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With the development of hydrogen fuel cell vehicles, hydrogen refuelling stations are required to operate at a higher pressure. However, the safety issue of high pressure hydrogen is always considered as the barrier of the wide application of such transportation infrastructures. In this paper, the safety evaluation is performed on a 70 MPa hydrogen dispenser, as one of the most vulnerable equipment to safety events in hydrogen refuelling stations. The numerical simulations are conducted for the hydrogen leakage and combustion for the prototype of the dispenser. The results show the high radiation during the combustion, and the environmental wind can reduce it by promoting the diffusion of hydrogen. Accordingly, the lethal ranges in different cases are manifested by radiation heat flux at the concerned height for the safety of humans. Furthermore, an improved design of the hydrogen dispenser is proposed to cancel the lower ventilation holes based on the analysis. As a result, the radiation heat fluxes due to the hydrogen combustion after leakage is significantly reduced and consequently lead to smaller lethal ranges, indicating the enhanced safety performance of the hydrogen dispenser. • A numerical study is conducted for the hydrogen combustion from a 70 MPa hydrogen dispenser. • The safety distance is evaluated for hydrogen leakage and combustion of dispensers under different wind conditions. • An improved design of the hydrogen dispenser is proposed and proved to be effective in enhancing the safety performance. [ABSTRACT FROM AUTHOR]

The secondary combustion between unburnt fuel in rocket plume and ambient air significantly affects the stealth characteristics of rocket motors. In order to reveal the effect of secondary boundary layer combustion of hydrogen on rocket plume heat release characteristics, a two-dimensional axisymmetric model for boundary layer combustion between the rocket plume and air is established. The results identifies significant exothermic effect due to secondary combustion reaction between the plume and air. Compared to the nozzle plume without considering secondary combustion, the average temperature of the plume with secondary combustion increases by 47%. As hydrogen content in the nozzle plume increases from 2.7% to 4.2%, the average temperature of the nozzle plume increases by 17.2% due to enhanced combustion heat release. The secondary combustion process is weakened with the increase of flight altitude. The average temperature of the nozzle plume decreases by 11.8% from 2 km to 8 km of flight altitude. This is because both the pressure and temperature of the ambient air decrease when the flying altitude rises, which leads to lower secondary combustion reaction and heat release rate. Moreover, as the ambient pressure decreases, the hydrogen concentration in the plume decreases due to plume expansion effect. The results indicate that hydrogen content and flight altitude affect secondary combustion by different mechanisms. The hydrogen content directly affects the concentration term of the reaction rate of secondary combustion. However, the flight altitude affects the kinetic rate of secondary combustion by changing both the temperature and partial pressure of oxygen. The present study provides better insight into the interaction mechanism between nozzle plume and ambient air. • Established numerical model for secondary combustion of rocket plume. • Higher hydrogen content enhances secondary combustion process. • Secondary combustion heat release is weakened as flight altitude increases. • Secondary combustion is controlled by shear mixing and heat transfer. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2) has been regarded as the most promising sustainable energy. Reliable numerical prediction of its combustion is one of the vital steps towards an ultra-clean energy system. This work was intended to examine the preferential diffusion (PD), which is a major feature of the H 2 fuel, using the Flamelet-Generated Manifold (FGM) combustion model. The major focuses were on the reduced treatment of the PD effects and the impacts on turbulent flame modelling with and without H 2 addition. It is found that the PD hardly influences the velocity prediction even with H 2 enrichment, which can be well modelled merely using a unity L e assumption. The quick burning of H 2 can be captured only when the PD effects are included, which is observed to reinforce the burning intensity near the flame root. The PD terms in the control variable equations are found to be less dominant and the by-effects are twofold: (1) the performance of different reduced PD models is validated to be close; (2) ignoring the PD terms and including the PD effects only in the flamelet-tabulation are acceptable. Nevertheless, for scalar predictions in the recirculation zone, preserving the PD terms is found to be essential. It is observed that a more complete PD model can increase the computation cost up to 11%, but a reduced method can save nearly a half of the cost increment. These observations are significant for accurate and efficient treatment of the PD effects in the turbulent flame simulation. • Different reduced preferential diffusion models in FGM are compared. • Preferential diffusion effects influence little on velocity prediction. • Preferential diffusion is essential to model the quick burning of H 2. • Preferential diffusion terms are negligible if without recirculation zone. • Including preferential diffusion only in flamelet-tabulation is acceptable. [ABSTRACT FROM AUTHOR]

Oil shale is a critical strategic resource with enormous reserves. In-situ combustion technology offers great potential for the development of oil shale reserves. In this study, the combustion behavior and kinetics of Domanik oil shale were investigated using High Pressure Differential Scanning Calorimetry. Additionally, the thermal behavior of the oil shale during combustion was studied by using a self-designed Porous Medium Thermo-Effect Cell. Furthermore, the stability of the combustion front and the upgrading effect of the combustion process were investigated with Visual Combustion Tube, and the produced oil was analyzed to evaluate its quality. The results showed that the combustion process of oil shale is characterized by two reaction stages. The oil shale was found to form enough coke residue during the oxidation reactions to allow for stable propagation of a combustion front. The produced oil was of better quality compared to the naturally produced bitumen in oil shale, which indicates that the combustion process had a good upgrading effect. The findings of this study provide a better understanding of the in-situ upgrading process of kerogen and provide significant knowledge about the combustion mechanism of oil shale for its potential development using the in-situ combustion technology. [ABSTRACT FROM AUTHOR]

One strategy for utilizing ammonia as an energy vector is to replace conventional hydrocarbons with hydrogen-enriched ammonia in existing or retrofitted combustors. However, the strong differential diffusion effect of hydrogen can significantly alter the combustion properties and cause challenges in combustor operability. Therefore, this numerical study performs a systematic investigation on the effect of differential diffusion on fundamental combustion properties of ammonia/hydrogen fuel blends. The investigated combustion properties span from the initiation of combustion, i.e., ignition, to stretched flame propagation and ultimately to flame stabilization mechanisms. The objective is to evaluate the feasibility of hydrogen/ammonia/air mixtures as substitutes for methane/air particularly considering the implications of differential diffusion effects. To this end, four fuel blends with similar unstretched burning properties are selected: fuel lean ammonia/hydrogen (AH-L), fuel rich ammonia/hydrogen (AH-R), fuel lean methane (M-L) and fuel lean methane/hydrogen (MH-L). First, the forced ignition and stretched flame propagation are evaluated. It is found that the AH-L (AH-R) mixture has a large negative (positive) Markstein length, and thereby among the selected fuel blends, AH-L (AH-R) has the lowest (highest) minimum ignition energy. Then flame stabilization mechanisms are investigated. For a stable flame, AH-L (AH-R) has an intensified (weakened) flame base and a weak (strong) flame tip, which shows a higher flashback (blow-off) propensity. Based on the critical gradient theory, a novel stability regime diagram is proposed. With the regime diagram, the flame stabilization limits (central flashback, boundary layer flashback, stable, and blow-off) and flow conditions can be determined for burners of different sizes. [Display omitted] • Feasibility of H 2 /NH 3 as a substitute fuel for CH 4 was evaluated (4 blends with equal s L 0). • A systematic analysis on ignition, flame propagation and stabilization was performed. • The rich (lean) H 2 /NH 3 mixture is more difficult (easier) to ignite than CH 4 mixture. • The rich (lean) H 2 /NH 3 flame is more prone to blow-off (flashback) than CH 4 mixture. • A flame stability regime diagram based on critical gradient theory was proposed. [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]

Ammonia is considered one of the most promising fuels, and mixing ammonia with hydrogen as fuel can achieve zero carbon emissions for engines. In this study, an experimental platform for an ammonia/hydrogen rotary engine was constructed, and successful ignition combustion was performed, demonstrating the possibility of the ammonia/hydrogen rotary engine. A 3-dimensional computational model of the ammonia/hydrogen rotary engine coupled with chemical reaction mechanisms was established, and the dependability of the model was confirmed using experimental data. Using numerical simulations, the impact of hydrogen injection position and time on the distribution of the fuel-air mixture, the propagation of flames, and the emissions of NO X in the cylinder under direct hydrogen injection have been studied. The research shows that the injection position and timing of hydrogen can affect airflow movement by changing the impingement angle and cylinder swirl intensity to alter hydrogen distribution in the cylinder under the guidance of the cylinder wall. Furthermore, with a delay in hydrogen injection timing, the turbulence kinetic energy in the cylinder gradually increases and is consistently more significant than that under premixed conditions, with turbulence kinetic energy in Case B-190 approximately 60% higher than that under premixed conditions. When more hydrogen is around the spark plug, the initial flame kernel is formed faster, resulting in a notable acceleration of the fuel-air mixture's combustion rate within the cylinder. In contrast to alternative hydrogen injection strategies, the injection strategy that employs nozzle A and an injection timing of 230°CA (BTDC) can achieve the highest cylinder pressure and lower NO X emissions. • A CFD computational model of ammonia/hydrogen rotor engine was established and validated. • Hydrogen has a greater impact on the flame development compared to ammonia. • Direct injection of hydrogen enhances the turbulent kinetic energy within the cylinder. • Optimizing the direct injection method of hydrogen can effectively reduce the emission of NOx. [ABSTRACT FROM AUTHOR]

Drop-in fuels for aviation gas-turbine engines have been introduced recently to mitigate global warming. Despite their similarity to the fossil fuel Jet A-1, their combustion in traditional combustors should be thoroughly analyzed to maintain engine health and low emissions. The paper introduces criteria for assessing the impact of the chemical composition of fuels on combustion in the DEGN 380 turbofan. Based on previous emission-test results, the power functions of carbon monoxide and its emission index were adopted as the model of combustion. Based on the general notation of chemical reactions leading to the production of CO in combustion, the regression coefficients were given a physical meaning by linking them with the parameters of the kinetic equations, i.e., the reaction rate constant of CO and CO2 formation expressed as exponential functions of combustor outlet temperature and the concentration of O2 in the exhaust gas, as well as stoichiometric combustion reactions. The obtained empirical functions show that, in the entire range of engine operating parameters, synthetic components affect the values of the rate constants of CO and CO2 formation. It can be explained by the change in activation energy determined for all chain-of-combustion reactions. The activation energy for the CO formation chain changes in the range between 8.5 kJ/mol for A0 and 24.7 kJ/mol for A30, while for the CO2 formation chain between 29.8 kJ/mol for A0 and 30.8 kJ/mol for A30. The reactivity coefficient lnαiCOACODCO changes between 2.29 for A0 and 6.44 for A30, while lnαiCO2ACO2DCO2 changes between 7.90 for A0 and 8.08 for A30. [ABSTRACT FROM AUTHOR]

The simulation of engine combustion processes, such as autoignition, an important process in the co-optimization of fuel-engine design, can be computationally expensive due to the large number of thermo-chemical scalars needed to describe the full chemical system. Yet, the inherent correlations between the different chemical species during oxidation can significantly reduce the complexity of representing this system. One strategy is to select a subset of representative species that accurately captures the combustion process at a fraction of the computational cost of the full system. In this study, we compare the performance of four different techniques to select these species. They include the two-step principal component analysis (PCA) approach, directed relation graphs (DRGs), the global pathway selection (GPS) approach, and the manifold-informed species selection method. A parametric study of the representative species selection is carried out on data from the simulation of homogeneous and perfectly stirred reactors by investigating seven cumulative variances and 47 different cut-off percentages for the two-step PCA, and 65 and 51 thresholds for the DRGs and GPS, respectively. Results show that these selection methods capture key important species that can accurately describe the chemical system and track each stage of oxidation. The two-step PCA is sensitive to the cumulative variance, and DRGs and GPS are sensitive to the choice of target variables. By selecting key representative species and reducing the number of thermo-chemical scalars, these three methods can be used to develop computationally efficient hybrid chemistry schemes. [ABSTRACT FROM AUTHOR]

Studying the relationship between electronic structure and activity helps to understand the catalytic mechanism since the catalytic combustion is a redox reaction dominated by electron transfer. Herein, we regulated the electron energy and O p-band center of La-based perovskite catalysts by a facile method of changing the B-site ion (B = Co, Mn, Fe). The crystal structure, morphology, reducibility, element valence distribution, and catalytic properties of prepared catalysts were characterized. Combining with DFT calculation, it was found that the low electron energy in (110) facets of LaCoO3/SiO2 catalyst contributes to the formation of reactive oxygen species and high-valence Co3+ ions. The highest oxygen adsorption activation capacity of LaCoO3/SiO2 originates from a moderate location of the O p-band center with respect to the Fermi level. As expected, the LaCoO3/SiO2 sample shows higher n-butylamine oxidation activity than that of LaMnO3/SiO2 and LaFeO3/SiO2. This work provides different insights into understanding the activity of La-based perovskite catalysts for oxidation reactions. [ABSTRACT FROM AUTHOR]

Methylcyclohexane (MCH) is the simplest alkylated cyclohexane, and has been widely employed in surrogate models to represent the cycloalkanes in real fuels. Thus, extensive experimental and kinetic modeling studies have been performed to understanding the combustion chemistry of MCH. However, through a detailed literature analysis, there still lack a systematic theoretical study on the abstraction reactions of MCH, which are the main initial oxidation pathway of MCH. Herein, this work reports a systematic ab initio chemical kinetic study on the abstraction reactions of MCH with different radicals/species. Specifically, reaction rate constants of 30 abstraction reactions of MCH with H/O/OH/O2/HO2/CH3 at different sites are computed using transition state theory (TST) by using quantum chemistry calculation results at DLPNO‐CCSD(T)/CBS//M06‐2X/cc‐pVTZ level. The computed results are incorporated into a detailed mechanism to simulate newly measured ignition delay times (IDTs) of MCH in this work at equivalence ratios of 0.5, 1.0, and 2.0, pressures of 2 and 5 bar, temperatures ranging from 1140 to 1640 K. The updated detailed mechanism demonstrates improvement in the prediction of IDTs, especially at fuel‐rich conditions. The fuel concentration and dilution effect on the IDTs are discussed, and a general Arrhenius expression is adopted to fit the IDTs from both this work and literature work. This work should be valuable for further optimization of detailed kinetic mechanisms and also for gaining insight into the combustion chemistry of MCH. [ABSTRACT FROM AUTHOR]

This study explores the transition in combustion technologies from dry micro-mix hydrogen-air to wet micro-mix hydrogen-oxygen configurations. The investigation involves a comprehensive analysis of the combustion processes currently being considered for converting methane gas turbines to methane-hydrogen mixtures and hydrogen, including wet premixed, dry low emission, sequential combustion, and micro-mix, examining key parameters such as efficiency, emissions, and overall performance. Then, the work considers the shift from utilizing air as an oxidizer to oxygen. Wet micro-mix hydrogen-oxygen combustion is then discussed for its impact on combustion dynamics and the potential for achieving zero emissions, cancelling NOx emissions in addition to CO 2 emissions. The findings contribute valuable insights into the feasibility and advantages of transitioning from conventional hydrogen-air combustion to innovative wet hydrogen-oxygen combustion, paving the way for more sustainable and environmentally friendly combustion technologies. Scheme of a hydrogen energy storage system comprising one electrolyser, two tanks for the hydrogen and the oxygen, and an O 2 /H 2 /H 2 O gas turbine power system. The system could be able to receive non-dispatchable electricity and release dispatchable electricity working as a battery but without any limitation on the amount of energy storable, or the time of the storage. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of nano-energetic materials has significantly advanced, leading to enhanced properties and novel applications in areas such as aerospace, defense, energy storage, and automobile. This research aims to engineer multi-dimensional nano-energetic material systems with precise control over energy release rates, spatial distribution, and temporal and pressure history. In this context, sol–gel processing has been explored for the manufacture of nanocomposite aluminum thermites using aerogels. The goal is to produce nano-thermites (Al/Fe2O3) with fast energy release rates that are insensitive to unintended initiation while demonstrating the potential of sol–gel-derived aerogels in terms of versatility, tailored properties, and compatibility. The findings provide insightful conclusions on the influence of factors such as secondary oxidizers (KClO3) and dispersants (n-hexane and acetone) on the reaction kinetics and the sensitivity, playing crucial roles in determining reactivity and combustion performance. In tandem, ignition systems contribute significantly in terms of a high degree of reliability and speed. However, the advantages of using nano-thermites combined with hot bridge-wire systems in terms of ignition and combustion efficiency for potential, practical applications are not well-documented in the literature. Thus, this research also highlights the practicality along with safety and simplicity of use, making nano-Al/Fe2O3-KClO3 in combination with hot bridge-wire ignition a suitable choice for experimental purposes and beyond. [ABSTRACT FROM AUTHOR]

A nanostructure of lithium-zinc copper ferrite (LiZnCu-Ferrite) prepared experimentally by the auto-combustion method depends on different parameters. The auto-combustion method operates at a temperature (160 °C) suitable for preparing the required nanostructure ferrite phase. The dependent composition was [Li 0.5-x Zn x Cu x Fe 2.5-x O 4 at (x = 0, 0.05, 0.15, 0.25, 0.35, and 0.45)]. A pre-firing at temperature (650 °C) was applied during the calcination process that was suitable to remove unwanted products. The sintering at temperature (800 °C) was suitable for a pelletized shape of ferrite samples. The X-ray diffraction (XRD) pattern showed a spinel structure of ferrite phase produced for all samples under study with the lattice constant in the range (8.345–8.368 Å) as a function of (x). The crystallite size was in the range (18.41–30.27 nm) calculated by the Scherrer method. The transmission electron microscope (TEM) showed a production of nanorods in the size range (10–45 nm) and nanoparticles in the size range (10–40 nm). There was a coincidence between the results of the XRD and TEM analyses. On the other hand, the scanning electron microscope (SEM) showed the surface morphology and the nature of grain size, which was a sign of the presence of nanostructure; it agreed with the XRD analysis. FTIR spectra showed evidence that the system Li0.5-xZnxCuxFe2.5-xO4 had spinal ferrite nanoparticles successfully prepared by sol-gel auto-combustion. A vibrating sample magnetometer (VSM) showed a change in magnetic parameters as compensation factor (x) increased for all composites of LiZnCu-ferrite such as saturation magnetization (Ms), initial magnetic permeability (μi), remanence (Mr), and coercive force (Hc) that measured from M − H loops. A saturation magnetization increased as a function of (x) and recorded a maximum value at (x = 0.15). While the coercivity, initial magnetic permeability (μi), and remanence magnetization enhanced as a function of (x) and recorded a maximum value at (x = 0.45). [ABSTRACT FROM AUTHOR]

Fugitive methane emissions account for a significant proportion of greenhouse gas emissions, and their elimination by catalytic combustion is a relatively easy way to reduce global warming. New and novel reactor designs are being considered for this purpose, but their correct and efficient design requires kinetic rate expressions. This paper provides a comprehensive review of the current state of the art regarding kinetic models for precious metal catalysts used for the catalytic combustion of lean methane mixtures. The primary emphasis is on relatively low-temperature operation at atmospheric pressure, conditions that are prevalent in the catalytic destruction of low concentrations of methane in emission streams. In addition to a comprehensive literature search, we illustrate a detailed example of the methodology required to determine an appropriate kinetic model and the constants therein. From the wide body of literature, it is seen that the development of a kinetic model is not necessarily a trivial matter, and it is difficult to generalize. The model, especially the dependence on the water concentration, is a function of not only the active ingredients but also the nature of the support. Kinetic modelling is performed for six catalysts, one commercial and five that were manufactured in our laboratory, for illustration purposes. [ABSTRACT FROM AUTHOR]

It is common knowledge that in-situ combustion is highly promising method for improving heavy oil recovery. The present research explores the effects of Cobalt-ligated catalysts derived from sunflower oil (CoSFO) and tall oil (CoTO) on heavy oil oxidation, aiming to enhance in-situ combustion process. Through differential scanning calorimetry (DSC) we assessed the oxidation kinetics of heavy oil in the presence and absence of these catalysts. Our findings indicate that both CoSFO and CoTO significantly improve the oxidation process, particularly in the high-temperature oxidation (HTO) phase crucial for combustion front stabilization. Notably, CoTO demonstrated superior efficacy in reducing oxidation times across all conversion levels, suggesting its potential to optimize the efficiency of EOR techniques. This research highlights the promise of Cobalt-ligated catalysts in advancing heavy oil recovery and suggests directions for future studies to further investigate their industrial applications. [ABSTRACT FROM AUTHOR]

Liquid rocket engines equipped with LOx/GCH4 pintle injectors represent a promising technology when a large throttling capability is required. Still, limited amounts of data are available in the literature about the numerical characterization of pintle injector configurations under reacting conditions, with the entirety of these studies resorting to global or quasi-global reaction mechanisms. To this end, the objective of the present work is to assess the impact of chemical kinetic modeling on the prediction of major combustion observables, thermal flow field, and gas–liquid interaction in a pintle configuration of interest. Specifically, we carry out three unsteady Reynolds-averaged Navier–Stokes simulations under an Eulerian–Lagrangian fashion through variable-fidelity kinetic schemes, namely, one quasi-global scheme and two skeletal schemes derived from the high-pressure Zhukov's detailed mechanism. On the one hand, employing quasi-global chemical kinetics delivers an inconsistent flame topology. On the other hand, the overall combustion characteristics remain unaltered regardless of the skeletal mechanism complexity, while significant discrepancies can be envisaged in the flame dynamics. Moreover, the computational burden exponentially increases with mechanism size, preventing high-fidelity skeletal schemes from being leveraged in design-oriented computational fluid dynamics. Based on these findings, quasi-global chemical kinetics should be discarded when targeting high-pressure rocket engine conditions, while ad-hoc optimized skeletal mechanisms should be developed. This way, the present study provides an insightful contribution to identifying the optimal complexity of chemical kinetic modeling to ensure reliable, still cost-effective numerical simulations of liquid rocket engine combustion devices. • Chemical kinetics modeling impacts LOX/GCH4 combustion predictions in pintle injectors. • Semi-global mechanisms overestimate mixture reactivity in oxidizer-rich regions. • Too compact skeletal schemes may predict local extinction in ultra-oxidizer-rich regions. • Optimal complexity in skeletal mechanisms should be pursued to restrain CPU cost. [ABSTRACT FROM AUTHOR]

The low flame speed and NO x emissions of ammonia are the key to affecting combustion temperature, stability, flame structure, and pollutant control, limiting its application in power generation devices. This study proposes oxy-ammonia combustion (oxygen content in oxidant = 100%, NH 3 /O 2 combustion) as a novel method for significantly enhancing ammonia combustion. A method for measuring the laminar flame speed using the NH* distribution of the Bunsen burner flame is proposed, and the measured data is close to the constant volume combustion bomb. 21 kinetic models were collected and optimized after comparison with the experimental data of constant volume combustion bombs, and results show that Han et al.'s model has higher prediction accuracy for NH 3 /O 2 flames. The preheating temperature was relevant to gas turbine combustors (298.15–500 K), and the equivalence ratio ranged from 0.7 to 1.6. At this extreme condition (oxygen content in oxidant = 100%), the results show that the maximum laminar flame speed reaches 1.25 m/s at ambient pressure and temperature, which is approximately 18 times that of NH 3 /air combustion, mainly due to the increased reaction rates of OH, H, O and NH 2 radicals in the reaction zone (primary ammonia decomposition and H/O radical pool). The NO emission of NH 3 /O 2 combustion at stoichiometric conditions is about 7216 ppmv@15%O 2 , 1.5 and 13 times that of NH 3 /air and CH 4 /air combustion, respectively. NO production and consumption may follow the N 2 O and NNH mechanism, and HNO is an important precursor for NO formation. Increasing the preheating temperature has less effect on the reaction pathway directions in the reaction network of nitrogen conversion but affects the path flux significantly. [Display omitted] • Oxy-fuel combustion enhances the ammonia combustion to "m/s" level. • Active radical pools and ammonia primary decomposition determine flame speeds. • N 2 O–NNH mechanism dominates nitric oxide production and consumption. • Preheating and fuel-lean conditions promote ammonia primary decomposition. • HNO is the dominant precursor of nitric oxide and competes with NH radicals. [ABSTRACT FROM AUTHOR]

In this work, the impact of rare earth element samarium "Sm" substitution on Ba 4 Co 2 Sm x Fe 36-x O 60 U-type hexaferrites was studied in detail. Five compositions with step size x = 0.00, 0.025, 0.050, 0.075 and 0.1 were synthesized. These five series were prepared using the sol-gel auto-combustion method and the samples were sintered for 6 h at 1250 °C. The synthesized samples were characterized by XRD, FTIR, Raman Spectroscopy, X-ray photoelectron Spectroscopy and vector network analyzer (VNA). The structure crystallography of Ba 4 Co 2 Sm x Fe 36-x O 60 was examined via XRD. The impact of Sm3+ substitution was assessed across all lattice parameters. Lattice constants 'a' and 'c' were found between 5.886 and 5.881 Å and 113.179 to 113.037 Å, respectively. FTIR was used to learn more about the crystal structure and atomic vibrations between 400 and 1000 cm−1 wave number, where higher frequency bands appear at 570 cm−1 (tetrahedral site) and the lower frequency band occurred at 424 cm−1 due to the metal-oxygen stretching vibration (Fe-O) bond at the octahedral site. Each spectrum supported a U-type hexagonal structure i.e. an investigation of the chemical and intermolecular bonds via Raman spectra. XPS confirms the presence of elements in materials. Different dielectric parameters were observed in the 1 MHz to 6 GHz range of all prepared samples. Cole-Cole graphs of prepared materials highlighted the influence of grain boundaries. A solitary semicircle in the impedance of a specific section of grain boundaries was evidenced through Cole-Cole plots. Dielectric properties strongly depend on electron hopping between Fe2+ and Fe3+ ions. The optimized parameters suggest the utility of these materials in microwave devices, multilayer chip inductors and high-frequency electrical circuit applications to reduce skin effects. [ABSTRACT FROM AUTHOR]

This study presented the development of a reaction kinetics scheme based on saturates–aromatics–resins–asphaltenes (SARA) fractions to represent the complicated chemical reactions occurring during high-pressure differential scanning calorimetry (HP-DSC) tests. The heat release characteristics during heavy crude oil combustion were analyzed from a set of HP-DSC results. On the basis of this analysis, an improved reaction kinetics model, including low-temperature oxidation (LTO) reactions of SARA fractions, cracking of oxidized asphaltenes, and coke combustion, was established. Following that, this model was incorporated into Computer Modeling Group STARS to simulate the HP-DSC results. Both activation energy and frequency factor of each reaction were continuously tuned until the correct kinetics parameters were obtained by matching the simulation data with the HP-DSC experimental data. The experimental results indicated that the heavy crude oil experienced greater heat release due to LTO rather than high-temperature oxidation at 5 MPa, which differed from the results observed at atmospheric pressure. The simulation results showed that the energy required to activate the oxidation reactions in the HP-DSC experiments was similar to that in the numerical simulation. However, the oil sample was subjected to higher molecular collision frequency in the HP-DSC experiments than in the numerical simulation. Therefore, more attention should be given to adjusting frequency factor when determining the oxidation kinetics parameters in the numerical model. Overall, the SARA-based oxidation kinetics model successfully simulated the exothermic characteristics of the heavy oil during heating. [ABSTRACT FROM AUTHOR]

This work presents the combustion behavior of different mean relative densities (MRD) of Indian thermal coal. Coal of different MRD in the range of 1.25 to 2.20 was prepared using the density separation method. Essential characterization of all MRD fraction coals was done by proximate analysis, ultimate analysis, gross calorific value, BET analysis, and ash analysis. The combustion behavior of all coal samples was carried out by a thermogravimetric analyzer (TGA). Combustion characteristics parameters such as ignition temperature (TIG), peak temperature (Tmax), burnout temperature (TBT) and maximum combustion rate (DTGmax) were evaluated using TGA-DTG data. Results show that with the increase of MRD from 1.25 to 2.20, TIG and Tmax increase from 324°C and 451°C to 426°C and 462°C, respectively, while DTGmax reduces from 9.52 to 1.68 mass%/min. The kinetic analysis demonstrates that coal combustion follows the first-order reaction model and can be separated into two stages. The thermodynamic parameters signify that lighter MRD coal requires lower endothermic energy than heavier MRD coal. [ABSTRACT FROM AUTHOR]

Pt-Pd-based noble metal catalysts are widely used in engine exhaust aftertreatment because of their better carbon soot oxidation performance. At present, the synergistic effect of Pt and Pd in CDPFs, which is the most widely used and common doping method, in catalyzing the combustion of carbon smoke has not been reported, and it is not possible to give an optimal doping ratio of Pt and Pd. This paper investigates the carbon soot oxidation performance of different Pt/Pd ratios (Pt/Pd = 1:0, 10:1, 5:1, 1:1) based on physicochemical characterization and particle combustion kinetics calculations, aiming to reveal the Pt-Pd synergistic effect and its carbon soot oxidation law. The results show that Pt-based catalysts doped with Pd can improve the catalyst dispersion, significantly increase the specific surface area, and reduce the activation energy and reaction temperature of carbon soot reactions, but excessive doping of Pd leads to the enhancement of the catalyst agglomeration effect, a decrease in the specific surface area, and an increase in the activation energy and reaction temperature of the carbon soot reaction. The specific surface area and pore capacity of the catalyst are the largest, and the activation energy of particle oxidation and the pre-exponential factor are the smallest (203.44 kJ∙mol−1 and 6.31 × 107, respectively), which are 19.29 kJ∙mol−1 and 4.95 × 108 lower than those of pure carbon soot; meanwhile, the starting and final combustion temperatures of carbon soot (T10 and T90) are the lowest at 585.8 °C and 679.4 °C, respectively, which are 22.1 °C and 20.9 °C lower than those of pure carbon soot. [ABSTRACT FROM AUTHOR]

Torrefaction and combustion have been applied to naturally decomposed red oak logging residues. The results indicated that four-year natural decomposition would lower the energy density of red oak from 20.14 to 18.85 MJ/kg. Torrefaction reduced the O/C and H/C ratios but improved the energy yield values. Two combustion stages were observed for all samples, and no hemicellulose derivative thermogravimetric peak appeared for torrefied samples. The differential scanning calorimetry exothermic heat flow increased after torrefaction. In addition, the Kissinger–Akahira–Sunose average activation energy of untorrefied samples decreased in the first stage (from 157.77 to 149.52 KJ/mol), while it increased in the second stage (from 131.32 to 181.83 KJ/mol). The ∆H, ∆G, and ∆S values of all samples decreased in the first stage, while they increased when the conversion rate was greater than 0.5 for torrefied samples. These findings can aid in a better understanding of the fuel performance of torrefied and untorrefied naturally decomposed red oak logging residues. [ABSTRACT FROM AUTHOR]

The combination of Al nanoparticles (ANPs) as fuel and H2O2 as oxidizer is a potential green space propellant. In this research, reactive force field molecular dynamics (ReaxFF-MD) simulations were used to study the influence of water addition on the combustion of Al/H2O2. The MD results showed that as the percentage of H2O increased from 0 to 30%, the number of Al-O bonds on the ANPs decreased, the number of Al-H bonds increased, and the adiabatic flame temperature of the system decreased from 4612 K to 4380 K. Since the Al-O bond is more stable, as the simulation proceeds, the number of Al-O bonds will be significantly higher than that of Al-H and Al-OH bonds, and the Al oxides (Al[O]x) will be transformed from low to high coordination. Subsequently, the combustion mechanism of the Al/H2O2/H2O system was elaborated from an atomic perspective. Both H2O2 and H2O were adsorbed and chemically activated on the surface of ANPs, resulting in molecular decomposition into free radicals, which were then captured by ANPs. H2 molecules could be released from the ANPs, while O2 could not be released through this pathway. Finally, it was found that the coverage of the oxide layer reduced the rate of H2O2 consumption and H2 production significantly, simultaneously preventing the deformation of the Al clusters' morphology. [ABSTRACT FROM AUTHOR]

This paper comprehensively assesses oil palm biomass and coal blends, focusing on evaluating thermodynamic and kinetics parameters. The experimental approach employs thermogravimetric differential thermal analysis (TG–DTA) with varying heating rates of 5, 10, 15, and 20 K min−1. Laboratory tests are conducted on six blended samples of different coal and oil palm biomass ratios. The evaluation encompasses key combustion parameters, including ignition index (Di), burnout index (Db), combustion performance index (S), reactivity (R), flammability index (C), and index of intensity (Hf). Additionally, thermodynamic parameters such as a change in enthalpy (ΔH), change in Gibbs free energy (ΔG), and change in entropy (ΔS) are analyzed. The results demonstrate that the optimal co-combustion material is a blend of 76% low-rank coal, 19% medium-rank coal, and 5% oil palm fronds, identified as L80M20F. This blend exhibits superior combustion performance, as evidenced by the highest values for Di (31.17 × 10–8% min−3), Db (28.91 × 10–11% min−3 K−1), and R (39.18 × 104 mg min−1). Furthermore, it displays the lowest ΔH of 73.11 kJ mol−1 and ΔS of − 0.0452844 J mol−1 K−1, along with the highest ΔG of 179.77 kJ mol−1. The accuracy of these findings is confirmed through verification with the Gram–Charlier peak function, which yields a negligible margin of error. In conclusion, this study provides crucial insights for decision-makers by assessing combustion and thermodynamic parameters of oil palm biomass and coal blends. The L80M20F, identified as the optimum blended fuel, showcases its potential to enhance combustion efficiency and contribute to the energy transition toward net-zero emissions. [ABSTRACT FROM AUTHOR]

The growth of hydrogen as an alternative clean fuel for fulfilling thermal energy needs of multiple economic sectors globally requires access to reliable, safe, energy efficient, emission free combustion technology. The work described in this short communication shows the applicability of a novel heterogeneous combustion design in utilizing a wide range of hydrogen blended methane concentrations to cleanly and safely generate thermal energy. The utilization of a simple first principles design approach along with engineered materials yielded a fuel-flexible hybrid infrared-convection burner design capable of lowering NOx emissions by more than 95% while simultaneously improving the heat transfer efficiency by 15% with a wide range of hydrogen concentrations. The safety and performance of the combustion design was demonstrated in an burner at capacities of up to 12,000 Btu/h in producing temperatures of 900 °C. The atmospheric burner concept was integrated in a cooktop configuration with combined thermal power rating of 30,000 Btu/h and operated with hydrogen blended natural gas. • Safe combustion of hydrogen-blended methane compositions was achieved. • Infrared thermal output lowered the NOx emissions by 90% compared with a conventional blue flame burner. • Safe combustion with hydrogen blends is enabled by the tortuous path of the heterogeneous media. • Heat energy utilization efficiency was enhanced by up to 15% due to radiative heat transfer. [ABSTRACT FROM AUTHOR]

The effects of fuel blends comprising ammonia and hydrogen on the technical, economic, and environmental indicators of an existing gas turbine unit with 7.6 MW output power were investigated and analyzed. Four models, each with different fuel-blending options, were designed by Aspen HYSYS and Ansys®Chemkin Pro to analyze the technical and chemical processes. Based on the technical and CO 2 emission values of each model developed in Aspen HYSYS, the focus was on Scenario 4 with ammonia and hydrogen co-firing. This scenario exhibited the highest electric efficiency and the lowest CO 2 emissions but had higher costs for generated electricity compared to other scenarios. Economic evaluations of all scenarios provided a clear understanding of each fuel cost and Levelized Cost of Electricity (LCOE). Initially, scenario 2, with ammonia co-firing, appeared to be an attractive option for further implementation. However, detailed analyses of the combustion process in each model dramatically changed the final decision and provided a good reason to focus on hydrogen fuel, which significantly reduced NOx emissions. In conclusion, Scenario 3 with hydrogen co-firing demonstrated attractive performance and favorable combustion kinetics. [Display omitted] • Performance of operating gas turbine with natural gas, NH 3 , and H 2 blends is investigated. • NOx emissions under H 2 and natural gas blend are within the requirements. • Natural gas, NH 3 , and H 2 blends enhance the performance of the cycle but costly and emit more NOx. • Hydrogen combustion remained the strongest alternative to natural gas. [ABSTRACT FROM AUTHOR]

Reactive Molecular Dynamics (MD) and Density Functional Theory (DFT) computations are performed to provide insight into the effects of external electrostatic fields on hydrocarbon reaction kinetics. By comparing the results from MD and DFT, the suitability of the MD method in modeling electrodynamics is first assessed. Results show that the electric field-induced polarization predicted by the MD charge equilibration method is in good agreement with various DFT charge partitioning schemes. Then, the effects of oriented external electric fields on the transition pathways of non-redox reactions are investigated. Results on the minimum energy path suggest that electric fields can cause catalysis or inhibition of oxidation reactions, whereas pyrolysis reactions are not affected due to the weaker electronegativity of the hydrogen and carbon atoms. MD simulations of isolated reactions show that the reaction kinetics is also affected by applied external Lorentz forces and interatomic Coulomb forces since they can increase or decrease the energy of collision depending on the molecular conformation. In addition, electric fields can affect the kinetics of polar species and force them to align in the direction of field lines. These effects are attributed to energy transfer via intermolecular collisions and stabilization under the external Lorentz force. The kinetics of apolar species is not significantly affected mainly due to the weak induced dipole moment even under strong electric fields. The dynamics and reaction rates of species are studied by means of large-scale combustion simulations of n-dodecane and oxygen mixtures. Results show that under strong electric fields, the fuel, oxidizer, and most product molecules experience translational and rotational acceleration mainly due to close charge transfer along with a reduction in their vibrational energy due to stabilization. This study will serve as a basis to improve the current methods used in MD and to develop novel methodologies for the modeling of macroscale reacting flows under external electrostatic fields. [ABSTRACT FROM AUTHOR]

Reduction of large combustion mechanisms is usually conducted based on the detection and elimination of redundant species and reactions. Reaction elimination methods are mostly based on sensitivity analysis, which can provide insight into the kinetic system, while species elimination methods are more efficient. In this work, the species‐targeted local sensitivity analysis (STLSA) method is proposed to evaluate the importance of species and eliminate non‐crucial species and their related reactions to simplify kinetic models. This paper comprehensively evaluates the effectiveness of STLSA across various combustion scenarios, including high and low‐temperature ignition and laminar flame speed, using diverse mechanisms like USC Mech II, JetSurf 1.0, POLIMI_TOT_1412, NUIGMech1.1 and so on. Comparisons with graph‐based methods, such as DRG and DRGEP, highlight STLSA's superior efficiency and accuracy. Moreover, STLSA is compared to species‐targeted global sensitivity analysis (STGSA), demonstrating significant computation cost savings and comparable model reduction capabilities. The study concludes that STLSA is a robust and versatile tool for mechanism reduction, offering substantial improvements in computational efficiency while maintaining high accuracy in predicting key combustion properties. [ABSTRACT FROM AUTHOR]

The goal of the present study is to build a computational combustion model and numerically investigate the stoichiometric mixture fraction generated from blending liquid n-pentane fuel with liquid hydrogen applied in the form of combustible spray droplets. The mixture fraction-probability density function is used to construct the combustion model. The role of the mixture fraction that is generated from blending n-pentane and hydrogen at different mass fraction ratios. From the numerical results, the increase in H 2 blending in the C 5 H 12 /H 2 mixture increases the temperature and velocity of the flame. Furthermore, the addition of hydrogen expands the reaction zone to locations downstream of the flame. The enrichment of the reactive mixture with H 2 reduces the emission of CO. Only in the reaction zone does hydrogen fuel enrichment decrease the mass fractions of CO and OH. The results confirm that the PDF-RANS model gives satisfactory agreement with the experimental data. [Display omitted] • The addition of liquid hydrogen to the n-pentane liquid fuel. • New implementation for the PDF combustion model. • The spray combustion model is being examined in relation to the addition of liquid hydrogen. • Simulation for the spray combustion cases in different blending ratios. • The analyses of the spray combustion zones are made. [ABSTRACT FROM AUTHOR]

The global transition towards low-carbon and renewable energy necessitates fuel flexibility, emphasizing the critical role of alternative fuel options. This study investigates the potential of Moderate or Intense Low Oxygen Dilution (MILD) combustion for binary blends of ammonia, methane, and hydrogen. Utilizing temperature-based criteria in perfectly stirred reactor (PSR) simulations, multiple detailed chemical kinetic schemes are employed to update combustion regime maps, incorporating NO x emissions. The analysis begins with an exploration of pure fuels and subsequently introduces binary blends, including CH 4 -H 2 , NH 3 -CH 4 , and NH 3 -H 2. The investigation focuses on their transition to the MILD combustion regime by achieving the requisite oxygen content (X O 2 ∗) at the minimum inlet temperature. Noteworthy findings include the non-monotonic behavior in self-ignition temperature observed in NH 3 -CH 4 combustion, influenced by the impact of nitrogen chemistry on CH 4 oxidation. To address uncertainties, three different kinetic schemes are employed. In NH 3 -H 2 blends, a modest addition of hydrogen (10%–20%) significantly reduces X O 2 ∗ , self-ignition temperature (T s i), and NO x emissions. However, further increases in hydrogen content yield diminishing effects. Importantly, ammonia blends require additional dilution (2%–6% oxygen) to maintain NO x levels at 100 ppm under stoichiometric conditions, surpassing traditional MILD criteria. The research underscores the significant potential of binary fuel blends for MILD combustion, offering valuable insights into their performance. The numerical findings on the target regime and emissions trends contribute to optimizing operating conditions and aiding combustion diagnostics. • Combustion regime maps for ammonia, methane, and hydrogen are presented. • The transition to MILD combustion of binary fuel blends is investigated. • Multiple detailed chemical kinetic schemes are assessed. • A decrease in self-ignition temperature is observed with the addition of ammonia to methane. • Ammonia blends require additional dilution for low NOx levels. [ABSTRACT FROM AUTHOR]

In order to comprehend the molecular composition of coal and better understand the process of coal combustion, this study involved the development of a molecular structure model for Heiyanquan coal in Xinjiang, as well as the optimization and annealing dynamics simulation of the model. Thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FTIR), and high-resolution transmission electron microscopy (HRTEM) were utilized to investigate the spontaneous combustion characteristics of coal at different temperatures (room temperature, 50–500 °C with 50 °C interval). The findings revealed that the coal primarily consists of aromatic carbon, with the aromatic structure mainly comprising naphthalene, anthracene, and phenanthrene, and the aliphatic carbon mainly consisting of CH2 and CH, along with a small quantity of minerals. The empirical molecular formula of Heiyanquan coal was determined to be C175H125O21N3. After the optimization, the total energy of the model was significantly reduced, and the aromatic layers tended to align in a regular parallel manner, with van der Waals energy playing a crucial role in maintaining structural stability. As the temperature increased, the activation energy of the three stages also increased, with the combustion stage exhibiting the highest activation energy. The presence of hydroxyl groups and oxygen-containing functional groups was found to mainly participate in the reaction, while the content of aromatic hydrocarbons remained relatively stable, C=C exhibited a decreasing trend, and C-O displayed an increasing trend. Moreover, it was observed that 1 × 1 and 2 × 2 were the predominant aromatic stripes in the coal samples, accounting for more than 90% of the total stripes. [ABSTRACT FROM AUTHOR]

The higher-order DNS simulations were carried out to study the turbulent jet combustion characteristics of pure ammonia and ammonia-hydrogen mixtures at the auto-ignition condition. It is found that blending just 5% H 2 into ammonia can significantly shorten its ignition delay time, enhance the reactive scalar dissipation rate, and thus produce much more fine structures in the turbulence domain. During the turbulent ignition process, the low-temperature ignition firstly occurred at the most reactive mixture fraction (ξ MR) that is located on the lean-side due to the spontaneous reactions, then the ignited reactive fronts propagated towards rich side by the deflagrative mode, which eventually ignited the high-temperature reactions near the stoichiometric mixture fraction (ξ st). The advancement of early-phase ignition at ξ MR as well as speed up of the subsequent deflagrative propagation was responsible for the acceleration of ammonia flame ignition in turbulence. The early-phase flame propagation was driven by chemical reactions, while in the high temperature post-ignition phase, flame curvature due to the sheared turbulence with a neutralizing balance with the normal diffusion was responsible for the motionlessness of reaction front at a fixed leaner mixture fraction near ξ st. The majority triple points with moderate scalar dissipation rate (χ) were propagated by the normal edge-flame propagation mode; in the ultra-lean fluids with low χ , the edge-flame propagation was governed by expanding flame kernels; and in the fluids with high χ , flame folding played a leading role in the ξ st iso-surface ignition. In overall, the flame folding regime was dominated in the turbulent edge flame propagation along the ξ st iso-surface. In spite of its marginal contribution to the global heat production and temperature rise, the deflagrative mode plays a significant role in regulating the ignition timing and thus optimizing the ammonia engine performance. • Conditional statistics and displacement speed analysis reveals the combustion modes. • Deflagrative mode is most important to the regulation of engine ignition timing. • Ammonia combustion with H 2 addition more likely resembles the homogenous ignition. • Tangential and normal diffusion balance leads to post-ignition flame anchor near ξ st. • Flame folding regime governs edge-flame propagation along the stoichiometry surface. [ABSTRACT FROM AUTHOR]

The combustion characteristics of ammonia/hydrogen/air mixtures flame under different equivalent ratios (0.6–1.0), and hydrogen ratio (0.3–0.5) in a wide range of turbulence intensity were investigated. The result shows both differential diffusion and flame chemistry affect the flame morphology and burning velocity of lean and stoichiometric mixtures. With the increase of hydrogen ratio, not only can chemical reaction be enhanced, but also heat and mass diffusion of the flame front can be promoted, thus accelerating flame propagation. In addition, the strong turbulent stretch of the turbulent field gradually plays a dominant role in the development of flame and causes the flame to wrinkle even more. Based on the turbulent flame Reynolds number (Re T,flame), the accelerated propagation processes are analyzed, and further, the influences of differential diffusion and turbulent stretching are taken into account by Le and Ka numbers. The general correlation of turbulent burning velocity (S T) is obtained, and the applicability of the correlation based on Da and Ka for ammonia/hydrogen/air mixtures turbulent combustion is verified. In addition, a unified scaling of turbulent burning velocity (S T) suitable for different equivalent ratios and hydrogen content conditions is obtained by rearranging with Le. • Effect of differential diffusion and turbulent stretch on S T are studied. • The self-accelerating propagation is verified and propose the correlation of S T. • A unified scaling of S T is obtained based on Da , Ka , and Le. [ABSTRACT FROM AUTHOR]

This work focused on the production of the MoAlB MAB phase through self-propagating, high-temperature synthesis in the thermal explosion mode. The influence of the method of a Mo-Al-B-powder reaction mixture preparation on the combustion temperature, mechanism, and stages of the MAB phase formation in the combustion process was investigated. The combustion temperatures of the mixtures obtained in the rotary ball mill and high-speed planetary ball mill were 1234 and 992 °C, respectively. The formation of intermediate compounds Mo3Al8 and α-MoB in the combustion front, along with MoAlB, was established using the time-resolved X-ray diffraction method. In the case of the mixture prepared in a ball mill, the primary interaction in the combustion front occurred through the Al melt, and in the case of using a planetary mill, solid-phase reactions played an important role. The mechanical activation of the mixture in a planetary mill also accelerated the processes of phase formation. The method of a reaction mixture preparation has virtually no effect on the MoAlB MAB phase content in combustion products (92–94%), but it does affect their structure. The synthesis products have a lamellar structure composed of MAB grains with a thickness of ~0.4 μm and a length of ~2–10 μm. [ABSTRACT FROM AUTHOR]

The development of a compact mechanism has made a great contribution to work on the combustion of hydrocarbon species and facilitates the investigations on chemical kinetics and computational fluid dynamics (CFD) studies. N-propylcyclohexane (NPCH) is one of the important components for jet, diesel, and gasoline fuels which needs a reliable compact reaction kinetics mechanism. This study aims to investigate the construction of a well-validated mechanism for NPCH with a simplified chemical kinetics model that delivers a good prediction ability for the key combustion parameters in a wide range of conditions (temperatures, pressures, and equivalence rates). The NPCH reaction kinetic mechanism was constructed with the aid of a coupling process, simplification process, rate modification, and a combination of standard reduction methods. The model includes a simplified sub-mechanism with 16 species and 58 reactions and a semi-detailed core mechanism with 56 species and 390 reactions. Two key parameters including ignition delay time and laminar flame speed are simulated by the use of ANSYS Chemkin-Pro. The simulation results for these parameters are validated against the available data in the literature, and the results show a good agreement compared to the experimental data over a wide range of conditions covering low to high temperatures at different pressures and equivalence ratios. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Nuclear power fire protection is an important part of nuclear safety, and strengthening fire protection technology research is essential for improving nuclear safety and fire protection. The operating platform inside a containment structure is one important element in fire risk evaluation in nuclear power plants. In this paper, a combustible nuclear-grade cable in a fire scenario was firstly selected as the research object, and then the nuclear-grade cable was separately subjected to a combustion test as well as a thermogravimetric test in order to obtain the relevant thermal parameters, which provide more accurate data support for the establishment of a cable fire development and spread model. The nuclear-grade cable material data obtained from the test were compared with a civil PVC cable in order to conduct a specific analysis of the fire risk of nuclear-grade cables. This study shows that the effects of different heating rates and heating atmospheres on the thermal decomposition behavior of cable materials are meaningful and helpful in understanding whether the materials will undergo combustion processes at high temperatures and whether fire spread will occur. [ABSTRACT FROM AUTHOR]

The fractional change in the reaction progress variable gradient depends on the flow normal straining within the flame and also upon the corresponding normal gradients of the reaction rate and its molecular diffusion transport. The statistical behaviours of the normal strain rate and the contributions arising from the normal gradients of the reaction rate and molecular diffusion rate within the flame were analysed by means of a Direct Numerical Simulation (DNS) database of statistically planar turbulent premixed flames ranging from the wrinkled/corrugated flamelets regime to the thin reaction zones regime. The interaction of flame-normal straining with the flame-normal gradient of molecular diffusion rate was found to govern the reactive scalar gradient transport in the preheat zone, where comparable timescales for turbulent straining and molecular diffusion are obtained for small values of Karlovitz numbers. However, the molecular diffusion timescale turns out to be smaller than the turbulent straining timescale for high values of Karlovitz numbers. By contrast, the reaction and hot product zones of the flame remain mostly unaffected by turbulence, and the reactive scalar gradient transport in this zone is determined by the interaction between the flame-normal gradients of molecular diffusion and chemical reaction rates. [ABSTRACT FROM AUTHOR]

In this study, process control factors such as dipping time, heat treatment time and curing conditions were optimized to prepare N-Si network sol–gel-based coatings on a cotton fabric. The dipping time was varied from 14 h to 30 min, the heat treatment time at ~90 °C was varied between no heating conditions to 15 h and the curing was performed at 165 °C. The microstructure of the coating was analyzed using low electron scanning microscopy (LV-SEM), while a compositional study of the coated substrate was carried out using FTIR and EDS techniques. From the thermal and combustion analysis of the coated samples using thermogravimetric and vertical flame test techniques, significant resistance to the degradation process was observed, particularly in the initial stages, in addition to the highest char residue for DI-0.5 h-15~32.93%. Similarly, for DI–5 h–RT, the peak degradation temperature was around ~372 °C, accompanied by a notable char residue of approximately 31.12%. The flame spread and burning rate profile further supported the findings; DI-0.5 h-15 and DI-5 h-RT had the lowest flame spread. [ABSTRACT FROM AUTHOR]

Hexamethyldisiloxane (HMDSO) is one of the main impurities in the syngas produced from sewage and landfill plants. In order to utilize this syngas or control the characteristics of the generated silica particles, it is crucial to understand the chemical kinetics of HMDSO combustion. This study investigated the process of HMDSO combustion using synchrotron radiation mass spectrometry (SRMS), gas chromatography (GC), and ReaxFF molecular dynamics simulations. First, the force field used for ReaxFF simulation was validated by comparing the energies of different bond lengths, bond angles, and dihedral angles with the ones from DFT calculations. Good agreements were found. Then, ReaxFF simulations of HMDSO combustion with this force field were conducted under various conditions, which include different equivalence ratios (0.67, 1.0, and 1.5) and temperatures ranging from 2000 to 3500 K. The oxidation characteristics of HMDSO were analyzed, including the evolution of gas products and particle formation. Finally, based on the results from experiments and ReaxFF simulations, the reaction pathways, reaction lists, and reaction kinetics data during HMDSO combustion were obtained. A detailed reaction mechanism was proposed and validated by applying it in modeling the H2/HMDSO/O2 combustion systems. The temperature and part of the gas products such as CO and CO2 as well as SiO could be well predicted. [ABSTRACT FROM AUTHOR]

An Arrhenius-based one-step scheme is derived for hydrogen-air combustion simulations. A Pre-Exponential Adjustment approach, based on an explicit analytical dependence of reaction rate parameters on equivalence ratio and pressure is adopted, together with a correction to improve the prediction of thermal flame thickness. The reduced scheme is validated by computations of one-dimensional unstrained and strained laminar premixed flames for a wide range of pressures ([1; 30] atm), unburned gas temperatures ([300; 800] K), and equivalence ratios ([0.4; 6.0]), with a good agreement of predicted main flame parameters between reduced and reference kinetic schemes. Coupled to a high-fidelity Navier–Stokes compressible solver, the reduced scheme is successfully proved for the numerical simulation of canonical configurations such as one-dimensional and two-dimensional premixed flames under several mixture conditions, with a significant improvement of computational efficiency. [Display omitted] • Derivation of a one-step scheme for hydrogen-air mixtures based on Arrhenius law. • Pre-Exponential Adjustment to match typical combustion systems' operative ranges. • Introduction of a correction to predict flame thickness in all mixture conditions. • Good agreement of reduced and reference schemes found for canonical configurations. • Sensible reduction (> 50%) of computational costs in CFD applications. [ABSTRACT FROM AUTHOR]

Chemical reaction is the major source of combustion irreversibility in premixed conditions, and revealing the details of exergy destruction can provide a more essential perspective on exploring high-efficiency combustion strategies. The present study focuses on the homogeneous combustion process of CH 4 /H 2 /air mixtures, aiming to reveal the exergy destruction behavior of chemical reactions from the viewpoint of different combustion stages and oxidation paths. Results indicate that exergy destruction is mainly accumulated in the ignition delay stage, and the exergy destruction caused by different elementary reactions depends on the temperature at which the reaction takes place and the resulting change of free energy. By dividing the chemical reactions into four groups, the main reaction channels that contribute to the change in exergy destruction with combustion boundaries have been identified. Global reaction flux analysis reveals the effect mechanism of different oxidation paths on exergy destruction. Furthermore, the staged combustion concept with endothermic reactions reacting firstly at lower temperatures followed by dilute combustion in the high-temperature heat release stage is discussed from the point of the exergy destruction evolution, which offers the potential to simultaneously reduce exergy destruction and suppress NO x formation. • Exergy destruction depends on the reaction temperature and free energy change. • The chemical reactions are classified into four groups. • Exergy destruction is significantly affected by the reaction paths. • H 2 addition effectively broadens the area of low exergy destruction. • A staged combustion concept for reducing combustion irreversibility is explored. [ABSTRACT FROM AUTHOR]

The addition of hydrogen to ammonia enhances combustion stability and widens the flame limits. However, it also brings the drawback of increased nitrogen oxide (NO) emissions. Therefore, this study employs a chemical kinetics simulation system to investigate the effects of OH concentration and hydrogen addition on NO emissions in a laminar premixed hydrogen/ammonia/air swirling flame at high pressures. The research reveals a distinct positive linear correlation between NO emissions and the peak mole fraction of OH radicals. Within the range of 1.0≤ φ ≤ 1.1 and 0≤ X H2 ≤0.5, as hydrogen content (0≤ X H2 ≤0.5) increases, the promoting effect of max(OH) on NO emissions continuously intensifies. Pressure, on the other hand, has virtually no impact on their correlation.Furthermore,the analysis of production rates, sensitivity, and reaction pathways indicates that NH 3 primarily transforms into NO through three pathways: NH 3 →NH 2 (NH)→HNO→NO, NH 3 →NH 2 →NH→NO, and NH 3 →NH 2 →NH→N→NO. The HNO intermediate pathway is the major route for NO generation, with OH radicals significantly promoting NO production via the NH→HNO intermediate pathway. This theoretically validates the correlation between max(OH) and NO emissions. Data analysis using MATLAB yields the relationship between max(OH) and NO emissions, providing a theoretical basis for the practical application of OH chemiluminescence detection. Additionally, NNH proves to be a crucial radical in ammonia oxidation chemistry and is involved in the NO formation process in reaction R69 NNH + O NH + NO. This study sheds light on the complex interplay between OH, hydrogen content, and NO emissions, providing valuable insights into combustion dynamics and emissions control. [Display omitted] • Effect of hydrogen addition on ammonia combustion emissions. • There is a clear linear relationship between max(OH) and NO emission. • HNO intermediate pathway is the main source of NO production. • NNH radical is a key radical in ammonia oxidation chemistry. [ABSTRACT FROM AUTHOR]

Boron is one of the most valuable fuels for rocket propellants. However, the boron oxide (B2O3) on the B surface has a high boiling point (1860°C), which hinders the contact between the internal active B and the oxidation component during the ignition and combustion process. As a result, the ignition energy of B is higher and the combustion reaction rate is lower. In order to improve the ignition performance and reaction rate of B, a surface modification of B by means of surface purification by a solvent, surface grafting, and making a composite with aluminum (Al), which has a high combustion temperature, has been prepared. Composite particles of B purified by ethanol and thick flake Al (TF-Al), denoted by EB/TF-Al, have the fastest reaction rate higher by 96.6% than that of raw B and TF-Al composite particles (RB/TF-Al). Surface grafting of B with TF-Al composite particles (KHB-3/TF-Al) ensure the minimum ignition energy, which is 29.1% lower than that of raw B. As the ignition performance and reaction rate of B are improved by means of surface modification, the performance of B-based rocket propellants is expected to be improved. [ABSTRACT FROM AUTHOR]

In this work the performance of various detailed reaction mechanisms of combustion of methane–hydrogen fuel mixtures is studied. The investigation is focused on the burner stabilized flame configuration and is undertaken for the normal pressure conditions, which is a starting point for the analysis of the combustion chemistry at elevated pressures met in rocket engine chambers. The study presents the experimental setup, computational approach and results of comparison, which allow us to access the properties of complex combustion systems in variety of dynamical regimes. The comparison of the predicted and measured characteristics of these regimes is used to test the performance of the reaction models. In particular, the critical behavior, e.g. for blow-up, onset of pulsations and quasi-steady flame front propagation and bifurcation between these regimes may be used to characterize and to study properties of combustion systems with mixed fuels. A neutral stability boundary for onset of pulsations is suggested to be used in this study. A method for automatic identification of the boundary is proposed and implemented with several detailed mechanisms. Although for pure methane the results look acceptable, they show gradual divergence with the increase of percentage of hydrogen addition. Significant quantitative differences between experiments and modeling with respects to frequencies of oscillations are reported even for 2:1 ratio of hydrogen to methane in the unburned mixture. The results of the work indicate that current reaction mechanisms need to be improved in order to gain the quantitative predictability of methane–hydrogen–air combustion at normal pressure before proceeding to the conditions fuel-oxygen high pressure combustion more relevant for rocket chamber. • Combustion systems with complex fuel composition — hydrogen addition. • Quantitative comparison of experiments and computations in transient combustion regimes. • Automatic procedure for parametric study to access onset of pulsations. • Mechanisms dependence — performance of existing and well-established mechanisms. • Validation of chemical reaction models via critical mixture composition. [ABSTRACT FROM AUTHOR]

Ultrafine materials with unique characteristics have a broad range of utilization. The motivation of this paper was to investigate the size effect on the thermo-oxidative degradation behaviors and chemical kinetics of polystyrene (PS) solid particles. In this study, microscopic PS particles with four different-diameter distributions, containing 5, 10, 15, and 50 μm, were picked as tested samples. Then, the thermogravimetry analysis test of PS samples was conducted under an air atmosphere with three different heating rates. Activation energies were calculated and validated by multiple traditional kinetic approaches, and a linear relationship between activation energy and the reciprocal of the particle diameter has been concluded. A distributed activation energy model (DAEM) with two pseudo-components was developed and employed to decouple the polyurethane pyrolysis in the air atmosphere. A set of nth-order reactions is hypothesized to occur with a constant pre-exponential factor and having a continuous activation energy distribution pattern conforming to the Gaussian density function in each kinetic process. A multi-parameter optimization program was developed to calculate ten DAEM parameters based on the experimental data from three different heating rates by avoiding the ill condition resulting from the kinetic compensation effect. Moreover, the numerical relationship between activation energies and particle diameter has been analyzed. The results of this study are instructive for the determination method of kinetic triplets, the modification of reaction models, and especially the construction of waste polymer kinetics and combustion models. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Due to the widespread use of lithium-ion batteries, evaluations of the flammability and explosive characteristics of carbon dust materials as anodes require attention. Carbon dust often reaches the micron/nano scale, and dust particle state and explosion risk generated in different industrial scenarios are different, which is in urgent need of research. Nanoscale dust has relatively static coagulation properties and shows characteristics of dispersion and reagglomeration under a certain airflow. The particle size characteristics affect its thermodynamic characteristics and various consequence parameters of dust explosion. The oxidation and combustion characteristics are mainly affected by dust particle size distribution characteristics. The apparent activation energy is mainly affected by the proportion of small and medium-sized particles and pre-exponential index factor is mainly affected by the dust overall average particle size and specific surface area. The explosion consequence parameters are affected by the thermodynamic parameters, by the disturbance state, particle distribution degree of dust cloud and other factors, which affect the heat radiation and heat transfer process to some extent resulting in different explosion consequence parameters. Due to the agglomeration characteristics of nano-level dust, the minimum ignition energy and minimum ignition temperature of nano-level dust are generally smaller than that of micron level dust. [ABSTRACT FROM AUTHOR]