Flame Propagation Velocity Research Articles

The influence of opening shape of obstacles on explosion characteristics of premixed methane-air with concentration gradients

By installing obstacle plates with different opening shapes in an experimental pipeline, the combined effect of vertical concentration gradients and obstacle shapes on methane-air explosion characteristics was experimentally investigated. The presence of obstacles and concentration gradients induced turbulent flame instabilities, which promoted the positive feedback between the combustible gas flow and combustion process. The combustion process caused the upstream lean methane, lighter than the unburned gas, to propagate through the obstacle and hence bubble-like local disturbances were generated in the central area downstream of the obstacle. Under the action of transverse waves, a "gap" appeared in the lower part of the flame front, and the flame front appeared concave. The effect of the concentration gradient and obstacles on the methane explosion gradually weakened, and hence the wrinkled flame surface gradually stabilized. Results show that the square-shaped opening affected the flame propagation and explosion evolution most significantly. As the concentration gradient increased, the combined effect undermined the positive feedback mechanism, and the maximum explosion overpressure and maximum rate of pressure rise were reached for the square-shaped opening at a low concentration gradient (0.5 %), while for the circular-shaped and quadrant-shaped openings the maximum values were reached at a higher concentration gradient (1.0 %). The effect of obstacles was more significant than the effect of concentration gradients with respect to the flame propagation velocity and rate of pressure rise.

Effects of nitrogen and argon on ammonia-oxygen explosion

The primary task of this work is to clarify ammonia-oxygen explosion characteristics under nitrogen and argon atmosphere. Firstly, the flame behavior and explosion pressure are experimentally obtained. Then their correlation is revealed quantitatively. The thermal, diffusive and chemical analysis is conducted at last. The results demonstrated that the variation tendency of flame propagation velocity (FPV), maximum explosion pressure (MEP) and maximum rate of pressure rise (MRPR) is completely consistent. All index of FPV, MEP and MRPR, becomes increased and decreased with increasing equivalence ratio, continues to decrease with increasing inert gas fraction. All index of FPV, MEP and MRPR under argon atmosphere is totally larger than that under nitrogen atmosphere. By considering the state equation of ideal gas, spherically smooth flame and adiabatic compression, the flame behavior and explosion pressure under nitrogen and argon atmosphere is significantly controlled by laminar burning speed (LBS). As the inert gas fraction and equivalence ratio change, the LBS under nitrogen and argon atmosphere is significantly controlled by adiabatic flame temperature. The joint action of adiabatic flame temperature and thermal diffusivity contributes to the LBS difference.

Flame propagation behaviours and overpressure characteristics of LDPE dust / ethylene hybrid mixture explosions

ABSTRACT It studied the explosion propagation of the hybrid mixture of LDPE dust and a small amount of ethylene (below its LEL) in a closed duct, to examine the impacts of dust concentration, dust particle size, and ethylene concentration on flame propagation behavior and overpressure characteristics. The dust concentration affected the explosion behavior of the LDPE dust/ethylene hybrid mixture in two ways. The flame gradually became discrete and unstable as the dust concentration increased, while the maximum and average flame propagation velocity, Pmax, and (dp/dt)max increased first and then decreased. The dust particle size and ethylene concentration had a significant effect on the hybrid mixture explosion. As the particle size decreased or the ethylene concentration increased, the discrete flames quickly merged into a bright continuous flame. Further, the maximum and average flame propagation velocity, Pmax, and (dp/dt)max increased, whereas the fluctuation degree of the flame propagation velocity with time showed a decreasing trend. There was no obvious agglomeration phenomenon among small LDPE particles. The explosion overpressure and flame propagation showed a strong synergistic effect. Compared with the semi-open duct, the closed duct with a more uniform dust/gas hybrid mixture showed a more continuous flame structure, a shorter flame propagation distance, and a lower flame propagation velocity. These conclusions can provide a scientific basis for explosion risk analyses and process safety designs involving the production of LDPE powder.

Synergistic inhibition of aluminum dust explosion by gas–solid inhibitors

The inhibition mechanism of gas-solid inhibitors on Al dust explosion was investigated experimentally in a closed cuboid chamber. The variation of parameters concerning flame propagation characteristic and explosion severity used to reflect the synergistic inhibition effect of gas-solid inhibitors on Al dust explosion were elucidated. The results showed that flame propagation velocity and explosion overpressure were inhibited with the increase of gas-solid inhibitors. The inhibition curves of gas-solid inhibitors within the experimental range were further obtained. The reason concerning the SEEP phenomenon was revealed through the GC-MS analysis. The combustion of ammonia enhanced the explosion overpressure when solid inhibitors performed at low concentration. The gas-phase product could be regarded as the inert gas as long as enough amount of inhibitors were added. To comprehend the inhibition mechanism of gas-solid inhibitors, X-ray diffraction was applied to figure out the crystal structure of explosion residue. The results indicated that both physical and chemical inhibition effects were imposed on Al dust explosion by gas-solid inhibitors, including endothermic decomposition, dilution of oxidizer, coverage of Al dust, and scavenger of free radicals. The results of this study will provide a scientific basis for the design of inhibition technology for the dust explosion.

The Effect of Gap Width on Premixed Flame Propagation in Non-adiabatic Closed Hele–Shaw Cells

ABSTRACT The premixed flame propagation with conductive heat loss in millimeter-scale narrow closed cells of different gap widths is investigated experimentally and numerically. The flame evolution is observed in a disc-shaped cell of which the width is varied from 2.0 mm to 5.0 mm. A non-monotonic relation between the flame propagation velocity and the gap width is found. Time-dependent numerical results exhibit good agreement with the experimental data and indicate that the flame behaviors are highly sensitive to the gap width. Since gap downsizing leads to significant heat loss and viscous friction from the wall, the propagation velocity will drop to almost laminar flame speed halfway for 2.0 mm width. For larger gaps, the flame propagation velocity is determined by the combined effect of the flame straining and the conductive heat loss. The former increases the flame front area while the latter strongly weakens the flame distortion. The trade-off of them yields the non-monotonic relation and an optimal width of 3.0 mm.

The past, the present and the future of nanotechnologies

Abstract Artists from the time of Mesopotamia or Egypt and in the Middle Ages astonished us with various coloured Stained-glass windows, prepared with the help of metal nanoparticles. The paper will deal with zeolites, nanoparticles and carbon nanotubes. The latter will be developed more extensively, because we have founded the Nanocyl company, selling carbon nanotubes and it has become the best European company. One carbon nanotube is 100,000 times thinner than a human hair, it is very light – twice as light as aluminium –, its mechanical resistance is much higher than that of steel and it conducts electricity better than metal conductors. The use of carbon nanotubes is very important in nanotechnology. For example, with the help of coiled carbon nanotubes, the weight of a single nanoparticle can be measured, it is equal to one femtogram (10−15 gram). Carbon nanotubes are used in car spray painting to cancel the build-up of static electricity. With the help of carbon nanotubes, it is possible to decrease the velocity of flame propagation, when they are included in composite materials. Carbon nanotubes are also very good as sensors for toxic gases. Their uses will take up the most part of this paper. The future of nanotechnology will be illustrated by nanomachines, by the lift between the Earth and the Moon, and by graphene (one single sheet of graphite). The use of carbon nanotubes will be evoked in waste water cleaning, in the production of drinking water from seawater.

Influence of concentration gradient on methane–air explosion propagation: An experimental study

ABSTRACT In underground coal mines, the methane distribution under actual conditions has a certain concentration gradient due to various factors such as air leakage and lower air velocity in local areas. In this paper, experiments were carried out to investigate the influence of the methane accumulation and concentration gradient on the methane–air explosion propagation. The experimental results show that in the process of methane explosion, the propagation distance of the flame and explosion wave in the rising stage are directly proportional to the methane accumulation. When the reaction time is less than a critical value, the flame propagation velocity and explosion overpressure with methane concentration distribution in the case of 9.5%–9.5%–3.5% are greater than those with a methane concentration change of 9.5%–9.5%–5.5%. However, when the methane concentration distribution is 9.5%–9.5%–0%, the flame propagation velocity and overpressure are less than those of the distributed methane in the working conditions of 9.5%–9.5%–3.5% and 9.5%–9.5%–5.5%.

Flame Propagation Velocity for Co-combustion of Pulverized Coals and Gas Fuels

A model was developed to evaluate the flame propagation velocity for co-combustion of pulverized coals and gas fuels such as ammonia, methane, hydrogen, and other fuels. For coal combustion, the maximum flame propagation velocity increased when the particle diameter decreased or the volatile content increased. The limit value of the maximum flame propagation velocity was extrapolated to zero particle diameter and 100% volatile matter (VM) content. The value became equivalent to the maximum flame propagation velocity of hydrocarbon fuels such as methane. However, the flame propagation velocity of coal was usually lower than that of gas fuels due to the delay of pyrolysis reactions. Also, residual solid particles (ash, char, and VM that have not been pyrolyzed yet) might slow down the gas combustion reactions. A model was developed to evaluate the flame propagation velocity for co-combustion. Previously, a model had been developed for solid fuels with diameter distribution. A weighting factor had been introduced to represent the contribution of each particle diamter. The factor had been the ratio of the number of particles. For gas fuels, instead of the number of particles, the weighting factor was expressed as a function of the equivalence ratio and the burning velocity of gas fuels. The flame propagation velocities were analyzed for co-combustion of coal–methane and coal–ammonia. The calculated results could reproduce the characteristics of the experimental results. Very recently, experimental results for coal–ammonia have been reported by Hadi et al. The flame propagation velocity for co-combustion was larger than the maximum value when ammonia or coal burned alone. This phenomenon was not observed for co-combustion of coal–methane. This phenomenon could be reproduced by the present calculation. The present model is useful for the design and development of burners for solid–gas co-combustion.

Experimental study and numerical simulation of the influence of vent conditions on hydrogen explosion characteristics

ABSTRACT In order to minimize the huge loss caused by hydrogen explosion in confined space, experimental and numerical simulation methods were used to study the effects of the vent position and number on hydrogen/air explosion characteristics in a straight pipe with 7.2 m in the length and 125 mm in the inner diameter. The results showed that the continuous emission effect of the vent can provide an induction effect to the flame propagation before the flame reached the vent and produce a continuous disturbance to the flow field, which increased the flame instability. The vent position has a significant influence on the explosion venting effect. In the experiment, the explosion venting effect was the best when the vent was set near the ignition end. The maximum explosion overpressure and flame propagation velocity were reduced by 21.2 and 26.7%, respectively, compared with the pipe without vent. The explosion venting effect was slightly weak when the vent was in the back of the pipe. The reflected waves caused by the collision between the shock waves and the blind plate promoted the emission effect of the vent. When the vent was set in the middle of the pipe, the flame passed through the vent with a higher speed, which limited the emission effect of the vent and led to the worst explosion venting effect. Multistage pressure relief can effectively reduce the explosion intensity of hydrogen in the pipe. In the experiment, the maximum flame propagation velocity and explosion overpressure gradually decreased with the vent number increasing. When the vent number was three, the maximum explosion overpressure and flame propagation velocity decreased by 47.3 and 68.4%, respectively, compared with the pipe without vent. Therefore, properly increasing the vent number is beneficial to improve the explosion venting effect and ensures the safety of equipment.

Dynamics of premixed hydrogen-air flame propagation in the duct with pellets bed

Hydrogen, as the promising clean alternative energy in the future, is in the spotlight now all over the world. However, its flammable and explosive hazards should be highly considered during its practical application. In this study, the experiments are performed to study premixed hydrogen-air flame propagation in the duct with pellets bed, especially for fuel-rich condition. High-speed schlieren photography is employed to capture flame front development during the experiments. As well as the pressure transducer, is used to track the pressure buildup in the flame propagation process. Different diameters of pellets and different concentrations of gas mixture are considered in this experimental study. The typical evolutions about the tulip flame are similar in all cases, although the tulip flame formation time caused by the laminar flame speed are different. The flame propagation velocity is pretty enhanced in fuel-lean mixture under the effect of large diameter pellets bed, but it is significantly suppressed in fuel-rich conditions. While for the small diameter pellets (d = 3 mm), the suppression effect on flame propagation and pressure is obtained over a wider range of equivalence ratios, especially a better suppression effect is generated near the stoichiometric condition.

Effect of Propane Addition and Oxygen Enrichment on the Flame Characteristics of Biogas

Mixing biogas with other fuels or increasing the oxygen fraction in the oxidizer can improve the combustion performance of biogas. In this study, we investigated the effects of propane addition and oxygen enrichment on the flame characteristics of biogas with a constant heating value in a half-open duct. The evolution of the flame structure revealed that the tulip structure took on two types of patterns at the oxygen fraction θ = 0.21. However, there was no salient tulip flame formation when θ > 0.21. Oxygen enrichment significantly increased the flame propagation velocity (V) and explosion pressure (P). Propane addition significantly reduced Vmax at θ = 0.25 and 0.29. The maximum rate of pressure rise [(dP/dt)max] exhibited a nonlinear dependence on the maximum flame velocity (Vmax). A similar trend was observed for the dependence of (dP/dt)max on the laminar burning velocity (LBV). Therefore, the LBV is an important parameter to predict Vmax and (dP/dt)max values of mixtures. Furthermore, by using the PREMIX code and the UC San Diego mechanism, we simulated laminar flame burning properties to reveal the macroscopic flame propagation characteristics. The rate of propane consumption was higher than the rate of methane consumption. Additionally, oxygen enrichment played an important role in the entire reaction process, leading to an increase in the molar concentrations of microscopic free radicals and a promotion of the rates of production (ROP) of free radicals. In contrast, the addition of propane decreased the molar concentrations of microscopic free radicals and inhibited the ROP of free radicals.

A novel reactive P-containing composite with an ordered porous structure for suppressing nano-Al dust explosions

A novel chemical suppressant ([email protected]2-MCM41) was synthesized via self-assembly. NH2-MCM-41 was prepared using diatomaceous earth (DE) as the silica source. FTIR spectra showed that phytic acid (PA) was successfully grafted onto synthesized NH2-MCM-41 via hydrogen bonding. The highly ordered mesoporous structure of [email protected]2-MCM41 was observed from TEM and small angle X-ray diffraction (SAXRD). The effectiveness of [email protected]2-MCM41 in the suppression of nano-Al dust explosions was investigated. Experimental results suggested that the addition of [email protected]2-MCM41 could effectively reduce the average flame propagation velocity (Vavg) and maximum explosion pressure (Pmax). After the addition of 16.7 wt% [email protected]2-MCM41, the Vavg of the gas-phase flame was reduced by 75%. With addition of 28.6 wt% [email protected]2-MCM41, the Pmax of nano-Al dust decreased by 65.7%. As the mass fraction of [email protected]2-MCM41was increased to 33.3%, nano-Al dust explosion was completely suppressed. The SEM, FTIR and EDS results showed that a complex sealing film was formed on the surface of the explosion products, which occupied the open sites on the Al surface and thereby interrupted the Al evaporation and surface reaction. Subsequently, the suppression mechanism by which phosphorus containing suppressants consume free radicals and the interaction of PA molecules with the aluminum particle surface were revealed in depth.

Characteristics of hydrogen-ammonia-air cloud explosion

The main task of this work is to study the hydrogen-ammonia-air cloud explosion characteristics. The flame behavior and explosion pressure are obtained experimentally by changing equivalence ratio (ER) and ammonia fraction (AF). Then the correlation between flame behavior and maximum explosion pressure is revealed. Finally, the thermal, diffusion and chemical factors affecting laminar burning velocity (LBV) are analyzed. The results indicated that averaged flame propagation velocity (AFPV) and maximum explosion pressure (MEP), become decreased continuously with increasing AF, become increased firstly and then decreased with increasing ER. Maximum value of both AFPV and MEP of AF = 0.1, AF = 0.3, AF = 0.5 and AF = 0.7 is reached at ER = 1.4, ER = 1.2, ER = 1.0 and ER = 1.0. the MEP could be underestimated and overestimated by laminar and turbulent flame model. The MEP is largely affected by LBV especially when the flame instabilities are ignored. With increasing AF, the reduction of adiabatic flame temperature and thermal diffusivilty contributes to the LBV reduction. With increasing ER, the main factor affecting LBV is the generation and consumption of H radical.

Research on burning velocity of R152a and its binary mixture

The burning velocity plays an important role in determining the safety level of new refrigerants. Based on the self-designed test system for burning velocity characteristics of flammable refrigerants, the burning velocities of R152a with different concentration were studied by vertical glass tube method. And the maximum burning velocity of R152a was analyzed, which was close to the standard recommended value. R1234yf with environmental advantages and lower flammability may form a new alternative refrigerant mixture with R152a. Therefore, the flame propagation and burning velocity characteristics of R152a+R1234yf were studied under the conditions of different component ratio and different concentration. Based on the theoretical analysis, three calculation methods for predicting the burning velocity of binary mixed flammable refrigerant were proposed for the first time. Then, three groups of predicted burning velocity of R152a+R1234yf under different composition or concentrations were calculated. Compared with the experimental data, it was found that the prediction accuracy of the component equivalent simplified method is the highest among the three methods. It was of great significance for the prediction of burning velocity and the assessment of safety level of new mixed refrigerant or flammable gas.

Study on the combined effect of duct scale and SBC concentration on duct-vented methane-air explosion

A gas explosion is often vented to a safe location by means of a discharge duct. However, the presence of a discharge duct increases the explosion severity in the vessel, inducing a higher explosion overpressure compared to a simply vented vessel. To reduce the explosion overpressure in the vessel, an experimental study was performed to suppress the methane-air explosions in a 5 L vessel connected to a discharge duct of different scales (e.g., length and diameter) and with various sodium bicarbonate concentrations. The results show that the initial flame propagation process in the vessel was basically similar in the simply vented vessel and in the vessel vented through a discharge duct (i.e., ducted-vessel). In the middle and late stages of flame propagation in the vessel, the flame fragmentation was more pronounced for the ducted-vessel. Moreover, the degree of flame fragmentation in the vessel increased with the duct length. The flame structure in the vessel was more irregular for a larger vent coefficient (Kv = 9.75). The more pronounced quenching in the short duct (250 mm duct) is related to the high inhibition efficiency due to the leakage of a large amount of sodium bicarbonate (SBC) powder into the discharge duct while in the long duct (750 mm duct) the disturbance is due to the strong turbulence. The appropriate SBC concentration can transform the mechanism for the pressure rise in the vessel. At high powder concentrations the maximum pressure in the vessel is dictated by the flame reaching the vessel wall, while at low concentrations the maximum pressure is dominated by the pressure (i.e., burn-up) in the discharge duct. There is an approximately linear correlation between the maximum pressure and the average flame velocity in the discharge duct for a given powder concentration, and a linear relationship between the maximum pressures in the vessel and the duct independent of the SBC concentration. Through the analysis of the flame dynamics (e.g. flame morphology, flame propagation velocity and turbulence) and friction resistance induced by the varying duct scales, the suppression efficiency of SBC powder in the vessel is higher for a longer and narrower discharge duct.

Wire-mesh inhibition of jet fire induced by explosion venting

Explosion venting is widely applied in industrial explosion-proof designs due to the convenient, economical and practical features of this method. Natural gas is usually stored in storage tanks. If the gas in the vessel is mixed with air and encounters an ignition source, explosion venting might occur, producing jet fire, generating new secondary derivative accidents and causing casualties and property losses. In this paper, a set of test platforms including wire-mesh suppression devices is established to study the inhibition of jet fire induced by explosion venting by wire mesh. The experimental research shows that a wire mesh significantly inhibits the jet fire induced by explosion venting. The flame propagation velocity and pressure clearly decrease with increasing numbers of wire-mesh layers. The wire-mesh structure significantly affects the flame propagation, and the more layers of mesh there are, the better the suppression effect is. The flame temperature gradually decreases with the addition of the wire mesh. The mesh size significantly affects the pressure propagation of explosion venting. The explosion pressure gradually decreases with the addition of the wire mesh. With increasing distance between the wire mesh and the explosion vent, the maximum temperature first increases and then decreases, and the maximum explosion pressure first decreases and then increases. In the case of single gas cloud, the flame suppression effect is the most obvious when the wire mesh is 0.2 m away from the explosion vent. In the case of double gas clouds, the flame suppression effect is the most significant when the distance between the wire mesh and the first gas cloud is 0.4 m.

The Effect of Initial Conditions on the Laminar Flame Front Velocity in Gas Mixtures

In this paper, we consider the scatter of the laminar flame front velocities caused both by an error in the composition of the combustible mixture and by artificial initial disturbances. It is shown how the configuration of the initial perturbations of an initially flat front of a laminar flame in a gas mixture with the constant composition affects the velocity spread of expanding spherical flames. The effect of the error in the composition of the combustible mixture on the parameters that determine the flame front velocity was analyzed from the literature data on the spread of the flame propagation velocity. These parameters were recalculated for the possible variation in the mixture composition obtained based on the data on the accuracy of the equipment used in the experiments.

End-Gas Autoignition Mechanism in a Downsized Spark-Ignition Engine: Effect of Inhomogeneity

ABSTRACT It is generally accepted that knock in spark-ignition engines is caused by end-gas autoignition. However, limited studies regarding to the effect of the inhomogeneity of temperature and composition on end-gas autoignition are presented. The major objective of this paper is to quantitatively understand the flame propagation velocity and the end-gas autoignition mechanism affected by the reactivity gradient formed by thermal stratification and composition stratification in the combustion chamber of a downsized SI engine. The conclusions were obtained based on a knock combustion case under an initial condition of high temperature and high pressure. In the present work, fuel stratification has a significant influence on the propagation velocity of the main flame. The flame propagation velocity declined with an increase in the level of fuel stratification. However, the temperature stratification had little effect on the flame propagation velocity. It was found that the onset of autoignition advanced with increasing the level of temperature stratification, which demonstrated an approximately linear relationship. It can be found that a high level of fuel stratification induced deflagration because of multi-spot spontaneous combustion. On the contrary, a very intense knock with detonation wave was observed under a slight level of temperature stratification. Under this condition, the temperature gradient near the nascent AI kernel was small and contributed to sequential spontaneous combustion. In fact, both the fuel stratification and temperature stratification are essentially the reactivity stratification. Therefore, similar results also can be conducted from fuel stratification. This work will give a new insight into suppressing knock mechanisms by different strategies.

The effects of addition of carbon dioxide and water vapor on the dynamic behavior of spherically expanding hydrogen/air premixed flames

Utilizing efficiently and securely hydrogen as clean energy source, it is required not only to analyze the experimental data under a certain condition but also to create the mathematical model for the prediction of flame propagation velocity under various conditions. Thus, it is significant to understand the characteristics of dynamic behavior of hydrogen/air premixed flames and to elucidate the effects of addition of inert gas, i.e. carbon dioxide CO2 and water vapor H2O. We performed the experiments of hydrogen explosion in two types of closed chambers to observe spherically expanding flames using Schlieren photography. Wrinkles on the flame surface were clearly observed in low equivalence ratios. Analyzing the Schlieren images, the flame propagation velocity depending on the flame radius was obtained. Increasing the addition of inert gas, the propagation velocity decreased, especially in the case of CO2 addition. The propagation velocity increased monotonically as the flame radius became larger. The appearance of flame acceleration was found, which was caused by the evolution of wrinkles on the flame surface. Moreover, the Markstein length decreased as the concentration of inert gas became higher, indicating that the addition of inert gas promoted the instability of hydrogen flames. Furthermore, the wrinkling factor, closely related with the increment in propagation velocity, decreased as the inert-gas concentration became higher. The wrinkling factor normalized by the propagation velocity of flat flame increased, on the other hand, under the conditions of high inert-gas concentration, except for near the quenching conditions. This indicated that the addition of CO2 or H2O promoted the unstable motion of hydrogen flames, which could be due to the enhancement of the diffusive-thermal effect. Based on the characteristics of dynamic behavior of hydrogen flames, the parameters used in the mathematical model on propagation velocity including flame acceleration was obtained, and then the flame propagation velocity under various conditions was predicted.

Improvement of Calculations for Turbulent Premixed Flame Characteristics Determination using PDF Monte Carlo Simulation

This study aims at simulating turbulent premixed flame in a constant-pressure vessel (P = 1 atm) where the turbulence is supposed to be homogeneous and isotropic. The mixture of gas is composed by iso-octane-air. The realized CFD were based on Lagrange approach in Monte Carlo simulations. We focused on calculations of; flame radii R F , the flame propagation velocity S t , flame-brush thick ness  t an d flammability limit. During the study, influencing crucial parameters such as, the equivalence ratio  and the turbulence intensity u’ were considered. Results show that the equivalence ratio enhances the flame propagation when passing from lean to stoichiometric flames. Also, the turbulence intensity yields a notable growth for the flame characteristics mentioned above. Moreover, we noticed that the flammability limit is strongly depending of the turbulence intensity and the equivalence ratio. More precisely, we remarked that the minimum ignition energy (MIE) was situated quite smaller than the stoichiometric condition. But, it increased with the turbulence intensity.