Search Results (233)

In this work, Direct Numerical Simulation (DNS) investigates the combustion behaviour of a reactive transverse lean premixed jet of an ammonia blend (10% NH₃, 11% H₂, 16% O₂ and 63% N₂ by volume) injected through a rectangular nozzle in a pre-heated non-vitiated air crossflow at a pressure of 5 bar. The configuration has been chosen from a Reynolds-Averaged Navier–Stokes (RANS) test campaign to ensure low NO and low unburned fuel, while maintaining a high temperature profile at the turbine inlet. The DNS shows that the flame stabilises on the leeward side of the rectangular jet, within and downstream of the recirculation region, while high scalar dissipation and short residence times prevent persistent anchoring on the windward side. Joint statistics reveal that the reaction does not follow a constant equivalence ratio path, since intermediate progress states are shifted towards leaner mixtures by entrainment, dilution and differential diffusion. The strongest heat-release and displacement-speed events occur in localised regions where mixture state, stretch and flame-front geometry act jointly. The displacement-speed budget is mainly controlled by the chemical source term, with diffusion reducing the net propagation speed and stratification-induced cross terms remaining small. Under intense stretch, positively curved flame elements exhibit larger displacement speeds, indicating a coupled effect of curvature, preferential diffusion and local radical transport. NO formation is dominated by fuel-nitrogen chemistry: HNO and NH₂ are the main NO-producing routes, whereas N₂ and N₂O provide the dominant NO-sink channels. The DNS predicts an outlet-averaged NO level of 400 dppm, while extended-domain RANS calculations indicate that longer residence times could reduce it below 100 dppm. Full article

To improve the efficiency of jet-based fire suppression for high-rise building façade fires, this study experimentally investigates the liquid film formation characteristics and fire suppression behavior of water jets impinging on insulated vertical surfaces. The effects of operating pressure (flow rate), nozzle-to-wall distance, and jet inclination angle on liquid film spreading morphology, wetted area, and effective water supply rate are systematically analyzed. The results show that increasing the flow rate significantly enlarges the wetted area, while reducing the effective water supply rate. As the nozzle-to-wall distance increases, the liquid film gradually develops a “top-wide and bottom-narrow” morphology. Although increasing the jet inclination angle decreases the wetted area, it enhances the continuity and stability of wall-adhering liquid film flow, thereby improving cooling efficiency near the flame root region. During the fire suppression experiments, low-flow-rate jets exhibit insufficient suppression stability, whereas high-flow-rate horizontal jets are capable of suppressing the flame to a residual burning state near the bottom of the façade. Further increasing the jet inclination angle enables complete flame extinguishment. This study reveals the relationship between jet parameters, liquid film behavior, and fire suppression performance, providing experimental evidence for the optimization of jet-based façade fire suppression strategies. Full article

Cavity flame holders are core stabilization components for Ma 1.6 low-supersonic scramjet combustors, where the axial location of upstream fuel injection significantly affects fuel-air mixing, flame holding, and combustion performance. Two four-orifice injection schemes (Far-Upstream Injection, FUI: 30 mm upstream of cavity leading edge (CLE); Near-Upstream Injection, NUI: 10 mm upstream of CLE) were experimentally studied under Ma 1.6 inflow ($T_0=660 \mathrm{K}, \varphi =0.2$) via synchronized high-speed schlieren and CH* chemiluminescence diagnostics. Results showed that FUI produced greater cold-flow jet penetration, but generated stronger shock structures and flow instabilities. Under combustion, the penetration gap between schemes narrowed substantially due to heat-release-induced thermal expansion, with NUI benefiting more. NUI achieved superior flame stabilization, uniform full-cavity heat release, and suppressed combustion instability through broadband flow fluctuations, whereas FUI exhibited a high-energy discrete dominant frequency and flame oscillation. 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 reveal the mechanisms by which obstacle distribution affects propane–air premixed deflagration under different blockage ratios, large eddy simulation (LES) was employed to investigate flame propagation and pressure rise in a confined duct with four obstacle distributions and four blockage ratios. The coupled effects of obstacle layout and blockage ratio on flame morphology, propagation velocity, vorticity evolution, and pressure rise rate were analyzed. The results show that obstacle distribution significantly changes flame front structures: One-side obstacles produce claw-like flames, center layout obstacles generate tongue-like flames with large vortex regions at low-to-moderate blockage ratios, and both-side or around layout obstacles form mushroom-like flames. At high blockage ratios, around layout obstacles redirect the flow into a high-speed axial jet, leading to the highest flame velocity and maximum pressure rise rate. These findings indicate that the dominant flame acceleration mechanism shifts from vortex-induced flame wrinkling at low-to-moderate blockage ratios to axial-jet-driven flame acceleration at high blockage ratios, providing guidance for obstacle layout optimization and explosion risk mitigation in confined propane–air systems. 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

Hyperspectral imaging was used for qualitative and quantitative monitoring of the distribution of a flame retardant on polyester fabrics. NIR reflection spectra show a specific band related to the flame retardant, which rises with increasing application weight. Multivariate data analysis tools based on the partial least squares (PLS) algorithm were applied for quantification of the spectra. Gravimetry was used as a reference method for the characterization of the calibration samples. The calibration method was optimized by the application of several spectral pretreatments and variation in the spectral range considered in the various models, which finally resulted in a prediction error of about 1.3 g/m². The prediction performance of the developed calibration model was proven in external validations using independent samples with application weights between about 5 and 25 g/m². Apart from the quantification, the homogeneity of the distribution of the flame retardant was investigated. It was shown that non-uniform distributions (e.g., gradients, droplets, irregular) can be detected by hyperspectral imaging. Some fabric samples were finished using a special ink jet printing technology for application to the polyester fabric. The spectral images of printed samples based on the previous calibration model achieved for samples made by impregnation do not only clearly show the different degrees of functionalization, but also the outstanding homogeneity of the distribution of the flame retardant. Moreover, printed samples finished with two different agents were analyzed. Full article

This paper conducts an experimental study to develop a response strategy for lithium-ion battery fires. Guided by the principle of “first control, then extinguish”, the strategy integrates a lithium-ion battery-specific fire-controlling blanket with castable fire-extinguishing agents. Both fire tests of e-bikes and lithium-ion batteries are conducted. From e-bike fire tests, the feasibility of rescuers conducting close-range disposal of LIB (lithium-ion battery) fires is analyzed from three perspectives, i.e., fire evolution stage, battery splashing and high temperature. The results indicate a high risk of fire spread, as well as a strong likelihood of human injury caused by flying LIB debris and extremely hot gases. Subsequently, the fire-controlling capability of the fire blanket is validated. It not only blocks splashing batteries and jet flames, reducing combustion intensity, but also offers a safe way for personnel to operate the portable fire extinguishers. Through two castable extinguishing agents tested, the perfluorohexanone-based agent outperforms the water-based alternative. The reasons are as follows. First, perfluorohexanone evaporates easily in the low-temperature, confined environment created by the fire blanket. Second, it possesses both physical and chemical fire-extinguishing capabilities, ultimately delivering a more potent combustion suppression effect. Full article

In this study, six serpentine resistive strain sensors are manufactured on two cantilevers made of FR-4 (Flame Retardant 4) with dimensions of 25 mm × 140 mm. Three strain sensors are printed on each substrate using particle-free EI 615 silver ink. The method of fabrication is hybrid in nature and consists of aerosol jet (AJ) printing a layer of conductive material and selectively sintering certain regions before removing the non-sintered material with 1-dodecene solvent. The gauges on one cantilever are coated with a 10 µm dielectric layer using Norland Electronic Adhesives (NEA) 121, which serves as the passivation layer, while the three gauges on the other cantilever are left exposed. The samples are subjected to two standard thermal–mechanical loading conditions: namely, a vibration test according to the MIL-STD-883 method 2007 Cond A and a high-temperature soak test according to the Mil-Std-883 method 1008 Cond B. The reliability of the devices is quantified by assessing the percent change in their resistances and gauge factors (GF) between tests. The percent change is then used to ascribe a reliability metric to the gauges. Full article

Hydrogen-enriched fuel injection in staged gas-turbine combustors is commonly achieved through jet-in-crossflow (JICF) configurations, where flame stabilization is governed by a local balance between flow-induced strain/mixing and chemical reaction rates. This work investigates turbulent reacting JICF relevant to staged combustion conditions using high-fidelity simulations with adaptive mesh refinement (AMR) and differential-diffusion effects together with Lagrangian particle statistics. Chemistry model uncertainties are incorporated by using a projection method that maps uncertainty estimates from detailed mechanisms into the model used in this work. Results show that the macroscopic flame topology remains in a stable two-branch regime (lee-stabilized and lifted) and is primarily controlled by the jet momentum–flux ratio J. Visualization of the normalized scalar dissipation rate reveals that the flame front resides on the low-dissipation side of intense mixing layers, occupying an intermediate region between over-strained and under-mixed regions. While hydrogen content does not significantly change the global stabilization mode for the cases studied, uncertainty analysis reveals composition-dependent differences that are not apparent in the mean behavior alone. In particular, visualization in Eulerian (χ, T) state-space analysis and particle statistics conditioned on the stoichiometric surface demonstrate that higher-hydrogen cases observe a lower scalar dissipation rate and exhibit substantially reduced variability in OH production under kinetic-parameter perturbations, whereas lower-hydrogen blends experience higher dissipation and amplified chemical sensitivity. These findings highlight that, even in globally similar JICF regimes, the hydrogen content can modify the local response of the flame to kinetic-parameter uncertainty, motivating uncertainty-aware interpretation and design for hydrogen-fueled staging systems. Full article

Aerial forest firefighting is a critical technology for wildfire suppression. Recent studies have examined suppression agent drop dynamics, deposition patterns, and optimization strategies. This review synthesizes advances from three perspectives: (i) in-flight suppression agent jet dynamics, (ii) ground deposition patterns, and (iii) suppression effectiveness, while outlining future research directions. Flight altitude, velocity, and momentum ratio govern jet behavior—affecting penetration, expansion, and breakup. Momentum ratio, shaped by drop velocity and aircraft speed, is pivotal in penetration depth and fragmentation. Deposition patterns vary with delivery systems and flight parameters: low-altitude/low-speed drops yield higher coverage density over smaller areas, whereas high-altitude/high-speed drops cover larger areas but less densely. Suppression efficacy depends on fire intensity–vegetation interactions, droplet size–coverage requirements, and operational parameters such as response time, aircraft capacity, and real-time intelligence. Large droplets excel in cooling high-intensity flames, while fine droplets provide efficient area coverage. Adequate resources and integrated data enhance outcomes. Future work should couple multi-physics models of terrain, meteorology, and fire plume dynamics, and develop integrated deposition models including wind, thermodynamics, terrain, and fire behavior to optimize aerial dispersion in diverse wildfire scenarios. Full article

Multicomponent diffusion modeling based on the Maxwell–Stefan formulation is widely used in high-fidelity combustion simulations due to its superior physical accuracy compared with simplified diffusion models. However, the computational complexity of the Maxwell–Stefan model, which arises from the solution of coupled multicomponent transport equations, becomes a major performance bottleneck in large-scale CFD simulations. In this work, a high-performance computing optimization strategy for the Maxwell–Stefan diffusion model is developed within the OpenFOAM framework. The proposed method improves computational efficiency through block-based computation and vectorization-oriented data organization to better exploit modern CPU architectures and SIMD instruction capabilities. The optimized implementation enhances memory locality, increases data reuse efficiency, and reduces cache miss penalties. Numerical validation is performed using two-dimensional laminar counterflow flame cases and ammonia–hydrogen turbulent combustion cases, including both premixed and non-premixed jet flames. Results demonstrate that the optimized Maxwell–Stefan implementation preserves numerical accuracy while significantly improving computational performance. Speedups of 2.5×–4.5× are achieved depending on the number of chemical species. The developed approach provides an efficient solution for detailed combustion simulations involving large chemical mechanisms. The test cases and source code are openly shared. Full article

With the advancement of low-carbon transition and deep load-following operation of coal-fired units, ammonia–coal co-firing is a retrofit-ready option for source decarbonization, but its coupled impacts on combustion and emissions remain to be quantified. A 350 MW corner-tangential pulverized-coal boiler at a 30% rated load was investigated using a three-dimensional ANSYS Fluent CFD model. Thirteen cases were designed by combining five ammonia shares (0–40%) with three injection locations (B, C, D). The temperature and key species fields were analyzed to track the reaction-zone shifts, and the outlet CO₂, SO₂, NO, and NH₃ were evaluated. Increasing ammonia reduced and contracted the high-temperature core, dispersed the flame, extended the ignition distance of the ammonia-laden primary jet, and shifted heat release downstream. CO₂ and SO₂ decreased with an ammonia substitution; at 40% co-firing, CO₂ fell by about 43% and SO₂ declined markedly. NO showed a nonlinear, location-dependent response: B and C injection may raise NO at low ratios, but reduce it at higher ratios under lower temperatures and stronger reduction, whereas D injection tends to maintain higher NO in the upper furnace. The findings guide coordinated selection of the co-firing ratio and injection location for low-load retrofits. Full article

The transition toward sustainable aviation fuels requires dedicated experimental platforms capable of evaluating alternative fuels under realistic propulsion conditions. This study presents the development and laboratory experimental validation of a modular testing installation designed for sustainable fuels derived from plastic waste pyrolysis, intended for aerospace engine applications. The proposed system is conceived as an integrated small-scale gas turbine assembly that reproduces the functional characteristics of a jet engine and enables controlled laboratory investigations of dynamic behavior, combustion stability, and performance. The installation comprises a compressor, annular combustion chamber, and turbine mounted on a common shaft, along with a fully autonomous fuel supply system equipped with electronically controlled pumping, safety devices, and thermal conditioning of the fuel mixture via an attached Stirling engine. Combustion processes are continuously evaluated using an exhaust gas analysis system to assess fuel composition and combustion quality, while a high-speed camera operating at 50,000 fps enables detailed visualization of flame stability. Operating parameters, including temperatures, pressures, rotational speed, mass flow rates, and thrust, are monitored and recorded through an integrated control and data acquisition system with real-time analysis capabilities. Experimental results demonstrate stable operation and reliable ignition using alternative fuel mixtures, confirming the suitability of the modular installation as a versatile research platform for the assessment and comparative analysis of sustainable aerospace fuels. Full article