h compared to a standard MPC. A full-scale prototype demonstrated average flame length, flame temperature, and NOx emissions of 4242.6 mm, 1729.4 °C, and 460.2 mg/m³, respectively, validating the accuracy of the proposed mathematical model and controller.

Study on the combustion characteristics and reaction mechanism of aluminum/alcohol-based nanofluid fuel

Enhancing the volumetric energy density of fuels is a crucial approach in the exploration of efficient energy sources. As a commonly used high-energy additive, Aluminum nanoparticles (Al NPs) holds broad application prospects. This study delves into the effects of Al NPs on the combustion characteristics of methanol and ethanol fuels through in-depth analysis of single droplet combustion and spray combustion experiments involving alcohol-based nanofluid fuels. The experiments revealed that adding Al NPs significantly enhances fuel combustion efficiency, shortening both the combustion life and ignition delay time. Spray combustion tests demonstrated that adding 2 wt% Al NPs increased the maximum and average flame propagation speeds of ethanol fuel spray by 48.93 % and 47.94 %, respectively, while the maximum explosion pressure rose from 0.66MPa to 0.83MPa, with a reduced time to reach peak explosion pressure by 106ms. Based on the SEM and XRD characterization results of the combustion residues and the analysis of flame morphology, a physical model of the alcohol-based nanofluid fuel spray combustion flame was established. Numerical simulations of the gas-phase kinetics model showed that the generation rates of radicals such as H, O, and OH were significantly increased with the addition of Al NPs, intensifying the combustion reaction. The findings provide a theoretical basis for future fuel design and combustion performance optimization.

Numerical analysis of thermal mechanism in downward flame spread over inverted surfaces of discrete inclined solid fuels

This investigation is propelled by engineering challenges associated with heat transfer during fire incidents on inclined surfaces, such as those observed in pitched roof fires, which hold significant implications for fire safety engineering and energy conservation. Drawing inspiration from real-world fire dynamics, this study delves into the downward flame spread over inverted solid fuel surfaces across a range of inclination angles, bridging the gap between theory and practice. Detailed analysis of temperature distribution, flame characteristics, and gas-phase reactions reveals critical insights into the complex interplay governing heat behavior under these conditions. The observed reduction in flame thickness and standoff distance with increasing inclination underscores the influence of buoyancy-induced plumes. This work developed a dimensionless formula that accounts for both buoyancy-induced plumes and diffusion rates perpendicular to the fuel, successfully capturing the variation in flame thickness with inclination angles. Furthermore, our findings show that the average flame spread rate escalates with higher inclination angles, attributed to enhanced gas-phase reactions near the flame front that lead to intensified heat transfer and a subsequent increase in temperature within the solid phase. The study also uncovers a competitive mechanism between flame “jumps” and heat transfer to the unburned zone, causing an initial increase and then a decrease in flame spread rates with increasing discrete gap size at larger inclination angles. Conversely, at smaller inclination angles, flame progression halts as the discrete gap size increases, due to inadequate heat transfer to the adjacent discrete fuel, resulting in the cessation of flame spread. This study not only advances our understanding of the thermal processes underpinning flame spread in inclined configurations but also offers crucial insights for developing more effective fire protection strategies and thermal protection systems in engineering applications.

Experimental Investigation and Theoretical Analysis of Flame Spread Dynamics over Discrete Thermally Thin Fuels with Various Inclination Angles and Gap Sizes

Flame spread over discrete fuels is a typical phenomenon in fire scenes. Experimental and theoretical research on flame spread over discrete thermally thin fuels separated by air gaps with different inclination angles was conducted in the present study. Experiments with six inclination angles ranging from 0° to 85° and various fuel coverage rates from 0.421 to 1 were designed. The flame spread behavior, the characteristic flame size, and the flame spread rate were analyzed. The results show that the flow pattern, stability, and flame size exhibit different characteristics with different inclination angles and gap sizes. As the inclination angle increases, particularly with smaller gaps, turbulent and oscillating flames are observed, while larger gap sizes promote flame stability. The mechanism of flame propagation across the gap depends on the interplay between the flame jump effect and heat transfer, which evolves with gap size. Average flame height, average flame width, and flame spread rate initially increase and then decline with the increase in fuel coverage, peaking at fuel coverage rates between 0.93 and 0.571 for different inclination angles. A theoretical model is proposed to predict the flame spread rate and the variation in the flame spread rate with inclination angle and fuel coverage. Furthermore, the map determined by inclination angle and fuel coverage is partitioned into distinct regions, comprising the accelerated flame spread region, the flame spread weakening region, and the failed flame spread region. These findings provide valuable insights into flame spread dynamics over discrete thermally thin fuels under diverse conditions.

Experimental study on flame morphology, ceiling temperature and carbon monoxide generation characteristic of prismatic lithium iron phosphate battery fires with different states of charge in a tunnel

Lithium-ion battery (LIB) fire in a tunnel can generate a high-temperature environment, massive toxic and harmful smoke in a short period. This work carried out a series of thermal runaway (TR) experiments on large prismatic lithium cells in a model tunnel. Results showed that the flame height of LIBs with above 50 % SOC was above 40 cm for much time of the stage (Ⅰ) and (Ⅱ). The average flame height is further proposed to quantify the flame profile at different phases. The greater the SOC was, the higher the ceiling temperature and peak CO concentration were also relatively. For example, while decreasing the distance to the fire source from 0 m to -0.7 m, the peak ceiling temperature of 25 Ah batteries with 100 % SOC decreases from 309 °C to 118 °C, with a decay rate of 62 %. The CO concentration showed a comparable variation pattern to the tunnel ceiling temperature. Finally, a dimensionless relationship was employed to describe the ceiling temperature decay. Meanwhile, the ceiling maximum temperature rise for different capacity battery fires in a tunnel was integrated into a relational correlation. The study results are expected to further understand the battery fire hazards in tunnel.

Study on Explosion Characteristics and Mechanism of Electrostatic Spray Powder.

In order to fully understand the explosion risk of electrostatic spraying powder, corresponding preventive measures are put forward. The explosion characteristics, ignition sensitivity, and flame propagation of three typical electrostatic spraying powders were tested using a 20 L spherical explosion test device, a G-G furnace test device, and a Hartmann tube test device, and the explosion process and mechanism of electrostatic spraying powders were discussed. The results show that the maximum explosion pressure and the maximum explosion pressure rise rate increase first and then decrease with the increase in mass concentration. The maximum explosion pressure and the maximum explosion pressure rise rate of acrylic powder coating are the largest, which are 0.75 and 85.4 MPa/s, respectively. The shortest burning time is 97.5 ms, and the highest explosion danger level is 23.46 MPa·m/s. The flame propagation of electrostatic spraying powder develops slowly; the flame front spreads linearly and the average flame velocity increases first and then decreases. The explosive development process of powder coating particles is concentrated in the three-phase system of solid particles, molten particles, and pyrolytic gasification combustible gas, which goes through the kinetic process of particle heating melting, cross-linking curing, pyrolytic gasification, combustion, and extinction.

Effect of width on the fire spreading characteristics of PE metal sandwich panels under the action of double fire sources

The exterior walls of high-rise buildings typically contain substantial thermal insulation materials. Once ignited, these materials can readily induce major fire accidents. In this study, through the constructed reduced-size experimental bench to evaluate the effect of window overflow fire and upper chamber fire on the fire spreading properties of PE metal sandwich panels with different widths. The result shows that the average flame height and flame oscillation intensity increased with an increase in fire source power and sandwich panel width. Temperature curves exhibited a consistent trend under different working conditions. Dimensionless analysis of the sandwich layer temperature indicated that under specific fire source power conditions, the 60 cm sandwich panel reached the highest peak temperature and posed the greatest fire hazard. Based on the width and length of the preheating zone, a model for the rate of flame spreading was created. At a constant sample width, the accelerated spread of the upper part of the plate by the action of fire source B was more obvious. These conclusions are instructive for the study of building facade fire.

Anti‐solvent method synthesized phosphorylated microcapsules with flame retardancy and self‐healing analysis

AbstractIn this study, an anti‐solvent method is employed to encapsulate linseed oil (LO) into phosphorylated ethyl cellulose (P‐EC), successfully preparing microcapsules (LO@P‐EC). Scanning electron microscopy and Fourier transform infrared spectroscopy experimental results indicate the introduction of phosphoric groups into P‐EC, and the successful encapsulation of LO within the microcapsules, which are spherical with an average diameter of 145 μm. Hartmann tests reveal that the introduction of phosphate groups reduces the microcapsule flame propagation height by 43.75% and the average flame propagation speed by 55.67%. Thermodynamic analyses based on the Coats‐Redfern equation are performed to determine the changes in activation energy during thermal degradation. Furthermore, fitting analysis shows that the apparent activation energy of microcapsules with shell material of P‐EC significantly increases, confirming the evident thermodynamic inhibition of microcapsule deflagration by P‐EC. This is mainly attributed to the formation of a char structure by the P‐EC shell during combustion, which hinders the progress of the combustion reaction. When immersed in 3.5 wt% NaCl corrosive solution for 15 days, the microcapsule‐filled epoxy resin (LO@P‐EC/EP) coating exhibits excellent corrosion resistance, which is mainly attributed to the excellent self‐healing properties of the microcapsule core LO.

Design Optimization of an Improved Mud Cookstove Using Computational Fluid Dynamics

ABSTRACT The present study focuses on optimizing the design and performance of natural draft mud-based cookstove (MBC) using the CFD tool ANSYS Fluent. The study simulates the performance of the MBC over different levels of three key factors, i.e. grate height, pot gap, and secondary hole diameter, against the targeted response parameters, which include average flame temperature, thermal efficiency, and combustion efficiency. Two-dimensional (2D) simulations of a real-world prototype of MBC were performed using ANSYS Fluent, solving governing equations for mass, momentum, energy, and species transport throughout the computational domain and employing a pseudo-transient accelerated solver approach to achieve a steady state. Grid independence was established to ensure reliable simulation results. It was observed that an optimized response was obtained at the grate height of 30 mm, pot gap of 30 mm, and secondary hole diameter of 8 mm, wherein the average flame temperature of 887 K, thermal efficiency of 27.64%, and a modified combustion efficiency of 98.97% was observed. The achieved thermal efficiency complied with the BIS IS 13,152:2013 standard for natural draft cookstoves, classifying it as a Tier 2 cookstove according to the performance targets outlined in ISO/TR 19,867-3:2018. The combustion efficiency exceeded 0.97, indicating pure flaming combustion. A full-scale field prototype was fabricated and successfully validated through laboratory and field experiments.

Experimental investigation on the suppression of aluminum dust explosion by sodium carbonate powder

To prevent the potential explosion accidents in industries involving aluminum powder, the effectiveness of Na2CO3 in inhibiting aluminum dust explosions was investigated using thermal methods and explosion tests. Furthermore, the surface morphologies and chemical compositions of the resultant explosion products were characterized to illustrate the inhibition mechanism of Na2CO3 powder. The results revealed a marginal increase in ignition temperatures and a decrease in combustion peak temperature as the proportion of Na2CO3 increased. Notably, within the range of 0–450%, a notable reduction was observed in both the maximum explosion pressure (from 0.68 to 0.06 MPa) and the maximum pressure rising rate (from 91.93 to 2.87 MPa/s). In particular, as the percentage of Na2CO3 increased, a gradual decrease in flame brightness and average flame velocity was observed. Moreover, a negative relationship was observed between ignition temperature and apparent activation energy with maximum explosion pressure and maximum pressure rising rate. An analysis of the explosion residues indicated the presence of Na2CO3, NaOH, Al2O3, Al(OH)3, Na(AlO)2, Na2O and unburned aluminum. The inhibition mechanisms of Na2CO3 involved heat absorption, isolation, and the consumption of free radicals. These results offer valuable insights that can aid in mitigating the risks associated with aluminum dust explosion.

Application of microencapsulated fibrous carrier inhibitors in suppressing flake aluminum dust explosion: Performance and mechanism

Flake aluminum powder (FAl), due to its larger specific surface area and higher reactivity, posing a potential threat to the process safety of involved enterprises. To mitigate the explosion caused during the production of FAl, a green composite inhibitor, Sep@CS@PA-Na, was successfully prepared in the aqueous phase using microencapsulation technology with sepiolite (Sep), chitosan (CS), and sodium phytate (PA-Na) as raw materials. The suppression of FAl explosions in a vertical combustion duct system by inhibitors with different inerting ratios (α) was investigated. The results showed that after adding Sep@CS@PA-Na with an α of 0.75, the maximum flame propagation velocity (Vmax), the average flame velocity (Vavg), and the velocity of the flame reaching the pipeline top (Vtop) decreased by 79.6%, 75.1%, and 86.2%, respectively, and the reduction of the maximum flame front pressure (Pmax) and the maximum flame pressure rise rate ((dP/dt)max) were 90.4% and 89.8%, respectively, and the peak temperature (Tp) dropped to 505°C. Combined with TG-DSC and explosion product analysis, Sep@CS@PA-Na possessed both gas-phase reaction and surface reaction suppression functions, which were mainly reflected in the dilution effect, quenching effect, and barrier effect. This work will provide technical support for the emergency prevention and control of energetic metal dust explosions.

Investigation of the effects of N2 and CO2 on the overpressure hazards, flame behaviors and reaction kinetics of LPG/air explosions

ABSTRACT To research the influence of inert gases on the explosion behaviors of LPG/air mixtures, LPG explosion tests suppressed by CO2 and N2 were conducted in a spherical chamber and the chemical reaction kinetic properties were analyzed. The results show that CO2 has a better inhibitory effect than N2, especially when the added amount is small. With the increasing volume fraction of inert gases, the LPG explosion flame propagation speed continuously decreases, and the phenomenon of flame uplift and wrinkling deformation occurs. The explosion pressure of LPG/CO2(N2)/air mixture and the average flame propagation speed in the initial stage follow an exponential function with an offset. The laminar flame structure of 4% LPG is similar to its mixtures with N2 and CO2. After adding inert gases, the maximum temperature of the LPG laminar flame decreases significantly, and the flame thickness increases. The key elementary reactions affecting the N2(CO2)/LPG/air explosions are given. The research results have important implications for suppression of LPG explosions.

Study on flame height and temperature distribution of double-deck bridge fire based on large-scale fire experiments

Vehicle fire is one of the important causes of bridge fires. This study conducted large-scale actual fire experiments by simulating heat release rates (HRR) of oil tank truck fires with 50 MW, 100 MW, and 200 MW in rectangular oil pans of varying sizes. The flame shape and spatial temperature distribution at different HRRs were studied bycontrollingvariables such as wind speed,firesource location, andlayer spacing. The results indicated that the actual HRR of the large-scale fire exceeded the anticipated value. In large-scale fire experiments, flame splitting into two main peaks was observed along the long side of the rectangular oil pan due to the coupling effect of ambient wind, long side, and sidewall effect of the diagonal web member. The average flame height was determined through image processing, and subsequently, a formula for predicting flame height during bridge fires under varying heat release rates was developed through the use of dimensionless analysis and feature length analysis. The spatial temperature distribution in the vertical direction of the axis of the center of the fire source, the temperature distribution of the diagonal web member and the bottom of the dense crossbeams, which are critical components of the bridge, were also analyzed. Furthermore, the conclusion that the flame in the lower bridge space which split into two main peaks is validated by the results. The results of this study can provide important theoretical support for investigating bridge fire resistance strategies.

Structure and NOx Emissions of Stratified Hydrogen-Air Flames Stabilized on a Coaxial Injector

Abstract In recent years, the need for low-carbon power has seen hydrogen emerge as a potential fuel to replace conventional hydrocarbons in combustion to limit CO2 emissions in several sectors, including aeronautics. The challenges posed by hydrogen combustion are similar to the issues of kerosene flames but more challenging, like nitrogen oxide (NOx) emissions and flame flashback. One potential solution to address these problems is to burn a rich mixture of hydrogen and air in globally lean conditions on a coaxial injector to obtain a stable and staged combustion and attempt to reduce emissions. In this article, the evolution of NOx production as more air is mixed into the fuel is studied, as well as the changes in flame size and structure. In particular, the appearance of a secondary flame front is observed and increasing the proportion of air in the fuel mixture both shortens the flame and reduces the NOx emission index. Additionally, the effect of the global equivalence ratio and flame thermal power is studied. Finally, existing models for NOx emission of hydrogen flames on a coaxial injector based on average flame residence time and strain rate are tested and shown to have promising results.