Search Results (136)

Conventional fire monitoring systems frequently exhibit high false alarm rates, delayed response times, and a lack of closed-loop control capabilities, which severely constrain their deployment in complex real-world environments. To address these issues, this paper proposes an embedded fire detection, tracking, and extinguishing system based on multimodal information fusion and a lightweight neural model. The system follows a “Perception–Decision–Execution–Feedback” closed-loop paradigm and is implemented on a heterogeneous cooperative computing architecture comprising OpenMV4 H7 Plus and STM32F103C8T6 microcontrollers. The perception layer implements a decision-level RGB-infrared fusion mechanism that incorporates a pruned, INT8-quantized lightweight FOMO model, enabling real-time fire detection with an inference latency of 210 ms and a model size of merely 1.8 MB under resource-constrained embedded conditions. The decision layer employs a Bayesian inference-based multimodal fusion framework that effectively suppresses spurious fire interference. The vision-only false detection rate is 15.3%. After infrared fusion verification, the system-level false alarm rate is reduced to 2.0% on the interference test set. In the execution layer, a sixth-degree polynomial jet trajectory model was established and combined with an improved PID–PI dual-loop controller to enable dynamic optimization of spray angle and flow rate in real time. Experimental results demonstrate that the proposed system achieves an average fire recognition accuracy of 95.6% with a false alarm rate as low as 1.4%. Furthermore, it realizes an extinguishing accuracy better than ±5 cm within an effective operating range of 10–60 cm and completes the entire perception-to-extinguishing cycle within 8.5 s under illumination conditions ranging from 50 to 100,000 lux. These results demonstrate the excellent real-time capability, robustness, and energy efficiency of the proposed system, providing a practical and scalable solution for autonomous embedded fire-fighting applications in household, industrial, and warehouse environments. Full article

This study explores key technological challenges and innovative strategies for improving the combustion performance and emission characteristics of low-carbon fuel engines, with a focus on natural gas applications. The core bottlenecks of natural gas combustion, including slow combustion speed and high methane slip under lean burn conditions due to wall quenching, crevice effects, and the long distance of flame propagation from the ignition zone to the whole cylinder, are analyzed. The decarbonization of engines further aggravates these issues. Technological solutions are summarized in four categories, including turbulence enhancement, high-energy ignition, fuel reactivity modification, and fuel synergy with zero-carbon fuels. Geometry modifications of the combustion chamber, dual-fuel operation, pre-chamber ignition, and fuel activation are systematically reviewed and evaluated. A fusion technology integrating diesel pilot ignition with jet flame propagation is analyzed as a new combustion concept, termed induced jet flame combustion. This approach demonstrates significant potential in enhancing both combustion efficiency and stability, especially for lean burn conditions. This work highlights the role of natural gas engines as a transitional technology and a support platform for ultralow-emission and high-efficiency power systems fueled with low/zero-carbon fuels in the context of global decarbonization goals. Full article

To address flow instability induced by tip leakage vortex breakdown in high thrust-to-weight ratio aero-engine compressors, this study conducts numerical investigations into the DTR transonic compressor rotor. The unsteady evolution of the tip leakage vortex and the corresponding stall inception mechanism under near-stall conditions are revealed. Active flow control using single-slot and dual-slot endwall synthetic jets is further explored. Results show that an optimized single synthetic jet slot improves the compressor stability margin by 11.24% and design-point efficiency by 0.57%. To address the flow instability on this, synergistic excitation using two slots positioned at 25% and 50% axial chord length further suppresses leakage vortex breakdown and passage blockage, raising the stability margin by an additional 13.68% and efficiency by 0.72% compared to the optimal single-slot configuration. For the baseline compressor under near-stall conditions, tip leakage vortex breakdown occurs near 25% axial chord, causing severe flow deterioration. With synthetic jet actuation, low-energy fluid at the tip is blown away or sucked out, delaying vortex breakdown and reducing flow losses, thereby enhancing stability without compromising aerodynamic efficiency. The underlying mechanism is that, during the blowing phase, the jet splits the large-scale leakage vortex and removes the low-energy blockage region; during the suction phase, it extracts the fluid trapped in the tip clearance, preventing re-accumulation of low-energy fluid. These findings provide theoretical guidance for stall suppression and high-performance design of transonic compressors. Full article

The transient mechanism of dual-boundary dynamic opening in the inlet during stage transition of an integral solid rocket ramjet (ISRR) remains insufficiently understood. To address this issue, a combined approach involving numerical simulations and free-jet experiments was employed. A parametric model describing the time-sequenced opening of inlet and outlet cover was established. The influences of sequence and progression of opening and flight conditions on transient flow evolution and inlet stability were systematically examined. It is found that when the inlet is opened first, a “dead cavity” tends to form inside the inlet, which subsequently triggers pronounced pressure oscillations. Under baseline conditions, the peak outlet pressure reaches approximately 0.90 MPa, with a dominant frequency of about 66.7 Hz. Conversely, when the outlet is opened first, the cavity-induced oscillation is effectively suppressed; however, a transient “flow choking” overpressure and a delayed establishment of the flow field are observed. The discrepancies between simulations and experiments for key pressure characteristics under two representative opening modes are maintained within 5%, confirming the robustness of the proposed methodology. Further analysis reveals that increasing the Mach number markedly intensifies flow instability and reduces the stability margin, whereas higher flight altitudes help attenuate cavity oscillations. A strong coupling between the opening rate and temporal sequence is also identified. Specifically, for inlet-first scenarios, a slower inlet opening combined with a rapid outlet opening is preferable, while for outlet-first cases, rapid opening on both sides yields better performance. On this basis, a “stability window map” defined by the temporal difference (Δt) and opening duration (Topen) is proposed. This map delineates the distributions of stable, transitional, and hazardous regimes under varying conditions, which may offer a quantitative reference for adaptive control strategies in the ISRR stage of transition. Interestingly, these findings suggest that slight timing adjustments could substantially reshape the transient flow behavior. Notably, the introduction of the dual-boundary temporally coordinated forcing leads to flow responses within the inlet that exhibits pronounced path dependence and non-uniqueness. Such behavior deviates from the conventional understanding established under the single-boundary frameworks, where transient mode-transition processes were typically assumed to be uniquely determined. More importantly, these findings offer a renewed physical interpretation of inlet mode-transition dynamics, thereby providing both quantitative support and practical guidance for the adaptive design of ISRR transition control strategies. In particular, the results suggest that incorporating multi-boundary temporal effects could significantly enhance the robustness and flexibility of the control-law formulation. Full article

The aviation sector is accelerating the transition toward low-carbon propulsion, and Sustainable Aviation Fuels (SAFs) represent a key leverage to reduce lifecycle emissions without modifying existing turbine architectures. Microturbines offer an effective and low-cost platform for assessing SAF behaviour under engine-representative conditions. In this work, a zero-dimensional performance and emission model of the GTM-140 microturbine was developed in GSP and validated against experimental data at 70,000–112,000 rpm for Jet A-1 and HEFA paraffinic blends. The model reproduces thrust and fuel-flow trends with good fidelity, with deviations typically below 6% across all operating points. Introducing 50% HEFA consistently reduces fuel consumption, leading to a TSFC decrease of 3–6%, with the strongest effect at high rotational speed, where compressor efficiency is highest. CO emission indices decrease by 6–9% at mid-load and converge at full power due to enhanced oxidation, while NO_x increases by 6–15%, driven by the higher adiabatic flame temperature associated with HEFA’s increased H/C ratio and heating value. These results confirm that simplified 0D modelling can reliably capture performance and emission trends of SAF-fuelled microturbines and demonstrate the dual effect of HEFA: improved combustion efficiency and CO reduction, at the expense of moderately higher NO_x formation. Full article

To elucidate the physicochemical mechanisms underlying the violent explosion triggered by nylon (PA) jet penetration into explosive reactive armor, the thermal decomposition behavior of RDX and the influence mechanism of PA on its thermal reaction were studied by reaction molecular dynamics simulation and quantum chemical calculation, which were compared with experimental research. The study reveals that the decomposition of RDX is primarily initiated through pathways such as N–NO₂ homolysis, HONO elimination, and concerted ring-opening. The addition of PA reduces the energy barrier for N–N bond homolysis and provides hydrogen atoms to initiate HONO elimination via a heterogeneous pathway with a lower energy barrier, thereby promoting the initial decomposition of RDX. The free radicals produced by the decomposition of PA and RDX participate in a synergistic reaction, efficiently yielding stable products and significantly altering the distribution of intermediate species. The introduction of PA lowers the activation energy barrier for RDX decomposition and supplies hydrocarbon fragments as fuel for the reaction, facilitating rapid decomposition and initiation. This work clarifies the dual mechanism by which PA promotes RDX detonation from the perspective of microscopic reaction kinetics, providing theoretical insights for understanding and modulating the response of explosives under complex impact conditions. Full article

The design of low-emission alternative-propulsion aircraft requires multidisciplinary collaboration across distributed academic and industrial environments, challenging the applicability of conventional Multidisciplinary Design Analysis and Optimization (MDAO) frameworks. This paper presents the Holistic Collaborative MDAO Selection (HCMS) methodology, which provides a structured approach for selecting MDAO architectures based on socio-technical feasibility (intellectual property protection, disciplinary autonomy, and IT governance) and computational feasibility (coupling strength and model fidelity). The methodology supports a transition from centralized to distributed workflows while ensuring secure and efficient cross-organizational integration. The approach is demonstrated through a multi-institutional case study of a dual-fuel (hydrogen and kerosene) business jet using Remote Component Environment (RCE) and Common Parametric Aircraft Configuration Schema (CPACS). Results demonstrate that the proposed methodology enables stable and scalable distributed MDAO execution while explicitly accounting for socio-technical constraints, with consistent convergence behavior and communication overhead (approximately 25 s per iteration) remaining small relative to disciplinary computation time. The case study further illustrates the impact of hydrogen integration, showing an increase in operating empty weight of approximately 14.06% for a 600 NM mission and a reduction in kerosene capacity of approximately 12.9%, while enabling hydrogen-powered operation for the primary mission segment. These findings confirm that the proposed framework effectively supports secure, collaborative MDAO under realistic socio-technical constraints while providing meaningful system-level design insights. Full article

Binder jetting relies on the infiltration of binder droplets into a porous powder bed, where the spatial arrangement of droplets critically influences feature formation and structural integrity. In particular, the role of droplet spacing in regulating infiltration behavior remains insufficiently understood. In this study, droplet infiltration is investigated using a reconstructed three-dimensional powder bed combined with a Volume of Fluid (VOF) model. Both single- and dual-droplet configurations are examined to isolate the effect of droplet spacing on spreading, merging, and capillary-driven penetration. The results show that droplet spacing governs the redistribution of liquid flow between lateral spreading and vertical infiltration. Three distinct regimes are identified as spacing decreases: independent infiltration at large spacing, cooperative merging at intermediate spacing, and over-penetration at small spacing. These regimes reflect a transition from isolated droplet behavior to strongly coupled infiltration within the pore network. An optimal spacing of approximately 150 μm is found to balance spreading and penetration, enabling continuous deposition with controlled infiltration depth. Experimental measurements show good agreement with numerical predictions, with an average deviation of 8.66%. The present study clarifies the mechanism by which droplet spacing controls infiltration behavior and provides practical guidance for parameter selection in binder jetting processes. Full article

This study investigates subauroral phenomena during the main phase of the 10 May 2024 geomagnetic storm using a combination of ground-based observations from the WD IZMIRAN observatory (magnetometer, ionosonde, and all-sky imager) and Global Self-consistent Model of the Thermosphere, Ionosphere, Protonosphere (GSM TIP) simulations. During 18:00–20:00 UT, we identified the simultaneous occurrence of ionospheric signatures of Polarization Jets (PJ)/Sub-Auroral Ion Drifts (SAID) and Strong Thermal Emission Velocity Enhancement (STEVE) over Kaliningrad, consistent with previously reported PJ/SAID identification from DMSP drift velocity measurements. This identification is supported by: (1) characteristic purple emissions (clearly visible in all three channels) moving rapidly westward; (2) U-shaped structures in ionogram sequences; (3) the reproduction of supersonic westward plasma drifts within a narrow latitudinal band by the first-principles model; and (4) observed and simulated significant Ne depletion. The estimated ion drift velocity from all-sky imaging (assuming an emission altitude of 200 km) is consistent with GSM TIP simulations, which predicted PJ/SAID velocities of ~750 m/s driven by a latitudinally narrow (~3°) but longitudinally extended (>50°) poleward electric field (40 mV/m). Simulations reveal that this PJ/SAID phenomenon causes a reversal of the zonal thermospheric wind at 250 km and induces Ne disturbances across the 200–700 km altitude range. The electron temperature enhancement (up to 1500 K) exhibits a “falling drop” shape, peaking at 350 km, while ion heating exceeds 150 K. The neutral temperature shows a dual response: frictional heating at 120–160 km and localized cooling at 175–250 km due to drop in electron density. Additionally, an increase in atomic oxygen concentration was predicted within the 90–200 km range across the PJ/SAID longitudinal sector. Full article

Aiming to address the problem of extracting the remote sensing FTIR spectral characteristics of the hot jet of a certain type of aero-engine under different working conditions, this paper proposes a feature construction algorithm for the remote sensing FTIR spectral characteristics of the aero-engine hot jet based on the fusion of the original spectral features and the deep spectral features. The infrared spectrum was collected at a distance of 280 m, covering the spectral range of 2.5–15 μm with a resolution of 1 cm⁻¹. The Neighborhood–Autoencoder Integration Dual-Branch Network (NAIDN) feature construction algorithm is proposed. This algorithm contains a neighborhood integration branch and an autoencoder branch. The neighborhood integration branch converts the radiation intensity values of discrete wavenumber points into local energy aggregation features through a sliding window, accurately extracting the key physical information in the original spectrum. The autoencoder branch uses a three-layer fully connected neural network architecture to mine the deep spectral features of the spectral data. The algorithms of the two branches not only retain the physical interpretability of spectral analysis but also capture the multi-parameter coupling information hidden in the hot jet spectrum through the representation learning ability of the autoencoder, achieving feature fusion across spatial dimensions. Compared with traditional feature construction algorithms, the dual-branch feature construction algorithm proposed in this paper has stronger comprehensive representation capabilities. The content of carbon dioxide (CO₂) and cyanide groups (-C≡N) in the hot jet under different operating conditions varies significantly. In the experiment, an unsupervised clustering algorithm, the Agglomerative Clustering classifier, is selected, and the classification accuracy of the features extracted by the algorithm in this paper reaches 92.97% on this classifier, thereby verifying the effectiveness of the algorithm in this paper. Full article

Fire trucks equipped with truck-mounted electric water cannons are key mobile firefighting assets for urban and industrial fire response. However, due to the inherent mechanical inertia of the cannon body, its low-frequency motion response cannot match high-frequency control commands, making the system prone to oscillations and control instability. To address this command–execution frequency mismatch, this paper proposes a decoupled dual closed-loop control architecture for truck-mounted electric water cannons on mobile fire trucks: the fast loop is used for fire-source tracking and rapid localization, while the slow loop is used for water-jet aiming alignment. In the fast loop, a 2-D quadrant positioning rule drives the pan–tilt unit to achieve rapid fire tracking and accurate centering. In the slow loop, Kalman-filter-based state estimation and delay-aligned prediction generate feedforward aiming commands; these commands are fused with error feedback and further processed through command limiting and trajectory optimization, ultimately producing smooth and executable angle references. The visual perception module ran at 58 FPS, satisfying the real-time requirement of the proposed system. In five repeated extinguishment tests under controlled open-site conditions, the proposed method successfully completed all trials and reduced the mean extinguishment time to 13.55 s, compared with 15.83 s for the incremental-PID baseline and 23.76 s for the coupled proportional baseline, while also showing smoother correction and less redundant oscillation. Full article

This paper presents the development of two adaptive autopilots for the Cessna Citation X business jet aircraft. The two adaptive control strategies, including a dynamic inversion controller and a neural network controller, provide dual adaptation. The control objective consists of tracking the vertical speed, altitude, and heading commands. Dynamic inversion is applied on each output variable, and then the neural network (NN) controller is updated using adaptive law, derived from backpropagation. Dynamic inversion (DI) is achieved locally using a Recursive Least Squares (RLS) algorithm for state estimation. An inner control loop for the pitch, roll and yaw rates is integrated within the autopilots. The longitudinal states were separated from the lateral states in order to differentiate between longitudinal and lateral control. Robustness tests were conducted under turbulence and wind-gust conditions. The autopilot results were compared with flight simulation data from a Cessna Citation X research flight simulator. Results have shown that the autopilots accurately track the vertical speed, altitude and heading reference signals. The flight simulation comparison has shown that the proposed adaptive controllers were better than the one currently on board the Cessna Citation X. Full article

In engineering flow systems such as hydraulic machinery and marine propulsion, interactions among cavitation bubbles can significantly influence collapse dynamics. This study investigates the collapse behavior of unequal-sized dual cavitation bubbles in a free field, focusing on jet formation modes, morphological evolution, and the characteristics of the Bjerknes force and Kelvin impulse. Particular emphasis is placed on the effect of the bubble radius ratio on the collapse dynamics. The results indicate that: (1) as the radius ratio decreases, the counter-directed jets formed during the collapse of dual cavitation bubbles gradually disappear; (2) with a decreasing radius ratio, the amplitude of the bubble wall velocity first decreases and then increases; and (3) both the Bjerknes force and the Kelvin impulse decrease as the radius ratio decreases. Full article

Accurately partitioning evapotranspiration (ET) into soil evaporation (E) and plant transpiration (T) is fundamental for improving water resource management, yet robust ET partitioning remains challenging. This study proposes a two-step ET partitioning strategy that first extracts pure E and T samples from long-term ET observations and then uses these samples to independently constrain E and T sub-models. The strategy was implemented in three classical two-source ET models: Shuttleworth–Wallace (SW), Priestley–Taylor Jet Propulsion Laboratory (PT-JPL), and FAO-56 dual crop coefficient (FAO56-DK), and was compared against the conventional one-step calibration approach. Results show that the two-step strategy consistently improves the estimation of ET components and the transpiration fraction (T/ET). For the PT-JPL model, RMSEs of E, T, and ET decreased from 0.04, 0.06, and 0.078 to 0.03, 0.03, and 0.04 mm/30 min, respectively. In FAO56-DK, R² values increased from 0.08, 0.55, and 0.65 to 0.10, 0.65, and 0.75. The RMSE of T/ET declined from 0.21 to 0.18 in SW and from 0.47 to 0.34 in FAO56-DK. The effectiveness of pure samples depends on model structure, with E samples most beneficial for SW, T samples for FAO56-DK, and both for PT-JPL. Overall, these results demonstrate that pure-sample constraints substantially enhance ET partitioning accuracy. Full article

Explosion venting is an important measure for mitigating gas explosion hazards in confined spaces; however, conventional venting processes often generate high speed, high temperature jet flames, leading to severe secondary hazards. To achieve flameless venting, an experimental study on methane explosions under the coupled effects of dual explosion vents and porous materials was conducted in a confined pipe. Porous silicon carbide foam ceramics with different pore densities (10, 20, and 25 PPI) were installed at the vent openings under various vent layout conditions. Combined with high-speed imaging and dynamic pressure measurements, the flame evolution, jet flame suppression, and explosion overpressure characteristics were systematically analyzed. The results indicate that porous materials effectively attenuate jet flame intensity without compromising venting efficiency and increasing pore density significantly enhances flame-quenching performance. In addition, explosion vents located closer to the ignition source facilitate earlier energy release, thereby improving the reliability of flameless venting. Full article