Numerical analysis on influence of hydrogen peroxide (H2O2) addition on the combustion and emissions characteristics of NH3/CH4-air (O2/N2)/ H2O2 mixture

In this work, extensive chemical kinetic modeling is performed to analyze the combustion and emissions characteristics of premixed NH₃/CH₄–O₂/N₂/H₂O₂ mixtures at different replacement percentages of air with hydrogen peroxide (H₂O₂). This work is comprehensively discusses the ignition delay time, flame speed, heat release rate, and NOx & CO emissions of premixed NH₃/CH₄–O₂/N₂/H₂O₂ mixtures. Important intermediate crucial radicals such as OH, HO₂, HCO, and HNO effect on the above-mentioned parameters is also discussed in detail. Furthermore, correlations were obtained for the laminar flame speed, NO, and CO emissions with important radicals such as OH, HO₂, HCO, and HNO. The replacement of air with H₂O₂ increases flame speed and decreases the ignition delay time of the mixture significantly. Also, increases the CO and NOx concentration in the products. The CO and NOx emissions can be controlled by regulating the H₂O₂ concentration and equivalence ratios. Air replacement with H₂O₂ enhances the reactions rate and concentration of intermediate radicals such as O/H, HO₂, and HCO in the mixture. These intermediate radicals closely govern the combustion chemistry of the NH₃/CH₄– O₂/N₂/H₂O₂ mixture. A linear correlation is observed between the flame speed and peak mole fraction of OH + HO₂ radicals, and 2nd degree polynomial correlation is observed for the peak mole fraction of NO and CO with HNO + OH and HCO + OH radicals, respectively.     

Experimental and numerical study of the laminar burning velocity of NH3/H2/air premixed flames at elevated pressure and temperature

Ammonia (NH₃) is a carbon-free fuel that shows great research prospects due to its ideal production and storage systems. The experimental data of the laminar burning velocity of NH₃/H₂/air flame at different hydrogen ratios (X_H2 = 0.1–0.5), equivalent ratios (φ = 0.8–1.3), initial pressures (P = 0.1–0.7 MPa), and initial temperatures (T = 298–493 K) were measured. The laminar burning velocity of the NH₃/H₂/air flame increased upon increasing the hydrogen ratios and temperature, but it decreased upon increasing the pressure. The equivalent ratio of the maximum laminar burning velocity was only affected by the proportion of reactants. The equivalence ratio value of the maximum laminar burning velocity was between 1.1 and 1.2 when X_H2 = 0.3. The chemical reaction kinetics of NH₃/H₂/air flame under four different initial conditions was analyzed. The less NO maximum mole fraction was produced during rich combustion (φ > 1). The results provide a new reference for ammonia as an alternative fuel for internal combustion engines.     

Numerical investigation on the effect of CO2 and steam for the H2 intermediate formation and NOX emission in laminar premixed methane/air flames

One-dimensional premixed freely-propagating flames for (CH₄+CO₂/H₂O)/air(79%N₂+21%O₂) mixtures were modeled using ChemkinⅡ/Premix Code with the detailed mechanism GRI-Mech 3.0. The investigation of the effects of CO₂ and steam addition on the H₂ intermediate formation and NO emission was conducted at the initial conditions of 1 atm and 398 K. Both physical and chemical effects of CO₂, H₂O on laminar burning velocities and adiabatic flame temperatures were also analyzed. The calculations show that with the increase of α_CO2 and α_H2O, both physical and chemical effects of CO₂ and H₂O result in the reduction of laminar burning velocities (LBVs) and adiabatic flame temperatures (AFTs) in which the chemical effects of CO₂ addition are more significantly than H₂O. Especially, the chemical effects of steam promote the increase of AFTs and the influence in rich BG65 flames are larger than in methane. With a proper amount of H₂O addition, the chemical effects of H₂O on the peak concentration of H₂ are more significantly than physical at Φ = 1.2. Moreover, CO₂, steam and their mixture addition have significant reduction on the NO emission. The most sensitive reaction for the formation of H₂ and NO emission were determined. The responsible reactions for H₂ formation and NO emission are R84 OH + H₂ <=> H + H₂O and R240 CH + N₂ <=> HCN + N (a prompt routine), respectively.     

Laminar burning velocities and flame stability analysis of H2/CO/air mixtures with dilution of N2 and CO2

Experimental measurement of the laminar burning velocities of H₂/CO/air mixtures and equimolar H₂/CO mixtures diluted with N₂ and CO₂ up to 60% and 20% by volume, respectively, were conducted at different equivalence ratios and conditions near to the sea level, 0.95 atm and 303 ± 2 K. Flames were generated using contoured slot-type nozzle burners and Schlieren images were used to determine the laminar burning velocity with the angle method. Numerical calculations were also conducted using the most recent detailed reaction mechanisms for comparison with the present experimental results. Additionally, a study was conducted to analyze the flame stability phenomenology that was found in the present experiments. The increase in the N₂ and CO₂ dilution fractions considerably reduced the laminar burning velocity due to the decrease in heat release and increase in heat capacity. At the same dilution fractions this effect was higher for the case of CO₂ due to its higher heat capacity and dissociation effects during combustion. Flame instabilities were observed at lean conditions. While the presence of CO in the fuel mixture tends to stabilize the flame, H₂ has a destabilizing effect which is the most dominant. A higher N₂ and CO₂ dilution fraction increased the range of equivalence ratios where unstable flames were obtained due to the increase in the thermal-diffusive instabilities.     

Numerical investigation on effects of high initial temperatures and pressures on flame behavior of CO/H2/Air mixtures near the dilution limit

This study investigates effects of initial temperatures and pressures on dilution limits of CO/H₂/air mixtures by numerical simulation of one-dimensional laminar premixed flames of CO/H₂/air mixtures (50%CO–50%H₂). Maximum flame temperatures, laminar flame speeds, mass burning rates and flame thickness near the dilution limits are analyzed. Results reveal that the dilution limits are extended at the elevated initial temperatures. The laminar flame speeds and mass burning rates at the dilution limits increase with the elevation of initial temperature, however, the flame thickness at the dilution limits decreases with increasing pressures and increases slightly with elevated initial temperature. The decreased flame thickness renders the flamelet modeling more favorable for turbulent combustion at elevated pressure conditions. The ratio of the flame thickness to the reaction thickness and the Zeldovich number increase first and then decrease with increasing pressure, but the non-monotonic trend of ratio of flame thickness to reaction thickness with the increasing pressures is unnoticeable. Sensitivity analysis suggested that the non-monotonic trend of the Zeldovich number could be caused by the combined effects of following elementary reactions: H + O₂ + M → HO₂ + M, 2HO₂ → H₂O₂ + O₂ and H₂O₂ + M → 2OH + M.     

Comparative study on the effect of CO2 and H2O dilution on laminar burning characteristics of CO/H2/air mixtures

A study on the effect of CO₂ and H₂O dilution on the laminar burning characteristics of CO/H₂/air mixtures was conducted at elevated pressures using spherically expanding flames and CHEMKIN package. Experimental conditions for the CO₂ and H₂O diluted CO/H₂/air/mixtures of hydrogen fraction in syngas from 0.2 to 0.8 are the pressures from 0.1 to 0.3 MPa, initial temperature of 373 K, with CO₂ or H₂O dilution ratios from 0 to 0.15. Laminar burning velocities of the CO₂ and H₂O diluted CO/H₂/air/mixtures were measured and calculated using the mechanism of Davis et al. and the mechanism of Li et al. Results show that the discrepancy exists between the measured values and the simulated ones using both Davis and Li mechanisms. The discrepancy shows different trends under CO₂ and H₂O dilution. Chemical kinetics analysis indicates that the elementary reaction corresponding to peak ROP of OH consumption for mixtures with CO/H₂ ratio of 20/80 changes from reaction R3 (OH + H₂ = H + H₂O) to R16 (HO₂+H = OH + OH) when CO₂ and H₂O are added. Sensitivity analysis was conducted to find out the dominant reaction when CO₂ and H₂O are added. Laminar burning velocities and kinetics analysis indicate that CO₂ has a stronger chemical effect than H₂O. The intrinsic flame instability is promoted at atmospheric pressure and is suppressed at elevated pressure for the CO₂ and H₂O diluted mixtures. This phenomenon was interpreted with the parameters of the effective Lewis number, thermal expansion ratio, flame thickness and linear theory.     

An experimental and numerical study on characteristics of laminar premixed H2/CO/CH4/air flames

The effects of variations in the fuel composition on the characteristics of H₂/CO/CH₄/air flames of gasified biomass are investigated experimentally and numerically. Experimental measurements and numerical simulations of the flame front position and temperature are performed in the premixed stoichiometric H₂/CO/CH₄/air opposed-jet flames with various H₂ and CO contents in the fuel. The adiabatic flame temperatures and laminar burning velocities are calculated using the EQUIL and PREMIX codes of Chemkin collection 3.5, respectively. Whereas the flame structures of the laminar premixed stoichiometric H₂/CO/CH₄/air opposed-jet flames are simulated using the OPPDIF package with the GRI-Mech 3.0 chemical kinetic mechanisms and detailed transport properties. The measured flame front position and temperature of the stoichiometric H₂/CO/CH₄/air opposed-jet flames are closely predicted by the numerical calculations. Detailed analysis of the calculated chemical kinetic structures reveals that the reaction rate of reactions (R38), (R46), and (R84) increase with increasing H₂ content in the fuel mixture. It is also found that the increase in the laminar flame speed with H₂ addition is most likely due to an increase in active radicals during combustion (chemical effect), rather than from changes in the adiabatic flame temperature (thermal effect). Chemical kinetic structure and sensitivity analyses indicate that for the stoichiometric H₂/CO/CH₄/air flames with fixed H₂ concentration in the fuel mixture, the reactions (R99) and (R46) play a dominant role in affecting the laminar burning velocity as the CO content in the fuel is increased.     

Experimental and numerical study on the effect of composition on laminar burning velocities of H2/CO/N2/CO2/air mixtures

Experimental and numerical study on laminar burning velocity of H₂/CO/N₂/CO₂/air mixtures was conducted by using a constant volume bomb and Chemkin package. Good agreement between experimental measurements and numerical calculations by using USCII Mech is achieved. Diffusional-thermal instability is enhanced but hydrodynamic instability is insensitive to the increase of hydrogen fraction in fuel mixtures. For mixtures with different hydrogen fractions, the adiabatic flame temperature is not the dominant influencing factor while high thermal diffusivity of hydrogen obviously enhances the laminar burning velocity. Laminar burning velocities increase with increasing hydrogen fraction and equivalence ratio (0.4–1.0). This is mainly due to the high reactivity of H₂ leading to high production rate of H and OH radicals. Reactions  and  play the dominant role in the production of H radical for mixtures with high hydrogen fraction, and reaction R31 plays the dominant role for mixtures with low hydrogen fraction.     

Effect of preferential diffusion and flame stretch on flame structure and laminar burning velocity of syngas Bunsen flame using OH-PLIF

By using OH-PLIF technique, experiments were conducted for laminar Bunsen flame of premixed CO/H₂/air mixtures with equivalence ratio ranging from 0.5 to 1.8. Reynolds number was varied from 800 to 2200, X_H2 = H₂/(H₂+CO) in the mixture was varied from 20% to 100% to study the effects of both preferential diffusion and flame curvature on flame structures and laminar flame burning velocities. Results showed that the combined effects of preferential diffusion and curvature gave an interesting phenomenon of the flame OH radical distributions on high hydrogen content flames. Furthermore, with the increase of H₂ fraction in fuel mixture, the effects of both preferential diffusion and flame curvature were increased. Interpretation of flame stretch effect on laminar burning velocity is also provided in this paper.     

Study of ozone-enhanced combustion in H2/CO/N2/air premixed flames by laminar burning velocity measurements and kinetic modeling

The enhancement effect of ozone addition for H₂/CO/N₂/Air premixed flames at ambient condition is investigated both experimentally and computationally. Adiabatic laminar velocities under different amount of O₃ addition were directly measured using the Heat Flux Method. The ozone concentration in the oxidizer is monitored online to ensure the precise control and stability of ozone injection. Experimental data shows significant enhancement of the burning velocities due to O₃ addition. With 8500 ppm ozone seeded, maximum 18.74% of burning velocity enhancement is observed at equivalence ratio Φ = 0.7. Kinetic modeling works were conducted by integrating ozone sub-mechanism with three kinetic mechanisms: GRI-Mech 3.0, Davis mechanism and USC Mech II. The modeling results were compared with experimental data. GRI-Mech 3.0 + Ozone mechanism demonstrated the ability to reproduce the experimental data. Extra OH radicals promoted by ozone was found in the pre-heat regime which initiates the chain-branching reaction and results in the combustion enhancement.     

Effects of dilution with carbon dioxide on the laminar burning velocity and flame stability of H2–CO mixtures at atmospheric condition

The objective of this investigation was to study the effect of dilution with CO₂ on the laminar burning velocity and flame stability of syngas fuel (50% H₂–50% CO by volume). Constant pressure spherically expanding flames generated in a 40 l chamber were used for determining unstretched burning velocity. Experimental and numerical studies were carried out at 0.1 MPa, 302 ± 3 K and ? = 0.6–3.0 using fuel-diluent and mixture-diluent approaches. For H₂–CO–CO₂–O₂–N₂ mixtures, the peak burning velocity shifts from ? = 2.0 for 0% CO₂ in fuel to ? = 1.6 for 30% CO₂ in fuel. For H₂–CO–O₂–CO₂ mixtures, the peak burning velocity occurred at ? = 1.0 unaffected by proportion of CO₂ in the mixture. If the mole fraction of combustibles in H₂–CO–O₂–CO₂ mixtures is less than 32%, then such mixtures are supporting unstable flames with respect to preferential diffusion. The analysis of measured unstretched laminar burning velocities of H₂–CO–O₂–CO₂ and H₂–CO–O₂–N₂ mixtures suggested that CO₂ has a stronger inhibiting effect on the laminar burning velocity than nitrogen. The enhanced dilution effect of CO₂ could be due to the active participation of CO₂ in the chemical reactions through the following intermediate reaction CO + OH ? CO₂ + H.     

Laminar burning velocities and flame instabilities of diluted H2/CO/air mixtures under different hydrogen fractions

An experimental study was conducted using outwardly propagating flame to evaluate the laminar burning velocity and flame intrinsic instability of diluted H₂/CO/air mixtures. The laminar burning velocity of H₂/CO/air mixtures diluted with CO₂ and N₂ was measured at lean equivalence ratios with different dilution fractions and hydrogen fractions at 0.1 MPa; two fitting formulas are proposed to express the laminar burning velocity in our experimental scope. The flame instability was evaluated for diluted H₂/CO/air mixtures under different hydrogen fractions at 0.3 MPa and room temperature. As the H₂ fraction in H₂/CO mixtures was more than 50%, the flame became more unstable with the decrease in equivalence ratio; however, the flame became more stable with the decrease in equivalence ratio when the hydrogen fraction was low. The flame instability of 70%H₂/30%CO premixed flames hardly changed with increasing dilution fraction. However, the flames became more stable with increasing dilution fraction for 30%H₂/70%CO premixed flames. The variation in cellular instability was analyzed, and the effects of hydrogen fraction, equivalence ratio, and dilution fraction on diffusive-thermal and hydrodynamic instabilities were discussed.     

Determination of laminar burning velocities for lean low calorific H2/N2 and H2/CO/N2 gas mixtures

Combustion of lean and ultra-lean synthetic H₂/CO mixtures that are highly diluted in inert gases is of great importance in several fields of technology, particularly in the field of post combustion for combined heat and power (CHP) systems based on fuel cell technology. In this case H₂/CO mixtures occur via hydrocarbon reforming and their complete conversion requires efficient, compact and low emission combustion systems. In order to design such systems, knowledge of global flame properties like the laminar burning velocity, is essential. Using the heat flux burner method, laminar burning velocities were experimentally determined for highly N₂ diluted synthetic H₂ and H₂/CO mixtures with low calorific value, burning with air, at ambient temperature and atmospheric pressure. Furthermore, numerical 1-D simulations were performed, using a series of different chemical reaction mechanisms. These numerical predictions are analysed and compared with the experimental data.     

Experimental and numerical study on the laminar burning velocity of hydrogen enriched biogas mixture

The laminar burning velocities of biogas-hydrogen-air mixture at different fuel compositions and equivalence ratios were determined and studied using the spherical flame method. The combined effects of H₂ and CO₂ on the laminar burning velocity were investigated quantitatively based on the kinetic effects and the thermal effects. The results show that the laminar burning velocities of the BG40, BG50 and BG60 are increased almost linearly with the H₂ addition owing to the improved fuel kinetics and the increased adiabatic flame temperature. The dropping trend of laminar burning velocity from the BG60-hydrogen to the BG40-hydrogen is primarily attributed to the decreased adiabatic flame temperature (thermal effects). The GRI 3.0 mechanism can predict the laminar burning velocity of biogas-hydrogen mixture better than the San Diego mechanism in this study. Whereas, the GRI mechanism still needs to be modified properly for the hydrogen-enriched biogas as the CO₂ proportion exceeds 50% in the biogas at the fuel-rich condition. The increased CO₂ exerts the stronger suppression on the net reaction rate of H + O₂=OH + O than that of H + CH₃(+M) = CH₄(+M), which contributes to that the rich-shift of peak laminar burning velocity of biogas-hydrogen mixture requires higher H₂ addition as the CO₂ content is enhanced. For the biogas-hydrogen fuel, the H₂ addition decreases the flame stability of biogas fuel effectively due to the increased diffusive-thermal instability and hydrodynamic instability. The improved flame stability of biogas-hydrogen fuel with the increased CO₂ content is resulted from the combined effects of diffusive-thermal instability and hydrodynamic instability.     

Laminar flame speed of H2/CH4/air mixtures with CO2 and N2 dilution

The laminar flame speeds of H₂/CH₄/air mixtures with CO₂ and N₂ dilution were systematic investigated experimentally and numerically over a wide range of H₂ blending ratios (0–75 vol%) with CO₂ (0–67 vol%) and N₂ (0–67 vol%) dilution in the fuels. The experimental measurements were conducted via the Bunsen flame method incorporating the Schlieren technique under the condition of equivalence ratios from 0.8 to 2.0. To gain an insightful understanding of the experimental observations, detailed numerical simulation was carried out using Chemkin-Pro with GRI3.0-Mech. The experimental measurements were also used to validate the corresponding performance of a semiempirical correlation derived through asymptotic analysis method coupled with the reduced chemistry mechanism. The results showed that at lower H₂ fraction (x_H2 ≤ 0.5), the laminar flame speeds of H₂/CH₄/air mixtures displayed great linearly increase with the growth of H₂ fractions. The combustion of mixtures with low H₂ contents was dominated by CH₄ conversion which was mainly controlled by the increasing OH radicals produced from the key oxidation reactions of H + O₂ = O + OH. With the further increase of H₂ fractions, the methane-dominated combustion gradually transformed into the methane-inhibited hydrogen combustion, resulting to the growth of laminar flame speeds was dramatical and non-linear. Due to the larger heat capacity and chemical kinetic effect, CO₂ presented a stronger dilution effect on reducing the laminar flame speeds than N₂. With the addition of CO₂, the increasing stronger competition for H radical through CO + OH = CO₂ + H with H + O₂ = O + OH due to the significant reduction of H mole fractions, leading to the larger decrease of laminar flame speeds of mixtures. Besides, although the contribution of thermal effect of CO₂ decreased near the equivalence ratio, the thermal effect of CO₂ still preformed the dominated contribution to the total dilution effect. A comparison between the experimental data and estimated results using the semiempirical correlation showed that, the correlation using new modified coefficients provided the satisfactorily accuracy predictions on the laminar flame speeds of diluted H₂/CH₄/air mixtures at lower x_H2 (x_H2 ≤ 0.5) and lower x_dilution (x_dilution = 0.25). The estimated results were generally located within a deviation range of ±20% errors except for two unsatisfactory eases occurred at conditions of x_H2 = 0.75 and x_CO2 = 0.67. The considerably poor predictions were attributed to the significantly variation of the chemical kinetics under high H₂ content and large CO₂ dilution conditions.     

Chemical kinetic modeling of ammonia oxidation with improved reaction mechanism for ammonia/air and ammonia/hydrogen/air combustion

To achieve comprehensive prediction of ammonia combustion in terms of flame speed and ignition delay time, an improved mechanism of ammonia oxidation was proposed in this work. The present model (UT-LCS) was based on a previous work [Song et al., 2016] and improved by relevant elementary reactions including NH₂, HNO, and N₂H₂. The model clearly explained reported values of laminar flame speed and ignition delay time in wide ranges of equivalence ratio and pressure. This suggests that NH₂, HNO, and N₂H₂ reactivities play a key role to improve the reaction mechanism of ammonia oxidation in the present model. The model was also applied to demonstrate NH₃/H₂/air combustion. The present model also appropriately predicted the laminar flame speed of NH₃/H₂/air combustion as a function of equivalence ratio. Using the model, we discussed the reduction of NO concentration downstream and H₂ formation via NH₃ decomposition in NH₃/H₂ fuel-rich combustion. The results provide suggestions for effective combustion of NH₃ for future applications.     

Numerical study on CH4 laminar premixed flames for combustion characteristics in the oxidant atmospheres of N2/CO2/H2O/Ar-O2

The freely-propagating laminar premixed flames of CH₄–N₂/CO₂/H₂O/Ar-O₂ mixtures were conducted with the PREMIX code. The effects of the equivalence ratio and various oxidant atmospheres on the basic combustion characteristics were analyzed with the initial pressure and temperature of 1 atm and 398 K, respectively, O₂ content in the oxidant of 21%. The chemical reaction mechanism GRI-Mech 3.0 was chosen to determine the effects of the oxidant atmospheres of N₂/O₂, CO₂/O₂, H₂O/O₂, and Ar/O₂ on the adiabatic flame temperature, laminar burning velocity, flame structure, free radicals, intermediate species, net heat release rate and specific heat of the fuel/oxidant mixtures. The numerical results show that the maximum adiabatic flame temperatures and laminar burning velocities are at Ar/O₂ atmosphere. The mole fractions of CO and H₂ increased fastest at CO₂/O₂ atmosphere and H₂O/O₂, respectively. The mole fractions of CH₃ and H follow the order Ar/O₂> N₂/O₂>H₂O/O₂>CO₂/O₂. In addition, for 4 oxidant atmospheres, the peak mole fraction of C₂H₂ is following the order H₂O/O₂>Ar/O₂>N₂/O₂>CO₂/O₂ and the net heat release rate is following the order Ar/O₂>N₂/O₂>H₂O/O₂>CO₂/O₂ for all equivalence ratios.     

The synergistic effect of equivalence ratio and initial temperature on laminar flame speed of syngas

The laminar flame speed of syngas (CO:H₂ = 1:1)/air premixed gas in a wide equivalence ratio range (0.6–5) and initial temperature (298–423 K) was studied by Bunsen burner. The results show that the laminar flame speed first increases and then decreases as the equivalence ratio increasing, which is a maximum laminar flame speed at n = 2. The laminar flame speed increases exponentially with the increase of initial temperature. For different equivalent ratios, the initial temperature effects on the laminar flame speed is different. The initial temperature effects for n = 2 (the most violent point of the reaction) is lower than others. It is found that H, O and OH are affected more and more when the equivalence ratio increase. When the equivalence ratio is far from 2, the reaction path changes, and the influence of initial temperature on syngas combustion also changes. The laminar flame speed of syngas is more severely affected by H + O₂ = O + OH and CO + OH = CO₂ + H than others, which sensitivity coefficient is larger and change more greatly than others when the initial temperature and equivalence ratio change. Therefore, the laminar flame speed of syngas/air premixed gas is affected by the initial temperature and equivalence ratio. A new correlation is proposed to predict the laminar flame speed of syngas (CO:H₂ = 1:1)/air premixed gas under the synergistic effect of equivalence ratio and initial temperature (for equivalence ratios of 0.6–5, the initial temperature is 298–423 K).     

Direct numerical simulation of lean premixed CH4/air and H2/air flames at high Karlovitz numbers

Three-dimensional direct numerical simulation with detailed chemical kinetics of lean premixed CH₄/air and H₂/air flames at high Karlovitz numbers (Ka ∼ 1800) is carried out. It is found that the high intensity turbulence along with differential diffusion result in a much more rapid transport of H radicals from the reaction zone to the low temperature unburned mixtures (∼500 K) than that in laminar flamelets. The enhanced concentration of H radicals in the low temperature zone drastically increases the reaction rates of exothermic chain terminating reactions (e.g., H + O₂+M = HO₂ + M in lean H₂/air flames), which results in a significantly enhanced heat release rate at low temperatures. This effect is observed in both CH₄/air and H₂/air flames and locally, the heat release rate in the low temperature zone can exceed the peak heat release rate of a laminar flamelet. The effects of chemical kinetics and transport properties on the H₂/air flame are investigated, from which it is concluded that the enhanced heat release rate in the low temperature zone is a convection–diffusion-reaction phenomenon, and to obtain it, detailed chemistry is essential and detailed transport is important.     

Laminar burning velocity and interchangeability analysis of biogas/C3H8/H2 with normal and oxygen-enriched air

Numerical and experimental measurements of the laminar burning velocities of biogas (66% CH₄ – 34% CO₂) and a biogas/propane/hydrogen mixture (50% biogas – 40% C₃H₈ – 10% H₂) were made with normal and oxygen-enriched air while varying the air/fuel ratio. GRI-Mech 3.0 and C₁–C₃ reaction mechanisms were used to perform numerical simulations. Schlieren images of laminar premixed flames were used to determine laminar burning velocities at 25 °C and 849 mbar. The mixture's laminar burning velocity was found to be higher to that of pure biogas due to the addition of propane and hydrogen. An increase in the laminar burning velocities of both fuels is reported by enriching air with oxygen, a phenomenon that is explained by the increased reactivity of the mixture. Additionally, an analysis of interchangeability based on both the Wobbe Index and the laminar burning velocity between methane and a biogas/propane/hydrogen mixture is presented in order to consider this mixture as a substitute for natural gas. It was found that the variations of these properties between the fuels did not exceed 10%, enabling interchangeability.