In this study, the inhibitory performance toward aluminum (Al) dust explosions, along with the atomistic mechanisms, were systematically elucidated through thermal analysis, dust explosion experiments, as well as ReaxFF simulations and kinetic modeling. To enhance the suppression efficiency of conventional MCA inhibitors in dust explosions, a hydrogen-bond network regulation strategy was proposed to develop silicon, boron, and phosphorus-modified MCA inhibitors (Si-MCA, B-MCA, and P-MCA). The modified inhibitors significantly increased the activation energy (Ea) of Al rapid oxidation, with P-MCA exhibiting the most pronounced effect and raising Ea by 41.5%. Complete suppression of Al dust explosion was achieved at concentrations of approximately 800, 600, and 550 g/m3 for Si-MCA, B-MCA, and P-MCA, respectively. Compared with pristine MCA, the inhibition efficiency was improved by approximately 20.0% and 26.7% for B-MCA and P-MCA, respectively. ReaxFF simulations revealed that the hydrogen-bonding effect in MCA promotes its preferential adsorption onto the Al particle surface in the flame front, thereby inhibiting oxygen adsorption and restricting the diffusion of Al atoms in the core region. Kinetic analysis further indicated that the modifications facilitate the earlier evolution of N-containing species and the formation of chain-terminating radicals, e.g., BO, HOPO2, and POx. Collectively, efficient inhibition is achieved through the synergistic effects of pyrolysis and combustion suppression, occupation of surface reactive sites, and gas-phase flame radical quenching, with phosphorus-modification showing superior overall performance in terms of dosage reduction and inhibition enhancement. These findings provide theoretical guidance for the rational design and mechanistic optimization of high-performance dust explosion inhibitors.

While methane has traditionally been employed to represent natural gas in combustion studies, actual natural gas contains higher alkanes (e.g., ethane, propane) that may alter fuel reactivity. Therefore, this study aims to investigate the impact of propane component on the combustion of ammonia/natural gas blends. In this work, the ignition delay times (IDTs) of ammonia/propane blends with different ammonia energy share were measured in a shock tube, at 1 atm and at stoichiometric condition, over the temperature range of 1200-1800 K. At the studied condition, the experimental results indicated that the ammonia ratio had small effects on the ignition delay times of ammonia/propane blends, and the small proportion of propane in actual natural gas had small effects on the auto-ignition behaviors of the ammonia/natural gas blends. Furthermore, a kinetic model was developed to simulate the new measured experimental results as well as experimental data in the literature. The model demonstrated good agreement with the measured ignition delay times of ammonia/propane blends, as well as the species profiles of the intermediates during the oxidation of ammonia/propane blends in a jet-stirred reactor at relatively low temperatures. Sensitivity analyses indicated that the interactions between ammonia and hydrocarbons played an important role in predicting the fuel reactivity of ammonia/propane blends at relatively low temperatures, with the effects gradually diminishing as temperature increased.

Underwater electrical wire explosion (UEWE) in planar arrays enables strong, spatially controllable shock waves (SWs). This work experimentally investigates the UEWE of a single copper wire and planar multiwire arrays with nearly identical total mass under an initial stored energy of 1.6 kJ. Discharge current and voltage waveforms are used to determine energy deposition before and after vaporization, while a pressure sensor measures the SW peak pressure, pulsewidth, impulse, and energy density at a fixed stand-off distance. Splitting a single wire into multiple parallel wires only slightly alters electrical matching but significantly increases energy deposition and strengthens the resulting SWs. Relative to a single wire, a nine-wire array enhances the SW peak pressure and energy density by about 124% and 272%, respectively, while nearly halving the pulsewidth. For both single- and split-wire configurations, the SW amplitude first rises and then falls with total wire mass, and a smaller mass produces steeper fronts and shorter pulses. Inter-wire spacing has little effect on deposited electrical energy but strongly influences SW convergence, yielding an optimal spacing that maximizes amplitude. A 3-D simulation model, extended from a single-wire configuration to planar arrays, reproduces the measured enhancement and shows that primary superposition in the gaps and secondary convergence of reflected compression waves dominate far-field amplification and wavefront uniformity. The combined results provide design guidelines for UEWE-based planar arrays, indicating that increasing wire multiplicity and choosing a spacing of roughly one quarter of the wire length effectively enhances SW amplitude and uniformity.

The influence of ammonia addition on the formation of polycyclic aromatic hydrocarbon (PAH) and soot in 2,5dimethylfuran (DMF) counterflow diffusion flames was investigated by means of laser-induced incandescence (LII) and laser-induced fluorescence (LIF) techniques. The results indicated that PAH emerged earlier and were more densely distributed in DMF flame than in n-heptane flame. Moreover, the addition of ammonia inhibited the formation of PAH (such as A2, A3, and A4) and soot in DMF flames. In DMF flames, there were two crucial pathways for PAH formation. Path 1 involved small molecules like C2H2, which were derived from the ringopening reaction of DMF, as the key building blocks. Path 2 (via the reaction R2451: 2C5H5 = A2 + 2H) utilizes C5H5, formed through the dehydrogenation and isomerization of DMF, as the key building block. Kinetic analysis revealed that the addition of ammonia initially heightened the competition for H and CH3 radicals in the vicinity of the fuel nozzle. This, in turn, inhibited the dehydrogenation and isomerization of DMF in Path 2 and promoted the ring-opening reaction of DMF in Path 1 (initial benzene ring formation). Further downstream, the increased H radicals inhibited the formation of A2 by suppressing reaction R2451 above. Finally, after the addition of ammonia, both the soot inception rate and the soot surface growth rate were reduced, resulting in a decrease in the soot volume fraction SVF.

Against the backdrop of decarbonization and energy transition, ammonia holds potential as a carbon-free fuel in internal combustion engines and gas turbines. To gain a further understanding of the turbulent combustion characteristics of ammonia-air mixtures under elevated-pressure conditions, the effects of initial pressure, turbulence intensity, and equivalence ratio on ammonia-air turbulent flame dynamics induced by adding initial turbulence are investigated in this study. A correlation for the turbulent burning velocity of ammonia-air mixture under elevated initial pressure is proposed. An explosion overpressure prediction method is established. The results indicated that, as the turbulence intensity increases, the Kolmogorov scale decreases, and the flame morphology transitions from large-scale distortion to a small-scale fragmented flame structure. As the initial pressure increases, the scale of the wrinkled flame structures decreases while the density increases. The introduction of the correction term [Da(P/P0)]0.25 effectively captures the behavior of turbulent burning velocity of ammonia-air mixtures under elevated pressures. The proposed turbulent-acceleration compensation function effectively reduces the prediction error, ensuring that the prediction model accurately captures the rising trend of explosion overpressure under elevated initial pressures and varying turbulence intensities. This finding highlights the critical role of turbulent flame acceleration in the explosion overpressure generation mechanism.

Polyethylene (PE) dust presents a severe deflagration hazard due to its high flammability, prompting the urgent need for novel suppressants with multi-mechanistic synergistic effects. This study selects a perovskite-structured material, zinc hydroxystannate (ZHS), and evaluates its suppression potential in polymer dust deflagrations using a macro-micro coupled method that integrates thermal analysis with reactive molecular dynamics. Experimental results show that ZHS exhibits excellent endothermic decomposition ability (22 % reduction in heat absorption) and water vapor cooling performance (47 % reduction in total heat release). The metal-oxidation barrier layer formed by its high-temperature decomposition significantly improves the thermal stability of materials, which delays the maximum decomposition temperature of PE to 421.67 degrees C and improves the carbon residual rate to 38.1 %. Molecular simulations reveal that the oxygen vacancies of ZHS facilitate oxygen adsorption and consumption. Its Zn/Sn-based reactive intermediates effectively interrupt radical chain reactions through C2H4 complexation (C2H4 + Zn2+ -> C2H4Zn) and OH/O high-reactive radicals capture (SnO + O-2 -> SnO3, etc.). These mechanisms collectively reduce the generation of C2H4 and CO by 23.6 % and 70 %, respectively. Compared to conventional physical suppressants, ZHS demonstrates an efficient dual-element synergistic suppression capability. The findings validate the suppression potential of ZHS and provide a promising strategy for the application of perovskite-based suppressants in polymer dust deflagration prevention.

Explosion inhibition is a crucial strategy for mitigating the consequences of dust explosions. This study presents the first computational fluid dynamics (CFD) model coupled with detailed chemical reaction mechanisms to investigate the inhibition effect and mechanism of micron-sized aluminum dust explosions by sodium bicarbonate (NaHCO3). Through combined numerical simulations and experimental comparisons, the early-stage flame dynamics and explosion parameters of aluminum dust explosions under varying NaHCO3 concentrations were systematically investigated. The results indicate that increasing NaHCO3 concentration substantially alters heat transfer and flow structures at the flame front, resulting in increasingly irregular and fragmented flame morphologies. These changes delay the interaction between pressure waves and flame propagation, thereby reducing the peak explosion pressure (Pmax) and the maximum pressure rise rate ((dP/dt)max). Analysis of the spatiotemporal distributions of gas-phase radicals and intermediates reveals that flame inhibition is governed by the combined effects of thermal attenuation and gas-phase chemical inhibition. In the high-temperature region near the flame front, gas-phase NaOH efficiently scavenges key radicals (e.g., O), thereby inhibiting chain-branching reactions and heat release. Meanwhile, CO2 acts as both a diluent and a heat-absorbing medium, and its synergistic interaction with NaOH significantly weakens the overall energy release of the system. From the perspectives of reactive flow and radical evolution, this study provides a mechanistic interpretation of the inhibition of aluminum dust explosions by NaHCO3. These findings provide a reliable numerical framework and theoretical foundation for dust explosion inhibition studies and the development of high-efficiency inhibition materials.

ABSTRACT This study integrated dust explosion suppression experiments with reactive force field molecular dynamics (ReaxFF‐MD) simulations to elucidate the suppressive performance and microscopic mechanisms of melamine cyanurate (MCA) in aluminum dust combustion and explosion. Experimental results demonstrated that MCA exhibited a pronounced suppression effect on aluminum dust, with a critical concentration of 750–800 g/m 3 required for complete suppression. The strong endothermic decomposition of MCA occurring below the endothermic melting temperature of aluminum dust enabled it to exert an effective suppressive effect during the early stages of combustion and explosion. ReaxFF‐MD simulations provided atomic‐scale insights into the influence of MCA on the heating and combustion behavior of aluminum particles. During the heating stage, the introduction of MCA significantly prolonged the disappearance time of the face‐centered cubic (FCC) lattice structure of the aluminum core, delaying the melting process of the aluminum core. During the combustion stage, the localized organic suppression layer formed by MCA on the surface of the aluminum particles reduces the oxidation degree and the combustion intensity of the core aluminum atoms. Compared with that of the Al/O 2 system, the maximum temperature rise rate of the Al/50% MCA system within the initial 50 ps was reduced by 58.4%, and the final combustion temperature decreased by 13.1%. Overall, MCA synergistically suppressed the aluminum‐oxygen reaction through physical dilution, endothermic decomposition, and radical scavenging. These findings provided a theoretical basis for optimizing conventional explosion suppressants and for the molecular design of novel suppressants.

The cabin environment of next generation inhabited spacecraft is characterized by sub-atmospheric pressures and elevated oxygen concentrations, creating unique combustion conditions for onboard solid materials. The influence of inert-gas dilution on flame spread and extinction is of critical importance for spacecraft fire safety. Experiments were conducted to investigate the opposed flame spread and extinction behaviors over a thick PMMA in low-velocity flow, focusing on the distinct influences of N2, Ar and CO2. The flamelets emerge under sub-atmospheric environment, and the critical flow-velocity decreases as oxygen concentration increases. The flame spread rate decreases with the reduced ambient pressure as predicted, but becomes independent of the gas species when the pressure is lower to a critical value. The decreased ambient pressure reduces the flame spread rate through thermal effect, although different dilutions influence through various effects. An effective Lewis number and Péclet number are proposed as the governing parameters for near-limit flames, since they represent the thermophysical properties of materials and environmental conditions, respectively. A normalized map is then established to compromise the effect of flow velocity, ambient pressure and gas dilution. These findings provide fundamental insights into flame spread and extinction under sub-atmospheric, diluted conditions relevant to microgravity spacecraft environment.

[Objective]The flame spread rate,burning rate,and heat release rate are the key aspects of flammability,which determines the fire development process and the intensity of the heat release.The burning characteristics of a solid fuel strongly depend on the environmental conditions,such as the oxygen concentration,flow rate,and ambient pressure.Most studies have focused on the flame spread rate,and only a few have focused on the burning rate,heat release rate,and soot generation characteristics.When the burning rate of solid materials exceeds the smoke point,the distribution of soot within the flame and the volume fraction of soot undergo a large transformation,thus affecting the heat release rate and changing the flame propagation process.In addition,the generation and transport of soot are crucial for fire safety.An urgent need exists to understand the combustion and soot behavior during flame propagation in real fire scenarios.[Methods]In this study,flame spread phenomena over a cylindrical polymethylmethacrylate(PMMA)at different airflow velocities have been experimentally studied under microgravity and normal gravity conditions.Microgravity experiments were performed in a drop tower.In microgravity experiments,flame spread in purely opposed flow was observed,and in normal gravity experiments,downward flame spread behaviors in the mixed flow with buoyancy-induced and forced flows were investigated.The airflow velocities used in both experiments were 1-35 cm/s,and the diameter of the solid sample was 2-10 mm.In the normal gravity environment,the variation in the sample mass during the flame spread process was recorded using an electronic balance,and the soot volume fraction inside the flame was tested using the light extinction method.In both sets of experiments,the luminescent flame and the stoichiometric flame contour photographed with the CH filter were recorded.[Results]The flame area,which is estimated from the stoichiometric contour of the CH radicals of the flame,shows a good linear correlation with the measured mass burning rate.Meanwhile,the flame area decreases with increasing flow rate in a normal gravity environment,while in a microgravity environment,the flame area increases to a maximum value and then decreases with increasing opposed flow velocity,indicating a nonmonotonic variation trend.The soot formation of PMMA specimens depends on the diameter of the specimen and the flow conditions,and the experiments in normal gravity show that larger specimen diameters and lower flow rates favor soot formation.However,the flow velocities corresponding to the smoke points of PMMA specimens in different gravity environments are quite different.The flow velocities corresponding to the smoke points of specimens in microgravity environments are even lower.In normal gravity,the soot concentration in the flame decreases with increasing flow velocity.In contrast,in microgravity,solid materials have different smoke points,and the soot concentration increases with the convection velocity.[Conclusions]The fuel burning rate and soot formation depend on the airflow velocity.The relationship between the flame area and the burning rate is independent of the fuel smoke point.Because of the variation in the flow condition,the resident time and oxidization time become different,resulting in variation in the soot formation characteristics.

Sodium-ion batteries (SIBs) have developed into prospective contenders in energy storage systems because of their significant superiority in abundant resources and low cost. The cycling performance and thermal stability at high potential hinder the commercial application of SIBs. The electrochemical performance is comprehensively investigated and degradation characteristics are elucidated through the incremental capacity-differential voltage and electrochemical impedance spectroscopy analysis combined with scanning electron microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffractometer characterizations. The loss of conductivity (LoC) and the loss of active material (LAM) are proven to be principal degradation modes. Key insights are that bulk degradation and structure evolution of NaNi1/3Fe1/3Mn1/3O2 (NFM) at high potential are pivotal factors leading to the decline of capacity and thermal stability. Meanwhile, the uneven cathode electrolyte interphase (CEI) due to the cathode/electrolyte interfacial side reactions simultaneously affect the cycling performance. In addition, it revealed that high potential weakens the thermal stability of NFM and the oxygen released from pyrolysis of NFM impacts the thermal stability of NFM/electrolyte system. These findings provide valuable insights for NFM material optimization in cycling stability and inspire concern about the material-level thermal safety design at high potential.

As a carbon-free energy carrier, hydrogen-ammonia mixture has significant development potential in internal combustion engine applications. To clarify the coupling mechanisms between flame acceleration and explosion overpressure generation, the effects of obstacle hole shape, obstacle position, and ammonia ratio on flame evolution, flame tip speed, and pressure dynamics on hydrogen-ammonia-air flame in a horizontal closed duct were investigated. Specifically, the obstacle positions in this study were determined based on the three different stages of flame evolution: 1) the finger-shaped flame acceleration stage, 2) the flame skirt-wall contact deceleration stage, and 3) the tulip flame speed fluctuation stage. The objective is to investigate the influence mechanisms of obstacles at each stage. For flame evolution and flame tip speed, the obstacle installed at the tulip flame stage (#3) induces the strongest flame turbulence intensity, followed by the obstacle located at the flame skirt wall-contact stage (#2), with the lowest turbulence intensity observed for the obstacle installed in the early finger-shaped flame stage (#1). The enhancement effect of obstacle #2 on flame acceleration is the most significant, as the flame tip speed reaches its peak at the flame skirt wall-contact stage (#2). For pressure dynamics, the pressure fluctuation amplitude is greatest under obstacle #2 condition, while it is smallest under obstacle #3 condition due to the irregular flame front disrupting the reflection of pressure waves. For the explosion overpressure generation mechanism, the theoretical model exhibits good predictive performance, with the theoretical results effectively reproducing the experimental explosion overpressure. The acceleration factor can quantify the flame acceleration effects well and also reveal that the flame acceleration effect on flame tip speed is a key factor influencing explosion overpressure and pressure rise rate.

Sustained rapid surface cooling is critical for flame suppression and reignition prevention during fire accidents. Water mist, with its high specific heat capacity and latent heat of vaporization, is widely used to cool hightemperature surfaces. However, its application is constrained by limited firefighting water resources. Previous studies enhanced the heat transfer efficiency of water by incorporating surfactants, nanoparticles, or lowmolecular-weight (low-MW) polymers. However, they hardly studied the problem of low water utilization caused by droplet boiling and breakup during the cooling process. To address this problem, this study improved the rheological properties of droplets by adding high-MW polymers to water. We used high-speed cameras and infrared thermal imagers to investigate the dynamic behavior and cooling performance when droplets impacted surfaces under contact boiling conditions. We found that low-concentration polymer additives suppressed droplet breakup, and splashing, prolonging the droplet-surface contact time. The droplets retained specific heat and latent heat of vaporization comparable to those of water. Temperature data indicated that the extended contact time enhanced the heat absorption of droplets (1.6-2.7 times of water) and improved liquid utilization (2-4 times of water). Furthermore, this study analyzed the force dynamics during droplet deformation and established a quantitative relationship between the maximum spreading factor and Weber (We) and Reynolds (Re) numbers, providing a theory for heat transfer rate analysis. This study revealed the coupling mechanism between the dynamic deformation and heat transfer processes during droplet impact on the heated surface, providing a new direction for developing fire-extinguishing additives for water mist.

Applying renewable hydrogen-ammonia mixed energy, composed of green hydrogen and green ammonia, in internal combustion engine can help reduce carbon emissions from the transportation sector. It is essential to understand the fundamental combustion characteristics to support its development. Therefore, the effects of equivalence ratio, ammonia ratio, and obstacle number on hydrogen-ammonia-air flame dynamics in an obstructed duct are obtained in this work. A prediction model is established to reveal the flame acceleration and overpressure generation. The results indicated that as the obstacle number increases, the flame structure within the main flame vortex transitions from wrinkled to filamentous fragmented flame structure; the flame tip speed increases, with the maximum value occurring at the cumulative acceleration stage. As the ammonia ratio increases, both the maximum flame tip speed and the speed fluctuation amplitude decreases. Regarding the explosion overpressure, the maximum explosion overpressure increases slightly with the increasing obstacle number. When the ammonia ratio is below 52 = 20 %, the obstacle #3 significantly increases the amplitude of explosion overpressure fluctuation. The prediction model can accurately predict the pressure rise rate under different experimental conditions and suggest that the flame stretching acceleration and the turbulent acceleration are the primary factors affecting the pressure rise rate.

In accordance with the United Nations Sustainable Development goal #7 - affordable and clean energy, the concept of reversible reactive flow (N2O4/NO2) inside ribbed channel is proposed for low-temperature waste heat recovery. Quasi direct numerical simulations are performed to reveal the relationship between flow, heat/mass transfer, and chemical characteristics with different rib inclined angles (90 degrees and 45 degrees). The analyses indicate that the reaction of N2O4 2NO2 has limited influence on flow patterns inside the ribbed channel, but intensifies the heat transfer considerably. For the 90 degrees reactive case, the enhancement of Nusselt number reaches 112.7 % when Reynolds number is 2000. Although non-equilibrium thermal-chemical phenomenon is observed by instantaneous snapshots, time-averaged results show that the forward endothermic reaction is concentrated close to the heated wall. The flow structures transport fluid pocket consisting of "overheated" gas and triggers local backward exothermic reaction, which decreases the thickness of thermal boundary layer and thereby intensifies the overall heat transfer. For the 45 degrees inclined reactive case, a flow circulation at local equilibrium between heat release and absorption is formed by the rib-induced large-scale vortices. The comprehensive thermal performance is further improved by 24.6 % compared to the 90 degrees reactive case, which attributes to higher Nusselt number and lower friction loss.

The characteristics of gas-solid hybrid explosions are heavily influenced by their components and suppressants, making this a critical focus in industrial explosion prevention research. The effects of ethylene (C2H4) on the explosion characteristics of polyethylene (PE) dust were investigated using a 20 L explosion sphere apparatus, and the suppressive performance of melamine polyphosphate (MPP) on C2H4/PE hybrid explosions was evaluated. The study systematically investigated explosion overpressure, flame propagation, explosion products, and the chemical reaction kinetics. The results indicate that as C2H4 concentration increases, the explosion intensity of the gas-solid hybrid mixture initially increases, reaching a maximum at 7 %, before decreasing. The incorporation of 70 wt% MPP reduced the maximum explosion pressure (Pmax) and flame propagation speed of the hybrid mixtures by 11.19 % and 37.74 %, respectively. The addition of C2H4 significantly accelerated the pyrolysis and oxidation of PE dust, leading to the release of highly reactive free radicals. These radicals enhanced the porosity and induced cracking in the explosion product particles. In contrast, the MPP inhibited the reactions through "HOPO PO2" and "HOPO2PO2" suppression cycles, which efficiently consumed H, OH, and O free radicals. This decreased the chain reaction intensity and suppressed combustion by forming phosphorus oxides and nitrogen-containing compounds. Although MPP showed some effect in inhibiting the explosion of the C2H4/ PE hybrid system, the presence of C2H4 significantly altered the reaction kinetics and radical generation pathways of the system, which made the difficulty of explosion inhibition increased compared to the original mixture without C2H4.

The pyrolysis of C2H4/NH3 mixtures was conducted in a plug flow reactor (PFR) in the temperature range of 973 K-1373 K. The pyrolysis products, including C2H4, NH3, C2H2, C6H6 and HCN, were quantified using gas chromatography (GC) and Fourier transform infrared (FTIR) spectroscopy to elucidate the thermal decomposition behavior of C2H4 and NH3, as well as the effects of NH3 on the formation of gaseous soot precursors. The results indicate that both C2H4 and NH3 conversion increase during co-pyrolysis compared to their individual pyrolysis. Moreover, C2H4 shows a more pronounced promoting effect on NH3 decomposition. Kinetic analysis reveals that the reactions C2H4 + NH2 and NH3 + CH3 are primarily responsible for the increased conversion of C2H4 and NH3, respectively. The effects of NH3 on soot precursors formation (e.g., C2H2 and C6H6) exhibit a non-monotonic trend with reaction temperature. Specifically, NH3 addition promotes soot precursors formation below 1273 K but inhibits it above 1273 K. This trend is determined by the competition between NH3-induced enhancement of C2H4 decomposition and the effects of C-N interactions. The former consistently promotes the formation of soot precursors, while the latter becomes significantly effective in inhibiting their formation only above 1273 K by removing C atoms from participating in soot precursors formation. This finding is supported by FTIR measurements with a significant increase of HCN being formed at temperature at 1273 K. It should be noted that as the temperature further increases, the concentration of HCN decreases due to its involvement in the formation of N-containing polycyclic aromatic hydrocarbons (NPAHs). Meaningfully, the molecular structure of NPAHs were identified using gas chromatography-mass spectrometry (GC-MS). Notably, existing kinetic mechanisms are unable to satisfactorily predict the quantitative trends of the experimental results, highlighting the need for further mechanism improvement and refinement.

Navigating multi-agent reinforcement learning (MARL) environments with sparse rewards is notoriously difficult, particularly in suboptimal settings where exploration can be prematurely halted. To tackle these challenges, we introduce Hierarchical Symbolic Multi-Agent Reinforcement Learning (HS-MARL), a novel approach that incorporates hierarchical knowledge into MARL to effectively reduce the exploration space. We design intermediate states to decompose the state space into a hierarchical structure, represented using the Hierarchical Domain Definition Language (HDDL) and the option framework, forming domain knowledge and a symbolic option set. We leverage pyHIPOP+, an enhanced hierarchical task network (HTN) planner, to generate action sequences. A high-level meta-controller then assigns these symbolic options as policy functions, guiding low-level agents in their exploration of the environment. During this process, the meta-controller computes intrinsic rewards from the environmental rewards collected, which are used to train the symbolic option policies and refine pyHIPOP+'s heuristic function, thereby optimizing future action sequences. We evaluate HS-MARL with comparison to 15 state-of-the-art algorithms across two types of environments: four with sparse rewards and suboptimal conditions, and a real-world scenario involving a football match. Additionally, we perform an ablation study on HS-MARL's intrinsic reward mechanism and pyHIPOP+, along with a sensitivity analysis of intrinsic reward hyperparameters. Our results show that HS-MARL significantly outperforms other methods in environments with sparse rewards and suboptimal conditions, underscoring the critical role of its intrinsic reward design and the pyHIPOP+ component. The code is available at: https://github.com/Mxc666/HS-MARL.git.

The rising global warming concerns make it inevitable to phase out fossil fuels sooner rather than later, as they contribute to about 60% of the greenhouse gas emissions in the world. One alternative to fossil fuels in heavy industry is green hydrogen. However, hydrogen combustion in air is known to emit the oxides of nitrogen (NOx) which are harmful to health. An improved comprehension of these NOx emissions and their formation pathways is the first step towards their mitigation. This paper intends to improve the methodology to understand the NO formation pathways in a non-premixed, swirl-stabilised, hydrogen/air gas-turbine combustor. To do so, high-fidelity large-eddy simulations (LESs), extended proper orthogonal decomposition (EPOD) technique and zero-dimensional (0D) perfectly stirred reactor (PSR) analyses are combined to utilise the merits of each of these techniques. While the LES ensures that the flow-field and reactions are well captured, EPOD is applied to identify two points featuring high positive and high negative fluctuations of the rate of production of NO, i.e. ROPNO, respectively. The 0D PSR provides a platform for a cost-effective yet detailed chemical pathway analysis at these identified points. Although both NO production and consumption reactions are prevalent at the chosen points, the net effect is that of NO production as was evidenced by the positive value of ROPNO at these points. However, the rate of production of NO differed between the two points. While the major NO formation and consumption reactions were found to be the same at both the points, their contributions to overall ROPNO varied. The major NO production reaction at both the points was NNH+O NH+NO, contributing to 37% and 26% at the points with high positive and high negative ROPNO fluctuations, respectively. Moreover, the species composition was different at the chosen points, which is expected in a non-premixed combustion configuration. For instance, the mass fractions of NNH and O, i.e. the reactants in the major NO production reaction, were respectively 18.28% and 8.77% higher at the point with high positive ROPNO fluctuation compared to the point with high negative ROPNO fluctuation. The above-mentioned differences in the reactions' contributions to ROPNO at the chosen points could be attributed to such variation in local composition, which is highly likely in non- premixed combustion. The methodology proposed in this paper enables a detailed chemical pathway analysis emphasising the points featuring high ROPNO fluctuations. This technique, which conducts a focused analysis of the NO formation pathways in a combustor, can be a useful tool in the effort towards designing cleaner hydrogen combustors.

In order to reduce the excessive nitrogen oxide (NOx) emissions from traditional swirl burners in heat treatment furnaces, a low nitrogen burner optimization method based on gas classification technology was proposed. Firstly, the ordinary swirl burner was used as the basic structure, and the gas grading structure was added without significantly increasing fuel consumption. Secondly, the ANSYS Fluent software system was used to simulate the influence of the blade angle and air flow rate of the first-stage stator cascade on the NOx generation. Finally, by comparing the mixing uniformity, temperature distribution and NOx concentration field, the optimal parameter combination was determined. The results show that the gas grading structure significantly improves the mixing efficiency of secondary gas and swirling air, the heat load distribution is more uniform, and the thermal NOx production is reduced. When the first-stage stator cascade blade angle is 30°, the air flow rate is 1.15 m/s, and the proportion of primary gas is 65%, the burner performance is optimal, and the NOx emission is significantly reduced compared to the traditional structure. This study provides an optimization direction for the design of low nitrogen burners and has reference value for the environmental protection transformation of industrial combustion equipment.