Laminar Burning Velocity Of Methane Research Articles

Methane deflagration promoted by enhancing ignition efficiency via hydrogen doping, with a view to fracturing shales

The enhancement of shale gas explosion pressure is an unresolved issue in the emerging in-situ methane explosive fracturing. An effective approach to further enhance combustion and explosion characteristics is to promote ignition via improver doping. In this work, the enhancement of EIE (excess ignition energy) on the deflagration characteristics of CH4–CO–H2 mixtures was tested using a 20 L spherical setup, whereby the contribution of hydrogen, as an improver with higher thermal conductivity, to the enhanced effects was first explored. It is discovered that hydrogen doping contributes to thermal expansion and combustion, and the explosion pressure, rise rate and laminar burning velocity of methane at 0.6 equivalence ratio have been increased by 1.2%, 19.7% and 3.9% after loading 1 kJ EIE compared to loading minimum ignition energy, and can be further enhanced by 0.2%, 7.2% and 2.8% via hydrogen doping. Moreover, the promotion of hydrogen doping on ignition efficiency was demonstrated by quantitatively analyzing the underlying heat loss of EIE. Results indicate that even at 1.0 equivalence ratio, EIE would experience a significant heat loss of 54% in methane, whereas more energy would be used to promote combustion after hydrogen doping, ultimately achieving an ignition efficiency of up to 87%.

Determination of laminar burning velocity of methane/air flames in sub atmospheric environments

The global energy demand enhances the environmental and operational benefits of natural gas as an energy alternative, due to its composition, mainly methane (CH4), it has low polluting emissions and benefits in energy and combustion systems. In the present work, the laminar burning velocity of methane was determined numerically and experimentally at two pressure conditions, 0.85 atm and 0.98 atm, corresponding to the city of Medellín and Caucasia, respectively, located in Colombia. The environmental conditions were 0.85 atm, 0.98 atm, and 295±1 K. The simulations and experimental measurements were carried out for different equivalence relations. Experimental laminar burning velocities were determined using the burner method and spontaneous chemiluminescence technique, flames were generated using burners with contoured rectangular ports to maintain laminar Reynolds numbers for the equivalence ratios under study and to reduce the effects of stretch and curvature in the direction of the burner's axis. In general, the laminar burning velocity fits well with the numerical results. With the results obtained, a correlation is proposed that relates the laminar burning velocity with the effects of pressure, in the form SL=aPb, where a and b are model constants. Sensitivity analysis was performed using the GRI-Mech 3.0 mechanism which showed that the most sensitive reaction was H+O2=O+OH (R38). Additionally, it was found that the reactions H+CH3 (+M)=CH4 (+M) (R52), 2CH3 (+M)=C2H6 (+M) (R158), and O+CH3=H+CH2O (R10) dominate the consumption of CH3 which is an important radical in the oxidation of methane, this analysis is carried out for equivalence ratios of 0.8 and 1.0, and atmospheric pressures of 0.85 atm and 0.98 atm

Laminar burning velocities of methane + formic acid + air flames: Experimental and modeling study

Laminar burning velocities of methane + formic acid + air flames were determined using the heat flux method at 1 atm and initial gas temperature of 353 K. For fuel mixtures containing 75 or 50% mole fraction of HCOOH, a range of equivalence ratios from 0.7 to 1.3 was covered. In stoichiometric mixtures burning velocities were measured varying fuel composition from pure methane to 85% of formic acid. Due to the relatively high initial temperature close to the operational limit of the present burner, an extrapolation procedure had to be used leading to rather high experimental uncertainties up to ± 2 cm/s. New measurements have been compared with the predictions of the recent kinetic model of the authors and the model of Glarborg et al. [34]. Both models failed, and the reasons for the disagreement were analysed. A modification of the rate constant of reaction HOCO(+M)=H+CO2(+M) was suggested that dramatically improved the present model performance. This model was then compared with the predictions of the model developed by Marshall and Glarborg [19] at the conditions of the available experimental data for HCOOH flames. The comparison indicates some inconsistencies in the recent measurements of the burning velocity of formic acid.

Safety parameters for oxygen-enriched flames

The utilization of low-quality gaseous fuel from biomass gasification and the abundance of oxygen-rich streams obtained as a by-product of nitrogen-air separation by membrane technology has incentivized the development of sustainable oxygen-enriched combustion technologies in the last decades. However, a dearth of experimental and numerical analysis addressing the reactivity and safety aspects of these mixtures at initial low temperatures can be observed in the current literature.In this work, the heat flux burner was adopted for the measurement of the laminar burning velocity of methane in oxygen enriched air at different equivalence ratios. Results were compared with numerical data obtained by means of detailed kinetic mechanisms developed at the University of Bologna and the Gas Research Institute (GriMech3.0). Simplified correlations for the estimation of the laminar burning velocity with respect to the oxygen content at any equivalence ratio were developed, tested and evaluated.An elemental reaction-based function was found appropriate for the estimation of the overall reactivity of the investigated mixtures. Besides, numerical analyses were performed to characterize the flame structures in terms of temperature and product distribution under several initial conditions. These results gave further insights into the reaction mechanisms of gaseous fuels in the case of oxygen-enriched air, highlighting potential bottlenecks for kinetic model refinements. Eventually, relevant safety parameters were estimated, in particular the flammability range of the fuel/oxidant mixture, in terms of lower and upper flammability limits.

Laminar Burning Velocity of Methane, Hydrogen, and Their Mixtures at Extremely Low-Temperature Conditions

Methane consumption is strongly increasing as a result of its abundance from natural gas, thus leading to reduced costs, and as a result of the reduced environmental impact in the case of combustion, with a lower carbon content with respect to traditional fuels. These advantages encourage its utilization in several industrial applications, such as methane steam reforming for the production of hydrogen and automotive applications. The necessity of transporting the gases and large-scale distribution systems is however one of the main issues. Innovative processes, such as cryogenic storage, cryo-compression, and liquefaction, require detailed information on the thermal and chemical properties of the methane–hydrogen mixture at low and ultralow temperatures. In this framework, detailed kinetic models for the total and partial oxidation of methane, hydrogen, and methane–hydrogen mixtures in air at low (273 > T > 200 K) and ultralow (T < 200 K) temperatures must be developed and validated. In this work, the lam...

The comparative and combined effects of hydrogen addition on the laminar burning velocities of methane and its blends with ethane and propane

Laminar burning velocities of hydrocarbon blends of relevance to natural gas combustion, with addition of 0, 10, 35 and 50% hydrogen, were measured using the heat flux method. Hydrocarbon blends were methane (80%)/ethane (20%), methane (80%)/propane (20%) and methane (80%)/ethane (10%)/propane (10%), and in addition experiments were performed using pure methane as a fuel. For the first time it was shown experimentally that hydrogen promotes laminar burning velocity of blends with heavier hydrocarbons to a smaller extent than the well-studied effect on methane. Measurements show that enrichment by hydrogen results in 20–40% lower increase in laminar burning velocity for hydrocarbon blends compared to pure methane, depending on stoichiometry. Modeling points at the importance of increasing concentrations of OH, O and H radicals in H2 enriched flames. At lean conditions increase in H atom concentration is of particular importance. The results are rationalized based on asymptotic flame theory analysis.

Experimental and numerical study of CO2 content effects on the laminar burning velocity of biogas

In the present work, the adiabatic laminar burning velocity of methane diluted with carbon dioxide, the two main components of biogas, is investigated both experimentally and numerically. The burning velocity of five mixtures with different CO2 content (up to 50% in fuel volume) were measured using the heat flux method at atmospheric conditions (298K and 1atm). The experimental results were compared to data and correlations form literature and also to predictions from four detailed kinetic mechanisms. Results showed that CO2 dilution reduces the burning velocity and shifts the maximum burning velocity towards leaner mixtures. The Gri-Mech 3.0 mechanism showed the best agreement with measurements for 10% and 20% CO2 fuel content mixtures. For 30%, 40% and 50% CO2 fuel content mixtures, the Konnov mechanism presented the highest determination coefficients. The numerical model is further explored to show that the shifting of the maximum burning velocity towards leaner mixtures is determined by a combination of CO2 dilution and reaction effects.

Measurements of Laminar Burning Velocities above Atmospheric Pressure Using the Heat Flux Method—Application to the Case of n-Pentane

A new adiabatic burner allowing the measurement of burning velocities at high pressure with the heat flux method has been developed. Experimental measurements of laminar burning velocities of methane and n-pentane were performed for pressures up to 6 atm at 298 K and at atmospheric pressure for temperatures from 298 to 398 K. Equivalence ratios varied from 0.6 to 1.9. The results for methane flames are in good agreement with the only results of literature obtained above atmospheric pressure using the heat flux method; those for n-pentane are to our knowledge the first application of this method to a flame of a liquid fuel above atmospheric pressure. Based on these measurements, empirical correlations of the variation of the measured laminar flame velocities with pressure and temperature have been proposed for methane and n-pentane. In the case of methane, these correlations lead to a satisfactory prediction of literature measurements made using constant volume bombs.

The effect of elevated pressures on the laminar burning velocity of methane + air mixtures

In spite of the large amount of research spent on the evaluation of the high pressure dependence of laminar burning velocity of methane+air flame, there still exists a large uncertainty in the data for various reasons. In order to reduce the scatter to acceptable levels, the Heat Flux Method (HFM), known as a potential method with high accuracy, has been extended to higher pressures. New measurements of the laminar burning velocity of methane+air flames are presented. Non-stretched planar flames were stabilized on a perforated plate burner which was placed in a high pressure environment. The experimental results are reported for a pressure range between 1 and 5atm. The equivalence ratio was varied from 0.8 to 1.4. Comparisons with several recent literature sources (experiments) show good agreement. An exhaustive literature survey was performed to study the numerous existing laminar burning velocity correlations for its pressure dependence. It is indicated from the literature that many of the deduced correlations use stretched laminar burning velocity results. Many used only few data points for the pressure behavior and correlations and therefore show wide discrepancies. As the heat flux method furnishes quality results with reduced errors, the results were further utilized in deducing a power-law pressure dependence. Numerical simulations were also performed using two widely used chemical reaction mechanisms, which were further involved in comparing correlations. The proposed power exponent β1 shows a non-monotonic behavior at equivalence ratio around 1.4 in experiments and simulations. Through species and reaction flux analysis it was observed that CH3 consumption through various reactions remain pressure dependent and show non-monotonic behavior at equivalence ratio around 1.4.

Direct prediction of laminar burning velocity using an adapted annular stepwise diverging tube

In a combustion study, laminar burning velocities of premixed flames are essential data. A number of experimental results for various fuels have been reported. Although there are many reliable experimental methods that provide precise burning velocities, these methods are not suitable for in situ monitoring in the field. In response to this limitation, a method using an annular diverging tube (ADT) was introduced in the previous study, and its feasibility was verified. In this study, an advanced technique using an annular stepwise diverging tube (ASDT) was introduced to enhance flow uniformity and to formulate flatter flames in the majority of experimental conditions. The configuration of the burner was gradually improved based on their flame propagation characteristics. An adapted burner configuration was developed and used to predict the laminar burning velocities of methane, propane, and DME. Two types of measuring methods were compared: a transient method, which was similar to the previous study, and a static method, which was used for a direct prediction of burning velocity. The static method predicts similar burning velocities when compared to the transient method. The results of both methods were sufficiently similar to the other’s previous results. Quenching distances could also be directly predicted using this adapted ASDT system. Therefore, the static method may be the easiest and fastest method to predict burning velocity, and quenching distance at the instant. This method can be applied to the energy field and aid in the understanding of flame characteristics in narrow combustion spaces.

High pressure laminar burning velocity measurements and modelling of methane and n-butane

A constant volume vessel has been used in conjunction with a numerical multi-zone model to calculate laminar burning velocities of methane and n-butane in the ranges φ = 0.8–1.4, T u = 320–470 K, p u = 1–15 bar from the pressure record. This multi-zone model has been compared with the analytical model of Luijten and de Goey. For methane, the experimental data have been compared with modelling data generated using the MIXFLA program of Warnatz. The MIXFLA data have further been used to examine the form of the correlation fitted to the experimental data, confirming the form used by Clarke. For methane, good agreement was found between the current experimental data and the literature at high pressures. For n-butane, poor agreement was found with the one data set available. However, the data from this reference did not compare well with other authors for methane.

Effects of hydrogen enrichment on adiabatic burning velocity and NO formation in methane + air flames

Experimental measurements of the adiabatic burning velocity and NO formation in methane + hydrogen + air flames are presented. The hydrogen content in the fuel was varied from 0% to 35%. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. The Heat Flux method was used to determine burning velocities under conditions when the net heat loss of the flame is zero. An overall accuracy of the burning velocities was estimated to be better than ±0.8 cm/s in the whole range of enrichment by hydrogen. A procedure for estimation of errors in equivalence ratio was extended to binary fuel mixtures. The relative accuracy of the equivalence ratio was found to be below 1.47%. Adiabatic burning velocities of methane + hydrogen + air mixtures were found in satisfactory agreement with the literature results and with the Konnov model predictions. A new correlation for the adiabatic laminar burning velocity of methane + hydrogen + air mixtures burning at standard conditions was derived. The NO concentrations as a function of equivalence ratio were measured using probe sampling at a fixed distance from the burner. In lean flames enrichment by hydrogen has little effect on [NO], while in rich flames the concentration of nitric oxide decreases significantly. The numerical predictions are in good agreement with the experiment.

Effect of Radiation Reabsorption on Laminar Burning Velocity of Methane Premixed Flame Containing with Steam and Carbon Dioxide

Flame properties in the ambience of steam and carbon dioxide are complicated because of the third-body effect and radiation reabsorption. Thus, we performed detailed chemical kinetic calculations that include the effect of radiation reabsorption to clarify the premixed laminar flame speed of such a mixture, being one of the most important properties for controlling combustion. Pressure was varied up to 5.0MPa to simulate the 1700°C class combined gas turbine system. The results show a marked increase in laminar burning velocity by considering radiation reabsorption. Laminar burning velocity was increased up to 150% in cases of methane-oxygen and steam or carbon dioxide mixtures. It was found that the preheating of the upstream, unburned mixture caused this increase. The influence of radiation reabsorption was much larger in the case of lower pressures.

96/00712 Measuring the laminar burning velocity of methane/diluent/air mixtures within a constant-volume combustion bomb in a micro-gravity environment

The laminar burning velocity of methane and air has been determined for a range of equivalence ratios, with various levels of carbon dioxide and nitrogen as diluents. Carbon dioxide and nitrogen are both present in natural gas, and in biogas there can be as much as 40% carbon dioxide. Furthermore, mixtures of carbon dioxide and nitrogen can be used to simulate the products of combustion, thus enabling measurements of the burning velocity to be made that correspond to conditions of exhaust-gas recirculation. The data presented here cover higher levels of diluents than previously reported, with up to 60% of either nitrogen or carbon dioxide as part of the fuel. Because of the effects of buoyancy during the combustion process within a constant-volume bomb, the centre of the flame kernel rises and the flame-front deviates from that of an ideal sphere at low values of burning velocity. This invalidates the analysis methods where the centre of the kernel is assumed to be stationary and the flame front is a perfect sphere. The problem may be overcome by use of a micro-gravity environment. Comparisons are reported between a detailed thermodynamic analysis and an approximate analysis, for computing the laminar burning velocity from the pressure/time record: it is concluded that the approximate analysis is satisfactory. A discussion is reported on the effects of flame stretch, from which it can be argued that, for the mixtures investigated here, the effects of stretch are negligible after the end of the initial pressure-rise period.