Search Results (20)

This study presents a detailed analysis of the combustion dynamics of stoichiometric H₂–air and CH₄–air mixtures in a 20 L closed vessel over an initial temperature range of 298–423 K. We integrate experimental pressure–time P(t) measurements with numerical analysis to extract laminar burning velocity (LBV) and deflagration index (K_G) values, and we assess three independent kinetic mechanisms (KiBo_MU, University of San Diego, Lund University) via simulations. For H₂–air, LBV increases from 0.50 m/s at 298 K to 0.94 m/s at 423 K (temperature exponent α ≈ 1.79), while for CH₄–air, LBV rises from 0.36 m/s to 0.96 m/s (α ≈ 2.82). In contrast, the deflagration index K_G decreases by ca. 20% for H₂–air and ca. 30% for CH₄–air over the same temperature span. The maximum explosion pressure (P_max) and peak pressure rise rate ((dP/dt)_max) also exhibit systematic increases with temperature. A comparison with model predictions shows agreement within experiments, providing data for safety modeling and kinetic mechanism validation in H₂- and CH₄-based energy systems. Full article

Industrial development and population growth have significantly escalated worldwide energy demand; in addition, the heightened consumption of primary energy sources such as hydrocarbons has profoundly impacted the atmospheric environment. Among all potential fuels, hydrogen provides the most significant advantages for energy supply and environmental sustainability. Nonetheless, the combustion of pure hydrogen has challenges related to its production, storage, and utilization. A more effective approach to improve combustion is to utilize hydrogen as an addition to fossil fuels. Hydrogen possesses numerous characteristics that render it a compelling fuel alternative. It possesses high energy density, offering triple the energy compared to liquefied petroleum gas. This indicates that hydrogen is able to deliver equal power output with reduced fuel usage, thus decreasing the fuel used and, consequently, greenhouse gasses linked to combustion. In this study, practical experiments and computer simulations were adopted to predict the behavior of some characteristics of the combustion of Iraqi liquefied petroleum gas, such as flame temperature and laminar burning velocity, in addition to the effect of changing the equivalence ratio and hydrogen enrichment at rates ranging between 5 and 20% at a constant atmospheric pressure and temperature. In the practical aspect, a counter-flow burner was developed at the Training and Workshops Center, University of Technology, Iraq, for the purpose of performing practical experiments. In addition, a MATLAB R2023b program code was developed based on flame front image frames to analyze data and measure flame parameters, i.e., laminar burning velocity, flame temperature, and flame front diameter. While the commercial CFD Ansys Fluent version 17.2 program was used to numerically simulate the premixed counter-flame, the steady laminar flame (SLF) was used. Also, in order to implement the continuity of the numerical simulation, the momentum and energy equations of the counter-flow burner were solved. The results showed that increasing the hydrogen percentage caused an increase in the laminar burning velocity as well as the flame temperature; when the hydrogen percentage in the mixture was 20%, the increasing percentages in the practical experiments were about 25% and 19.6%, respectively, and the percentages in the numerical simulation were about 22.6% and 20.5%, respectively. Also, changing the equivalence ratio from 0.4 to 1.4 had an effect on the shape, color, and method of flame spread, where at the higher percentage, the shape changed and the color concentration increased, meaning that the temperature rose and the method of spread changed to an irregular one. Additionally, several recommendations are suggested for future endeavors in this domain. Full article

The aim of this work is to provide new experimental data on laminar burning velocities for a new synthetic mixture composed of Camisea natural gas and CO₂. It was found that the relevant published experimental background data are limited to mixtures composed of methane and CO₂; considering the fact that Camisea natural gas is widely used in Peru, this experimental research will serve as a supportive resource for further experimental and industrial implementations in this country, such as the design and modeling of new engines or industrial burners that are designed to be fueled by this mixture. An experimental setup for analyzing three types of flame geometry, which is feasible to implement for a wide range of conditions, was built in PUCP PI0735 laboratory and all the measurements were obtained for a range of mixtures (0%, 21.2%, 28.5%, 38.9%, 50% CO₂) and ratios from around 0.55 to 0.95 at atmospheric conditions. The laminar burning velocities results obtained were analyzed in groups based on %CO₂. In addition, the experimental margin error was determined by considering all the sources. The following conclusions were reached: (1) The laminar burning velocity decreases with the increase in CO₂ percentage in the mixture due to the CO₂ decreasing the flame temperature effect. (2) The flat flame type provided the highest value of burning velocity for each group of CO₂ percentage in which it appears. (3) The highest obtained laminar burning velocity value was 22.64 ± 0.15 cm/s, for a flat flame with a ratio of 0.72 and 29.98% of CO₂, while the lowest obtained value was 6.78 ± 0.15 cm/s for a conical trunk flame with a ratio of 0.59 and 49.83% of CO₂. (4) The highest evaluated CO₂ percentage was 50.97% for a conical trunk flame with a ratio of 0.69 and a burning velocity value of 11.04. Full article

Ammonia is carbon-free and is a very promising renewable fuel. The ammonia/diesel dual-fuel combustion strategy is an important combustion strategy for ammonia internal combustion engines. To achieve clean and efficient combustion with a high ammonia blending ratio in ammonia engines, it is important to thoroughly investigate the combustion characteristics and chemical reaction mechanisms of ammonia/diesel fuel blends. Based on the constant volume combustion vessel experiments, the laminar burning velocities (LBVs) of ammonia/n-heptane blends were measured at the conditions of an ammonia–energy ratio of 60–100%, at initial pressures of 0.1–0.5 MPa and initial temperatures of 338–408 K, and under an equivalence ratio regime of 0.8–1.3. The experimental results indicate that the laminar burning velocities of ammonia/n-heptane fuel blends increase with a decreasing ammonia–energy ratio. Specifically, with an ammonia–energy ratio of 60%, an initial temperature of 373 K, an initial pressure of 0.1 MPa, and an equivalence ratio of 1.1, the measured LBV is approximately 20 cm/s, which is about 61% faster than that of pure ammonia flames under the same conditions. A previously developed chemical kinetic mechanism is employed to simulate the new experimental data, and the model exhibits overall good performance. The sensitivity analyses have been conducted to highlight the important reaction pathways. The elementary reaction O₂ + Ḣ<=>Ö + ȮH demonstrates the most significant promotional effect on the laminar burning velocities, while the interaction reaction pathways of via H-abstraction from n-heptane by ṄH₂ radicals are not showing obvious effects on the simulation results under the studied conditions. Full article

In this work, the overall activation energy of the combustion of lean hydrogen–methane–air mixtures (equivalence ratio $\phi$ = 0.7−1.0 and hydrogen fraction in methane $\alpha =0$, 2, 4) is experimentally determined using thin-filament pyrometry of flames stabilised on a flat porous burner under normal conditions ($p=1$ bar, T = 20 °C). The experimental data are compared with numerical calculations within the detailed reaction mechanism GRI3.0 and both approaches confirm the linear correlation between mass flow rate and inverse flame temperature predicted in the theory. An analysis of the numerical and experimental data shows that, in the limit of lean hydrogen–methane–air mixtures, the activation energy approaches a constant value, which is not sensitive to the addition of hydrogen to methane. The mass flow rate for a freely propagating flame and, thus, the laminar burning velocity, are measured for mixtures with different hydrogen contents. This mass flow rate, scaled over the characteristic temperature dependence of the laminar burning velocity for a one-step reaction mechanism, is found and it can also be used in order to estimate the parameters of the overall reaction mechanisms. Such reaction mechanisms will find implementation in the numerical simulation of practical combustion devices with complex flows and geometries. Full article

Biogas is a gas resulting from the digestion of biomass, which means transforming organic waste into energy. It is composed essentially of methane (CH₄) and carbon dioxide (CO₂) and can also contain ammonia (NH₃) as an impurity. Biogas is generally used to generate electricity or produce heat in a cogeneration system. With the renewed interest in ammonia and the increasing development of biogas caused by the urge for an energetic transition, those two carbon-neutral fuels are being investigated as a mixture in this study through the laminar burning velocity (LBV). In this paper, the LBV of biogas ammonia air mixtures are investigated experimentally for the first time over a wide range of equivalence ratios and ammonia concentrations. The biogas studied was 60% CH₄ and 40% CO₂ in volume. The NH₃ concentration in the fuel varied from 0 to 50% vol. while the equivalence ratio varied from 0.8 to 1.2. The experiments were conducted at constant pressure in a constant volume vessel at 300 K and 1 bar. Adding ammonia to biogas decreases the LBV while the Markstein length is not very sensitive to ammonia addition. The CEU-NH3-Mech-1.1 and Okafor mechanisms show good agreement with the experimental laminar burning velocity. The effect of radiative heat losses on the measurement is also investigated. Full article

Understanding and controlling the combustion of clean and efficient fuel blends, like methane + hydrogen, is essential for optimizing energy production processes and minimizing environmental impacts. To extend the available experimental database on CH₄ + H₂ flame speciation, this paper reports novel measurement data on the chemical structure of laminar premixed burner-stabilized CH₄/H₂/O₂/Ar flames. The experiments cover various equivalence ratios (φ = 0.8 and φ = 1.2), hydrogen content amounts in the CH₄/H₂ blend (X_H2 = 25%, 50% and 75%), and different pressures (1, 3 and 5 atm). The flame-sampling molecular-beam mass spectrometry (MBMS) technique was used to detect reactants, major products, and several combustion intermediates, including major flame radicals. Starting with the detailed model AramcoMech 2.0, two reduced kinetic mechanisms with different levels of detail for the combustion of CH₄/H₂ blends are reported: RMech1 (30 species and 70 reactions) and RMech2 (21 species and 31 reactions). Validated against the literature data for laminar burning velocity and ignition delays, these mechanisms were demonstrated to reasonably predict the effect of pressure and hydrogen content in the mixture on the peak mole fractions of intermediates and adequately describe the new data for the structure of fuel-lean flames, which are relevant to gas turbine conditions. Full article

Ammonia (NH₃) is considered a promising zero-carbon fuel and was extensively studied recently. Mixing high-reactivity oxygenated fuels such as dimethyl ether (DME) or dimethoxymethane (DMM) with ammonia is a realistic approach to overcome the low reactivity of NH₃. To study the combustion characteristics of NH₃/DMM and NH₃/DME mixtures, we constructed a NH₃/DMM chemical mechanism and tested its accuracy using measured laminar burning velocity (LBV) and ignition delay time (IDT) of both NH₃/DMM and NH₃/DME mixtures from the literature. The kinetic analysis of NH₃/DMM flames using this mechanism reveals that the CH₃ radicals generated from the oxidation of DMM substantially affects the oxidation pathway of NH₃ at an early stage of flame propagation. We investigated the formation of nitrogen oxides (NO_x) in NH₃/DMM and NH₃/DME flames and little difference can be found in the NO_x emissions. Using NH₃/DMM flames as an example, the peak NO_x emissions are located at an equivalence ratio ($\phi$) of 0.9 and a DMM fraction of 40% in the conditions studied. Kinetic analysis shows that NO_x emission is dominated by NO, which primarily comes from fuel nitrogen of NH₃. The addition of DMM at 40% significantly promotes the reactive radical pool (e.g., H, O, and OH) while the maintaining a high concentration of NO precursors (e.g., HNO, NO_2, and N₂O), which results in a high reaction rate of NO formation reaction and subsequently generates the highest NO emissions. Full article

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. Full article

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. Full article

The present work aims to evaluate the performance of the constant-volume method by several sets of experiments carried out in three different closed vessels (a sphere and two cylinders) analyzing the obtained results in order to obtain accurate laminar burning velocities. Accurate laminar burning velocities can be used in the development of computational fluid dynamics models in order to design new internal combustion engines with a higher efficiency and lower fuel consumption leading to a lower degree of environmental pollution. The pressure-time histories obtained at various initial pressures from 0.4 to 1.4 bar and ambient initial temperature were analyzed and processed using two different correlations (one implying the cubic low coefficient and the other implying the burnt mass fraction). The laminar burning velocities obtained at various initial pressures are necessary for the realization of a complete kinetic study regarding the combustion reaction and testing the actual reaction mechanisms. Data obtained from measurements were completed and compared with data obtained from runs using two different detailed chemical kinetic mechanisms (GRI 3.0 and Warnatz) and with laminar burning velocities from literature. Our experimental burning velocities ranging from 35.3 cm/s (data from spherical vessel S obtained using the burnt mass fraction) to 37.5 cm/s (data from cylindrical vessel C1 obtained using the cubic law) are inside the interval of confidence as reported by other researchers. From the dependence of the laminar burning velocity on the initial pressure, the baric coefficients were obtained. These coefficients were further used to obtain the overall reaction orders. The baric coefficients (ranging between −0.349 and −0.212) and the overall reaction orders (ranging between 1.42 and 1.50) obtained in this study fall within the reference range of data specific to methane–air mixtures examined at ambient initial temperature. Full article

Combustion and explosion of combustible mixtures are a major hazard that can occur anywhere from industry to energy use in households and, therefore, protective measures must be taken to limit these undesirable events. This study pays attention to the laminar burning velocity, an important parameter involved in the combustion process. The experimental laminar burning velocities of stoichiometric methane-nitrous oxide mixtures in the presence of diluents (50 vol% inerts: argon, helium, and carbon dioxide) were calculated from pressure-time records obtained in a spherical vessel with central ignition, using a correlation based on the cubic law of pressure rise during the early stage of explosion. The nitrous oxide (N2O)-based mixtures are frequently used as propellants in propulsion systems and supersonic wind tunnels, due to the nontoxicity, high saturation pressure, and the exothermic property during decomposition. However, N2O is an oxidizer that can cause safety concerns in technical applications where it is involved. The experimental data were compared with data from the literature on stoichiometric methane-nitrous oxide mixtures diluted with nitrogen and with the calculated laminar burning velocities obtained by numerical modelling of their premixed flames. The modelling was performed with Cosilab package, using GRI 3.0 mechanism, based on 53 chemical species and 325 elementary reactions. The influence of initial pressure (0.5 bar–1.75 bar) of stoichiometric inert-diluted methane-nitrous oxide mixtures on laminar burning velocities, maximum flame temperature, heat release rate, and peak concentrations of main reaction intermediates was investigated and discussed. Using the correlations of the laminar burning velocities with the initial pressure, the pressure exponent and overall reaction order of methane oxidation with nitrous oxide were determined. Obtaining a clear perspective on the laminar burning velocities of these flammable mixtures is of great importance for both assessing fire and explosion risks and guaranteeing safety in chemical and process industries. Full article

This paper explores the effects of root-mean-square turbulence fluctuation velocity (u′) and ignition energy (E_ig) on an ignition kernel delay time (τ_delay) of lean premixed n-butane/air spherical flames with an effective Lewis number Le ≈ 2.1 >> 1. Experiments are conducted in a dual-chamber, fan-stirred cruciform burner capable of generating near-isotropic turbulence with negligible mean velocities using a pair of cantilevered electrodes with sharp ends at a fixed spark gap of 2 mm. τ_delay is determined at a critical flame radius with a minimum flame speed during the early stages of laminar and turbulent flame propagation. Laminar and turbulent minimum ignition energies (MIE_L and MIE_T) are measured at 50% ignitability, where MIE_L = 3.4 mJ and the increasing slopes of MIE_T with u′ change from gradual to drastic when u′ > 0.92 m/s (MIE transition). In quiescence, a transition of τ_delay is observed, where the decrement of τ_delay becomes rapid (modest) when E_ig is less (greater) than MIE_L. For turbulent cases, when applying E_ig ≈ MIE_T, the reverse trend of MIE transition is found for τ_delay versus u′ results with the same critical u′ ≈ 0.92 m/s. These results indicated that the increasing u′ could reduce τ_delay on the one hand, but require higher E_ig (or MIE_T) on the other hand. Moreover, the rising of E_ig in a specific range, where E_ig ≤ MIE, could shorten τ_delay, but less contribution as E_ig > MIE. These results may play an important role to achieve optimal combustion phases and design an effective ignition system on spark ignition engines operated under lean-burn turbulent conditions. Full article

This paper presents the experimental and numerical study of the laminar burning velocity and pollutant emissions of the mixture gas of methane and carbon dioxide. Compared to previous research, a wider range of experimental conditions was realized in this paper: CO₂ dilution level up to 60% (volume fraction) and equivalence ratio of 0.7–1.3. The burning velocities were measured using the heat flux method. The CO and NO emissions after premixed combustion were measured by a gas analyzer placed 20 cm downstream of the flame. The one-dimensional free flames were simulated using the in-house laminar flame code CHEM1D. Four chemical kinetic mechanisms, GRI-Mech 3.0, San Diego, Konnov, and USC Mech II were used in Chem1D. The results showed that, for laminar burning velocity, the simulation results are all lower than the experimental results. GRI Mech 3.0 showed the best agreement when the CO₂ content was below 20%. USC Mech II showed the best consistency when the CO₂ content was between 40 and 60%. For CO emission, these four mechanisms all showed a small error compared with the experiments. When CO₂ content is higher than 40%, the deviation between simulation and experiment becomes bigger. When the CO₂ ratio is more than 20%, the proportion of CO₂ does not affect CO emission so much. For NO emission, when the CO₂ content is 40%, the results from simulation and experiment showed a good agreement. As the proportion of CO₂ increases, the difference in NO emissions decreases. Full article

Within this work the effects of blending oxymethylene ethers (OME_n) to a diesel surrogate (50 mol% n-dodecane, 30 mol% farnesane, and 20 mol% 1-methylnaphthalene) were investigated by performing two different types of experiments: measurements of the sooting propensity and of the laminar burning velocity, each in laminar premixed flames. For the sooting propensity, OME₃, OME₄, and OME₅ were considered as blending compounds—each in mass fractions of 10%, 20%, and 30%. The sooting propensity was found to depend strongly on the OME_n blending grade but not on its chain length. In addition, the effect on the laminar burning velocity was studied for OME₄ and the admixture of 30% OME₄ with diesel surrogate for the first time. This admixture was found to lead to increased burning velocities; however, much less than might be foreseen when considering the respective values of the neat fuels. Full article