Flame Burning Velocity Research Articles

Combustion Chemistry of Rich Methanol–Air Mixtures

Chain branching and heat release processes and their influence on the burning velocity of premixed rich and near-stoichiometric methanol–air flames were studied by numerical simulation and sensitivity analysis. The phenomenon of superadiabatic temperatures in these flames due to the kinetic mechanism of methanol combustion was first detected. Comparison of the simulation results of the structure of methanol and formaldehyde flames shows that the formation of water in superequilibrium concentrations in flames does not necessarily lead to superadiabatic temperatures, as believed earlier. It was first found that decreasing the dilution of the CH3OH/O2/N2combustible mixture with nitrogen at a constant equivalence ratio enhances the superadiabatic temperature effect. According to simulation results, in a rich near-limit methanol flame, the role of the chain branching reactions H + O2 = O + OH and O + H2 = H + OH is negligible due to their low rate. At relatively low temperatures, branching occurs mainly in reactions involving HO2and H2O2peroxide compounds, whose concentration is orders of magnitude higher than the concentration of the main chain carriers H, O, and OH. From the sensitivity analysis, it follows that the burning velocity of methanol flames is positively influenced mainly by the reactions of formation of chain carriers and is negatively influenced by the reactions of consumption of chain carriers. reactions having a major contribution to heat release but are not involved in the formation and consumption of radicals have small sensitivity coefficients.

Experimental and kinetic modeling study of laminar burning velocities of NH3/syngas/air premixed flames

Ammonia (NH3) can be used as carbon-free alternative fuel for modern energy and transportation systems. Co-firing NH3 with syngas can overcome the high ignition energy and low burning velocities of pure NH3 flames on the one hand, while regarding the characteristics of syngas on the other hand, this strategy may have low-emission potential in real application, and a corresponding research can be helpful for validating or developing NH3 co-firing mechanisms with more complex fuels. The present study experimentally investigated laminar burning velocities of NH3/syngas/air flames at atmospheric pressure and 298 K using the heat flux method. Two types of syngas components were used, i.e., SYN_A: 5 vol% H2 + 95 vol% CO and SYN_B: 50 vol% H2 + 50 vol% CO, and the measured conditions cover wide ranges of mixing ratios and equivalence ratios. Several literature kinetic mechanisms were tested and a new mechanism was proposed. Results calculated by the present mechanism agree well with experimental data of the burning velocities and the ignition delay times of NH3, NH3/H2, NH3/CO, and NH3/syngas flames at various mixing ratios, equivalence ratios, and pressures. The present mechanism also reproduces the trend of NOx emission characteristic in literature. Detailed kinetic analyses using the present mechanism were carried out, showing the NH3 oxidation processes in NH3/syngas/air flames and the most rate-limiting reactions for predicting the laminar burning velocities. Important reactions with different rate parameters from different sources were labeled, which could be helpful for future organization or optimization of NH3 kinetic mechanisms.

Characterization of Turbulence in an Optically Accessible Fan-Stirred Spherical Combustion Chamber

ABSTRACT Fundamental characteristics of fan-generated turbulence inside a constant-volume combustion chamber (CVCC) with 400 mm inner diameter under high-pressure and high-temperature conditions have been investigated to establish benchmark data for studies of turbulent premixed flame propagation. Here, the CVCC was designed to withstand up to 1.0 MPa initial pressure and 600 K initial temperature and equipped with four fans oriented in a tetrahedron configuration. A time-resolved particle imaging velocimetry (TR-PIV) is employed to characterize the turbulence under various thermodynamic conditions. Additionally, stereoscopic TR-PIV measurements were conducted to characterize the three-dimensional turbulent flow field inside the chamber. The results showed that the chamber could achieve homogenous and isotropic turbulence. A reasonably isotropic stationary turbulence with large turbulence intensities (up to ≈ 4.7 m/s) was achieved in the central region extending to almost 50 mm radius. This has been manifested by near-zero mean velocities and directional invariance of turbulence intensities. Global homogeneity and isotropy ratios in the chamber were close to unity, indicating weak anisotropy. The spectral energy spectra of the generated turbulent flow fields were in satisfactory agreement with the well-known Kolmogorov’s – 5/3 law associated with homogeneous isotropic turbulence irrespective of the intensity of the turbulence. Various spatio-temporal length scales characterizing the turbulent flow field including the integral, Taylor, and Kolmogorov length scales were reported. Turbulence statistics and inherent parameters were investigated at elevated pressure and temperature conditions as well as results from test cases to determine turbulent–flame propagation speeds were reported. Accordingly, the present canonical configuration apparatus can be conveniently adopted for several turbulent combustion studies including mainly the determination of turbulent burning velocity for gaseous and liquid premixed flames in nearly homogeneous isotropic turbulence.

Numerical Studies of the Pilot Flame Effect on a Piloted Jet Flame

ABSTRACT In a piloted jet flame, the pilot flame has an effect of stabilizing the main flame. Detailed mechanisms of pilot flame/main flame interaction are however not well studied. It is expected that the pilot flame affects the main flame through the following mechanisms: (a) the pilot flame provides the heat and radicals to the reaction zone of the main flame, (b) the pilot flame prevents the cold ambient air from being entrained into the main flame, and (c) the pilot flame modifies the stretch rate of the main flame. In this paper, detailed numerical simulations of piloted laminar methane/air jet flames are carried out to elucidate the effect of pilot flame on the structure and burning velocity of the main jet flame. One-dimensional (1D) freely propagating flame is also simulated to investigate the effect of hot gas mixing with the unburned fuel/air mixture, and 1D counter-flow flame is simulated to study the diffusion of the hot gas from the pilot flame to the reaction zone of the main flame and the effect of flame stretch. The results showed that heat transfer from the pilot flame to the main flame has a more significant effect on the structures and propagation of the main flame than the mass transfer from the pilot flame to the main flame. The heat and mass transfer from the pilot flame affects the local equivalence ratio and temperature of the unburned mixture, which gives rise to a significant enhancement of burning velocity. When the hot gas from the pilot flame is at sufficiently high temperatures, an ultra-lean fuel/air mixture can burn at equivalence ratio below the flammability limit. The reaction rate and burning velocity of ultra fuel-lean flames are enhanced by the strain rate, whereas for a main flame with the equivalence ratio closer to that of pilot flame, the reactivity and burning velocity of the main flame decrease with increasing strain rate.

Investigation of the physical and chemical effects of fire suppression powder NaHCO3 addition on methane-air flames

In this study, the influence of fire suppression powder NaHCO3 on premixed flames was investigated experimentally and numerically. To better understand the suppression mechanism of the powder, the physical heat sink and chemical reaction contributions of the addition of the powder on the laminar burning velocity of methane-air flames were analyzed. An improved model was developed to predict the influence of the physical heat sink effect on burning velocity, and the model aligned well with the experiment. The results demonstrated that the physical effect had a non-negligible impact on flame suppression. Thereafter, the chemical reaction effect of NaHCO3 powder was investigated, and the results showed that the chemical effect suppressed flames by scavenging free radicals. When a large quantity of agent was added, the equivalence levels of the free radical concentration resulted in the saturation of the chemical effect. The influence of the initial temperature and pressure on the chemical effect was also studied. Finally, the exact contributions of the two effects were compared under different sizes of the powder particles. The results indicated that the suppression mechanism was under the thermodynamic control when the particle size was large, as that the physical heat sink effect played a more important role than the chemical effect. Conversely, the suppression mechanism was under the kinetic control when the particle size was small, as the chemical reaction effect occupied the dominant position.

Experimental and kinetic investigation on the effects of hydrogen additive on laminar premixed methanol–air flames

The effects of hydrogen addition on laminar premixed methanol–air flames were studied both experimentally and numerically. To achieve this, a constant volume chamber (CVC) and the premix code in CHEMKIN were used. During the experiments, the equivalence ratios (ϕ) and hydrogen mole fractions (Xh) were set to 0.6 to 1.8 and 0%–100%, respectively. In addition, initial environmental conditions were set to 375 K and 1 atm. The results indicate that the laminar flame speed (LFS) and burning velocity (LBV) both increase when more hydrogen is added into the methanol–air mixtures. For premixed methanol–air flames, the Markstein length (Lb) decreases monotonically with an increase in the equivalence ratio; however, when the hydrogen fraction is greater than 40%, an increasing trend in the Markstein length is presented as the mixtures move toward the fuel-rich side. The variation in Markstein length is non-monotonic with the hydrogen fraction. A kinetics analysis indicates that methanol is mainly consumed by the dehydrogenation reaction caused from the impact of the active free radicals (OH and H). Reactions involving active free radicals and light intermediate species have the highest sensitivity and contribute the most to the propagation of a laminar flame. Therefore, the promotion effect of hydrogen additive is due to an enhancement in the radical pooling of H, OH, and O. The chain branching reaction R5 (O2 + H = O + OH) is essential for the geometric growth of free radicals. In addition, the amount of formaldehyde decreases owing to the hydrogen blending.

Analytical Model of Recirculation Influence on Premixed Combustion of Lycopodium Dust Particle: Studying Thermal Resistance and Random Distribution of particles

In this work, a comprehensive mathematical method is developed to model the flame propagation through organic particles with air as a two-phase mixture, considering random distribution and particles thermal resistance. For this purpose, the structure of flame contains a preheat-vaporization zone, a reaction zone where vaporization and convection rates of particles are negligible and a post flame zone where diffusive terms are negligible in comparison of other terms zone. In order to enhance the combustion efficiency, the exhausted heat from the post flame zone is recirculated back to the preheat zone. Since this stream consists of high temperature gaseous mixture, it can enhance the temperature of the initial two-phase mixture entering the combustion chamber. The obtained results show great compatibility with the experimental findings. Apart from the randomness distribution of particles and heat recirculation phenomena, the effect of thermal resistance on the combustion properties such as flame temperature and burning velocity is studied through non-zero Biot numbers in this model. Additionally, the variation of several parameters including equivalence ratio, particle diameter and Lewis number are studied in this research.

Measurement and modelling of the laminar burning velocity of methane-ammonia-air flames at high pressures using a reduced reaction mechanism

Ammonia and blends of ammonia with methane are gaining increased interest as fuels for gas turbine applications and hence optimized reduced reaction mechanisms for the fuels are required for the development of combustors. However, there is a scarcity of measured data on the laminar burning velocity of the fuels for optimizing and validating reaction mechanisms especially at high pressures. In this study, an extensive set of measurements of the unstretched laminar burning velocity and Markstein lengths of CH4NH3-air flames at high pressures are reported for the first time and an optimized reduced reaction mechanism is proposed. The experiments were conducted in a constant volume chamber for various ammonia heat fractions in the fuel ranging from 0 to 0.30, equivalence ratios ranging from 0.7 to 1.3, and mixture pressures ranging from 0.10 to 0.50 MPa. The reduced reaction mechanism was developed from a detailed reaction mechanism for CH4NH3-air flames by Okafor et al., and optimized against the present measurements and data in the literature. It is shown that the reduced mechanism models the unstretched laminar burning velocity of NH3/air and CH4NH3-air flames with high fidelity at all studied conditions. It also models satisfactorily NH3, NO and CO concentration in CH4NH3O2N2 oxidation in a laminar flow reactor. Furthermore, the reduced mechanism is demonstrated to predict NO, OH, and NH profiles in a premixed stagnation NH3-air flame satisfactorily. The experimental measurements were also used to validate selected detailed reaction mechanisms. It was found that the significant over-prediction of NO production from NH3 oxidation by GRI Mech 3.0 is primarily due to the influence of the reaction NH+H2OHNO+H2, which in fact may not be important in fuel NO chemistry.

Yet another kinetic mechanism for hydrogen combustion

Recent suggestion by Burke and Klippenstein (2017) that chemically termolecular reactions H + O2 + R may significantly affect kinetic pathways under common combustion situations requires careful analysis, since, if included in contemporary kinetic mechanisms, these reactions affect global reactivity and calculated burning velocities of laminar premixed flames. In the view of their impact, a detailed kinetic scheme for hydrogen combustion was revisited to elucidate how to counterbalance enhanced chain termination caused by chemically termolecular reactions in attempt to keep or improve model performance. First, recent experimental and theoretical kinetic studies of hydrogen reactions were analyzed. In the new mechanism four reactions were introduced and three rate constants were updated. These changes, however, significantly reduce calculated burning velocities of H2 + air flames as compared to experimental data and earlier model predictions with the major impact from chemically termolecular reactions. It was then found that implementation of the new theoretical transport database developed by Jasper et al. (2014) significantly improves the performance of the updated kinetic model. The new kinetic mechanism for hydrogen combustion which includes updated kinetics and new transport properties was found in good agreement with the consistent dataset of the burning velocity measurements for hydrogen flames obtained using the heat flux method at atmospheric pressure for which the behavior of the previous model of the author was not satisfactory.

Effects of Integral Scale on Darrieus–Landau Instability in Turbulent Premixed Flames

Previous studies have revealed the existence of distinct regimes of DL-stable and unstable turbulent flames, depending on whether the DL instability could be minimized or not. The mechanism of how mixture composition, flame macroscale and turbulence intensity, etc. act on DL instability has been extensively studied. Even though, the role played by turbulent length scale on DL instability is still unclear. The present study has been experimentally focused on the effect of turbulent integral scale on DL instability of premixed turbulent Bunsen flames. Flame fronts of C3H8/air mixture (ϕ = 0.8) under different turbulence conditions are captured by OH-PLIF technique. It is observed that the DL-unstable flames, obtained at relatively large integral scale and with cusps observed on the flame fronts, transform to be DL-stable flames with planar or disorderly wrinkled flame fronts as the integral scale decreases, indicating the indispensable role of integral scale on DL instability. These cusps on DL-unstable flame fronts decrease flame surface density while enlarge flame volume. Turbulent burning velocities of DL-unstable flames are augmented compared to DL-stable flames, leading to a similar dual-propagation model as observed in literatures. The threshold where turbulence shadows DL instability is analyzed by upgrading a previous model of [Phys. Rev. E 84 (2011) 026322]. The modified model is more reliable to demonstrate the DL-stable and unstable regimes in the Peters-Borghi’s diagram.

Simulating upstream flame propagation in a narrow channel after wall preheating: Flame analysis and chemistry reduction strategy

The response of a premixed laminar flame, stabilised in a narrow channel (ℓi=5 mm), is investigated for an amount of heat supplied upstream through the wall. The first objective is to determine the set of canonical problems that a reduced chemistry must accurately reproduce to simulate the flame/wall coupling under such circumstances. The second objective is to identify the major energy transport mechanisms at play, i.e. convective heat transfer in the gas or conductive in the solid wall. The stoichiometric methane-air flame numerical simulations performed include complex molecular transport and the fully coupled solving of heat transfer at and within the wall. Initially, the flame is stabilised by an inlet mass flow rate matching the flame burning velocity. A reference simulation is first performed with a comprehensive methane-air chemistry. Then, two chemistry reduction strategies targeting a different set of canonical problems are applied and the results compared to conclude on the necessary constraints for chemistry reduction under such flow configuration. Various heating intensities are considered and a minimum heating supply is found necessary to initiate a complete upstream flame translation. A specific attention is paid on the relative contributions of heat convection in the flow and heat conduction in the solid. The heat transfer mechanism triggering the flame movement is revealed to be mainly convective. The flame translation is found to be organised in two stages, with first a downstream movement due to fresh gases expansion because of heating by the wall, followed by the upstream propagation due to the enhancement of the burning rate by the preheating of the mixture. The shape, the flash back speed, and the final position of the flame vary with the amplitude of the heat flux brought to the external surface of the wall.

Parametrization of the temperature dependence of laminar burning velocity for methane and ethane flames

The power exponent α in the temperature dependence of laminar burning velocity SLSL0=TuTu0α is usually considered an empirical parameter extracted from measurements performed at different temperatures. In this paper an analytical derivation of α is proposed, calculating the power exponent from the overall activation energy as: αTu0→Tu=Ea2R·X+x. This relation is verified against experimental burning velocity data measured with the heat flux method and chemical kinetic models for flames with equivalence ratios, Φ, from 0.6 to 1.6 at up to 368 K unburned gas temperature and 1atm. Both methane and ethane were used as fuel. Laminar burning velocity predictions at elevated temperatures are made using proposed relation and the resulting values are in good agreement with existing data for methane flames up to 500 K. This indicates that the proposed mathematical derivation of α is accurate. In addition to providing a reliable extrapolation of the burning velocity at varying temperatures, isolating the temperature dependence of the power exponent α enables more accurate quantification of other factors, e.g., Φ, the unburned gas temperature and pressure, that influence laminar burning velocity. Additionally, it provides a simple means to evaluate the overall activation energy, Ea.

Mechanism of flame acceleration and detonation transition from the interaction of a supersonic turbulent flame with an obstruction: Experiments in low pressure propane–oxygen mixtures

The present paper seeks to determine the mechanism of flame acceleration and transition to detonation when a turbulent flame preceded by a shock interacts with a single obstruction in its path, taken as a cylindrical obstacle or a wall in the present study. The problem is addressed experimentally in a mixture of propane–oxygen at sub-atmospheric conditions. The turbulent flame was generated by passing a detonation wave through a perforated plate, yielding flames with turbulent burning velocities 10 to 20 larger than the laminar values and incident shock Mach numbers ranging between 2 and 2.5. Time resolved schlieren videos recorded at approximately 100 kHz and numerical reconstruction of the flow field permitted to determine the mechanism of flame acceleration and transition to detonation. It was found to be the enhancement of the turbulent burning rate of the flame through its interaction with the shock reflection on the obstacle. The amplification of the burning rate was found to drive the flame burning velocity close to the speed of sound with respect to the fresh gases, resulting in the amplification of a shock in front of the flame. The acceleration through this regime resulted in the strengthening of this shock. Detonation was observed in regions of non-planarity of this internal shock, inherited by the irregular shape of the turbulent flame itself. Auto-ignition at early times of this process was found to be negligibly slow compared with the flow evolution time scale in the problem investigated, suggesting that the relevant time scale is primarily associated with the increase in turbulent burning rate by the interaction with reflected shocks.

Analytical correlation to model diluent concentration repercussions on the burning velocity of biogas lean flames: Effect of [formula omitted] and [formula omitted

The application of alternative and more sustainable fuels such as biogas or diluted natural gas can dramatically decrease greenhouse gas emissions and their impact on global climate. To do so, a knowledge on its typical combustion characteristics is crucial so that it can be burned in an efficient way in safe conditions. Simulations using CANTERA with the latest USC-Mech chemical-kinetic mechanism were conducted to assess the influence of diluents (CO2 and N2) on the laminar burning velocity of lean CH4/air flames, as biogas behaves fundamentally as a CH4/diluents blend. Equivalence ratios tested ranged from 0.7 to 1.0 and diluent mass fractions (ydil) from 0 to 0.38. A new analytical correlation relating SL and ydil, SL/SL,ref=(p/pref)σ(Tu/Tu,ref)γ(1+αydil+βydil2) was obtained from the simulations and validated with experimental results available in the literature. Good agreement was found between the correlation predictions and the experimental results indicating that it can be used to predict SL in the ranges of this work: up to yCO2,dil=0.38 and yN2,dil=0.28, 298K<Tu<500K and 1atm<p<10atm. It was verified that N2 and CO2 produce noticeably different effects when reducing SL, with the latter exhibiting a characteristic contribution for small diluent concentrations, mainly due to a chemical impact.

Laminar combustion regimes for hybrid mixtures of coal dust with methane gas below the gas lower flammability limit

Understanding flame propagation in dust clouds and hybrid mixtures requires knowledge of the fundamental combustion processes and their coupling interaction. The objective of this work is to use computational fluid dynamics to classify laminar flame structure in hybrid mixtures where the initial gas concentration is below the lower flammability limit. Particular focus is given to the role of reaction chemistry and overall equivalence ratio on flame structure and burning velocity. Through this study, five flame regimes were determined: fuel-lean flames (Type I), volatile-lean flames (Type II), volatile-rich flames (Type III), transition flames (Type IV), and kinetic-limited flames (Type V). Gas-phase chemistry was found to play a critical role in burning velocity for Type III, IV, and V flames. Burning velocities at hybrid volatile component equivalence ratios less than 0.9, were found to be less sensitive to reaction kinetics. Further research using this model will focus on initial gas concentrations above the lower flammability limit, exploring the flammability limits of hybrid mixtures, and extending the results to turbulent flames in system geometries relevant to industrial safety.

Effects of N2 and CO2 dilution on the combustion characteristics of C3H8/O2 mixture in a swirl tubular flame burner

Premixed C3H8/O2 combustion has been investigated by adopting N2, CO2 and their mixture (50% N2-50% CO2 by volume) as the diluents, respectively. The oxygen content (mole fraction) in the oxidizer is varied from 0.13 to 0.35, which covers the operating conditions of EGR and OEC. The flame structures, temperatures, burning velocities and NOx emissions are examined under various oxygen contents. Detailed observations show that a steady, uniform tubular flame can be obtained over a wide range from lean to rich. By increasing oxygen content, the flame diameter increases slightly; the flame length decreases significantly, which is almost inversely proportional to laminar burning velocity. During decreasing the burning velocity to less than about 20 cm/s, a turning point appears and the flame length becomes extensively large. With the same oxygen content and equivalence ratio, by replacing half or all of the N2 diluent with CO2, the flame temperature and burning velocity decrease significantly. To obtain the same adiabatic flame temperature, the CO2 diluted mixture requires the highest oxygen content among the three diluents, however, its measured flame temperature is also highest. In the N2-CO2 diluted combustion, owing to thermal and chemical effects of CO2, the NOx emission reduces remarkably comparing with N2 dilution; under the same flame temperature, the NOx concentration reduces to almost 1/5 of that diluted by N2. The lean extinction limit raises by increasing CO2 content in the diluent, while the limit decreases with increasing oxygen content.

Effects of stretch and thermal radiation on difluoromethane/air burning velocity measurements in constant volume spherically expanding flames

Compared to current refrigerants, next-generation refrigerants are more environmentally benign but more flammable. The laminar burning velocity is being used by industry as a metric to screen refrigerants for fire risk and it is also used for kinetic model development and validation. This study reports measurements of difluoromethane/air flame burning velocities for equivalence ratios from 0.9 to 1.4 in a spherical, constant volume device. Experimental burning velocities produced with the aid of an optically thin radiation model are about 17% greater than those obtained with an adiabatic model. Characterization of flame stretch based on the product of Markstein and Karlovitz numbers indicates that while many experimental data are nearly stretch-free, those for slower burning velocities, smaller flame radii, and leaner conditions may not be. Limiting the data to regions estimated to be stretch-free requires extrapolation away from the experimental conditions to extract burning velocities near ambient conditions, e.g., at (298 K, 101 kPa). Lower uncertainty, desirable for kinetic model validation, is obtained by interpolating between experimental conditions, e.g., at (400 K, 304 kPa). Since thermal radiation and flame stretch were found to affect the inferred burning velocities of difluoromethane/air constant volume spherical flames, these effects should also be considered during data reduction of other mildly flammable refrigerants.

Investigation on spherically expanding flame temperature of n-butane/air mixtures with tunable diode laser absorption spectroscopy

Abstract A joint schlieren imaging, pressure recording and tunable diode laser absorption spectroscopy (TDLAS) thermometry technique was developed to simultaneously determine the flame radius, pressure and line-of-sight averaged temperature of spherically expanding flames of n-butane/air mixtures at initial temperature of 298 K, initial pressure of 1 atm and equivalence ratios of 0.9–1.5. To probe the flame temperature, a mid-infrared interband cascade laser at 4.2 µm was used to measure the time-resolved direct absorption spectra of CO2 which are strongly related to flame temperature, CO2 mole fraction, flame radius and pressure. Quantitative line-of-sight averaged temperatures of burnt gas were obtained by fitting the normalized absorbance spectra. Three typical stages, including the spark affected initial stage, quasi-steady stage and the pressure induced growing stage are determined from the evolution of measured temperature as a function of time and flame radius. The relation between flame temperature, stretch rate and burning velocity of burnt gas are analyzed. Stretch rate is found to have minor effect on the measured temperature in the quasi-steady stage. The relative variation of temperature is much smaller than that of velocity. The flame with lower normalized temperature tends to propagate slower.

Reviewing H2 Combustion: A Case Study for Non-Fuel-Cell Power Systems and Safety in Passive Autocatalytic Recombiners

This Review looks at past and current research and development (R&D) on H2 combustion in terms of power generation in gas turbines and safety in passive autocatalytic recombiners (PARs). The drive toward reducing greenhouse gas emissions has forced researchers to look at carbon-free alternatives for power generation. Fortunately, H2 is one such fuel source and has been proposed as a fuel in gas turbines for large-scale power production. The effects of H2 on the heating values, flame speed, burning velocity, flammability range, flashback, blow-off, ignition delay, and emissions have been reported, and the trends and gaps in R&D identified. Properties such as flame speed, burning velocities, and flammability limits at typical gas turbine conditions (high pressures, high temperatures, lean equivalence ratios, and turbulent conditions) still need to be determined experimentally for H2 fuel mixtures, especially for mixtures with higher H2 concentrations and fuel mixtures with other fuels (such as biogas) as an...

Data consistency of the burning velocity measurements using the heat flux method: Hydrogen flames

Consistent datasets of experiments are highly important both for validation and optimization of kinetic mechanisms. An analysis of the data consistency of all available burning velocity measurements of hydrogen flames using the heat flux method at atmospheric pressure is performed in the present work. A comparison of many experiments performed in several laboratories with different types of dilution by various inerts was guided by kinetic modeling using two kinetic mechanisms. Konnov (2015) and ELTE (Varga et al., 2016) models demonstrated a uniform trend at all conditions tested: the second mechanism predicts lower burning velocities which are in better agreement with the heat flux measurements from different groups. Some experimental datasets, however, significantly disagree with one or both models; these conditions were revisited experimentally in the present work. The laminar burning velocities of H2 + O2 + N2 mixtures with 7.7% O2 in O2 + N2 oxidizer and of 85:15 (H2 + N2) and 25:75 (H2 + N2) fuel mixtures with 12.5:87.5 (O2 + He) oxidizer have been measured. It was concluded that the results of Hermanns et al. (2007) are somewhat higher than those of other studies at similar conditions and a possible reason of this disagreement was suggested. Analysis of the measurements performed by Goswami et al. (2015) on a high-pressure installation suggests an equipment malfunction that led to the erroneous values of the equivalence ratio for hydrogen and syngas flames. The ELTE mechanism developed using an optimization approach shows a very good performance in predicting laminar burning velocities of hydrogen flames measured using the heat flux method.