Shuiqing Li

CH4/NH3 cofiring represents an effective technical approach to overcome the inferior combustion characteristics of NH3. The combustion characteristics and pollutant formation mechanism during the cofiring constitute important research directions. Hence, it is of considerable significance to gain a comprehensive understanding of the CH4/NH3 cofiring and its mutual influence mechanism. This paper first demonstrates that the general “atmospheric type” blending model in the existing literature may lead to extreme hypoxia during the simulation, thereby overestimating the pollutant formation characteristics. Compared with the “fuel-type” blending model proposed in this paper, it is believed that the new model can precisely analyze the cofiring and reaction mechanism of multiple fuels. Subsequently, the “fuel-type” blending model was used to systematically study the effects of temperature, ammonia blending ratio (ENH3), and equivalence ratio (φ) on the cocombustion. Third, by sorting out the reaction network, it was discovered that under the stoichiometric condition, CH4 and NH3 react independently of each other, which is distinct from the phenomenon in the “atmospheric type” blending model. Contrarily, in the fuel-rich scenario, a coupling mechanism occurred between CH4 and NH3. NO can react with the excess CHi groups in the system through NO + CHi → CHiNO → CHiN → HCN/CN, then decouple to generate CO and N/NH, and then further reduce to N2. Finally, the C–N coupling mechanism was investigated to correct the Okafor mechanism and improve the prediction effect of NO and HCN. These findings not only provide a reference for the subsequent ReaxFF MD study of multiple fuels to construct reaction systems in reality but also provide solutions for reducing NO emissions from CH4/NH3 in actual industry.

We report computer simulations on the adhesive loose packing (ALP) limit of monodisperse axisymmetric ellipsoids, spherocylinders, and polymers by the random ballistic deposition method with the hit-stick-freeze assumption. The mean-field results demonstrate that the global packing fraction reaches a maximum value of 0.1469 for spheres, and it is nicely correlated with the aspect ratio in the 1 and -2 power-law relations for extremely oblate and prolate particles, respectively. For a given aspect ratio λ, the density follows the sequence of decreasing packing fraction: spheres > prolate ellipsoids > spherocylinders > polymers for λ spherocylinders > prolate ellipsoids > polymers for λ≥3. In addition, we highlight that the local coordination number excellently follows the normal distribution with a universal mean value of 2.001, regardless of the particle type and aspect ratio. The standard deviation is 0.730 for spheres, which increasingly approaches the asymptotic values of 0.850 for λ→0 and 1.112 for λ→+∞. Furthermore, we find that the radial distribution function is dominantly governed by the first contact shell with three distinct features, corresponding to the local minor-to-minor, minor-to-major, and major-to-major contacts between two particles. Finally, we present the universal correlation forms for both the global packing fraction and the standard deviation of coordination number, covering the wide aspect ratio range of 0.003-60 for ellipsoids and 1-60 for spherocylinders and polymers. We emphasize that the ALP limit represents the minimum-density state achievable via random ballistic deposition of strongly adhesive particles, while looser structures may be obtained by other cluster aggregation processes.

Oxyfuel combustion of zero-carbon fuels offers a promising pathway to carbon-neutral energy and propulsion systems but requires robust laboratory-scale flat-flame burners for fundamental research. This study introduces a laboratory-scale multi-element diffusion burner fabricated via additive manufacturing of 316L stainless steel, featuring an integrated micro-channel architecture for leak-free micro-mixing of fuel and oxidizer and structural fins for enhanced thermal resilience. The burner demonstrates superior flame stability and versatility across a wide range of conditions. These include CH4/NH3/H2 fuel blends with arbitrary compositions, wide global equivalence ratios (0.2–4.0 for CH4/H2 and 0.2–1.6 for NH3), O2 fraction in oxidizer up to 100%, and power loads varying by several orders of magnitude. In situ N2 spontaneous Raman scattering thermometry reveals uniform temperature distributions in CH4/NH3/H2–O2 flames, with post-flame temperatures up to 3000 K, while OH planar laser-induced fluorescence imaging confirms homogeneous radical distributions, stable flame anchoring, and well-defined reaction zones across varied operation regimes. These properties establish the burner as a reliable platform for investigating the kinetics of zero-carbon fuel combustion while also providing a quasi-one-dimensional, high-temperature environment for heterogeneous combustion studies.

Packing of charged micron-sized particles on surfaces is ubiquitous in both natural and industrial processes, where the packing structures critically determine system properties and performance. In practice, the materials of the surfaces can vary widely, giving rise to distinct particle-wall electrostatic interactions that drastically modulate the packing process. Therefore, we perform numerical simulations to study the packing of identically charged micron particles under different electric boundary conditions. We show that the maximum number of deposited particles is strongly influenced by particle-wall interactions, governed by the competition between incident particle kinetic energy and the repulsion from previously deposited particles. Furthermore, the resulting packing structures differ qualitatively: looser packings form near noninteracting or dielectric walls, whereas conducting walls yield much denser configurations. By quantifying energy changes induced by both deposited particles and other incoming particles, we identify two competing electrostatic mechanisms and derive an effective adhesion parameter that captures these effects in a unified framework. Our results highlight the critical role of particle-wall electrostatic interactions in predicting and controlling the packing behavior of charged particles.

The detailed mechanism of how the electronically excited species of air plasma promote the combustion of ammonia remains unclear. Herein, the reactions of NH₂ radical with both singlet and triplet oxygen molecules are investigated by high‐level theoretical calculations. A minimal‐energy crossing point is found on the ²A″ and ²A′ potential energy surfaces of H₂NOO radical, which plays an important role on the product distributions of NH₂ + O₂(a¹Δ_g) reaction. The temperature‐ and pressure‐dependent rate constants of the reactions are predicted by Rice–Ramsperger–Kassel–Marcus theory and master equation simulations. Subsequently, the influence of O₂(a¹Δ_g) on the ignition delay time of ammonia is assessed by updating the existing ammonia combustion model with the computed reaction parameters. The results indicate that 5% O₂(a¹Δ_g) in the total oxygen dramatically accelerate the ignition of ammonia by more than one order of magnitude at ≈1000 K and 1 atm, mainly via the NH₂ + O₂(a¹Δ_g) = H₂NO + ³O reaction. Further, the catalytic effects of ammonia, water, and formic acid on the isomerization of the adduct, H₂NOO radical, of NH₂ + O₂ are studied, which will have implications for modeling the oxidation kinetics of ammonia in both atmospheric and combustion conditions.

Particle resuspension is a common phenomenon in nature and industries but not fully understood yet. In this work, we report direct experimental evidence for turbulence-induced resonance of wall-adhered particles before detachment. The recorded frequency is one or two orders of magnitude lower than that normally predicted by the Rock n' Roll model. The frequency ratio ϕ, between the natural frequency of particle adhesion and wall turbulence frequency, is found to be the key parameter that determines the occurrence of turbulence-induced resonance. This work may shed light on the resonance-enhanced cleaning of very small particles.

Theoretical calculations suggest that there exist other allotropes of cyclo[18]carbon that exhibit either aromaticity or antiaromaticity.