Search Results (550)

The global shift toward cleaner energy has positioned hydrogen-enriched methane (CH₄/H₂) as a practical bridge fuel. While it burns more efficiently and produces fewer carbon emissions than traditional hydrocarbons, it introduces operational and safety challenges. Hydrogen’s high reactivity and rapid burning velocity increase risks such as flashback and premature ignition. This study employs Computational Fluid Dynamics to examine the combustion behavior of methane−hydrogen blends in a 2D axisymmetric chamber based on RANS equations. Using ANSYS Fluent 19.1, the research utilizes a validated equilibrium mixture-fraction/PDF framework to ensure accuracy against physical experiments. The simulation framework successfully captures the complexity of non-premixed turbulent combustion by combining a probability density function approach with a realizable k-ε turbulence model. Moreover, this research explores how varying hydrogen concentrations and air mass flow rates, covering the full spectrum from lean to fuel-rich conditions, affect fluid dynamics, turbulence, and the development of recirculation zones. The data show that adding hydrogen fundamentally reshapes velocity fields and thermal profiles, which in turn dictate combustion efficiency and pollutant formation. It has been demonstrated that the optimal blend for combustion performance is the case containing 30% hydrogen. Furthermore, evaluations involving higher-fraction blends (approaching the 70% enrichment range) suggest that configurations exceeding this level necessitate a redesign of the injector near field to mitigate localized heat release and accelerated NO_x emissions. By identifying the operational limits for CH₄/H₂ blends in industrial settings such as steam boilers, this study offers a technical roadmap for engineering more stable, high-performance, and low-carbon energy infrastructure. Full article

The transition to a low-carbon energy paradigm requires reducing nitrogen oxide NO_x and carbon monoxide CO emissions to 5–9 ppm. This study investigates the impact of the primary zone excess air ratio α and mixing quality on pollutant yields, addressing the “seesaw” trade-off mechanism between NO_x and products of incomplete combustion. Analysis of Lean Premixed and Micromix technologies demonstrates that achieving NO_x levels below 5 ppm requires local α fluctuations to remain within a root-mean-square deviation of 3–4%. An original burner design with an intelligent emission control system is presented, enabling dynamic adjustment of local αin to maintain combustion within a narrow stability window. Experimental results confirm that minimum toxicity, with NO_x concentrations below 20 ppm, is achieved at α_in = 1.7–1.8. The implementation of this technology ensures stable operation across transient and part-load regimes while mitigating thermal NO_x formation and thermoacoustic instabilities. Full article

Efficient liquid-fuel combustion in micro-combustors strongly depends on fuel atomization, evaporation, and fuel-air mixture preparation. However, conventional straight vaporizer tubes often provide limited droplet breakup and insufficient gas liquid heat and mass transfer. In this study, a honeycomb-corrugated vaporizer tube was proposed to enhance fuel atomization and evaporation before combustion. A computational fluid dynamics model combined with an orthogonal design was employed to investigate the effects of corrugation height, corrugation radius, honeycomb-hole diameter, and number of honeycomb plates on gas–liquid two-phase flow, the Sauter mean diameter (SMD), and fuel evaporation rate. The results showed that corrugation height and the number of honeycomb plates were the dominant factors affecting atomization and evaporation performance. The optimized tube, with a corrugation height of 1.0 mm, a corrugation radius of 4.0 mm, three honeycomb plates, and a honeycomb-hole diameter of 0.6 mm, reduced the outlet SMD from 79.0 μm to 42.6 μm and increased the fuel evaporation rate from 1.5% to 42.0%. These findings provide a feasible structural approach for improving fuel atomization, evaporation, and mixture preparation in small-scale liquid-fuel combustors. Full article

Flue gas recirculation (FGR) is an effective technique for reducing thermal nitrogen oxide (NO_x) emissions of gas turbines. However, variations in inlet oxygen concentration significantly alter the internal combustion characteristics of staged swirl combustors and induce combustion instability. To clarify the coupling mechanism between oxygen content and combustion stability under diverse operating conditions, three-dimensional numerical simulations are performed on a staged swirl combustor. The effects of oxygen mass fraction ranging from 11% to 23%, together with multiple operating parameters including inlet temperature, inlet velocity and operating pressure, on flame morphology, velocity fluctuation, heat release fluctuation and pressure fluctuation, are systematically investigated. The results show that increasing the inlet temperature optimises the uniformity of heat release, compensates for the combustion inhibition under low-oxygen conditions, and effectively improves combustion stability. Oxygen content exhibits a non-monotonic regulatory effect on combustion pulsation characteristics. Appropriate reduction of oxygen content narrows the high-temperature reaction zone and suppresses pressure fluctuations, thereby improving combustion stability, whereas a moderate low-oxygen condition of 17% aggravates velocity fluctuations and deteriorates combustion stability. Although elevated oxygen content enhances the overall heat release intensity, it increases the amplitude and dominant frequency of heat release fluctuations, which triggers combustion instability. Furthermore, high inlet velocity and high operating pressure amplify the disturbance of low-oxygen environments on the flame field and further degrade combustion stability. This study clarifies the competitive and coupling relationships among oxygen concentration, operating parameters and combustion dynamic characteristics, providing a theoretical basis for the stability optimisation and low-oxygen combustion regulation of gas turbine combustors with flue gas recirculation. Full article

Preliminary aerodynamic assessment provides an efficient means of investigating internal flow organization in aircraft gas turbine combustors before more computationally demanding three-dimensional and reactive-flow simulations are undertaken. This study presents a preliminary CFD investigation of cold-flow phenomena in the annular combustion chamber of the F100-PW-229 low-bypass turbofan engine. A two-dimensional planar model was intentionally adopted to identify dominant flow structures and assess their response to representative engine operating conditions at reduced computational cost. Numerical simulations were performed in ANSYS Fluent using a pressure-based coupled solver and the k-ω SST turbulence model for idle, cruise, and maximum rotational speed conditions. Additional simulations were performed at cruise conditions for an altitude of 11 km to examine the influence of reduced ambient pressure and air density on the internal flow field. The results show that increasing engine rotational speed primarily changes the intensity of the aerodynamic field while preserving its dominant spatial organization. The maximum velocity at idle was approximately 55% lower than that at maximum rotational speed, while the corresponding value at cruise was 20.1% lower. Similarly, the maximum stagnation pressure at idle was approximately 67.1% lower than that at maximum rotational speed, while the difference between cruise and maximum speed was 24.2%. A distinct vortex structure was identified in the outer annular passage between the liner and casing, with its location shifting downstream as the operating condition changed. At 11 km altitude, the calculated pressure level was approximately 81% lower and the characteristic flow velocity approximately 9% lower than under corresponding ground-level conditions, while the dominant flow topology remained similar. These results highlight the role of combustor geometry and secondary-air distribution in governing global pressure redistribution, velocity development, and recirculation behavior. Within the scope of the adopted two-dimensional non-reacting formulation, the obtained flow patterns provide an initial aerodynamic reference for identifying regions of interest for subsequent high-fidelity simulations. The proposed approach is therefore intended as a computationally efficient preliminary engineering tool rather than a substitute for validated three-dimensional combustor modelling. Full article

This paper presents a G-Agent, a large language model (LLM)-driven multi-agent framework that automates the optimization workflow for an axisymmetric cavity-based scramjet combustor. The framework integrates a supersonic compressible reacting flow solver with the Qwen3-VL-2B-Instruct model. It consists of four specialized agents: Interactor, Runner, Corrector, and Optimizer. The Interactor parses user requirements and generates simulation input files. The Runner manages mesh generation, solver configuration, and simulation execution. The Corrector diagnoses failed cases by analyzing fault logs and applies corrective actions. The Optimizer coordinates the optimization process using a trust-region response surface method to maximize thrust. The framework employs Latin hypercube sampling (LHS) to explore the design space defined by three key geometric parameters: isolator length, cavity depth, and fuel injector position. Without manual intervention beyond initial specifications, the G-Agent successfully conducted multiple optimization iterations. Starting from a baseline thrust of 489.4 N, the optimized configuration achieved 523.5 N after three iterations, reaching a relative improvement of 6.97%. Our proposed agent achieves closed-loop control of the entire optimization process, significantly lowering the technical barrier and human effort in scramjet combustor design. Full article

Startup transients are critical in gas generator cycle liquid rocket engines because pressure overshoot, mixture-ratio excursions, and turbopump instability can occur before steady operation. This study compares conventional pyrostarter and tank head start sequences using a system-level transient model of propellant feed lines, valve motion, gas generator ignition, turbopump acceleration, and chamber pressurization. The engine configuration is used as a representative system-level case rather than a detailed reproduction of a specific flight engine. The integrated solver was checked against coupled startup data reported by Moon et al. using hydrogen as the turbine driving gas. Both sequences were evaluated under identical engine requirements using sustained convergence of pressure, speed, and flow as the startup-completion criterion. The pyrostarter and tank head cases reached steady operation at 2.41 s and 3.73 s, respectively, while discharging 123.596 kg and 95.134 kg of propellant through the combustors. The tank head sequence was further evaluated over a pump-inlet-pressure range using valve commands adjusted to preserve the target propellant arrival order in the gas generator and main chamber. Under these sequence-preserving schedules, increasing pump inlet pressure reduced steady-state arrival time from 3.80 s to 3.23 s but increased cumulative combustor discharge from 84.013 kg to 130.526 kg. These results characterize tank head start performance under physically admissible valve schedules, with startup time and propellant consumption forming competing design objectives. Full article

Compared with single-swirl configurations, linearly arranged multi-swirl burners introduce complex inter-jet interactions that significantly alter flame dynamics; however, the underlying mechanisms remain poorly understood. In this study, direct numerical simulation (DNS) is employed to investigate a lean-hydrogen multi-swirl flame, aiming to elucidate its flame structure and dynamic evolution. The flame development region is divided into upstream (Region 1) and downstream (Region 2) regions, based on the critical location where the flame stretch transitions from positive to negative. The flow field, flame morphology, thickness, stretch, curvature, and their joint statistical relationships are systematically compared between the two regions. The results show that in Region 1, the flame stretch is dominated by positive strain rate, and the flame maintains a continuous structure and a small thickness. In Region 2, the curvature stretch becomes dominant, leading to severe flame wrinkling, local extinction and breakup, with the mean flame thickness increasing to about 1.5 times that of the laminar flame. Joint PDF analyses reveal that negative flame stretch is correlated with a large negative curvature in Region 2, whereas in Region 1, it is not affected by the curvature sign. The downstream flame also exhibits higher displacement speeds, indicating intensified turbulence–flame interaction. This study reveals the streamwise transition mechanism of the multi-swirl flame from strain-dominated to curvature-dominated dynamics, clarifies the distinct coupling modes of upstream stabilization and downstream fragmentation, and provides new theoretical guidance for stable combustion and wide-operability design of lean-hydrogen swirl combustors. Full article

Commercial aviation contributes approximately 3% of global CO₂ emissions, while nitrogen oxides (NO_x) remain a major environmental concern. Hydrogen is a promising carbon-free fuel for future gas turbine engines and offers a potential pathway towards net-zero aviation. This study presents the aerothermal design and CFD-based iterative refinement of an annular combustor for a hydrogen-fuelled CFM56-class large-bypass turbofan. The combustor was initially sized using established design correlations, with GasTurb14 providing the engine-cycle boundary conditions. CFD simulations were performed to evaluate the airflow distribution, temperature field, pressure loss and NO_x formation, and to optimize the cooling-hole arrangement. The final combustor achieved the target exit temperature of 1500 K with a pressure loss of 5.9%, meeting the design objective of approximately 6%. Relative to the initial hydrogen-fuelled configuration, the redesigned cooling-hole layout reduced the fuel-to-air ratio required to achieve the target exit temperature from 0.009 to 0.0073 (18.9%) and reduced the exit NO mass fraction from 0.003443 to 0.002223. A separate Large Eddy Simulation (LES) of the final combustor geometry was conducted to compare the combustion characteristics of hydrogen and Jet-A under identical operating conditions. The results demonstrate that cooling-hole configuration has a significant influence on combustor thermal performance and NO_x emissions, providing design guidance for future hydrogen-fuelled gas turbine combustors. Owing to the absence of experimental data for this configuration, the results are presented as a computational design study supported by a benchmark comparison rather than as an experimental validation. Full article

For coupling a transonic high-pressure turbine vane with a rotating detonation combustor, several integration approaches have been considered. Endwall diffusion in the vane row can facilitate coupling by enabling a higher turbine inlet Mach number operating range. Nonetheless, the introduction of diffusive axisymmetric endwalls may promote flow separation and enlarged secondary flows, leading to an overall reduction in turbine stage efficiency. To address this, the present study introduces a shape optimization framework based on computational fluid dynamics for designing diffusive non-axisymmetric endwalls in a transonic vane downstream of a rotating detonation combustor. The reference geometry is a transonic vane with diffusive axisymmetric endwalls, previously analyzed in numerical studies. Both hub and shroud endwalls are parameterized using 20 design variables, and a random sampling approach generates 1000 distinct geometrical configurations. Each design undergoes geometry generation, meshing, and steady Reynolds-averaged Navier–Stokes computation under transonic conditions using a three-dimensional commercial solver. Aerodynamic performances are assessed, and a genetic aggregation method is employed to construct a response surface. A gradient-based optimization algorithm identifies the optimal non-axisymmetric endwall configuration, which is then simulated. Comparative analysis shows that the optimized non-axisymmetric endwall significantly mitigates hub and shroud vortex effects, enhancing aerodynamic efficiency and supporting integration within turbine systems equipped with rotating detonation combustors. Full article

Accurate prediction of NO emissions is important for the development of low-emission gas turbine combustors. This study evaluates several NO formation models for a 78 MW F-class gas turbine using a decoupled post-processing framework. Steady RANS simulations were performed with a partially premixed flamelet/PDF combustion model. Thermal NO, prompt NO, the N₂O intermediate pathway, and turbulence–chemistry interaction were assessed at 50% and 100% load. Thermal NO was the dominant pathway and showed strong load dependence. Using partial equilibrium for O radicals increased outlet NO by 16.46% at 50% load and 43.69% at 100% load. Including partial-equilibrium OH further increased NO by 8.67% at 50% load but had little effect at full load. Prompt NO remained on the order of 10⁻³ ppm. The N₂O pathway and turbulence–chemistry interaction also affected the prediction, especially at full load. The selected model was further compared with field measurements during load ramping and pilot-ratio variation. Most load-ramping predictions agreed with measurements within 18%. The results demonstrate the applicability of the proposed framework for engineering NO emission prediction while also identifying limitations under transitional operating conditions. Full article

When methane (natural gas) fuel gas turbines switch to hydrogen–ammonia co-fuel, their thermodynamic performance undergoes significant changes. To expand the operating range of heavy-duty gas turbines when using hydrogen–ammonia co-fuel and to improve their thermodynamic performance, based on the 255.6 MW heavy-duty gas turbine at the Banshan Power Plant in Hangzhou, China, a simulation model was established. A strategy based on changing the angle of the compressor inlet guide vanes (IGVs) was proposed. The thermodynamic performance, turbine stage supercritical flow velocity, and flow matching characteristics of gas turbines were studied under different hydrogen–ammonia mixing ratios. The results indicate that the developed model can accurately predict the performance of the gas turbine under rated operating conditions, yielding a rated output power of 254.59 MW and an efficiency of 36.33%, with relative errors of −0.4% and −1.54% compared with the design values, respectively. When hydrogen–ammonia blended fuel is employed, the outlet Mach numbers of the second- and third-stage turbine stators exceed the safety limit unity. Reducing the IGV angle effectively decreases the turbine stator outlet Mach number and improves operational safety, although a slight reduction in gas turbine efficiency is observed. As the ammonia volumetric fraction in the blended fuel increases, the gas turbine output power increases while the efficiency decreases slightly, accompanied by a reduction in turbine stator outlet pressure and an increase in outlet temperature. Further investigation shows that, after IGV regulation, the combustor outlet pressure, gas turbine power output, and efficiency all increase. Under a fixed IGV opening condition, the gas turbine efficiency gradually decreases with increasing ammonia volumetric fraction. Under off-design fuel flow conditions, increasing the relative fuel flow leads to higher combustor outlet pressure and temperature, whereas increasing the ammonia volumetric fraction causes a slight reduction in these parameters. This research can provide theoretical support for the optimal design and operation of gas turbines using hydrogen–ammonia mixed fuel. Full article

Existing NH₃/CH₄ combustion reaction mechanisms still exhibit a pronounced trade-off between predictive accuracy and computational efficiency. It is difficult to guarantee global optimality, which limits their application in gas turbine combustion simulations. The objective of this study was to introduce machine learning methods into the parameter optimization process of combustion reaction mechanisms and to construct an optimized mechanism (Bys-BP Mech) with both high accuracy and high computational efficiency. First, a reduced mechanism was obtained through mechanism coupling and the DRGEP method. Subsequently, the pre-exponential factors and activation energies of three key reactions were optimized based on sensitivity analysis. An artificial neural network was used to construct the model, and cross-validation combined with Bayesian optimization was employed to achieve automatic hyperparameter optimization. Validation results showed that the optimized Bys-BP Mech achieved an average relative error of 4.56% for LBV, and the average relative error of IDT decreased to 17.16%. CFD simulations indicated that the minimum prediction error of NO emissions was 3.74% when the CH₄ co-firing ratio ranged from 40% to 70%. This mechanism addressed the limitations of existing mechanisms in combustor-scale validation under variable operating conditions and reduced the computational time of combustion simulations by half. Full article

A Realizable k−ε turbulence model and a finite-rate/eddy-dissipation combustion model, together with experimental validation, were used to investigate the flow and combustion characteristics of a novel triple-swirler combustor under multiple operating conditions. The results show that, compared with the conventional baseline configuration, the ring-cooled radial structure induces a third-stage swirl through inclined cooling holes. This swirl regulates the recirculation structure formed by the first two axial swirlers, transforms the core reaction zone from a single large-scale recirculation vortex into multiple vortical structures, forms a low-temperature cooling coverage outside the main reaction zone, and weakens the near-wall entrainment and high-speed sweeping induced by the kidney-shaped vortex pair downstream of the primary holes. The peak temperature of the outer liner is reduced by 14.72%, and the wall-temperature uniformity is improved by 36.02%. The outlet temperature distribution factor (OTDF) decreases by 14.81% and 15.79% under high and medium operating conditions, respectively, indicating an improved outlet temperature field. This study provides engineering guidance for the design of high-performance combustors. Full article

Selective energy conversion in confined catalytic nanocavities is examined through a coupled reactive–photonic framework. The practical target is a combustor-integrated selective emitter for thermophotovoltaic (TPV) conversion and cascaded thermoelectric (TEG) recovery, in which Pt-coated anodic porous alumina (APA) functions simultaneously as a catalytic reactor, a cavity-modified electromagnetic environment and a heat-routing structure. Visible/near-infrared spectra (380–780 nm) show that Pt-coated APA exhibits a substantially stronger non-grey red-edge depression than a smooth zirconia reference. This observation establishes a spectral contrast in the measured window but is not used to identify an experimental cutoff wavelength, because a finite, open, lossy and array-coupled pore does not exhibit the abrupt edge predicted for an ideal cylindrical waveguide. For the mid-infrared, analytical scaling shows that the principal H₂O and CO₂ bands at 2.7, 4.3, 6.3 and 15.0 µm all lie deep in the evanescent regime relative to the ideal TE₁₁ cutoff wavelength λc ≈ 0.513 µm for a 300 nm pore. A converged finite-difference time-domain benchmark at the CO₂ 4.3 µm band yields a source-local Purcell factor F_p ≈ 0.38, indicating suppression of the total local density of optical states, while aperture flux is more than six orders of magnitude smaller than the near-field power budget. The specific contribution is therefore not the established fact of below-cutoff attenuation, but the co-design and separate quantification of a catalytic nanocavity as a reactive compartment, photonic environment and energy-branching element. The results provide a bounded mechanistic basis for combustor-integrated TPV and hybrid TPV/TEG architectures. Full article