• Flame propagation of iron–methane–air mixtures was investigated experimentally. • Flame speed decreased near stoichiometric methane due to iron particle heat loss. • Under lean methane, iron oxidation supplied extra heat and enhanced propagation. • XRD showed Fe 2 O 3 formation under lean and FeO/Fe 3 O 4 under stoichiometric condition of methane-air. • Results clarify gas–solid interactions governing hybrid flame propagation. Recently, interest in metal powders such as iron has grown due to their high energy density and carbon-free combustion, making them promising sustainable energy carriers. However, their heterogeneous combustion and low burning velocity limit standalone use, and hybridization with gaseous fuels is often required to support ignition and stable propagation. Nevertheless, the interaction between gas and solid phases during ignition and flame propagation remains insufficiently understood. In this study, the flame propagation behavior of iron–methane–air hybrid mixtures was experimentally investigated under various methane equivalence ratios. Combustion tests were performed in a 4.2 L closed chamber equipped with a schlieren visualization system and a high-speed camera. Spherical iron powders were dispersed into methane–air mixtures and ignited by spark discharge, and the resulting flame radius and propagation speed were measured and compared with those of pure methane–air flames. Results show that near the stoichiometric methane condition, the flame propagation speed of hybrid mixtures decreased to roughly half that of methane–air flames, as the heat losses outweighed the heat released from iron combustion. In contrast, under lean methane conditions, the propagation speed exceeded that of methane–air flames, indicating additional heat release and volumetric expansion from iron combustion.

Fig. 1 The macroscopic particle distribution of pulverized coal particles at 9 s and 13 s:(a) semi-vertex angle75°; (b) semi-vertex angle 65°;(c) semi-vertex angle55°; (d) semi-vertex angle45°; (e) semi-vertex angle35°; (f) semi-vertex angle 25°; (g) semi-vertex angle15°. • The discharge characteristics of eccentrically bent hoppers is simulated by DEM. • A regression model is established to fix the contact parameters of coal powder. • A smaller semi-vertex angle is conducive to the flow of pulverized coal. • The unloading stability of the eccentric conical coal hopper is better. Particle blockage is a persistent issue during the discharge of coal bunkers. To achieve stable and rapid discharge, an eccentrically bent hopper is proposed, and this structure combines the advantages of both curved and eccentric hoppers. This paper employs Discrete Element Method (DEM) to investigate the discharge characteristics of eccentrically bent hoppers with semi-vertex angles ranging from 15° to 75°. The results show that when the semi-vertex angle exceeds 45°, the average mass flow rate of pulverized coal does not change significantly with semi-vertex angle, and the velocity distribution of coal particles during discharge exhibits an asymmetric pattern. In contrast, when the semi-vertex angle is less than 45°, the average mass flow rate increases obviously as the semi-vertex angle decreases, and the asymmetry of velocity distribution during discharge is reduced. Furthermore, the stability of coal particle discharge with respect to the semi-vertex angle is analyzed using the coefficient of variation ( C v ) over both the stable discharge period and the entire discharge process. When semi-vertex angle is greater than 45°, the discharge stability of pulverized coal is relatively poor. As semi-vertex angle is less than 45°, the C v remains at a stable value, indicating smooth and stable discharge of pulverized coal.

This study establishes a holistic strategy for high-performance Fe 80 Si 5 B (11-x) P x Nb 3 Cu 1 soft magnetic composites (SMCs) through phosphorus(P) alloying design and low-pressure thermal encapsulation molding process(LHP). A spheroidization-solidification competition parameter η (η = t sph /τ) is proposed to quantify morphology evolution, revealing that η ≤ 0.6 achieves >92 % spherical powders (D 50 = 20 μm), while η ≥ 1 induces dendritic defects. Fig. Schematic diagram of internal structure of Fe 80 Si 5 B 8 P 3 Nb 3 Cu 1 powder sample after annealing treatment. The as-quenched Fe 80 Si 5 B 8 P 3 Nb 3 Cu 1 powder form a heterogeneous amorphous matrix due to rapid solidification, resulting in atomic-scale dense-packed and loose regions. Annealing treatment can cause structural relaxation in the amorphous matrix, leading to the diffusion of atoms from the dense region to the loose region. The atomic density in the loose region increases, making the microstructure inside the material more uniform and releasing internal stress. The internal structural evolution process can be summarized into three stages: stress-relief stage and Nanocrystallization stage and secondary phase precipitation stage. • A spheroidization-solidification competition parameter η is proposed to quantify morphology evolution. • When η ≤ 0.6 achieves > 92 % spherical powders, while η ≥ 1 induces dendritic defects. • Annealing optimizes magnetic properties via dual-phase evolution. • Spherical powder combined with LHP enables defect-free monolithic inductors. This study establishes a holistic strategy for high-performance Fe 80 Si 5 B (11-x) P x Nb 3 Cu 1 soft magnetic composites through phosphorus alloying design and low-pressure thermal encapsulation molding process. A spheroidization-solidification competition parameter η is proposed to quantify morphology evolution, revealing that η ≤ 0.6 achieves >92 % spherical powders, while η ≥ 1 induces dendritic defects. P addition tunes η by elevating undercooling and viscosity, enabling precise morphology control. The research indicate that the addition of P enhances glass forming ability by reducing the liquidus temperature and stabilizing the deep eutectic composition, achieving a completely amorphous structure and suppressing the crystallization of α-Fe (Si, B). P-induced Fe-P-B covalent clustering reduces coercivity but slightly lowers saturation magnetization due to disrupted exchange coupling. Annealing optimizes magnetic properties via dual-phase evolution: low-P systems (x ≤ 2) exhibit α-Fe(Si,B) coarsening-driven Hc spikes, while high-P alloys form amorphous/nanocrystalline composites with exchange-spring effects. Cu/Nb synergistically stabilize nanograins and suppress coarsening. Spherical powder combined with LHP enables defect-free monolithic inductors, achieving a 4-fold higher DC breakdown voltage (>1000 V) and 23.8 % improved saturation current compared to cold-pressed counterparts. LHP minimizes residual stress, restricting permeability fluctuations to ≤3 % under thermal stability testing, versus ≥10 % in cold-pressed processes.