Search Results (511)

A solar–air source absorption heat pump (SAAHP), which mainly consists of a solar collector, a fan coil, and an absorption heat pump equipped with a gas-fired combustor, was proposed for water heating. This system runs in either SD (solar-energy-driving) or GD (gas-combustion-heat-driving) mode and is designed to utilize renewable energies whenever possible. The models for each component were built, and the corresponding heat and mass balance equations were established. The SAAHP’s performance with the LiBr/H₂O and LiNO₃/H₂O working fluids was simulated and compared with an air source absorption heat pump (AAHP) using LiBr/H₂O. The results indicated that the LiNO₃/H₂O-based SAAHP has a higher solar energy utilization rate than the LiBr/H₂O-based pump due to its lower solar collector inlet temperature in SD mode. Similarly, it achieved a higher primary energy COP throughout the year than both the LiBr/H₂O- and LiNO₃/H₂O-based SAAHPs. Compared to a gas-fired hot water boiler, the SAAHPs based on LiNO₃/H₂O and LiBr/H₂O achieved yearly primary energy-saving rates of 46.2% and 40.0%, respectively, whereas the AAHP only achieved a rate of 12.2%. Thus, the LiNO₃/H₂O-based SAAHP shows significant energy-saving potential in building energy use. Full article

This study investigates mechanism-based modeling and simulation of a single-shaft heavy-duty industrial gas turbine. Taking the PG9171E gas turbine as the case study, component-level steady-state and dynamic models are developed. The steady-state model is established using the constant mass flow (CMF) method. For dynamic modeling, both the CMF approach and the inter-component volume (ICV) approach are implemented to enable a comparative assessment of the two methods. On the basis of the steady-state model, an improved Dung Beetle Optimization (DBO) algorithm is proposed to perform model correction using measured operational data from the gas turbine. After model correction, the maximum relative error between the simulated results and the measured operating data is reduced to 1.01 × 10⁻⁵%. Following high-accuracy model correction, sensitivity analysis and a comparative dynamic study are conducted for the two dynamic modeling approaches. The results indicate that the most influential sensitivity parameter is the rotor rotational inertia, followed by the virtual volume of the combustor. Moreover, the primary discrepancy between the ICV and CMF approaches arises from differences in the operating trajectories on component characteristic maps. The ICV-based model exhibits a pronounced response lag; however, it requires less computational time than the CMF-based model, making it more suitable for rapid engineering simulation and practical applications. Full article

As a multiple-energy carrier, hydrogen can facilitate the transition to a low-carbon future, and coupling renewable energy sources with hydrogen-power generation systems (e.g., gas turbines) can markedly enhance gas turbine combined cycles (GTCCs) power generation regarding cleanliness and flexibility. Conventional gas turbines fuel the natural gas–hydrogen mixture and encounter issues like unstable combustion and elevated nitrogen oxide (NO_x) emissions. Initially, the alterations in combustion characteristics resulting from the fuel transition are analyzed, and the principal technical challenges of hydrogen-mixed combustion are summarized. It is found that hydrogen exhibits a laminar flame speed approximately 7–10 times higher than that of methane, and a hydrogen blending ratio beyond 30% significantly increases the risk of flashback and thermoacoustic oscillations. The existing technical proficiencies of advanced hydrogen combustion strategies are delineated to offer decision-making assistance for the industry. For instance, micromix combustors can achieve NOx emissions below 20 ppm even with 100% hydrogen, while axial staging technology expands the stable operating range to 25–106% load. Additionally, current research on hydrogen-fueled gas turbines primarily focuses on enhancing traditional combustor designs. Conversely, the focus on the overall alteration of gas turbines has been relatively restricted. It further examines component failure issues arising from elevated temperatures and material hydrogen embrittlement, highlighting that X80 pipeline steel experiences a 17-fold increase in hydrogen embrittlement index when the hydrogen blending ratio rises from 1% to 20%, as well as safety concerns related to fuel transitions from conventional gas turbines to hydrogen gas turbines, offering technical references for the comprehensive optimization of hydrogen-fueled gas turbines. Full article

This work numerically examines the premixed combustion of partially cracked ammonia/air in a cavity-stabilized micro-combustor. Effects of the equivalence ratio (Φ) and inlet temperature (T_in) on the combustion features, flame–wall heat transfer and nitrogen-containing emissions are investigated quantitatively at a cracking ratio of 0.6. Results show that increasing Φ from 0.8 to 1.2 shifts the high-temperature region downstream and causes it to elongate axially. This spatial expansion decreases peak temperatures and distributes heat release over a longer distance. Mean wall temperature and overall heat loss are thus decreased due to weakened near-wall thermal interaction. NO formation closely follows the high-temperature and OH-rich zones. However, at Φ = 1.2, oxygen limitation suppresses NO production and redirects fuel-bound nitrogen towards N₂O, enhancing its outlet emissions. As T_in increases from 300 K to 500 K, the improved reactivity of the mixture promotes an upstream shift of the main reaction zone. The reaction zone becomes more concentrated within the cavity. Such structural changes intensify NO formation but simultaneously compress the high-temperature zone, which reduces the wall-averaged temperature and overall heat loss. In the extended downstream post-flame region, lower temperatures and limited radical activity suppress NO₂ formation and N₂O decomposition. As a result, NO₂ emissions decrease monotonically, while N₂O emissions exhibit a gradual increase. These findings provide useful insights into the effects of operating parameters on combustion stability, heat transfer and nitrogenous pollutant evolution in microscale partially cracked ammonia flames. Full article

Advances in high-performance computing have expanded the use of computational fluid dynamics (CFD) for reacting-flow analysis; however, simulations involving detailed flame kinetics remain computationally intensive for many practical systems. Efficient modeling approaches are therefore essential for predicting flame behavior in swirl-stabilized combustors. This study examines the influence of main-stage swirl intensity on near-lean blow-off characteristics in a multistage swirl combustor using a hybrid RANS–LES framework. The Stress Blended Eddy Simulation (SBES) model, coupled with a Flamelet Generated Manifold (FGM) combustion formulation, is employed to capture key turbulence–chemistry interactions. Results indicate that reducing swirl intensity suppresses the formation of a swirl-stabilized flame, while excessive swirl negatively affects emission performance. For the baseline (S2) and high-swirl (S3) configurations, flame lift-off height increases by 21.0% and 11.96%, respectively, for every 0.1 reduction in equivalence ratio. The S3 case also demonstrates reduced combustion efficiency, with CO emissions rising by 156.4% relative to S2. Local flame extinction is observed in regions of strong droplet–flame interaction, highlighting enhanced quenching susceptibility under near-blow-off conditions. The present study investigates the flame dynamics in a multi-stage swirl combustor using high-fidelity CFD simulations. This study has yet to be validated through experimental analysis and the results presented in this work are entirely computational. Further experimental validation is necessary to verify the results. Full article

Under the vision of carbon neutrality, the global energy system urgently requires storable, transportable, and tradable zero-carbon carriers. Iron, due to its high crustal abundance, low cost, environmentally friendly reaction products, and ease of closed-loop cycling, is being reconsidered as a potential “metallic energy” alternative to fossil fuels. This paper systematically reviews the conceptual evolution, scientific lineage, and paradigm shift logic of iron-based energy within the framework of dual pathways: combustion and electrochemistry. On the combustion front, a multi-level understanding has been established—ranging from microscopic reaction mechanisms to macroscopic flame propagation, and from unit combustors to diversified thermal power systems—laying a methodological foundation for an integrated “solid fuel–thermal–power” approach. In parallel, the electrochemical pathway has developed both liquid and solid routes, integrating energy storage, pollution control, and resource recovery within a single device through multi-valent redox reversibility, thereby expanding the concept of generalized energy storage under the “battery-as-factory” paradigm. Current research is shifting its focus from single performance metrics toward synergistic optimization of efficiency, lifespan, cost, safety, and environmental impact, marking a transition in technological paradigm from “material trial-and-error” to “mechanism design.” Looking forward, to advance iron energy beyond the experimental validation stage, it is imperative to establish a cross-scale, closed-loop scientific characterization system, develop recycling strategies with low entropy and low energy consumption, and deeply integrate with renewable electricity, hydrogen, and high-temperature heat sources to form spatiotemporally transferable zero-carbon energy systems. In this way, iron may integrate into global energy trade as a “metallic energy in specific scenarios like ports/islands,” offering a scalable, hydrocarbon-independent technological option for achieving carbon neutrality. Full article

Hydrogen-fueled gas turbines face challenges related to flashback risk, nitrogen oxide (NO_x) emissions, and operational flexibility. In this study, a Center-Graded Spiral Micromixing (CGSM) combustor was designed and experimentally investigated to enhance the robustness of fuel–air mixing under hydrogen-rich conditions. The proposed CGSM concept employs spiral microtubes to induce curvature-driven secondary flows, promoting mixing through airflow-controlled mechanisms rather than relying solely on fuel jet momentum. Numerical simulations were conducted to qualitatively analyze the internal flow and mixing characteristics of the spiral microtubes, followed by pressurized combustor experiments at an inlet pressure of 0.3 MPa and elevated air temperatures. The experimental results demonstrate stable combustion of pure hydrogen under lean conditions, with NO_x emissions being maintained below 25 ppm, corrected to 15% O₂, without observable flashback or combustion oscillations within the designated operating range (from ignition to full load). The combustor further exhibits stable operation with blended hydrogen–methane and hydrogen–ammonia fuels, enabling online fuel switching without hardware modification. Application tests on an 80 kW micro-gas turbine indicate that the CGSM combustor can support stable operation across the full range of load conditions, from ignition to full-load operation, under both simple- and reheat-cycle modes, with performance characteristics that are consistent with established operational standards for micro-gas turbines. These results suggest that the CGSM concept provides a feasible micromixing strategy for hydrogen and hydrogen-rich fuels at a moderate pressure and micro-gas turbine scale. Full article

This study investigates the emission characteristics and flame behavior of an air-staged swirl burner operating on LPG. The burner is equipped with a 45° vane swirler and an adjustable secondary-air section. Experiments were conducted at air velocities ranging from 20 to 43 m/s using a Testo 350 gas analyzer, while temperature measurements were obtained with thermocouples positioned 90 mm downstream of the burner exit. The results show that increasing the secondary-air opening leads to a monotonic decrease in the mean exit temperature and NO_x formation over the entire velocity range. In contrast, CO concentrations increase at higher air velocities and larger secondary-air fractions due to reduced residence time and partial quenching of the reaction zone. The fully staged configuration (100%) achieved the lowest NO_x levels (≤3 ppm) at 20 m/s, whereas the non-staged case resulted in the highest temperatures and NO emissions. Overall, the experimental results demonstrate that a moderate secondary-air opening provides the best compromise between low NO_x emissions and acceptable CO levels for compact LPG-fired swirl combustors. Full article

This study presents the high-speed visualization of the detonation wave structure in a small-scale hydrogen–oxygen rotating detonation combustor. A 68 mm Rotating Detonation Combustor was modified with a quartz-glass ring, such that radial optical access into the annular detonation chamber was realized. The optical access window covers approximately the first 22 mm of the detonation chamber. The modified experiment was hot-fire tested with the propellant combination gaseous hydrogen–oxygen. Simultaneous high-speed imaging from the back-end of the chamber and normal to the chamber axis allows a thorough investigation of the detonation wave characteristics. Both high-speed cameras were operated at 180,000 frames per second in order to resolve and capture the detonation waves. The downstream camera was used in order to investigate the number of waves and the spinning direction. A stable regime of three co-rotating waves was observed. The wave speed achieved 71% of the theoretical CJ-velocity. The second camera recorded the passing detonation waves through a quartz ring via OH* emissions. From the post-processed OH* images, a better understanding of the detonation wave structure, including the filling height of the fresh gas mixture as well as the approximate angles of the detonation and the shock wave, could be gained. The obtained height of the detonation wave is about 11–12 mm or 6–7 detonation cell sizes for the given setup and experimental conditions. Full article

The liner temperature distribution of an aero-engine combustor is a critical parameter for evaluating its cooling effectiveness. It provides essential guidance for designing the combustor cooling flow field, assessing combustion performance, identifying critical regions, and predicting service life. However, current research on surface temperature field measurements in real or model aero-engine combustors remains limited. Existing studies focus primarily on the liner temperature measurement under near-steady-state conditions, with less attention to its dynamic changes. This study employs Laser-Induced Phosphorescence (LIP) thermometry to measure the effusion-cooled liner temperature field of an aero-engine model combustor under various CH₄/Air swirling premixed flame conditions and varying blowing ratios. Based on the geometric characteristics of the effusion-cooled liner, an optimization method for matching phosphorescence images of different wavelengths is proposed. This enhances the applicability of phosphorescence intensity ratio-based LIP thermometry in high-vibration environments. The study specifically focuses on the dynamic response of LIP thermometry for monitoring combustor liner temperature. The instantaneous effects of blowing ratio variations on liner temperature rise rates were investigated. Additionally, the influence mechanisms of a broad range of combustion conditions and the blowing ratios on the combustor liner temperature distribution and cooling effectiveness were examined. These findings provide theoretical and technical support for cooling design and dynamic liner temperature field measurement in real aero-engine combustors. Full article

Ammonia (NH₃) is a promising carbon-free energy carrier for low-carbon power generation. However, in turbulent ammonia–methane (NH₃-CH₄) premixed swirling flames, operating at lean conditions to limit NO_X, emissions can trigger strong thermoacoustic oscillations. This study investigates thermoacoustic oscillatory instability in an NH₃-CH₄ swirl-stabilized combustor using the chemiluminescence of CH*, OH*, and NH* over a wide range of ammonia fuel fraction (X_NH3). Combined spectral measurements and 2D chemiluminescence imaging are employed to obtain the global emission characteristics and spatial distributions of OH* and NH* in the UV band and CH* in the visible band. A custom-designed intensified CMOS (ICMOS) camera based on a high-gain UV–visible image intensifier with direct coupling is developed to enable sensitive OH* and NH* imaging (gain > 10⁴). Frequency analysis of continuous CH* imaging, together with morphology-based principal component analysis and k-means clustering of 46 image features, shows that oscillatory combustion occurs for X_NH3 < 0.40, whereas X_NH3 ≥ 0.40 leads to multimode, stable combustion. As X_NH3 increases, OH* and NH* fields progressively decouple from CH*, becoming more elongated and shifting downstream. These results demonstrate that UV radical chemiluminescence provides indispensable information on NH₃ reaction zones and should be combined with CH* diagnostics for reliable thermoacoustic analysis and control in practical NH₃-fueled combustion systems. Full article

This paper presents an experimental investigation of hydrogen enrichment effects on combustion behavior and exhaust emissions in a self-developed micro gas turbine fueled with a propane–butane mixture. Hydrogen was blended with the base fuel in volume fractions of 0–30%, and combustion was examined under unloaded operating conditions at three global equivalence ratios (ϕ = 0.7, 1.1, and 1.3). The global equivalence ratio (ϕ) is defined as the ratio of the actual fuel–air ratio to the corresponding stoichiometric fuel–air ratio, with ϕ < 1 representing lean, ϕ = 1 stoichiometric, and ϕ > 1 fuel-rich operating conditions. The micro gas turbine is based on an automotive turbocharger coupled with a custom-designed counterflow combustion chamber developed specifically for alternative gaseous fuel research. Exhaust gas emissions of CO, CO₂, and NO_x were measured using a laboratory-grade FTIR analyzer (Horiba Mexa FTIR Horiba Ltd., Kyoto, Japan), while combustion chamber temperature was monitored with thermocouples. The results show that hydrogen addition significantly influences flame stability, combustion temperature, and emission characteristics. Increasing the hydrogen fraction led to a pronounced reduction in CO emissions across all equivalence ratios, indicating enhanced oxidation kinetics and improved combustion completeness. CO₂ concentrations decreased monotonically with hydrogen enrichment due to the reduced carbon content of the blended fuel and the shift of combustion products toward higher H₂O fractions. In contrast, NO_x emissions increased with increasing hydrogen content for all tested equivalence ratios, which is attributed to elevated local flame temperatures, enhanced reaction rates, and the formation of locally near-stoichiometric zones in the compact combustor. A slight reduction in NO_x at low hydrogen fractions was observed under near-stoichiometric conditions, suggesting a temporary shift toward a more distributed combustion regime. Overall, the findings demonstrate that hydrogen–propane–butane blends can be stably combusted in a micro gas turbine without major operational issues under unloaded conditions. While hydrogen addition offers clear benefits in terms of CO reduction and carbon-related emissions, effective NO_x mitigation strategies will be essential for future high-hydrogen microturbine applications. Full article

To meet stringent efficiency and environmental targets, future gas turbines require increased turbine inlet temperatures while maintaining low NO_x emissions and accommodating hydrogen-blended fuels. Axially staged combustion has emerged as a key technology to address these challenges. This paper presents a mathematical model for the rapid prediction of NO emissions in axially staged combustors fueled with hydrogen-blended methane. The model integrates a simplified thermal NO mechanism with a set of dimensionless staging variables, providing a unified description of flow, mixing, and reaction processes. Its accuracy was validated against a detailed chemical reaction network (CRN). The model was applied to identify feasible low-emission staging windows across different hydrogen-blending ratios and to systematically analyze the effects of secondary-stage mixing quality, operating parameters, and fuel composition on optimal staging and emissions. Results demonstrate that coordinating the combustion strategies of the primary and secondary stages enables effective NO control across a wide fuel range. This work provides a theoretical foundation for the design of low-emission, fuel-flexible axially staged combustors. Full article

This study examines the high-temperature degradation of Hastelloy C276, a corrosion-resistant nickel-based alloy, during exposure to combustion products generated by methane and 99% cracked ammonia. Using a high-pressure optical combustor (HPOC) at 4 bar and exhaust temperatures of 815–860 °C, standard tensile specimens were exposed for five hours to fully developed post-flame exhaust gases, simulating real industrial turbine or burner conditions. The surfaces and subsurface regions of the samples were analysed using scanning electron microscopy (SEM; Zeiss Sigma HD FEG-SEM, Carl Zeiss, Oberkochen, Germany) and energy-dispersive X-ray spectroscopy (EDX; Oxford Instruments X-MaxN detectors, Oxford Instruments, Abingdon, United Kingdom), while mechanical properties were evaluated by tensile testing, and the gas-phase compositions were tracked in detail for each fuel blend. Results show that exposure to methane causes moderate oxidation and some grain boundary carburisation, with localised carbon enrichment detected by high-resolution EDX mapping. In contrast, 99% cracked ammonia resulted in much more aggressive selective oxidation, as evidenced by extensive surface roughening, significant chromium depletion, and higher oxygen incorporation, correlating with increased NO_x in the exhaust gas. Tensile testing reveals that methane exposure causes severe embrittlement (yield strength +41%, elongation −53%) through grain boundary carbide precipitation, while cracked ammonia exposure results in moderate degradation (yield strength +4%, elongation −24%) with fully preserved ultimate tensile strength (870 MPa), despite more aggressive surface oxidation. These counterintuitive findings demonstrate that grain boundary integrity is more critical than surface condition for mechanical reliability. These findings underscore the importance of evaluating material compatibility in low-carbon and hydrogen/ammonia-fuelled combustion systems and establish critical microstructural benchmarks for the anticipated mechanical testing in future work. Full article