The increased penetration of inverter-based resources is reducing system inertia and challenging traditional frequency modeling approaches based on a single global frequency. Accurate estimation of local bus frequencies has therefore become essential for dynamic analysis and control. This paper proposes a near real-time bus frequency estimation framework that combines the analytical structure of the frequency divider (FD) formulation with the distributed inference capability of the Gaussian belief propagation (GBP) algorithm. By representing the power system as a factor graph, the proposed method enables iterative and fully distributed computation of bus frequencies without matrix inversion. The proposed algorithm enables estimation on a much smaller time scale than classical approaches, allowing faster detection of frequency deviations. Simulation studies on standard test systems demonstrate that the GBP framework achieves the same accuracy as the classical FD, while offering improved scalability and suitability for distributed implementation.
The recent availability of a consistent electron collision cross-section set for the ultra-low GWP HFO-1234ze(E) (HFO) enables performance simulations of resistive plate chambers (RPCs) operated with HFO-based gas mixtures. We present a simulation framework that reproduces key detector observables measured in trigger-purpose RPCs, such as detection efficiency and cluster size. The simulation additionally provides new insights into streamer formation through a novel streamer inception criterion that captures the observed trends in streamer probability. For mixtures containing CO2, HFO, SF6, and isobutane, the Pareto front between avalanche-streamer separation and relative CO2 equivalent emissions is evaluated using a multi-objective Bayesian optimization approach under a low working point constraint, so the mixture can be used with already installed infrastructure. The optimization confirms that the ECO2 gas mixture (60% CO2, 35% HFO, 4% isobutane, 1% SF6), previously identified through experimental studies, is a Pareto optimal choice when the operation is constrained to a low working point. If higher working points are acceptable, mixtures with a higher HFO percentage provide larger avalanche-streamer separation while enabling a reduction of the SF6 percentage, thereby reducing the environmental impact even further.
This study examines how nozzle geometry and surface structure govern flash-boiling of liquid ammonia for steady state injection conditions for a 100 μm nozzle diameter. Conventionally manufactured stainless-steel nozzles are compared with optically transparent fused silica glass nozzles fabricated by Selective Laser-induced Etching (SLE) using nominally identical CAD geometries and length-to-diameter ratios L/D=2.5, 5, and 10. The manufactured internal geometries are quantified by μCT and optical microscopy, which reveal nanoscale surface features most likely relevant to heterogeneous nucleation. High-speed shadowgraphy across injection pressures ranging from 0.86 MPa–1.45 MPa and superheat pressure ratios of Rp=3--12 provides visualization of internal two-phase flow and external spray morphology as a function of boundary conditions.Steel nozzles exhibit substantial deviations from nominal geometry and pronounced inlet roughness, leading to asymmetric sprays and significant nozzle-to-nozzle variability. SLE nozzles reproduce the target geometry and generate axisymmetric sprays with reduced dispersion in cone-angle, but somewhat attenuated flashing, consistent with smoother internal surfaces and more controlled nucleation. Transparent SLE nozzles reveal previously inaccessible internal phenomena, including (i) pulsating atomization driven by pre-existing bubbles in the feed system and (ii) cavitation-enhanced flash-boiling via thin vapor ligaments and Rayleigh-type bubble chains in the orifice. The results demonstrate that flash-boiling of liquid ammonia is controlled by a tightly coupled interplay of superheat, geometry, surface structure, and manufacturing route. This establishes SLE-fabricated fused silica nozzles as a platform for mechanistic studies and design of flash-assisted LNH3 injection systems for low-emission ammonia combustion.
Tire-pavement interaction produces a spatially heterogeneous boundary traction that cannot be fully represented by uniform vertical pressure, particularly when braking, driving, or lateral slip generates appreciable tangential loading. Existing layered pavement models mainly address forward response prediction and provide limited capability for reconstructing unknown contact tractions and mechanically admissible transient subsurface fields from sparse observations. This study develops a physics-informed neural network (PINN) framework for inverse tire-contact traction reconstruction and dynamic finite-layer pavement response. The tire footprint is represented by a total normal contact pressure and longitudinal and lateral traction components, without imposing a mechanically unidentifiable decomposition of the normal pressure. A three-dimensional transient finite-element reference model provides mechanics-consistent displacement, stress, strain, reaction, and strain-energy fields under a time-dependent moving load. These fields are coupled with neural reconstruction through dynamic equilibrium, constitutive, boundary, interface, force-closure, initial-condition, and regularization constraints. Source realizations are partitioned before training, and held-out contact fields are reconstructed from sparse displacement and stress histories without including their prescribed source values in the inverse loss. The framework therefore provides a unified differentiable setting for contact-traction identification, transient pavement-response reconstruction, source-disjoint evaluation, stability assessment, domain transfer, and robustness analysis.
A novel autoignition-assisted, high-temperature High-Pressure Well-Stirred Turbulent Combustor (HP-WSTC) has been developed for detailed kinetic studies of fuels under gas-turbine conditions that were difficult to obtain with conventional reactors and flame chemistry facilities. It is designed for operations at 1–20 atm, 1200–2200 K, and residence times of 1–100 ms, enabling treatment as a zero-dimensional premixed-combustion system. Methane combustion experiments at 1–10 atm were compared with 0D simulations, showing good agreement for major species across a wide equivalence-ratio range, demonstrating the reliability of the HP-WSTC. Although methane combustion kinetics are well established, NO predictions still show large discrepancies, even at atmospheric pressure. Sensitivity analyses identify CH-pool reactions, including CH2 + O2 = CH2O + O and CH + CO2 = HCO + CO, as key uncertain reactions. The developed HP-WSTC provides a new platform for fuel kinetic investigations and bridges the gap between reactor and flame facilities for high-temperature kinetic studies under gas-turbine conditions.
