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The laminar burning velocity (LBV) and cellular instability of ammonia/syngas/air were investigated using the spherically expanding flame method at an initial pressure of 3 atm and temperatures of 298–448 K. The impacts of equivalence ratio, temperature, and hydrogen ratio on LBV were scrutinized. The results demonstrate that the LBV varies non-monotonically with the equivalence ratio and increases with increasing temperature and hydrogen ratio. Flame instability was analyzed using flame uplift rate, Lewis number, thermal expansion ratio, flame thickness, critical radius, critical Peclet number and logarithmic growth rate of perturbation in combination with the schlieren images. Of these, the flame uplift rate is used to quantify buoyancy instability, a flame instability that has received little attention. At high pressures, lower LBV makes the flame susceptible to buoyancy instability. The flame uplift rate increases with increasing flame radius, suggesting that the buoyancy instability becomes increasingly significant as the spherical flame expands. The diffusional-thermal instability is weaker at the fuel-rich side and enhanced at the leaner side. As the hydrogen ratio increases, the flame instability increases. Hydrodynamic instability is not susceptible to temperature, which is only slightly weakened with increasing temperature. Additionally, the phenomenon of superadiabatic flame temperature (SAFT) in ammonia/syngas/air flames was first found and analyzed its temperature dependence. Increasing the initial temperature suppresses SAFT occurrence. [Display omitted] • LBVs of ammonia/syngas/air mixtures were measured at 298–448 K and 3 atm. • The buoyancy instability was studied in detail using flame uplift rates. • The effect of initial temperature on the flame instability was analyzed in detail. • The phenomenon of SAFT in ammonia/syngas/air flames was first found. [ABSTRACT FROM AUTHOR]

The determination of the characteristics and main combustion properties of fuels is necessary for post-implementation in different applications. Among the most important combustion properties of a fuel are the combustion products, flame temperature and laminar burning velocity. Therefore, this paper describes the step-by-step development and coding of a MATLAB application that can determine 12 combustion products, flame temperature and laminar burning velocity in order to understand the logic of calculus procedure, so any user would be able to make improvements of new functionalities (add more fuels, add more combustion products, etc.). The numerical procedure and methods (Gaussian elimination, Taylor Series and Newton–Raphson) parallel with their implementation as code lines for the development of the application are carried out using flow charts. In addition, simulations in Ansys Chemkin were performed and included in the application as part of the results comparison. It was found that: (1) The MATLAB Application codification and development were successfully explained in detail, (2) the functions and execution sequence are described by using flow charts and code extract, (3) the application is available to everyone for modifications, (4) the application can only be used for hydrocarbons fuels, (5) the application execution time registered was less than 8 s. [ABSTRACT FROM AUTHOR]

Hydrogen and ammonia are playing an increasingly vital role in combustion technologies. Recently, some detailed reaction mechanisms (DRMs) can predict reliable laminar burning velocities (LBVs). Meanwhile, despite their broad applicability in practical combustion engineering, global reaction mechanisms (GRMs) suitable for ammonia and its mixtures with hydrogen or nitrogen have yet to be reported. This study aims to address this gap by investigating new GRMs. Five DRMs were used to calculate the LBVs, and their average values were employed as a reference. First, a single-step GRM was developed for hydrogen (H 2 + 0.5O 2 → H 2 O), and another single-step GRM was developed for ammonia (NH 3 + 0.75O 2 → 0.5N 2 + 1.5H 2 O). However, their combined GRM did not provide reasonable predictions of LBVs for the H 2 +NH 3 mixtures. Therefore, a 4-step GRM was developed consisting of the single-step hydrogen and three additional reactions, i.e., an endothermic ammonia decomposition (NH 3 + 0.5O 2 → NO + 3H), an exothermic NO reduction (NO + 2H → 0.5N 2 + H 2 O), and an exothermic H recombination (H + H → H 2). In conclusion, this 4-step GRM and its revisions could predict reasonable LBVs, flame temperatures, and primary product compositions for mixtures of hydrogen, ammonia, and cracked ammonia gas over a wide range of temperatures (300–600 K) and pressures (1–5 atm). • Global reaction mechanisms (GRMs) were investigated for H 2 +NH 3 +N 2 mixtures. • Laminar burning velocities (LBVs) from the detailed reaction mechanisms were compared. • Single-step GRMs were improved for the individual fuels H 2 and NH 3. • Available ranges were extended in temperatures (300–600 K) and pressures (1–5 atm). [ABSTRACT FROM AUTHOR]

The next-generation energy economy relies heavily on hydrogen. Handling hydrogen during production, storage, and transportation requires risk mitigation. In this regard, the application of halide-free additives is very crucial. The present study experimentally and theoretically investigates the individual and combined inhibiting effect of propane and propene on hydrogen-air explosions. The experiments are carried out at 298 K and 1 bar, with additives ranging from 0.5 to 5% for the individual and 1–2% each for the combined effect in the 20–50% hydrogen-air mixture. Experimentally, the additive content in the stoichiometric and rich mixture decreases the explosion pressure, maximum pressure rise (MPR) rate, laminar burning velocity (LBV), and flame temperature, while increasing minimum ignition energy. For instance, the addition of 2% propane in a 50% hydrogen-air mixture, reduces the MPR rate by 98%, whereas such an effect is observed with 2.5% propene. Theoretical study shows that 3% equivalent additive augments inhibiting reactions, countering the main flame-promoting reaction R1 (H + O 2 O + OH) and thereby reducing LBV. Due to its low activation energy, propene consumes the active radicals twice the rate of propane, while propane not only scavenges the active radicals but also promotes oxygen consumption in the prior phase of combustion, weakening flame propagation. Overall, this approach exhibits a significant step forward in harnessing the potential of hydrogen while mitigating the safety risks associated with its use. [Display omitted] • The effect of C 3 -Hydrocarbons and their Mixtures on H2-air explosion is explored. • The additives decrease explosion pressure, MPR rate and LBV while increasing MIE. • Propene increases the consumption rate of active radicals in the additive mixtures. • Propane promotes oxygen consumption in the prior phase of combustion, countering R1. [ABSTRACT FROM AUTHOR]

The laminar burning velocity and NO formation process of ammonia-hydrogen combustion within a two-stage combustion chamber were investigated numerically in the present study. A chemical reactor network method involving perfectly stirred reactor, plug flow reactor, and partially stirred reactor configurations with the 24-species Xiao mechanism was implemented to simulate the premixed ammonia-hydrogen-air combustion process. The effects of inlet temperature and pressure conditions on the laminar burning velocity were investigated. Results proved that elevated pressure condition decreased primary flame thickness leading to lower laminar burning velocity while inlet temperature increased flame temperature which in turn increased the laminar burning velocity. Investigation of the effect of humidification on the laminar burning velocity showed that humidification can counteract the effect of high inlet temperature. The NO emission studies indicated a twofold impact of pressure on NO formation processes: preventing NO formation in the primary combustion zone, and promoting thermal NO formation in the lean combustion zone. The minimum amounts of NO emission were obtained at total equivalence ratios of 0.4. Humidification prevented the NO formation in the lean combustion through the competitive effect of H2O on O, whilst temperature effect was comparatively small. Humidity and pressure were optimized in the two-stage configuration achieve both low emission and high efficiency. [ABSTRACT FROM AUTHOR]

This study measures the accurate Laminar Burning Velocities (LBVs) of (H 2 /NH 3 /CH 4) ternary fuels-air flames under elevated pressure and oxygen enrichment using a constant volume chamber, providing reliable experimental data to verify the detailed chemical kinetic mechanism. Results show that the LBV values for blending ratios of H 2 /NH 3 of 10%–50% demonstrate a suitable alternative energy-generated fuel for conventional fuels in industrial applications, and the maximum value of LBV is achieved at an equivalence ratio close to 1.05. Increasing H 2 blends will increase LBV non-linearly under any conditions and decrease with an increase in ammonia blends. Increasing the initial pressure decreases LBV; at 10% H 2 , LBV decreases by 33% at 0.3 MPa and 45% at 0.5 MPa compared to atmospheric pressure. Furthermore, increasing oxygen content improves the reactivity of the mixture and accelerates LBV due to increasing the OH, NH 2 , and CH 3 radicals. Maintaining a constant value of LBV requires controlling the blending ratio of the ternary fuels, where increasing LBV values shift the blending of the mixture towards higher hydrogen and methane concentrations and fewer ammonia concentrations. Finally, the effect of maintaining a constant value of adiabatic flame temperature and density ratio on flame characteristics is explained, making the selection of an alternative ternary blending fuel more precise. [Display omitted] • LBV of H 2 /NH 3 /CH 4 -air flames at elevated pressures and oxygen enrichment were measured. • H 2 /NH 3 /CH 4 mixture can be considered a suitable alternative for conventional fuels in industrial applications. • Different blending ratios maintain a consistent laminar burning velocity at different fuel blends and initial pressures. • The effect of constant adiabatic flame temperature and density ratio on LBV was evaluated. [ABSTRACT FROM AUTHOR]

The determination of the characteristics and main combustion properties of fuels is necessary for post-implementation in different applications. Among the most important combustion properties of a fuel are the combustion products, flame temperature and laminar burning velocity. Therefore, this paper describes the step-by-step development and coding of a MATLAB application that can determine 12 combustion products, flame temperature and laminar burning velocity in order to understand the logic of calculus procedure, so any user would be able to make improvements of new functionalities (add more fuels, add more combustion products, etc.). The numerical procedure and methods (Gaussian elimination, Taylor Series and Newton–Raphson) parallel with their implementation as code lines for the development of the application are carried out using flow charts. In addition, simulations in Ansys Chemkin were performed and included in the application as part of the results comparison. It was found that: (1) The MATLAB Application codification and development were successfully explained in detail, (2) the functions and execution sequence are described by using flow charts and code extract, (3) the application is available to everyone for modifications, (4) the application can only be used for hydrocarbons fuels, (5) the application execution time registered was less than 8 s.

In this work, the laminar premixed flames for methane and propane at atmospheric pressure were numerically investigated with respect to different hydrogen concentrations, ranging from 5 % to 25 % (by vol.). Based on the two-dimensional (2D) flame predictions, hydrogen decreased the maximum temperatures and species concentrations such as formaldehyde (CH 2 O), acetylene (C 2 H 2), carbon monoxide (CO) and nitric oxide (NO) for methane and propane. However, the CH 2 O mole fractions were raised by a maximum deviation of 10 % when hydrogen was added into the fuel lean and stoichiometric propane mixtures. The decrease in C 2 H 2 eventually lowered the soot volume fractions and number densities. Besides, the axial locations of the maximum species concentrations, soot volume fractions and number densities were also affected by hydrogen. Meanwhile, the addition of hydrogen increased the flame temperatures and laminar burning velocities for the one-dimensional (1D) premixed flames of methane and propane. This trend was identically predicted for the formation of intermediate species such as CH 2 O, hydroperoxyl (HO 2) and hydroxyl (OH) whereas C 2 H 2 , CO and NO were lowered, as justified by the sensitivity analyses. For propane at an equivalence ratio (φ) = 1.3, the rates of production (ROPs) of C 2 H 2 were increased linearly with hydrogen, which resulted in higher C 2 H 2 concentrations. • Methane and propane coflow flames with hydrogen addition are modelled in 1D and 2D. • Hydrogen lowers flame temperatures, CH 2 O, C 2 H 2 , CO and NO for 2D flames. • For 1D flames, hydrogen raises flame temperatures and intermediate species. • Effects of hydrogen on emissions depend on fuel types and mixture conditions. [ABSTRACT FROM AUTHOR]

In the present paper, it was aimed to consume pure NH 3 by using an existing non-premixed burner with H 2 blending strategy, and to examine the temperature and NO emission profiles emerged in a model combustor for NH 3 /H 2 and pure NH 3 fuel compositions. The Mixture Fraction/PDF combustion model with a reduced reaction mechanism was used for the numerical modelling. During the experimental studies, a stable NH 3 /air flame was able to achieve by introducing H 2 into the burner since NH 3 /air mixture has a low reactivity and needs a high ignition energy. However, any flashback or lift-off tendency was not observed for NH 3 /H 2 /air or NH 3 /air flames. The numerical and experimental results showed that H 2 addition into NH 3 /air mixture provided higher temperature values both in the flame region and in the entire combustor. As the concentration of H 2 in the mixture was raised, the flame approached towards to the burner outlet with increment effect in burning velocity. However, H 2 addition into NH 3 /air mixture led to more NO emissions formation in the combustor. This can be attributed with that H 2 addition promoted both thermal and fuel-NO mechanisms because H 2 addition induced to increase the decomposition rate of NH 3 and flame temperature of NH 3 /air mixture. This finding was validated with the prediction of the concentrations of O and HNO radicals for all fuel compositions. Consequently, H 2 introduction contributed to the flame stability of NH 3 /air mixture even if more NO formation was observed. • H 2 addition on the performance of NH 3 /air combustion have been investigated. • A stable flame for NH 3 /air combustion has been achieved. • H 2 addition provided higher flame temperature distributions in the combustor. • H 2 addition promoted NO emissions in the combustor. [ABSTRACT FROM AUTHOR]

This study utilizes numerical methods with Chemkin 19.2 and Matlab R2020a to investigate the relationship between laminar burning velocity and free radical concentration, the relationship between laminar burning velocity and ignition delay time, and the relationship between NO emissions and free radical concentration for ammonia-syngas-air combustion. Additionally, it explores the mechanisms by which these three relationships change with variations in the initiate temperature and chamber pressure of the combustion chamber. Furthermore, to understand the theoretical foundation of these relationships, the study examines four global flame parameters: adiabatic flame temperature (T ad), activation energy (Ea), Zeldovich number (Ze), and Lewis number (Le). The results indicate that changes in initial temperature and pressure influence the laminar burning velocity by modifying the concentration of H + NH 2 radicals. Simultaneously, alterations in initial temperature and pressure also adjust the quantitative relationship between laminar burning velocity and the concentration of H + NH 2 radicals. Additionally, the results reveal that variations in initial temperature and pressure impact NO emissions by altering the concentration of H + NH 2 radicals. Following a comprehensive examination of both the theoretical relationship between laminar burning velocity and ignition delay time and the empirical relationship between laminar burning velocity and ignition delay time, a relationship between the density-weighted collision rate B C in the laminar burning velocity expression and the pre-exponential factor A in the theoretical expression for ignition delay time was observed, where B C 2 A = C 0 ∙ T u δ ∙ P ε (where C 0 , δ and ε are constants). This offers a potential methodology for investigating thermal effects, chemical effects, and transport effects in complex mixed fuel combustion processes. Further investigation demonstrates that an increase in the initial temperature within a gas turbine combustion chamber will, by promoting thermal effects, inhibiting transport effects, and altering chemical effects, affect the quantitative relationship between laminar burning velocity and ignition delay time. Further research reveals that an increase in the initiate temperature of the gas turbine combustion chamber affects the quantitative relationships between laminar burning velocity and ignition delay time by promoting thermal effects, suppressing transport effects, and chemical effects. An increase in chamber pressure influences these relationships by enhancing chemical and transport effects while inhibiting thermal effects. Moreover, the functions characterizing chemical effects, transport effects, and thermal effects can be reasonably approximated in this study as functions of initial temperature and pressure, especially under the specific F-class gas turbine conditions presented herein. This finding holds significance for the design of combustion chambers under actual gas turbine operating conditions. • The relationship between radicals concentration and laminar burning velocity is influenced by temperature and pressure. • The functions formed by several flame parameters can be approximated as functions of initial temperature and pressure. • The variations of flame parameters with initial temperature and pressure are presented. [ABSTRACT FROM AUTHOR]

Ammonia allows for long-distance and large-scale storage transport of renewable energy sources. The reactivity of NH 3 -Air flame can be enhanced by doping with hydrogen and by increasing the initial temperature. The flame combustion characteristics of NH 3 –H 2 -Air are studied in a rectangular closed pipe with a mole fraction of 45% H 2 , an equivalence ratio (φ) of 0.8–1.2 and 0.1 MPa. The initial temperatures (T u) of the mixture are 300 K, 375 K and 450 K. Experimental studies of flame front speed, flame tip structure evolution, and overpressure dynamics are performed. Laminar burning velocity (S L), peak mole fraction of key radicals, and flame instability of NH 3 –H 2 -Air flames are simulated in Chemkin Pro-software using the Mathieu and Petersen mechanism. The results show that the relatively low equivalence ratio and initial temperature promote the structural changes of the flame tip, forming a "tulip" flame and a distorted "tulip". As the equivalence ratio increases, the flame front speed and overpressure increase and the flame oscillates slightly. The distortion in the lip of the "tulip" is more pronounced. The increase in temperature promotes flame propagation in the early stages and the pressure decreases. Reactive activity increases with increasing temperature, the peak mole fraction of NH 2 and H radicals increases, and S L increases. At normal temperature, the flame is affected by thermo-diffusive instability only when lean mixture. The Darrieus-Landau instability increases as the equivalence ratio increases. Conversely, the Darrieus-Landau instability decreases with increasing temperature. Therefore, the current experimental and simulation results help to understand the laminar combustion characteristics of NH 3 –H 2 -Air at high temperatures. • The distortion of "tulip" is most obvious at T u = 300 K and φ = 1.1. • Increased temperature promotes flame propagation in the finger-shaped phase. • As The temperature increases (300–450 K), the H and NH 2 mole fractions increase. • DL instability decreases with increasing initial gas temperature. [ABSTRACT FROM AUTHOR]

The reaction mechanism of hydrogen-enriched methane (HEM) combustion is significant in the combustion process. In this study, four widely used reaction mechanisms for methane combustion are simplified to investigate the pollutant emission characteristics of a gas-fired boiler used for HEM combustion. The laminar burn velocity (LBV) and ignition delay time (IDT) of the four detailed and four simplified mechanisms are compared, and the simplified San Diego mechanism is identified as the optimal mechanism using relative error and population standard deviation analysis. The temperatures and key components of the simplified San Diego mechanism are also compared with those of the detailed San Diego mechanism under various X H2. Based on the simplified San Diego mechanism, a chemical reactor network model for gas-fired boilers is further established to investigate the pollutant emissions of HEM combustion, in which the hydrogen doping ratio X H2 ranged from 0 to 80% and the inlet air and fuel temperature T in ranged from 300 K to 600 K. Results showed that at T in = 300 K with X H2 ranging from 0 to 80%, the mole fraction of NO increase by 1.94 times because of the increase in peak flame temperature; moreover, the mole fractions of N 2 O, CO, and CO 2 decrease by approximately 25%, 50%, and 52%, respectively. With X H2 ranging from 0 to 40% and T in ≥ 500 K, the mole fraction of NO decreases because the reduction reaction of NO + H = N + OH is promoted, whereas when X H2 is further increased to 80%, the increased H promotes the increase in NO again. CO emissions decreased as X H2 increased from 0 to 80%, whereas they increased by approximately 1.3 times as T in increased from 300 K to 600 K because of the CO 2 decomposition. N 2 O emissions decreased by more than 25% as X H2 increased from 0 to 80%. Additionally, CO 2 emissions decrease by 52% with an increase in X H2 and by only 5% with an increase in T in , indicating that X H2 has a larger impact on CO 2 emissions. The proposed optimal HEM combustion mechanism is conducive to improving the efficiency of numerical calculations. • Four detailed mechanisms for hydrogen-enriched methane combustion were simplified. • The simplified San Diego mechanism was optimal according to error analysis. • Emissions at various hydrogen doping ratios and inlet temperatures were studied. • NO increased, while N 2 O, CO, and CO 2 decreased with X H2 ranging from 0 to 80%. [ABSTRACT FROM AUTHOR]

A ratio of turbulent burning velocity to laminar flame speed is well known to be abnormally high in lean hydrogen-air mixtures, with this phenomenon being commonly attributed to differential diffusion effects. Magnitude of such effects is known to be increased by pressure, but a few recent studies have indicated that the effects are mitigated when reactants are preheated. It is not yet known, however, which of these two counteracting trends is of more importance under elevated pressures and temperatures associated with combustion in engines. Accordingly, it is not yet clear whether or not models of differential diffusion effects are required for research and development of future ultra-clean and highly efficient engines that burn hydrogen (the emphasized effects are typically ignored in engineering computations). To clarify the issue, numerical simulations of lean complex-chemistry hydrogen-air strained laminar flames are performed by varying strain rate, pressure 1 ≤ P ≤ 50 bar, temperature 300 ≤ T u ≤ 900 K, and equivalence ratio (Φ = 0.4 , 0.55, and 0.7). This simple problem is selected because maximal consumption speeds reached in critically strained (close to extinction) lean hydrogen-air laminar flames are considered to characterize the influence of differential diffusion on turbulent burning rates within the framework of Zel'dovich's leading point concept, which was well supported in recent studies. Computed results show that, even at T u = 900 K, the aforementioned consumption speeds are significantly larger than the unperturbed laminar flame speeds if the mixture is sufficiently lean (the equivalence ratio Φ = 0.55 or lower) and pressure is sufficiently high (P ≥ 30 bar). Therefore, differential diffusion effects are expected to be of importance when burning so lean hydrogen-air mixtures in engines and should be properly modeled. • Magnitude of differential diffusion effects is increased by pressure. • Magnitude of such effects is decreased with increasing temperature. • These trends are controlled by variations in Zel'dovich number. • Differential diffusion effects are of importance under engine conditions. [ABSTRACT FROM AUTHOR]

Due to zero-carbon nature of ammonia and hydrogen, their blend fuel is proposed in many fields of combustion. In this study, the feasibility of using Bunsen flame burning ammonia-hydrogen-air for impingement heating is evaluated. It is found that within the ranges of Re and Ф , there exists a threshold value of X H2 beyond which cone-shaped flames stably burn on Bunsen burner. For X H2 = 5–50%, addition of hydrogen promotes flames stability by increasing laminar burning velocity to match the high flow speed at 800 ≤ Re ≤ 1000. Besides, richer mixture also improves flame stability due to more abundant radicals. In the range of 0.8 ≤ Ф ≤ 1.4, shorter flame height while higher flame temperature occurs near stoichiometric conditions of 1.0 ≤ Ф ≤ 1.2, which is favorable for compact and rapid heating applications. Examination of NO formation mechanism from free flame reveals that increasing X H2 or decreasing Ф leads to more NO emission, finding that it is much sensitive to the operational parameters of X H2 , Ф and Re. But NO emission becomes less sensitive when the flame is under impingement. Further, NO emission becomes lower, which a favorable feature of using ammonia-hydrogen-air flame for impingement impinging. Lastly, comparison of thermal power and efficiency between natural gas and ammonia-hydrogen reveals that the latter fuel is sufficient to replace the former in industrial heating applications. • Stable Bunsen flame of ammonia-hydrogen-air relies on hydrogen fraction over a threshold value. • Increased laminar burning velocity by hydrogen addition boosts ammonia flame stability. • Hydrogen addition promotes ammonia flame temperature. • NO emission declines during the impingement course. • Similar heating efficiencies between the flames of ammonia-hydrogen-air and natural gas. [ABSTRACT FROM AUTHOR]

Global emissions of nearly 30% stem from fossil fuel combustion for long-distance transportation vehicles. Therefore, investigations on newer alternatives for clean and green fuels is desired in pursuance of net-zero carbon emissions by 2050. Given this contemplation, the current study aims at studying the effect of ammonia addition, a carbon-free fuel, on laminar burning velocity of CH 4 /H 2 fuel blends at high-pressure and high-temperature conditions utilizing the high-pressure diverging-channel method. The NH 3 varies from 0% to 30% in the CH 4 /H 2 fuel blend by volume. With regard to adiabatic flame temperature, this NH 3 /CH 4 /H 2 mixture is comparable to pure CH 4 -air mixtures, but with a reduction in carbon emissions of about 26.6%. The research involves conducting measurements at high temperatures between 300 K and 750 K, pressures between 1 atm and 5 atm, and equivalence ratios between ϕ = 0.7 and 1.4. When the pressure is 5 atm, the obtained burning velocities of NH 3 /CH 4 /H 2 blends are analogous to that of CH 4 -air mixtures. The temperature exponent, α, does not change when the NH 3 fraction or pressure changes, but at high temperatures there is a slight shift in the pressure exponent, β. The experimental results suggest that the Okafor and Li kinetic models align well with the measurements made in the current work up to 5 atm, while the Reduced GRI Mech 3.0 mechanism overestimates the burning velocity values. Additionally, an increase in NH 3 fraction and pressure results in a decrease in burning velocity and NO formation due to the presence of NH i (i = 0–2) radicals. Overall, this study convincingly demonstrates the viability of NH 3 /CH 4 /H 2 -air mixtures as a practical alternative to reduce carbon emissions. • LBV measurement of NH 3 /CH 4 /H 2 -air flames at elevated temperature and pressures. • Co-dependency of α and β proposed in LBV correlation for varying NH 3 concentrations. • NH 3 addition reduces burning velocity and NO formation due to presence of NH i radicals. • Reaction pathway elucidates 34.2% reduction in NH 2 → HNO at high pressure condition [ABSTRACT FROM AUTHOR]

The present work reports experimentation and numerical simulations of laminar burning velocity, emission analysis, and flame structure of dimethyl ether-hydrogen mixtures. The volumetric hydrogen addition is considered into the DME fuel for a range of mixture equivalence ratios (0.6< ϕ < 1.7). The initial mixture temperature is raised to 373 K at constant atmospheric pressure of 1.0 bar. The heat flux method is utilized to investigate the laminar burning velocity in laminar premixed planar adiabatic flames. The laminar burning velocity (LBV), along with the flame position and emission measurements, are extracted from these flames. The computations were performed with freely propagating flames (LBV, species, sensitivity, etc. data), and the burner stabilizes flames (flame position and emission analysis) for the same mixture and initial conditions using various detailed mechanisms. An emphasis is paid to a newly developed Shrestha mechanism, which includes a radiation model and NO sub-mechanism. Both experimental data and competition results were validated against the pure DME air mixture data available in the existing literature, and further analysis was carried out. It is observed that planar flames can be stabilized only up to a hydrogen addition of 40%. Adding hydrogen enhanced the flame temperature, heat release rates, and burning velocity while reducing the CO and NO emissions. A slight shift of peak burning velocity on the rich side of the equivalence ratio (from 1.05 to 1.2) is observed with hydrogen addition (0–40%). The mixture temperature also enhances the flame temperature and laminar burning velocity. It is interesting to note that hydrogen-added mixtures show a relatively lower dependency on initial mixture temperature. The variation of dominant species and heat release rates are also discussed in detail. The sensitivity analysis is carried out to get information on dominant reactions participating in the combustion of DME hydrogen mixtures. • Influence of H2 content on the LBV of premixed laminar DME flames was measured. • Influence of H2 content on the NOx Emission and temperature was measured. • Study of the flame structure characterized by the HRR and species profiles. • Experimental data compared with simulation results of 5 reaction mechanisms. [ABSTRACT FROM AUTHOR]

The laminar combustion characteristics of CH4/air premixed flames with CO2 addition are systemically studied. Experimental measurements and numerical simulations of the laminar burning velocity (LBV) are performed in CH4/CO2/Air flames with various CO2 doping ratio under equivalence ratios of 1.0–1.4. GRI 3.0 mech and Aramco mech are employed for predicting LBV, adiabatic flame temperature (AFT), important intermediate radicals (CH3, H, OH, O) and NOx emissions (NO, NO2, N2O), as well as the sensitivity analysis is also conducted. The detail analysis of experiment and simulation reveals that as the CO2 addition increases from 0% to 40%, the LBVs and AFTs decrease monotonously. Under the same CO2 doping ratio, the LBVs and AFTs increase first and then decrease with the increase of equivalence ratio, and the maximum of LBV is reached at equivalence ratio of 1.05. The mole fraction tendency of important intermediates and NOx with equivalence ratio and CO2 doping ratio are similar to the LBVs and AFTs. Reaction H + O2 ⇔ O + OH is found to be responsible for the promotion of the generation of important intermediates and NOx under the equivalence ratios and CO2 addition through sensitivity analysis. The sensitivity coefficients of elementary reactions that the increasing of CO2 doping ratio promotes or inhibits formation of intermediate radicals and NOx decreases. [ABSTRACT FROM AUTHOR]

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Experimental and dynamic analyses of the deflagration characteristics of laminar premixed syngas-air at different preheating temperatures and with different CO 2 volume fractions were carried out in a rectangular half-open pipe. The effects of CO 2 concentration and different initial temperatures on the flame structure evolution, flame structure profile and reaction rate of critical radicals, flame propagation speed, overpressure dynamics and hydrodynamic instability of syngas-air mixture were studied. The FFCM-1 mechanism was used to predict the laminar burning velocity of syngas-air under relevant conditions. The results revealed that the addition of CO 2 inhibited the flame propagation and reduced the concentration of H, OH and O, thus reduced the laminar burning velocity. The increase in temperature promotes the chemical effect of CO 2 , and the interaction between the flame front and the pressure wave is more pronounced, prolonging the duration of the " tulip " flame. Adding CO 2 reduces the flame front speed and overpressure, decreases the oscillation amplitude in late flame propagation, and inhibits the explosion intensity. Meanwhile, the temperature increase accelerates the flame propagation in the spherical and finger stages, and the maximum flame propagation speed and peak pressure appear earlier. In addition, as CO 2 content and temperature rise, flame hydrodynamic instability is difficult to ignore. However, there is a lack of data from studies of syngas deflagration dynamics at higher temperatures and with higher CO 2 additions. This suggests a focus on studies at higher temperatures as well as with higher CO 2 additions to enable the development of accurate kinetic models for wide range of syngas combustion. Also, the higher the initial temperature, the longer the time required for heating. • The appearance time of the tulip flame increased with the initial temperature. • CO 2 inhibits flame propagation and reduces the concentration of H, OH and O. • The maximum flame front speed appear earlier as the initial temperature increases. • The peak pressure decreases with increasing initial temperature. [ABSTRACT FROM AUTHOR]

Currently, hydrogen-enriched n-butane blends present a real interest due to their potential to reduce emissions and increase the efficiency of combustion processes, as an alternative fuel for internal combustion engines. This paper summarises the recent research on laminar burning velocities of hydrogen-enriched n-C4H10–air mixtures. The laminar burning velocity is a significative parameter that characterises the combustion process of any fuel–air mixture. Accurately measured or computed laminar burning velocities have an important role in the design, testing, and performance of n-C4H10–H2 fuelled devices. With this perspective, a brief review on the influence of hydrogen amount, initial pressure and temperature, and equivalence ratio on the laminar burning velocity of hydrogen-enriched n-C4H10–air mixtures is presented. Hydrogen has a strong influence on the combustion of butane–air mixtures. It was observed that a parabola with a maximum at a value slightly higher than the stoichiometric ratio describes the variation in the laminar burning velocity of hydrogen-enriched n-butane–air mixtures with the equivalence ratio. An increase in initial pressure or hydrogen amount led to an increase in this important combustion parameter, while an increase in initial pressure led to a decrease in laminar burning velocity. Overall, these studies demonstrate that hydrogen addition to n-C4H10–air mixtures can increase the laminar burning velocity and flame temperature and improve flame stability. These findings could be useful for the optimisation of combustion processes, particularly in internal combustion engines and gas turbines. However, the literature shows a paucity of investigations on the laminar burning velocities of hydrogen-enriched n-C4H10–air mixtures at initial temperatures and pressures differing from those in ambient conditions. This suggests that experimental and theoretical investigations of these flames at sub-atmospheric and elevated pressures and temperatures are necessary. [ABSTRACT FROM AUTHOR]

Willow wood presents a real interest for biomass pyrolysis due to its fast growth, renewability, and high energy density. Following the pyrolysis of willow wood in an inert atmosphere, a multi-fuel gaseous mixture was obtained, with the following composition (by volume): 38.20% CO/21.87% H2/17.44% CH4/1.15% O2/17.15% CO2/4.19% N2. The propagation of laminar premixed flames in these multifuel mixtures with air was investigated numerically for initial temperatures from 298 to 500 K, initial pressures from 1 to 20 bar, and fuel equivalence ratios between 0.60 and 2.00. The combustion of these gaseous mixtures as free laminar premixed flames was simulated by means of the INSFLA package and an extended reaction mechanism with 592 elementary reactions and 53 species. The modelling of the gas-phase combustion delivered several important parameters: the laminar burning velocities, Su, the maximum flame temperatures, Tfl,max, the flame front thicknesses, dfl, and the peak concentrations of the main reaction intermediates. The obtained parameters, discussed in correlation with the initial pressure and temperature, afforded the determination of the overall activation parameters of multifuel oxidation with air. [ABSTRACT FROM AUTHOR]

Diluents have an essential effect during combustion. Discovering the influence of CO2 and H2O as diluents on laminar burning velocity (LBV) is helpful for combustion control and optimization. In this study, CH4/air/CO2/H2O mixtures were investigated and validated using the FFCM‐Mech 1.0 over extensive boundary conditions. The chemical effects of the diluents CO2 and H2O were separated using a decoupling method. It was found that an increase in initial temperature promotes the chemical effects, while an increase in initial pressure does the opposite. In addition, the inhibiting effect of CO2 on LBV is stronger than that of H2O. Sensitivity, mole fraction, and rate of production (ROP) analyses were used to reveal that the sum of the chemical effects of adding CO2 and H2O separately was greater than the chemical effects of adding equal amounts of CO2 and H2O simultaneously. This paper not only investigates the effect of CO2 and H2O on the LBV under wide boundary conditions, but also offers a valuable guide for studying the operating conditions and intensity settings of exhaust gas recirculation (EGR) and theoretical guidance for further research on the combination of EGR and in‐cylinder water injection technology. [ABSTRACT FROM AUTHOR]

The characterization of a specific fuel has always been an important point for developing and designing new components or systems with the maximum efficient possible. Studying the laminar burning velocity can lay a necessary prerequisite for the accurate poststudy of the turbulent range and to understand how the combustion process takes place. The study of the combustion products from a specific reaction is a requisite for any system in order to understand the elements that are taken in the process and if it is possible to improve it. In this study, a new open code methodology was developed for the determination of combustion products, flame temperature and laminar burning velocity using numerical methods (Newton–Raphson, Taylor series and Gaussian elimination) in an application codified in MATLAB. The MATLAB application was applied for the study of Saudi LPG setting parameters such as initial temperature, pressure and equivalence ratio that are meaningful because they have a great effect on the results. In addition, simulation in Ansys Chemkin using San Diego and RedSD mechanisms was carried out. The results from the MATLAB application were compared with other experimental research and Ansys Chemkin simulation. These are presented in different plots and it is shown that: (1) For the laminar burning velocity results, the numerical method agrees with the experimental results for ratios (0.6–1.2) by other authors and the simulation in Ansys Chemkin. (2) For the highest studied equivalence ratios (1.3–1.7) the laminar burning velocity results between all the resources have more difference. (3) The combustion products calculated by the MATLAB application agree with those simulated in Ansys Chemkin except N and NO. (4) The MATLAB application gives a maximum value of 40.35 cm/s, that is greater than 35 ± 0.91, the one determined by Bader A. Alfarraj. (5) The flame temperature calculated by the MATLAB application overestimates that simulated in Ansys Chemkin but has the same behavior for all the calculated ratios. (6) The MATLAB application has also been developed for the study and analysis of other fuels. [ABSTRACT FROM AUTHOR]

Variations in methane–ammonia blends with hydrogen enrichment can modify premixed flame behavior and play a crucial role in achieving ultra-low carbon emissions and sustainable energy consumption. Current combustion units may co-fire ammonia/methane/hydrogen, necessitating further investigation into flame characteristics to understand the behavior of multi-component fuels. This research aims to explore the potential of replacing natural gas with ammonia while making only minor adjustments to equipment and processes. The laminar burning velocity (LBV) of binary blends, such as ammonia–methane, ammonia–hydrogen, and hydrogen–methane–air mixtures, was investigated at an equivalence ratio of 0.8–1.2, within a constant volume combustion chamber at a pressure of 0.1 MPa and temperature of 298 K. Additionally, tertiary fuels were examined with varying hydrogen blending ratios ranging from 0% to 40%. The results show that the laminar burning velocity (LBV) increases as the hydrogen fraction increases for all mixtures, while methane increases the LBV during blending with ammonia. Hydrogen-ammonia blends are the most effective mixture for increasing LBV non-linearly. Enhancement parameters demonstrate the effect of ternary fuel, which behaves similarly to equivalent methane in terms of adiabatic flame temperature and LBV achieved at 40% hydrogen. Experimental data for neat and binary mixtures were validated by different kinetics models, which also showed good consistency. The ternary fuel mixtures were also validated with these models. The Li model may qualitatively predict well for ammonia-dominated fuel. The Shrestha model may overestimate results on the rich side due to the incomplete N2Hisub-mechanism, while lean and stoichiometric conditions have better predictions. The Okafor model is always overestimated. [ABSTRACT FROM AUTHOR]

Adding the product of water electrolysis (i.e. 2:1 volume of H 2 and O 2) is an effective strategy to enhance the combustion intensity of NH 3 /air mixtures. In this work, the laminar burning velocity (LBV) of the obtained NH 3 /H 2 /O 2 /air mixtures was measured at 303 K, 0.1 MPa and compared with the values predicted by seven mechanisms. To improve the prediction performance, a new mechanism is developed based on the existing mechanism and adopted for numerical simulation. The results of this study show that the LBV of NH 3 is significantly increased by additional H 2 and O 2. By comparison, it is found that H 2 shows a more significant promoting effect on LBV when the volume ratio of additional H 2 and O 2 is 2. The concentration of key radicals and the flame temperature increase remarkably due to the addition of H 2 and O 2 , which promote the flame propagation. Furthermore, the experimental results also indicated that the additional H 2 and O 2 make the burned gas Markstein length decrease on the lean side and increase on the rich side. • The combustion of NH 3 was enhanced by 2:1 volume of H 2 and O 2. • The laminar burning velocity of NH 3 /H 2 /O 2 /air was measured. • A new kinetic model for NH 3 /H 2 /O 2 /air was obtained based on the existing model. • The promotion effect of H 2 and O 2 was analyzed. • The effect of H 2 /O 2 on flame instability was analyzed. [ABSTRACT FROM AUTHOR]

Mixtures of CH4 and CO2, known as biogas, are considered as renewable gas with low heat energy, which makes it extremely difficult to use as fuel in conventional natural gas equipment. To better understand the behavior of biogas mixtures and their properties, numerical results of the impact of carbon dioxide on laminar burning velocity and flame temperature of methane (CH4)–carbon dioxide (CO2)–air combustion were done. One of the most promising methods to enhance combustion is the use of a plasma source to assist unstable flames. For this purpose, experimental results to investigate the effect of microsecond pulsed plasma on non-premixed biogas flames were conducted. In the first section, laminar burning velocities and adiabatic flame temperature have been numerically calculated by one-dimensional steady code using several chemical kinetic mechanisms. Numerical results were compared with several experimental results from the literature. The laminar burning velocity and the adiabatic temperature of biogas/air combustion were calculated with CO2 concentration ranging from 0% to 50% in the mixture. The equivalence ratio was varied from 0.4 to 1.4, the initial pressure was set at 1 bar, and the temperature was set to 300 K. The impact of CO2 addition on the CO and NOx emissions at equivalence ratios from lean to rich (0.4–1.4) was investigated. It was found that increasing CO2 in the biogas lowers NOx and increases CO. In the second section, the effects of microsecond pulsed plasma on non-premixed swirling biogas/air flames were experimentally investigated. The plasma-assisted combustion was carried out in a coaxial burner. It consists of two concentric tubes; the central tube delivers the biogas flow to the injector and the annular tube contains a swirler and supplies the airflow. To create plasma in the stabilization zone of the flame, a rod-ring microsecond plasma configuration was used. OH* chemiluminescence measurements are used to describe the structure and stability of the flame. Results showed that plasma generated by microsecond high-voltage (HV) pulses can improve flame stability. An analysis of the optical emission spectra (OES) showed that plasma generates chemically active species such as excited N2*, CH*, OH* molecules, and H* atoms, leading to improved flame stability. The dependence of their intensities on both the pulse repetition frequency (PRF) and the input electrical voltage was investigated. The gas analysis of the exhaust gas was carried out with and without plasma. The exhaust gas concentration measurements revealed that the rod-ring pulsed plasma reduces CO with a low impact on the NOx level. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is a promising carbon-free fuel. However, modifying its high ignition temperature and low flame speed remains challenging. In this study, NH3 combustion was numerically investigated using hydrogen peroxide (H2O2) of different concentrations as the oxidizer to overcome these limitations. Adiabatic, free-propagating laminar burning velocities for NH3/H2O2/H2O mixtures were examined using a detailed chemical model. The maximum flame temperature between equivalence ratios is not considerably different at high concentrations of H2O2 (>80%), because the heat release is dominated by H2O2 decomposition. The equivalence ratio does not significantly affect the flame speed when the H2O2 concentration is less than 50%. The impact of H2O2 on the burning velocity at low concentrations is mainly attributed to the chemical effect. The chemical effect gradually decreases and the thermal effect increases because of the high heat release at high H2O2 concentrations. Moreover, the different concentrations of H2O2 consequently divide the flame into two sections. The first section is dominated by H2O2 reactions and the second by NH3 reactions. However, when the H2O2 concentration is 90 or 100%, flames do not appear in both sections. Finally, a quasilinear relationship between the flame speed and (NH2+OH)max mole fraction is identified. [ABSTRACT FROM AUTHOR]

Biomass-derived syngas is prone to leakage during transportation. To safely use biomass-derived syngas, we need to study the combustion characteristics of material syngas the purpose of this paper is: at T = 303 K, P = 0.1 MPa, under the condition of the spherical expansion flame method, calculate the laminar burning velocity, and used the Chemkin module of ANSYS to simulate four mechanisms (GRI-3.0, FFCM-1, Li-2015, SanDiego +NOx-2018) to compare, select more appropriate reaction mechanism through experimental data for related research. It was found that the chemical reaction mechanism of GRI-3.0 is more in line with the experimental results. It is found that the experimental results are in good agreement with the linear extrapolation method. When the H2 concentration increases from 22-42%, the peak laminar burning velocity moves in the direction of the lean fuel side. When the H2 concentration increases to 42%, the laminar burning velocity is the fastest, reaching 0.78 m/s. The effect of H2 on thermal diffusivity is high. When H2 concentration reaches 42%, its thermal diffusivity is much higher than other gas components. The adiabatic flame temperature of F1 (22% H2, 45% CO, 9.6% CH4, 23.4% CO2)-air mixtures is the highest, approaching 2196 K. The peak adiabatic flame temperature of F5 (42% H2, 25% CO, 9.6% CH4, 23.4% CO2)-air mixtures is 2082 K, which is comparatively low. Nonetheless, the H2 concentration in F5-air mixtures is higher than that in F1-air mixtures, indicating that H2 has less influence on adiabatic flame temperature than CO. The positive reactions to accelerate laminar burning velocity mainly include R99, R38, and R46. The R52 and R35 can inhibit laminar burning velocity. There are many factors affecting laminar burning velocity, among which high reactive free radicals are the main factors, and the competition between chain branching reaction and chain termination reaction for high reactive free radicals also affects laminar burning velocity. With the increase of concentration of H2, participate in the reaction of the molar mass fraction of highly reactive free radicals and the laminar burning velocity. [ABSTRACT FROM AUTHOR]

A single-step chemical-kinetic mechanism is developed that provides good predictions of laminar burning velocities and auto-ignition times. Reasonably accurate adiabatic flame temperatures and (consequently) total amounts of heat release are first obtained through asymptotic expansions of equilibrium expressions for the production of H, O, and OH radicals from the stable products, H 2 O along with H 2 and O 2. By ignoring the inner flame structure, this yields minimal computational stiffness for a wide range of equivalence ratios and pressures. In the single-step rate expression, a passive scalar carrying the radical pool is then introduced that enables reasonable laminar flame structures and burning velocities to be calculated. An additional passive scalar measuring pre-heat-release radical build-up serves to track auto-ignition properly as well, thereby providing reasonable predictions for time-dependent as well as steady-state conditions. The results from this computationally convenient formulation are useful for describing a number of combustion processes, including counter-flow flames. Novelty and significance statement Hydrogen combustion plays a key role in the carbon-free energy transition. The CPU cost/accuracy balance between detailed and reduced chemistries makes it hard to get the full approval of the CFD community. This balance is more likely in single-step mechanisms due to errors in flame temperature predictions and narrow application conditions. In this study, we apply the novel formalism of varying stoichiometric coefficients to construct a single-step mechanism that accurately reproduces adiabatic temperatures. A global reaction rate constructed from the flame chain-branching analysis and the flammability limits is proposed. Furthermore, an optional passive scalar coupling is presented to extend the capabilities of the present mechanism to autoignition predictions. This work provides an efficient and accurate alternative scheme for CFD hydrogen combustion applications, valid for a wide range of conditions. [ABSTRACT FROM AUTHOR]

• The oxidation process of R152a/R1234ze(E) mixture had been first studied by the synchrotron vacuum ultraviolet photoionization mass spectrometry. • The laminar burning velocities and flammability limits of R152a/R1234ze(E) were measured by a constant-volume combustion bomb. • Species of CH 2 :CHF, CH 3 -CHF 2 , CHFCHCF 3 , CHF:CHF, CH 2 :CF, CF 2 :O, C 2 H 2 , and CH 4 were identified in R152a/R1234ze(E) oxidation. • An improved flame retarding model for R1234ze(E) was developed. • The flame retarding mechanism of R1234ze(E) on R152a was revealed in terms of oxidation products, reaction pathways and flame characteristic parameters. R1234ze(E) (1,3,3,3-tetrafluoro-1-propene), with low global warming potential (GWP), is considered as environmentally friendly refrigerant for refrigeration and heat pump systems. Although R1234ze(E) is classified as weakly flammable refrigerant, it is non-flammable under low humidity conditions. Therefore, R1234ze(E) can be a flame retardant in blended refrigerants. This study analyzed the oxidation process of the mixture of R1234ze(E) and flammable R152a via the Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry (SVUV-PIMS). The oxidation species of CH 2 :CHF, CH 3 -CHF 2 , CHFCHCF 3 , CHF:CHF, CH 2 :CF, CF 2 :O, C 2 H 2 , and CH 4 were identified by experiments. Besides, the laminar burning velocities and flammability limits of R152a/R1234ze(E) were measured on a constant volume combustion bomb. Based on these experimental results, a new kinetic model was developed to describe the inhibition of R1234ze(E) on the combustion process of R152a. In order to analyze the flame retarding effect of R1234ze(E), sensitivity analysis of key groups, generation and consumption paths of major components, distribution of important products and free radicals, and the adiabatic flame temperature were revealed. It was found that the addition of R1234ze(E) introduced new inhibitory pathways and suppressed the reactions between R152a and H, O and OH radicals. Furthermore, R1234ze(E) reduced the concentrations of flammable radicals H, O, and OH in freely propagating flames, while it increased the number of flame retarding radicals CF 2 and CF 3. The adiabatic temperature of R1234ze(E)/R152a decreased with the increasing proportion of R1234ze(E) as well. This study can provide valuable reference for the application of R1234ze(E) in the field of new flame retardants. [ABSTRACT FROM AUTHOR]

• New measurements of Benzene flame speed in air. • Prediction of UFL and LFL at different pressures, temperatures and dilutions. • Quantification of the relevance of soot for flammability limits. • First comprehensive interpretation of all existing benzene flammability data. • Approach applicable to other high-sooting fuels. This research introduces an innovative approach to predict benzene Lower and Upper Flammability Limits (LFL and UFL). The focus of this study is on predicting the flammable range of benzene/air/steam mixtures utilizing a freely-propagating flame method, incorporating an optically-thin approximation to model soot radiation. The investigation delves into the consequences of dilution by inert gases (N 2 and steam), along with the impacts of pressure and initial temperature. Soot is recognized as essential not only for its role in flame chemistry under rich conditions but also for its influence on radiation, thereby affecting the flammable region of hydrocarbons especially at higher temperatures and pressures. To address the significant formation of soot during benzene combustion near the UFL, the study integrates the kinetic model for benzene combustion with a recently developed soot mechanism based on the discrete sectional method, which has been validated extensively against a large database of sooting flames, encompassing various hydrocarbons, including benzene. To limit the computational effort associated with predicting flammability limits, a skeletal version (with 136 species and 4788 reactions) of the overall kinetic model covering benzene combustion and soot formation is developed and validated in this work. The kinetic model was first validated against new and existing benzene flame speed data at different pressures and initial temperatures. Then it was used to investigate the flammable range. The model predictions align remarkably well with the available experimental data in the literature for the LFL, for the effect of dilution with inert gases, and with some experimental measurements for the UFL. An extensive review of these experimental data revealed significant uncertainty in characterizing benzene's UFL experimentally, both in terms of absolute value and effect of initial temperature. The comprehensive model predictions provide valuable insights, enabling differentiation among various UFL datasets for benzene. [ABSTRACT FROM AUTHOR]

To demonstrate the effect of propane co-firing on the explosion characteristics of the oxygen-enriched biogas, deflagration experiments were conducted in a semi-open duct. The results show that the tulip flame transforms from an existence to a disappearance with increasing oxygen fraction. The increasing brightness of the flame indicates that the increase in oxygen fraction can enhance the explosion strength and accelerate flame propagation. A clear backward motion of the burnt gas is clearly distinguished in the direct imaging of flame propagations. The propane effect is discernible when the flame evolves in a dynamic manner shortly after the flame skirt is in touch with the sidewalls. Moreover, the oxygen fraction impacts the extent of this dynamic feature and thus the magnitude of the propane effect. The laminar burning velocity S L can be singled out to forecast the flame propagation speed. The propane effect on S L and [H+OH+O] max gradually strengthens with increasing oxygen enrichment. [H+OH+O] max is well related to the fundamental properties of the mixture, such as S L , the expansion ratio, initial temperature and flame thickness, which in turn dominate flame propagations in the duct. [ABSTRACT FROM AUTHOR]

Three-dimensional simulations of laminar flame propagating downwards the vertical surface of a rigid polyurethane slab heated by a radiative panel are presented and compared with the measurement data. The gas-phase model (ANSYS Fluent) allows for finite-rate volatile oxidation, soot formation and oxidation, emission, transfer, and absorption of thermal radiation. The solid-phase model Pyropolis considers heat transfer across the material layer and generation of combustible volatiles in thermal decomposition of the material. Kinetic model of material decomposition is derived to obey the microscale combustion calorimetry data for different heating rates. Transient behavior of propagating flame and pyrolysis zone, as well as spatial distributions of heat flux components, temperature, and mass burning rates over the specimen surface are examined. Variation of the thermal properties of the material during its thermal decomposition, as well as the specimen surface emissivity and reradiation are shown to be the important issues strongly affecting model predictions. Two distinct modes of counterflow flame spread, thermal and kinetic, are identified. In the thermal mode corresponding to fast chemistry in the gaseous flame, the flame propagation velocity is governed by the heating rate of the combustible material ahead of the flame front. Alternatively, in the kinetic mode, it is limited by the burning velocity of the volatile-air mixture forming ahead of the flame front. Simulation results are favorably compared with the measured propagation velocity. [ABSTRACT FROM AUTHOR]

With the development of the uses of hydrocarbon compounds in many industrial fields, especially in the field of energy liberation through oxidation of gases, as previous research specialized in improving the combustion processes of gases by adding particles of other gases that contribute to improving the combustion of these compounds in terms of temperatures and speed of flame combustion. The previous study aimed to improve the flame speed by adding different gases to several compounds. In this research paper, propane gas C3H8 is used as the main gas to improve its combustion properties. N2 and H2 gas were added in different proportions, through which a clear effect on the combustion properties can be seen in terms of combustion speed. Flames and exhaust as CO and NOx. As the auxiliary gases were added in this improvement at rates of 20%, 30% and 40%, and then these tests were analyzed, where it was concluded that H2 gas clearly contributed to improving the combustion speed of the flame, as the flame combustion velocity reached 58.3 cm/s by 40%. [ABSTRACT FROM AUTHOR]

The characterization of a specific fuel has always been an important point for developing and designing new components or systems with the maximum efficient possible. Studying the laminar burning velocity can lay a necessary prerequisite for the accurate poststudy of the turbulent range and to understand how the combustion process takes place. The study of the combustion products from a specific reaction is a requisite for any system in order to understand the elements that are taken in the process and if it is possible to improve it. In this study, a new open code methodology was developed for the determination of combustion products, flame temperature and laminar burning velocity using numerical methods (Newton–Raphson, Taylor series and Gaussian elimination) in an application codified in MATLAB. The MATLAB application was applied for the study of Saudi LPG setting parameters such as initial temperature, pressure and equivalence ratio that are meaningful because they have a great effect on the results. In addition, simulation in Ansys Chemkin using San Diego and RedSD mechanisms was carried out. The results from the MATLAB application were compared with other experimental research and Ansys Chemkin simulation. These are presented in different plots and it is shown that: (1) For the laminar burning velocity results, the numerical method agrees with the experimental results for ratios (0.6–1.2) by other authors and the simulation in Ansys Chemkin. (2) For the highest studied equivalence ratios (1.3–1.7) the laminar burning velocity results between all the resources have more difference. (3) The combustion products calculated by the MATLAB application agree with those simulated in Ansys Chemkin except N and NO. (4) The MATLAB application gives a maximum value of 40.35 cm/s, that is greater than 35 ± 0.91, the one determined by Bader A. Alfarraj. (5) The flame temperature calculated by the MATLAB application overestimates that simulated in Ansys Chemkin but has the same behavior for all the calculated ratios. (6) The MATLAB application has also been developed for the study and analysis of other fuels.

Measurements of how the flame speed in suspensions of metal fuels depends on the initial temperature of the unburned mixture are important for understanding the role of mixture preheat by radiation heat transfer. This preheat can be an important stabilization mechanism for metal dust flames in energetic devices. A newly constructed counter-flow flat-flame metal dust burner allows for the measurement of burning velocities in aluminum-air suspensions preheated to temperatures up to 524 K using Particle Image Velocimetry (PIV). The experimental method was verified by measuring and comparing burning velocities in preheated methane-air mixtures at different fuel-oxygen equivalence ratios with previous experimental data and theoretical predictions. Whereas the flame speed in methane-air mixtures increases by 2.75 times with an increase in temperature to about 524 K, the flame speed in aluminum-air mixtures increases by less than 2 times over the same temperature interval. The independence of the adiabatic flame temperature of aluminum-air flames on the initial temperature of the mixture suggests practically constant reaction rates either for kinetically- or diffusion-controlled aluminum combustion. Thus, the observed moderate dependence of the aluminum-air flame speed on mixture initial temperature can be explained by a cumulative effect of the increased heat diffusivity, decrease in the amount of heat required to reach the particle ignition temperature, and increased flame sensitivity to preheat due to discrete source effects discussed in recent flame models. [ABSTRACT FROM AUTHOR]

To understand the effect of hydrogen addition on the laminar burning velocity (LBV) of ethanol–air mixtures, experiments were conducted in a constant volume combustion chamber with the high-speed schlieren photography technique. The experiments were carried out under the equivalence ratios (ERs) of 0.7–1.4, an initial temperature of 400 K, an initial pressure of 0.1 MPa, and hydrogen fractions of 30% and 90% by volume, respectively. The effects of ER, initial temperature, initial pressure, and hydrogen fractions on the LBV were investigated. Moreover, adiabatic flame temperature (AFT), heat release rate (HRR), flow rate sensitivity analysis, and ROP (rate of production) analysis were also performed. Results showed that LBV increased with increasing hydrogen addition and temperature but decreased with increasing pressure. The hydrogen addition significantly increased the HRR of ethanol–hydrogen–air flames. The sensitivity analysis showed that R5 (O2 + H = O + OH) significantly influenced the LBV. [ABSTRACT FROM AUTHOR]

A natural-draft, heavy-duty cooking burner was designed and developed as a fuel-flexible burner capable of burning both liquefied petroleum gas (LPG) and Ethanol. The burner has great potential to replace LPG with ethanol to reduce the consumption of fossil fuels. Ethanol is a renewable fuel; it can be produced domestically from agricultural products. However, its heating value is lower than that of LPG. Thanks to the advantage of combustion in a porous medium to create heat recirculation, the flame temperature is higher than that of the free flame. Using a column embedded in the burner wall, liquid ethanol is vaporized without external heating and atomization. A critical criterion for the burner is to stabilize the flame inside the porous medium so that flow velocity equals burning velocity. A common gas injector can be used to switch between LPG and ethanol while maintaining better combustion and thermal performance compared to a conventional LPG burner and previous ethanol burners. The proposed burner has a compact combustion chamber, but it yields a higher combustion temperature because it stabilizes the flame at greater amounts of primary air with a high turn-down ratio. [ABSTRACT FROM AUTHOR]

• The laminar burning velocity of DEK/NH 3 -air mixtures was measured at elevated pressures for the first time. • A new kinetic model for DEK/NH 3 mixtures was developed and validated through experimental data. • The effect of NH 3 on DEK/NH 3 -air mixture kinetics was analyzed, highlighting the impact of active radical concentration variations on LBV. 3-pentanone (DEK) is a biomass oxygenated fuel with high energy density and low emissions. It shows promising potential in increasing the combustion of NH 3. This study examines the laminar burning velocity (LBV) of a fuel mixture composed of DEK/NH 3 -air. The LBV of DEK/NH 3 -air was determined with a constant-volume combustion bomb under the following conditions: initial temperature (T) of 448 K, pressure (P) of 1 to 3 atm, equivalence ratio (ϕ) between 0.7 and 1.3, and NH 3 mole fraction (X NH 3) varying from 0 % to 90 %. A combustion kinetic model for DEK/NH 3 mixed fuel was developed and verified using experimental results. Overall, the model can capture the trend of LBV well. Subsequently, a comprehensive kinetic analysis was conducted utilizing this mechanism to elucidate the effect of NH 3 mixing on DEK/NH 3 -air mixed fuel. The results indicate that LBV of DEK/NH 3 -air mixture declines as X NH 3 increases, primarily attributed to the reduction in radical pool concentration. Conversely, the effect of the decrease in flame temperature is relatively minor. Furthermore, as X NH 3 mole fraction decrease, there is a slight alteration in the consumption pathway of NH 3. The elevation in DEK mole fraction leads to an increased production of radicals, thereby amplifying the oxidation process of NH 3. The proportion of the oxidation of N H i pathway also increases. Finally, the change of NO content in DEK/NH 3 -air flame was observed. The rise in X NH 3 leads to a gradual increase in the content of NO until it reaches a peak, after which it starts to decline. This phenomenon is dependent on the presence of O, OH, and N H i radicals. In addition, it has been discovered that augmenting ϕ can significantly reduce the concentration of NO in DEK/NH 3 -air mixture. [ABSTRACT FROM AUTHOR]

• The ammonia and toluene reference fuel semi-detailed kinetic mechanism was proposed. • The NH 3 /TRF mechanism was validated by ignition delay time and laminar burning velocity. • Sensitivity and reaction pathway analysis was performed for the addition of NH 3 combustion. • The auto-ignition process in NH 3 /TRF blend mixture is dominated by NH 3 chemistry. C-free fuel ammonia has a high auto-ignition temperature and low flame speed compared to conventional hydrocarbon fuels, which limits its application in internal combustion engines (ICEs). Blending ammonia (NH 3) with a highly reactive fuel can effectively solve this problem, and traditional macromolecular hydrocarbon fuels are a good choice because of their practicality and economy. However, the chemical reaction mechanism for the combustion of NH 3 /macromolecular hydrocarbons is not yet fully understood. In this study, a detailed kinetic mechanism for NH 3 and toluene reference fuel (TRF) is proposed with 250 species and 4272 reactions. The developed NH 3 /TRF mechanism was validated by a single component (NH 3 , n-heptane, iso -octane, and toluene) and multiple components (NH 3 /n-heptane, NH 3 / iso -octane, NH 3 /toluene) with ignition delay time, laminar burning velocity, and key intermediate component distribution. The current NH 3 /TRF mechanism showed good performance compared with previous mechanisms. The co-combustion of NH 3 /TRF blends was performed with different NH 3 energy fractions, and sensitivity and reaction pathway analyses were performed to reveal the effect of TRF addition on NH 3 combustion. The results showed that the OH radical is mainly produced through N-containing reactions rather than C-containing reactions under T = 1000 K, P = 40 atm, and ϕ = 1 with more than 30 % NH 3 addition. The HO 2 radical is the most important radical for NH 3 ignition, in addition to OH radicals, and its reactions with N-containing radicals (NH 2, H 2 NO, and NO) contribute to the majority of OH radicals. [ABSTRACT FROM AUTHOR]

Zero-carbon fuels such as hydrogen and ammonia play a pivotal role in the energy transition by offering cleaner alternatives to natural gas (methane), especially in industrial combustion systems. Binary and ternary blends of these fuels offer a transitionary, low-carbon solution in the near future. Laminar burning velocity (LBV), as a fundamental combustion property, is significantly different for ammonia, hydrogen, and methane. Although the LBV of binary blends of these fuels is well-studied, ternary blends have not been extensively studied. In this study, the primary objective is to employ a simple ensemble learning method to predict the LBV of ternary ammonia/hydrogen/methane/air mixtures. The training dataset consists of experimental data sourced from a large number of publications (3,846 data points), as well as synthetic data generated by 1D freely propagating premixed flame simulations in Cantera using a detailed chemical kinetic model. Three machine learning algorithms, namely artificial neural networks, gaussian process regression, and extreme gradient boosting trees are trained and optimised. Then, a simple ensemble averaging method is used to reduce overfitting and improve robustness. The ensemble model achieves coefficient of determination (R 2) of 0.991 on the test set with an inference time that is approximately 8,000 times faster than the 1D simulation run time. The ensemble model is capable of predicting LBVs of ammonia/hydrogen/methane/air mixtures for T = [ 295 – 756 K ] , P = [ 1 – 10 bar ] , ϕ = [ 0. 5 – 1. 8 ] across all possible blending ratios. • LBV of ternary NH 3 /H 2 /CH 4 /air mixtures are predicted by a data-driven ML model. • ML model can speed-up LBV prediction by up to 28,000 times compared to 1D models. • Wide range of mixture ratios and conditions where experimental studies do not exist are investigated. • Ternary mixtures where LBVs are comparable to that of stoichiometric CH 4 /air mixtures are identified. [Display omitted] [ABSTRACT FROM AUTHOR]

• Laminar burning characteristics at high temperatures and pressures were studied. • The laminar burning velocities and Markstein lengths were measured and analyzed. • Trends in hydrodynamic instability with temperature and other factors were studied. • The simulation of ammonia/ethanol mechanism is higher than experimental value. • The sensitivity of laminar flame speed and N-containing reaction paths was analyzed. Ammonia, as a carbon free fuel, is expected to play a key role in carbon neutrality and social energy shortages. However, the flame propagation speed of ammonia is low. Blending ammonia with ethanol is one of the methods to increase laminar burning velocity of ammonia, but the existing research on the combustion characteristics of ammonia/ethanol focuses on low temperature and pressure. This paper investigated the effect of ethanol addition on ammonia combustion characteristics under high temperature and pressure. The initial conditions for this work include initial temperature (400, 450, and 500 K), initial pressure (0.5, 1.0, 1.5 MPa), equivalence ratio (0.8–1.3), and ethanol energy fraction (0 %, 20 %, 40 %, 60 %, 80 %). The results illustrate that the laminar burning velocity has a positive correlation with the ethanol energy fraction and the initial temperature, but is negative correlation with initial pressure. And the laminar burning velocity and the adiabatic flame temperature appear to be maximum when the equivalence ratio is between1.0 and 1.1. The strongest hydrodynamic instability occurs within the equivalence ratio range from 1.0 to 1.1. In addition, initial pressure increased flame hydrodynamic instability and initial temperature has little effect on it. The changes in initial pressure and temperature have little effect on thermal diffusion instability. When the ethanol energy fraction is less than or equal to 20 %, ammonia has a significant impact on the Markstein length, but ethanol dominates the Markstein length with a proportion of ethanol energy over 40 %. Under current experimental conditions, the existing ammonia/ethanol mixing mechanisms cannot comprehensively and accurately predict laminar combustion velocity. The CEU mechanism is relatively accurate, especially under lean combustion and high pressure. The three most sensitive reactions to laminar burning velocity are H + O2<=>O + OH, H + O2(+M)<=>HO2(+M), and NH2 + NO<=>NNH + OH. When adding 40 % ethanol compared to 20 % ethanol, the molar fraction of OH and O free radicals is higher, and the peak value of NO total ROP is higher. [ABSTRACT FROM AUTHOR]

• The characteristics of laminar combustion of NH 3 -CH 4 -air at high temperatures and pressures are investigated in CVCC. • The mechanism of OTOMO has the greatest agreement with the NH 3 -air laminar burning velocity, and the mechanism of OKAFOR has the greatest agreement with the NH 3 -CH 4 -air laminar burning velocity. • The reaction order of ammonia is calculated in the range from 1.24 to 1.48 and the temperature exponent is calculated in the range from 1.88 to 2.68. • The laminar burning velocities and Markstein lengths of NH 3 -CH 4 -air are measured, and their trends with temperature, pressure and equivalence ratio are analyzed. • Trends in hydrodynamic instability, thermodynamic instability, and buoyancy instability of flames with temperature, pressure, equivalence ratio, and methane energy ratio are investigated. Nowadays, ammonia is considered a potential carbon-free fuel. However, the research on the combustion characteristics at high temperatures and pressures which has significance to the research of real engine in-cylinder combustion is little. In this study, the Laminar Burning Velocity (LBV) and Markstein Length (L b) of NH 3 -air at high temperature and high pressure were investigated within a constant volume combustion chamber, and methane with various energy ratios was introduced for comparative analysis, as well as the reaction order and temperature exponent were calculated. Furthermore, flame instability in spherical expansion flames has also been studied in depth. The results show that when initial temperature (T u) = 450 K, the reaction order of ammonia ranges from 1.32 to 1.48, when T u = 500 K, the reaction order of ammonia ranges from 1.24 to 1.41. The temperature exponent is calculated between 1.88 and 2.68, when T u from 400 K to 550 K. In the range of T u from 400 K to 500 K, initial pressure (p) from 0.5 MPa to 1.5 MPa, Φ from 0.8 to 1.3 and methane energy ratio (E CH4) from 0 to 0.8, increasing T u and E CH4 , decreasing p all have the potential to increase the LBV. Notably, the optimal equivalence ratio shifts from 1.1 to 1.0 with the increase of E CH4. The L b is unaffected by variations in temperature, decreasing with increasing pressure but increasing with increasing equivalence ratio. As the E CH4 increases, L b increases within 0.8 < Φ < 1.0, but decreases within 1.1 < Φ < 1.3. As the p and E CH4 increase, the hexagonal structure of the flame surface by an increasing trend, indicating an increase in hydrodynamic instability, while the temperature has little effect on this instability. In addition, as the equivalence ratio increases, the hydrodynamic instability first increases and then decreases. With an increase in T u , Φ , and E CH4 , the thermal diffusive instability is slightly weakened, and the response to pressure is not significant. Lower flame velocity of ammonia, and decreasing T u , increasing the p , and decreasing E CH4 enhances the effect of buoyancy on the flame, which becomes more pronounced as the flame develops. [ABSTRACT FROM AUTHOR]

In this work, the effects of oxygen enrichment coefficient (Ω = 0.21 − 0.42) and initial temperature (T u = 298 − 448 K) on the laminar burning properties of NH 3 /H 2 /O 2 /N 2 flames are systematically investigated by using the spherical flame propagation method at equivalence ratios (Φ = 0.8 − 1.4) and initial pressure (P u = 3 atm). LBV is analyzed by obtaining experimental data. In order to analyze flame instability, thermal diffusion and hydrodynamic instability are separated by linear stability theory. The thermal and chemical effects of oxygen enrichment on LBV and its effect on heat release rate are analyzed by numerical simulation. The results show that the laminar burning velocity (LBV) exhibits a positive correlation with both the oxygen enrichment coefficient and the initial temperature. The temperature index (α) exhibits a non-monotonic variation in response to the initial temperature of the NH 3 /H 2 /O 2 /N 2 flame. Le eff is insensitive to temperature and positively correlated with the oxygen enrichment coefficient. The NH 3 /H 2 /O 2 /N 2 flame is mainly affected by hydrodynamic instability when the oxygen enrichment coefficient is large. The peak NHRR scales positively with the oxygen enrichment coefficient. Oxygen enrichment helps to contribute to the overall net reaction rate. • The LBV of mixture flame with oxygen enrichment coefficient 0.21–0.42 was measured. • The effects of initial temperature on the LBV of the mixture flame were studied. • Thermal and chemical effects of oxygen enrichment were analyzed by adding virtual gas. • Diffusion thermal and hydrodynamic instability were separated by linear stability theory. [ABSTRACT FROM AUTHOR]

The present work reports experimental investigations on laminar burning velocity variation of CH 4 +H 2 +air mixtures at elevated temperatures (300–650 K) using an externally heated diverging-channel method. The effect of mixture equivalence ratio (ϕ = 0.7–1.3) and H 2 fraction (0–50% by volume) on burning velocity have been reported at elevated temperatures. The experimental measurements are compared with numerical simulations using GRI Mech 3.0 and FFCM-1 kinetic models. The obtained results exhibit an increase in the laminar burning velocity with H 2 fraction due to the formation of H-atom as an intermediate. The temperature dependency is established through a power-law correlation. The temperature-exponent shows a parabolic variation with a minimum value at ϕ = 1.1. Reaction pathway diagram interprets the major oxidation paths followed by reactants for higher carbon-consumption with varying H 2 fraction. The P2 pathway involving ethane breakdown plays a major role in enhancing the burning velocity at rich mixture conditions. • Laminar burning velocity of CH 4 +H 2 +air flames measured at elevated temperatures. • Burning velocity dependency on temperature established for elevated temperatures. • H 2 addition raises burning velocity with increased presence of H, O, and OH species. • Reaction pathway elucidates the role of P2 pathway in C atom consumption. [ABSTRACT FROM AUTHOR]

The laminar burning velocities of a stoichiometric CH4–N2O mixture diluted with N2 [30–60% (by volume)] at various initial pressures (1–10 bar) and various initial temperatures (273.15–423 K) are obtained by numerical modelling of their premixed adiabatic flames. The modelling is performed with the Cosilab package using the GRI-Mech 3.0 mechanism based on 53 chemical species and 325 elementary reactions. The calculated laminar burning velocities are compared with available literature data. The influence of the initial conditions (pressure, temperature, and N2 concentration) of CH4–N2O–N2 mixtures on the laminar burning velocities, maximum flame temperature, heat release rate, and peak concentrations of the main reaction intermediates is investigated and discussed. Using the correlations of the laminar burning velocities with the initial pressure and the average flame temperature, the overall activation parameters of CH4–N2O oxidation are determined. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The aim of the present work is to contribute to the better understanding of the combustion process and the laminar flame properties of methane/hydrogen-air flames at elevated temperatures and pressures. The heat flux method provides an accurate and direct measurement of laminar burning velocities (LBV) at elevated temperatures, while the constant volume chamber method provides measurements at elevated pressures. In the present work, a database of more than 250 experimental points for the range of temperature (298–373 K) and pressure conditions (1–5 bar) for mixtures up to 50% hydrogen in methane was generated using these two methods. Comparison with the sparse literature data shows quite good agreement. A power-law correlation for temperature and pressure is proposed for methane/hydrogen-air mixtures, which has a practical application in estimating the LBV of a natural gas/hydrogen mixture intended to replace pure natural gas in different processes. The power-law temperature exponent, α, and the pressure exponent, β, show inverse trends. The former decreases almost linearly and the latter increases approximately linearly when the hydrogen content is increased. The power-law exponents are highly affected by the mixture equivalence ratio, ϕ , showing a parabola like trend. However, for the pressure exponent this trend becomes almost linear for 50% H 2 in the mixture. The power-law correlation has been validated against experimental data for a wide range of temperature (up to 573 K), pressure (1–7.5 bar), equivalence ratios (ϕ between 0.7 and 1.3) and H 2 contents up to 50%. [Display omitted] • Heat flux method and constant volume chamber were used to investigate the LBV. • 50% H 2 in CH 4 were investigated at ϕ = 0.6–1.6, p gas = 1–5 bar and T gas = 298–373 K. • Combined power law correlation for T and p of CH 4 /H 2 /air mixtures was proposed. • Correlation validated against the dataset with the highest T and the highest p. • Correlation validated against literature up to 50% H 2 , up to 7.5 bar and up to 573 K. [ABSTRACT FROM AUTHOR]

The prospects of 2-methylfuran (2MF) as a biofuel and gasoline blend stock are quite high. Therefore, a skeletal chemical kinetic mechanism – containing 238 species and 1156 reactions – for the simulation of premixed flames involving isooctane (representing gasoline)/2MF blends is proposed in the present work. The proposed model has been validated against a wide range of experimental data at various pressures, temperatures and compositions. It is demonstrated in the present work that the proposed mechanism can predict the concentrations of gaseous soot precursors as well. Moreover, the compatibility of the NOx sub-mechanism in the present model has been assured through validations against a wide range of recent experimental data. The results obtained in this work suggest that there are little chances of co-oxidation reactions among the species generated from the initial decomposition of both isooctane and 2MF. Furthermore, there is around 26% variation in the peak laminar burning velocity when the mole fraction of 2MF is increased from 10% to 90% in isooctane/2MF blend. [ABSTRACT FROM AUTHOR]

The high-pressure leakage of underground pipeline could entrain the nearby sands and soils, and thus cause the jet fire of gas-solid mixtures. In addition, the thermal runaway of Lithium ion batteries could also cause a typical gas-solid jet diffusion flame. In comparison with the gaseous jet diffusion flame and the gas-solid-air jet premixed flame, the gas-solid jet diffusion flame lacks of exploration. Thus, a new facility consisting of a jet fire apparatus and a sand feeder, was designed to explore the gas-solid jet fire. The test repeatability was justified for the proposed facility. The dynamical differences of gas-solid and gaseous jet fires are clarified. It is found that the gas-solid jet fire holds a larger lift-off height, a less visible flame height and a less radiative fraction than the purely gaseous jet fire. In particular, for gas-solid jet fires at high exit velocities, the lift-off height increases, but the visible flame height and radiative fraction seem to decrease, as the particle size of sand decreases to increase the jet height of sand. (1) Inside the flame volume, the sand plays a role of heat sink to decrease the flame temperature and thus the flame burning velocity. Moreover, in the lift-off region, the sand dilutes the gas fuel and isolates the surrounding oxygen to inhibit the combustion. Both effects of sand cause a large lift-off height, especially for the sand of little particle size. (2) A large lift-off height means the increase of the air mass entrained from flame base or the portion of the premixed flame to the whole flame. In addition, the sand particle-laden flow would significantly increase the ambient air entrainment rate of fire plume. Both effects result in a less visible flame height. (3) The portion of the premixed flame increases in the bottom, which reduces the total soot amount inside the whole flame volume. The decrease of the flame temperature and the total soot amount reduces the radiative fraction. (4) The sand significantly affects the flame geometry and radiative fraction, which alters the radiant heat flux distribution and challenges the development of thermal radiation model for gas-solid jet fires. The gas-solid jet fire holds a less peak radiant heat flux but a higher positon of peak radiant heat flux than the gaseous jet fire. In addition, the line source radiation model available in literature is revised to well predict the radiant heat flux distribution of the gas-solid jet fires. [ABSTRACT FROM AUTHOR]