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This paper investigates the combustion dynamics of interacting lazy multi-component gas plumes (i.e., buoyancy-dominated gas releases with a low initial momentum flux), a configuration relevant to coal mining waste emissions. By coupling a three-dimensional large eddy simulation (mesh size of 10−2 m; paralleling with 2048 processors) with detailed chemical kinetics (GRI-Mech 3.0), we analyzed the sensitivity of the flow structure and plume stabilization to the vent spacing of twin hydrogen-rich multi-component gas plumes (H2-CO-CH4-air). The results identified a distinct topological transition. While gas plumes from vents spaced at δ/D=5 (δ and D are the spacing and width of gas vents, respectively) evolve independently, those at closely spaced sources (δ/D=5/4) exhibit rapid coalescence driven by hydrodynamic shielding. This hydrodynamic merging results in a unified column with an effective hydraulic diameter of Deff≈2D. This leads to a significant reduction in the surface-to-volume ratio available for ambient air entrainment, maintaining a coherent combustible-rich core to higher altitudes than isolated-source correlations would predict. However, despite this mass retention, the rapid vertical acceleration of buoyancy-dominated flows induces high strain rates, significantly disrupting the reaction zone structure. These findings establish that, for clustered emission sources, the dispersion hazard is governed by a coupling between hydrodynamic coalescence, which maintains reactant concentration, and finite-rate chemistry, restricting oxidation efficiency. This paper provides critical insights for designing gas capture infrastructure and assessing flammability limits in multi-vent systems.

Bifurcation of the characteristic cells into multiple smaller cells and decay of those cells into single large characteristic cell is observed frequently. In the present study the bifurcation phenomenon of the detonation front is investigated for marginally unstable detonations using decomposition technique. Numerical analysis is carried out with detailed chemical kinetics for detonation propagation in H2/O2 mixtures at 10 kPa. The dynamic characteristics of the instability at the detonation front, such as the local oscillation frequency and the coherent spatial structure of the oscillation are also studied with dynamic mode decomposition (DMD) technique. The coherent structures of the primary and secondary detonation cells are analyzed during the cell bifurcation process and the mechanism in which the secondary cells are formed is investigated. It is demonstrated that the modal analysis categorizes the instability phenomena clearly and can be effectively utilized to identify the origin and source of the instability.

In this work, the overall activation energy of the combustion of lean hydrogen–methane–air mixtures (equivalence ratio φ = 0.7−1.0 and hydrogen fraction in methane α=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.

The increased energy demand and restrictions regarding pollutant emissions have sparked the search for different renewable energy sources, as well as for the improvement of thermal processes, with a focus on reducing the consumption of fossil fuels. Renewable gaseous fuels seem to be a promising alternative for solving this issue, along with the different high-efficiency, low-emissions technologies that operate at low and moderate temperatures (600-1000 K). However, the implementation of these approaches is limited by the autoignition phenomenon and the different difficulties in predicting its occurrence in the aforementioned operation range. To identify the reasons for this fact, we carried out a review of the different research works conducted in the field. It was evidenced that most studies focus on performing adjustment processes that require prior experimentation. This allowed identifying the need to conduct a research work focused on the autoignition phenomenon in the low and moderate temperature range while using renewable gaseous fuels, as well as on improving the predictive models for calculating ignition delay times. El aumento en la demanda energética y las restricciones respecto a la emisión de contaminantes han suscitado la búsqueda de diferentes fuentes de energía renovables, así como del mejoramiento de los procesos térmicos enfocados en reducir el consumo de combustibles fósiles. Los combustibles renovables gaseosos se muestran como una alternativa útil para resolver este problema, al igual que diferentes tecnologías de alta eficiencia y bajas emisiones que operan a temperaturas bajas y medias (600-1000 K). Sin embargo, la implementación de estos enfoques se ve limitada por el fenómeno de autoignición y las diferentes dificultades para predecir su aparición en el mencionado rango de operación. Para identificar las razones de este último hecho, se llevó a cabo una revisión de los diferentes trabajos de investigación realizados en el área. Se evidenció que la mayoría de los estudios se centran en realizar procesos de ajuste que requieren una experimentación previa. Lo anterior permitió identificar la necesidad de llevar a cabo una investigación enfocada en el fenómeno de autoignición en el rango de bajas y medias temperaturas usando combustibles renovables gaseosos y en el mejoramiento de los modelos predictivos para el cálculo del tiempo de retraso de la ignición.

Molecular beam mass spectrometry was used to measure mole fraction profiles of the reactants, major reaction products and intermediates, including precursors of polycyclic aromatic hydrocarbons, in a premixed fuel-rich (equivalence ratio of 1.75) n-heptane/toluene/O2/Ar flame stabilized on a flat burner at atmospheric pressure. The ratio of the liquid volumes in the n-heptane/toluene mixture was 7: 3. The chemical structure of the flame was modeled using a detailed mechanism of chemical reactions tested against experimental data of other authors on n-heptane/toluene flames and comprising the reactions of formation of polycyclic aromatic hydrocarbons. The mechanism was extended with cross-reactions involving derivatives of n-heptane and toluene. Overall, the new experimental data are in satisfactory agreement with the numerical simulation results; however, there are differences between the measured and calculated mole fraction profiles of some species. Analysis shows that in the n-heptane/toluene flame, the main reactions leading to the formation of low-aromatic compounds (benzene and phenyl) are reactions typical of the pure toluene flame.

This study was performed to predict numerically the homogeneous combustion characteristics where the fuel combustion mechanism was modified in a DME fueled CI engine. To achieve this, detailed chemical kinetic reaction mechanisms were used for the prediction of homogeneous combustion of hydrocarbon fuels (diesel and DME). The results were compared in terms of cylinder pressure, heat release rate, and CO and NO X emissions. Calculations were performed using the detailed chemical kinetic mechanism, including 671 species and 2933 reactions for n-heptane (n-C 7 H 16 ) and 96 species and 453 reactions for dimethyl ether (CH 3 OCH 3 ). In addition, a modified NO X mechanism was added to investigate the accumulated results of NO X production. The engine experiments were conducted using a single cylinder CI engine with a common-rail injection system. The fuel injection quantity was set to 8 mg, and the injection pressure was maintained at 50 MPa at 1500 RPM. In this study, DME and diesel fuels were injected for inducing the homogeneous combustion at BTDC 60 and BTDC 40 degree. The modified mechanism hardly affected the overall chemical reactions, which was almost identical in comparison to the results of the conventional mechanism. In addition, the ignition delay was slightly faster in the calculation of the n-heptane mechanism because it showed that a high reaction rate was involved in the fuel oxidation and reaction of the NTC region. The combustion and exhaust emission characteristics of the homogeneous combustion simulation were in good agreement with the engine experimental results at BTDC 60 degree of injection timing, but the CO emission was over predicted when the n-heptane mechanism was employed in the DME combustion simulation. The chemical reactions of the DME combustion process were dominated by the forward reaction, which were CH 3 OCH 3 +O→CH 3 OCH 2 +OH and CH 3 OCH 3 +OH→CH 3 OCH 2 +H 2 O reactions. Furthermore, this study confirmed that an increase of OH radicals promotes the fuel oxidation reaction, and it can influence the combustion temperature, which also affected the processes of NO X production and CO oxidation reactions.

The L, H and C curves in P-T phase are proposed to describe the minimal, maximal and critical characteristics of ignition time of H2/O2 combustion system, respectively. The features of H2/O2(Air) combustion system, including explosion or not as well as the time delay to achieve its explosion status, can be well shown by explosion limits and these proposed curves. These curves can be described by 1.2k1=ks[Ms], (k11/k10+1)k1=ks[Ms], and 2k1=ks[Ms], respectively, which provide a physical explanation for these curves and give another way to establish them. Based on the contour of ignition time, the Z-type explosion limits can be explained by thermal explosion theory. Furthermore, the ignition distance of supersonic combustion is predicted according to the ignition time obtained in a Semenov system, which is very reasonable.

The present study reported an updated reduced chemical kinetic model for PAHs formation in the nheptane combustion. The detailed reaction mechanism (including 101 species and 544 reactions) of the ethane combustion in modeling polycyclic aromatic hydrocarbon (PAHs) formation is reduced by adopting net reaction rate analysis and sensitivity analysis, and a reduced mechanism (including 52 species and 83 reactions) is developed. The formation of PAHs in the ethane premixed combustion is simulated using this reduced mechanism. The computational results for the species mole fractions distributions of the main reactants and main products using this reduced mechanism agree with experimental data. Furthermore, incorporating the reaction mechanism of n-heptane destruction and oxidation (including 27 species and 36 reactions) into this reduced mechanism, a reduced mechanism of PAHs formation in n-heptane flame (including 62 species and 119 reactions) is developed. The formation of PAHs in n-heptane partially premixed combustion is simulated using this reduced mechanism. The computational results for temperature profile, the species mole fractions distributions of the main reactants and main products using this reduced mechanism agree with measurements.

Predictions based on detailed reaction mechanisms indicate a decreasing ignition delay time with increasing hydrogen content for methane/hydrogen, and carbon monoxide/hydrogen mixtures. This is more pronounced in the high-temperature region (T > 1000 K). In methane/ hydrogen blends, a decreasing ignition delay time with increasing pressure was predicted, whereas a reverse trend was observed for carbon monoxide/hydrogen blends for temperatures between 900 and 1200 K. Ignition delay time shows an increasing trend with increasing equivalence ratio, which is, however, rather mild. For standard, non-reheat gas turbine applications, autoignition at rather low temperatures is of interest. In this region, measurements show a quite large spread, depending on the experimental conditions. Plug flow reactor calculations are observed to deliver quite different results depending on the detailed reaction mechanisms used, which may also be different from the measurements. Thus, for the estimation of the ignition time, correlations based on “relevant” experimental data may be favored to detailed kinetics calculations.

To identify promising sustainable fuels, e.g., to select novel synthetic fuels with the greatest impact on minimizing global warming, new methods for rapid and economical technical fuel assessment are urgently needed. Here, numerical models that are capable of predicting technical key data quickly and without experimental setup are necessary. One method is the use of chemical kinetic models, which are able to predict the technical key parameters related to combustion behavior. For a rapid technical fuel assessment, these chemical kinetic models need to be validated for new fuel components and for different temperature and pressure ranges. This work presents a new approach to extend the existing semi-detailed chemical kinetic models. For the application of the approach, the semi-detailed reaction mechanism DLR Concise was selected and extended for the low temperature combustion modeling of n-heptane and isooctane. The open-source software reaction mechanism generator (RMG) was used for this extension. Furthermore, an optimization of the merged chemical kinetic model with the linear transformation model (linTM) was conducted in order to improve the reproducibility of ignition delay times. The improvement of the predictive performance of ignition delay times at low temperatures for both species was successfully demonstrated. Therefore, this approach can be used to quickly add new species or reaction pathways to an existing semi-detailed reaction mechanism to enable a model-based technical fuel assessment for the early identification of promising fuels.