bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of NO-Formation in Humid, Ammonia-Doped Combustion
Authors: Dybe Simeon , Helbig Hannah , Yasir Muhammad , Güthe Felix , Alemela Reddy , Bartlett Michael , Paschereit Christian Oliver , Bohon Myles D. 
Published: August 2024

Abstract
Decarbonizing the energy sector promotes the utilization of renewable fuel sources like Syngas from biomass. Syngas typically comprises small quantities of fuel-bound nitrogen (FBN) like ammonia which is associated with high NO-emissions when combusted in a customary gas turbine system.
In atmospheric combustion experiments conducted at TU Berlin, small quantities of ammonia were added to both natural gas and a surrogate Syngas representing Syngas derived from biomass. This results in an ammonia-to-NO conversion rate of around over 70%, which decreases with increasing ammonia concentration. A difference in conversion rate between surrogate Syngas and natural gas is particularly noticeable at lower ammonia concentrations, which diminishes as concentration increases.
The experimental combustion process is validated with a Chemical Reactor Network (CRN) using Cantera, which captures the emission behaviour observed in the experiment well. The chemical reactor representing the flame is additionally modeled as a 1D-flame in Cantera, providing the input for an in-depth investigation of the flame kinetics with a sub-mechanism accounting and reaction tracing algorithm (SMART) to investigate the NO-formation. NO is primarily generated within the flame zone predominantly through the fuel pathway, although production is diminished by the DeNOx pathway.
Finally, NO-formation is investigated for varying combustor diameter. NO-emissions decrease with increasing diameter of the combustion chamber. SMART analysis shows that with increasing the combustor’s diameter, the increase in NO depletion via the DeNOx pathway surpasses that of production via the Fuel NO pathway. Consequently, this results in a slight reduction in the overall NO output, which could arise from increased heat loss with increased diameter.
Interplay Between Unburned Emissions and NOx Emissions From a Dual Swirl Hydrogen Air Injector
Authors: Magnes Hervé , Vilespy Martin , Selle Laurent , Poinsot Thierry , Schuller Thierry 
Published: August 2024

Abstract
OH planar laser induced fluorescence and particle image velocimetry are employed to analyze the structure of hydrogen/air flames stabilized by a dual swirl injection system under globally lean and atmospheric conditions with preheat air temperature varied from ambient up to 673 K. The flames exhibit two distinct reaction branches. The first, located in the central recirculation zone, is a diffusion-controlled reaction layer characterized by a relatively large thickness associated with low strain rates. The second branch, stabilized in the shear layer of the swirling jet, is strongly influenced by large coherent structures. Depending on operating conditions, this front may adopt either the form of a fully diffusive strained reaction layer anchored to the hydrogen injector lip or a lifted diffusion front with a leading-edge flame evolving into a partially premixed flame at high air injection velocities. Flue gas analysis indicates NOx emission levels, typically below 10 ppm at 15% O2, for sufficiently large air injection velocities. Air preheating barely increases NOx emissions at lean operating conditions. The injector operational range is constrained only by the ultra-lean blowout limit reached for global equivalence ratios below 0.02. Furthermore, it demonstrates remarkable resilience to large and rapid drop in fuel flowrate. However, combustion efficiency drops close to the lean blowout limit due to intermittent fragmentation of the flame wings that progresses further upstream as the equivalence ratio drops. It is demonstrated that this fragmentation results from the combined drop in temperature of the central recirculation zone and the flame wings subjected to high shear stress. It is also shown that combustion efficiency at ultra lean conditions rapidly increases as the air preheat temperature increases.
Variable Cycle Engine Concepts and Component Technologies - An Overview
Authors: Zenkner Sebastian , Carvalho Francisco , Brakmann Robin G. , Goinis Georgios 
Published: August 2024

Abstract
The variable cycle engine (VCE) is of interest for military and supersonic civil platforms due to its improved operational flexibility. However, the increase in design and control degrees of freedom results in a more complex engine architecture. Numerous different VCE concepts have been proposed and studied in literature. This paper provides an overview of VCE concepts and technology. A historical outline moof important activities, investigated concepts and technical advancements is given and the main objectives and use cases of the technology are described. In addition, specific challenges and technical solutions for variable compressors and turbines are discussed in detail. Important VCE concepts are qualitatively evaluated and their advantages and disadvantages for specific applications highlighted.
Numerical Investigation on the Geometrical Scaling of Hydrogen Micromix Injectors
Authors: Sun Xiaoxiao , Morsy Mohamed , Wijesinghe Charith , Singh Gaurav , Sethi Vishal , Rimmer John , Young Kenneth 
Published: August 2024

Abstract
For future hydrogen-fuelled aircraft, the hydrogen needs to be stored in liquid phase. Converting liquid hydrogen into a gaseous state for combustion requires transitioning from extremely low temperatures (∼20.25K) to high temperatures (at least above 300K) to avoid compromising aero-engine thermal efficiency. Within the scope of the HYEST project, a hydrogen pre-conditioning system to provide the heat input is being designed and tested. The system comprises a pre-heater which provides the heat input for a downstream heat exchanger. The main requirements of the pre-heater include but are not limited to, uniform combustor outlet temperature and velocity distributions, low pressure loss, acceptable NOx emissions, stable operation for all engine power settings and minimum size and weight. Due to its unique configuration of repeating injector arrays, a hydrogen micromix combustor is a promising candidate to fulfil these requirements.
For a hydrogen micromix combustor, NOx production is very sensitive to flame-flame interactions and hot gas recirculation as well as the hydrogen jet diameter. Smaller hydrogen jet diameters will yield lower NOx emissions and will achieve a uniform outlet temperature distribution within a shorter distance downstream of the injector plate. However, to reduce manufacturing and maintenance complexity, a feasibility study on scaling up the hydrogen injection diameter of hydrogen micromix injectors was conducted using numerical CFD simulations on a pair of injectors. The resulting flames were evaluated and compared in terms of flame structure, total pressure loss, NOx emissions and outlet temperature uniformity.
It was concluded that for the pre-heater design a hydrogen injector diameter of 0.6mm fulfils all the requirements. A 0.6mm design reduces the number of injectors by 3/4 compared to a 0.3mm injector design without producing significantly more NOx. Additionally, it reduces the minimum distance to achieve a uniform radial temperature distribution by 50% compared to a 1.0mm injector design.
Although this study is specifically related to the preheater fuel conditioning system, the lessons learned are equally applicable to the design of hydrogen micromix combustion systems for both aero and stationary gas turbines.
Coupled Design of Multi-Component Distortion-Generating Devices for Aircraft Engine Ground Tests – Part II: Experimental Characterization in a Closed-Loop, High Speed Test Rig
Authors: Boufidi Elissavet , Madasseri Payyappalli Manas , Grondin Julissa , Leborgne Michaël , Baert Lieven , Gouttière Alexandre , Dieu Donavan , Wunsch Dirk , Spriet Tony , Talbotec Jérôme , Fontaneto Fabrizio 
Published: August 2024

Abstract
Next generation aircraft engine configurations, featuring a higher level of engine-airframe integration, are subjected to increased flow distortion levels at the fan inlet. The presence of such non-uniformities should be considered as early as possible in the design cycle, as it can have an impact on the engine performance, operability and vibration. Since testing under realistic distorted inlet flow is crucial in order to evaluate such effects, there is a clear need for devices able to generate complex distortion patterns. Part I of this two-part paper presents a numerical methodology enabling to design distortion generating devices capable of reproducing complex steady combined total pressure and swirl angle distortion patterns. The methodology has been applied to generate four different sets of distortion screens: one honeycomb total pressure screen, one swirl vane assembly, and two devices consisting of a coupling of the two components. The second part of the paper focuses on the experimental characterization of the distortion screens in the VKI R4 high speed test rig. The closed-loop facility has undergone major design modifications in order to implement the new distortion devices test section and reproduce engine-like flow conditions. The measurements have been carried out by means of stereo-PIV and multi-hole aerodynamic pressure probes. The cross-comparison between the two techniques allows to discuss the limitations of each technique. Finally, the comparison between the experimental results and the simulated patterns is presented and discussed.
Thermal Performance Characterization of Dry Gas Seals in a sCO2 Compressor
Authors: Bidkar Rahul A. , Kumar Uttara , Zhang Xiaohua , Molino Nora , Neveu Joshua , Klaerner John , Johnson Jeremy , Moore J. Jeffrey 
Published: August 2024

Abstract
Commercially available dry gas seals (DGS) are the seal-of-choice for shaft-end sealing locations in compressors used in the oil and gas industry, and supercritical carbon dioxide (sCO2) power cycles. Typically, a DGS operates with a very thin gas/supercritical fluid film (typically 2 to 7 microns thin). DGS reliability is tied to how well this ultra-thin film is sustained under varying pressure, thermal, and speed conditions. Recent sCO2 turbomachinery development efforts have experienced a couple of catastrophic DGS failures at the compressor shaft-end locations. A suspected root cause of these DGS failures is thermal deformations caused by the excessive windage heating expected with the supercritical CO2 working fluid when the compressor operates at high pressures and high rotational speeds. In this paper, the thermal behavior of a DGS operating in a typical sCO2 compressor is investigated. Specifically, test data are presented for a specially instrumented, commercially available DGS operating in the GE-SwRI sCO2 compressor. The test data include temperatures measured on the seal stationary ring and DGS housing locations using several embedded metal thermocouples to monitor the thermal behavior of the DGS during typical sCO2 compressor missions. This paper describes how an existing GE-SwRI sCO2 compressor housing was modified to accommodate and route temperature sensors to the instrumented DGS. Test data shows higher than expected temperatures (about 180 to 190 °C) in the cavities surrounding the DGS, which provides useful insights to turbomachinery designers for designing seal cavities. The main reason for these high temperatures is the low sCO2 flow purging the seal cavity. Furthermore, the measured temperatures are compared with the predictions of a steady-state thermal model of the GE-SwRI sCO2 compressor. The thermal model uses a 1D flow advection network (accounting for cavity swirl, windage and heat transfer coefficients for sCO2 flow, air flow and bearing oil flow) exchanging heat with the surrounding structure, along with heat transfer through the structure. The thermal model uses CFD-based flows to account for the sCO2 flow past the DGS. The predictions of the thermal model match reasonably well with the measured temperature data, thereby providing validation to the modeling assumptions. The high structural temperatures in the regions around the DGS that are predicted by the model as well as measured during the tests point to the importance of devising cooling strategies for reliable operation of the DGS.
Modal Identification of Rotating Blades by Tip Timing and Strain Gauge Measurements in Operating Condition
Authors: Guida Roberto , Carassale Luigi , Marrè-Brunenghi Michela 
Published: August 2024

Abstract
The modal identification of rotor blades in operating conditions is difficult for several reasons including the unavoidable transient effects that arise when resonances are crossed relatively fast. Algorithms to deal with this problem are available for the case of time-resolved signals (e.g. strain gauges), while for blade tip timing (BTT) data, the experience is much more limited, in particular as far as engines in operating conditions are concerned. This paper aims to contribute to the development and validation of system identification techniques applicable in transient conditions using BTT data. To this end, one method based on the fitting of the transient response and one method based on the fitting of the synchronous response are formalized, applied and compared to analyze the behavior of an operating engine in which both BTT and strain gauge measurements are available.
The Hybrid Pathway to Flexible Power Turbines: Part D, Automated Construction of Mesh Derived Thermal Network Models for Fast Full-Machine Thermal Analysis
Authors: Baker Mark , Rosic Budimir 
Published: August 2024

Abstract
The global drive towards renewable energy is imposing challenging operating requirements on power turbines. Flexible load-leveling applications must accept more frequent and demanding start-stop cycles. Full transient analyses are too computationally expensive for real-time simulation across all operating regimes so monitoring relies on sparse physical measurements. Alone, these sparse data lack the fidelity for real-time prediction of a complex thermal field. A new hybrid methodology is proposed, coupling data across a range of fidelities to bridge the limitations in the individual analyses. Combining several fidelity methods in parallel: low-order models, corrected by real-time physical measurements, are calibrated with high-fidelity simulations. The multi-faceted hybrid approach enables the real-time speed of low-order analysis at high resolution. This paper series develops the critical enabling features of the hybrid method. Fast 3D thermal simulation is fundamental to the methodology. Low-order network models enable the real-time thermal calculation of regions inaccessible to monitoring and facilitate clearance and stress simulation necessary for flexible turbine operation. A novel automated construction method is presented, allowing complex full turbine thermal networks to be built with ease. Developed in Tensorflow, the thermal networks directly support GPU acceleration and neural network integration for seamless data transfer within the hybrid system. Capturing flow and material physics from high fidelity data, the hybrid network method demonstrates comparable accuracy at greatly reduced computational cost. The method is validated using real-machine data capturing a period of flexible transient operation.
Flame Interaction and Stabilization Mechanisms in a Dual Premix Swirl Combustor With a Pilot Bluff Body
Authors: Li Linye , Tian Xiaojing , Yin Shengming , Zhang Haodong , Yang Yifan , Wang Guoqing , Feng Zhenzhen , Xu Liangliang , Xia Xi , Qi Fei 
Published: August 2024

Abstract
The utilization of centrally-staged lean-premixed swirl combustion is prevalent due to its capacity for stable flame maintenance and reduced emissions. The configuration of the pilot and main flames, whether they are stratified or merged, significantly influences flame behavior and combustion dynamics. This study explores the underlying mechanisms of merged and stratified flames in a newly designed dual-swirl model combustor. Utilizing a 10 kHz PIV/OH* synchronized measurement and a 20 kHz CH2O PLIF method, we delineate the flame and flow structures under varying Air Split Ratios (ASR) and Stratification Ratios (SR). The results indicate that ASR alters the heat release intensity by modifying the flame’s radial dimensions, whereas SR determines the spatial separation between the pilot and main flames. The merged flame displays a single-layer M-shaped structure, with the inner flame front perturbed by vigorous vortex shedding. In contrast, the stratified flame exhibits a dual-layer structure with an M-shaped pilot flame and a V-shaped main flame, where a precessing vortex core (PVC) emerges whose frequency correlates positively with the equivalence ratio of the pilot flame. The formation of these two modes is attributed to the stabilization of the outer branch of the pilot flame, governed by the interplay between flame propagation and flow convection of the pilot stage.
Experimental Investigation on Laser Ignition and Flame Stabilization in an Oxygen/Methane CO2-Diluted Combustor at Elevated Pressures
Authors: Di Sabatino Francesco , Partridge Kendyl , Connolly Brian , White Steve 
Published: August 2024

Abstract
Direct-fired oxy-fuel supercritical carbon dioxide (sCO2) combustors present a novel approach for near-total carbon capture. However, maintaining a stable flame under extreme pressure and temperatures, characteristic of these combustors, poses significant challenges. Re-ignition failure could necessitate depressurization to atmospheric levels, leading to substantial time and energy losses. This study experimentally investigates laser ignition and flame stabilization in a simplified oxygen/methane-fired, CO2-diluted combustor across various thermodynamic conditions. The test rig comprised a seven-hole showerhead nozzle installed in a pressure vessel, producing a jet flame at pressures up to 5 bar. Non-reactive laser-induced plasma kernel generation experiments were also performed to assess the effect of pressure on kernel dimensions up to 25 bar. The optical access of the combustor enabled plasma kernel generation and laser ignition by focusing a 532-nm laser beam, produced by a 10 Hz Nd:YAG laser, approximately 5 mm from the nozzle tip. The optical access also allowed the collection of images of the flame’s CH* chemiluminescence to assess flame stabilization and plasma kernel dimensions. The results indicate that pressure and CO2 dilution have a considerable impact on flame stabilization. Furthermore, the diameter of the plasma kernel was observed to decrease with increasing pressure, highlighting the importance of laser ignition testing at elevated pressures.
Investigation of an Ammonia-Fuelled SOFC-mGT Hybrid System: Performances Analysis and Comparison With Natural Gas-Based System
Authors: Anfosso Chiara , Crosa Silvia , Iester Federico , Bellotti Daria , Magistri Loredana 
Published: August 2024

Abstract
Among power generation systems, Hybrid Systems (HS) are very attractive due to the opportunity to reach higher power outputs and efficiencies by coupling different technologies. Among Solid Oxide Fuel Cell plants, one of the most studied innovative HS is the SOFC-Micro-Gas Turbine (mGT) integrated system: in the pressurized configuration, the Fuel Cell (FC) is in the place of the mGT combustion chamber, and an afterburner is used to complete the fuel combustion upstream the expander. Several system configurations, designs, and control system challenges have been studied in the last decades, and prototypes have been already developed around the world with satisfactory results in terms of system efficiency. However, these systems have been deeply studied feeding the FC with Natural Gas (NG) and Biogas, not completely allowing to reach zero carbon emissions. The growing global demand for carbon-free energy production is increasing, highlighting the importance of alternative fuels in the power generation sector: among them, thanks to its chemical and physical properties, ammonia is gaining more and more interest. In the present work, the authors want to investigate an innovative Ammonia-to-Power (A2P) system based on a SOFC-mGT HS, focusing on the main thermodynamic parameters, the system’s features, and critical aspects, from a technical and environmental point of view. To perform this analysis, a MATLAB/Simulink model has been developed, starting from a fully validated model of the HS fueled by NG and considering the FC operating with an anodic ejector recirculation. In the new plant configuration, the SOFC pre-reformer has been substituted by an ammonia cracker, permitting to investigate the effects of the anode gas recirculation and properly design the whole system. In particular, the operating parameters, such as anodic recirculation factor, fuel utilization, performance, gas turbine size, and features are presented and discussed. Finally, a comparison between hybrid systems and mGT fed by methane, biogas, and ammonia is carried out.
Transient Thermo-Structural Analysis of a Throttle Valve Operated With sCO2
Authors: Bianchini Cosimo , Bertini Davide , Sandrin Simone , Mariotti Vanessa , Maceli Nicola , Arcangeli Lorenzo 
Published: August 2024

Abstract
This paper presents thermo-structural analyzes performed on a throttle valve operated with CO2 at supercritical conditions. In more detail, the study started with the thermal characterization of the steady-state behavior under different load conditions. During this phase, a numerical methodology for the evaluation of thermal maps was defined based on a loosely coupled Conjugate Heat Transfer approach that exploits a flow network and a 3D finite element thermal solver. A decoupled CFD analysis helped defining the thermal loads on the sealing system around the stem. The following step was dedicated to the analysis of a typical start-up ramp. The start-up sequence was built by linearly increasing the sCO2 flow from zero to the design value and then holding it constant until the metal temperature reaches the steady state. The performed thermo-structural analysis allowed the calculation of the relative displacements between the stem and the valve casing along the entire transient process.
Non-Synchronous Vibration and Related Tip Clearance Flow Characteristic in a Low-Speed Axial Fan
Authors: Zhang He , Zhang Ming , Dong Xu , Sun Dakun , Sun Xiaofeng 
Published: August 2024

Abstract
An experimental study investigating non-synchronous vibration due to rotating instability was conducted on a singlestage axial fan. The experiment monitored high-amplitude vibrations that could lead to high-cycle fatigue of the blades, and a wire mesh casing treatment was successfully employed to suppress the vibration. Two blade materials, metal and nylon, were used in the experiment under two different tip clearance conditions. Under the small tip clearance condition, no vibration causing high-cycle fatigue was observed, and there was no indication of rotating instability flow. For the case of enlarged tip clearance with nylon blades, as throttling proceeded, the azimuthal mode decreased. When the frequency in the rotating frame of reference closely matched the blade vibration frequency, it induced high-amplitude non-synchronous vibration. In response to this phenomenon, the paper conducts a mechanism analysis on the mode and frequency of the rotating source. Under the same enlarged tip clearance configuration, a wire mesh casing treatment was tested. While expanding the stability margin, it successfully suppressed the high-amplitude vibration phenomenon occurring in the near-stall area.