Reliable ignition and rapid heat release are key issues for hydrocarbon-based scramjet combustors. H-2 enrichment is one of the commonly employed techniques for improving hydrocarbon reactivity. However, it is observed that the extent of improvement is highly dependent on the inherent chemical kinetics of the parent fuel. H-2-assisted combustion of CH4 and C2H4-based scramjet combustor fuel blends is analyzed using a hybrid approach of detailed chemistry and reacting flows. To assess the role of H-2 as a pilot fuel, ensuring hydrocarbon-based combustion, the mole fraction of H-2 is varied from 5 to 45%. Using 2D RANS simulation with finite rate chemistry, flame structures, temperature distribution, and combustion efficiency are analyzed. Additionally, detailed chemistry is employed for calculating ignition delay, laminar flame speed, and reaction sensitivity. From the simulation results, it is observed that C2H4-based blends exhibit rapid ignition characteristics even with low fractions of H-2. However, for CH4-based blends, higher fractions of H-2 are required for reliable ignition characteristics. For CH4-based blends with higher fractions of H-2, it is observed that a maximum combustion efficiency of 58% is attained. However, for C2H4-based blends, combustion efficiency greater than 75% is observed for relatively low fractions of H-2. H-2 addition for CH4-based blends reduces the ignition delay and improves heat release rates and flame stabilization. Thus, it is observed that for highly reactive hydrocarbon-based fuel blends, such as C2H4, H-2 addition is not significant. However, for less reactive hydrocarbon-based fuel blends, such as CH4, H-2 addition is highly significant for reliable scramjet combustor operation.
Coal spontaneous combustion is a critical underground mining hazard, driven primarily by O-2 adsorption/activation on coal pore surfaces. MD and GCMC simulations using Materials Studio investigated competitive adsorption of CH4, CO2, and O-2 on an anthracite model (C142H62N2O10S) from Yangmei No. 5 Mine, Shanxi. The model was built from C-13 NMR, FTIR, and XPS. Simulations ran at 283.15, 298.15, and 313.15 K, 0-25 MPa, covering single, binary, and ternary mixtures. A previously unreported finding is the identification of O-2-specific adsorption sites within anthracite that selectively accommodate CO2 while excluding CH4, revealing a displacement mechanism by which CO2 replaces pre-adsorbed O-2. At 298.15 K and 25 MPa, saturated capacities follow CO2 (6.4) > O-2 (5.6) > CH4 (3.6 molecules/cell). At low pressures, CO2 adsorption exceeds 85% of saturation, whereas CH4 and O-2 reach only similar to 50%. Isosteric heats (CO2: 35.2; O-2: 27.6; CH4: 19.8 kJ & centerdot;mol(-)(1)) confirm physisorption. In mixtures, CO2 exhibits the highest selectivity, with CO2/CH4 >1.0 across all conditions; CO2/O-2 shows minimal temperature dependence, indicating effective O-2 displacement across a wide temperature range. These findings provide a molecular-level foundation for optimizing CO2 injection. Limitations include the use of a single coal model; future work should incorporate varying ranks and moisture effects.
Current research on faulty coal-fired swirl burners has shortcomings in secondary air distribution, limited understanding of multi-jet interactions, and a primary focus on full-load conditions, which hinders achieving stable combustion at 20%-30% boiler rated load. This work implemented a self-developed flame stabilization technology, combining gas-solid experiments using a laser particle dynamic anemometer (PDA) with full-furnace simulations. PDA results showed that at inner secondary air (ISA) ratios of 38%, 43%, and 47%, the recirculation zones formed annular structures, originating at distances of 0.3d, 0.1d, and 0.1d from the burner outlet, with maximum diameters of 0.578d, 0.448d, and 0.598d, respectively (where d represents the inner diameter of the burner outlet). A net flux ratio metric was proposed to quantitatively assess the annular recirculation zone. With an ISA ratio of 43%, the total net flux was positive, reflecting weak recirculation; at 38% and 47%, the total net flux was less than zero, indicating a strong overall recirculation tendency. The full-furnace simulation revealed a low-velocity zone under hot-state conditions that closely matched the recirculation distribution obtained from the gas-solid experiments. An increase in the ISA proportion led to a larger low-velocity zone and strengthened the flame's radial spreading. The novel technology increased the temperature of the main combustion zone, reduced fly ash carbon content, and substantially lowered NOx emissions. At 20% and 30% load, operating only the new burners maintained the main combustion zone temperature above 1000 degrees C.
Explosive ignition, often described as detonation-like in previous studies, has been reported in hypergolic bipropellant thrusters and may result in catastrophic system failure. Explosive ignition occurs on a significantly shorter timescale than conventional ignition and can be accompanied by a rapid rise in chamber pressure, potentially leading to severe thruster damage or failure. However, the underlying mechanisms, specifically whether a shock wave is generated, remain poorly understood. This study employed high-speed visualization to investigate the generation of shock waves and to estimate their origin at the fuel/oxidizer interface. In combustion tests, hydrazine (N2H4) droplets were introduced into a pool of dinitrogen tetroxide containing 3 wt % nitrogen monoxide (MON-3). Explosive ignition occurred on a substantially shorter timescale than non-explosive ignition, accompanied by rapid flame propagation and the clear presence of a shock wave. Immediately preceding ignition, a localized orange emission was observed at the N2H4/MON-3 interface, followed by a sudden interface deformation. These observations suggest that interfacial heating associated with the localized emission induces rapid gas generation, leading to a strong pressure disturbance that is consistent with the observed shock wave formation. This study provides new experimental evidence regarding the mechanism of explosive ignition in hypergolic bipropellant thrusters.
Reliable ignition of turbojet engines at high altitude remains a critical challenge because reduced pressure and temperature impair fuel atomization and evaporation while also increasing flame kernel instability, thereby reducing ignition reliability and flame stabilization. Existing studies predominantly focus on material-level combustion behavior or laboratory-scale evaluations, often lacking validation under engine-relevant conditions. In this study, a system-level approach is presented by integrating material optimization, surface-coverage-based coating considerations, pellet-based configuration, and controlled processing to improve pyrotechnic ignition performance. Mg-KNO3-Al-Viton compositions were systematically investigated, yielding a maximum flame temperature of 3369.91 K for Mg-KNO3-Viton (32.5/62.5/5 wt%) and up to similar to 3760 K with aluminum addition (27/60/8/5 wt%). The binder content (5 wt% Viton) was selected based on a theoretical surface coverage analysis using the calculated specific surface area of the powder mixture, providing adequate particle coverage and improved particle dispersion. The prepared compositions were compacted into pellets to achieve consistent geometry and reproducible ignition performance. Experimental results show sustained combustion exceeding 7 s. The findings suggest that aluminum addition alone is insufficient to achieve high-performance ignition, and that ignition behavior is governed by the coupled interaction of composition, multi-metal effects, and binder-related interfacial processes. The proposed approach establishes a formulation-to-system-level framework for improving ignition reliability under conditions where atomization-driven mechanisms are limited, offering a practical and scalable strategy for advanced pyrotechnic ignition systems.
