Thèses sur le sujet « Lean burn aero-engine combustor »

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (p. 95-97).
Lean operation of spark ignition (SI) automotive engines offers attractive performance incentives. Lowered combustion temperatures inhibit NO[sub]x pollutant formation while reduced manifold throttling minimizes pumping losses, leading to higher efficiency. These benefits are offset by the reduced combustion speed of lean mixtures, which can lead to high cycle-to-cycle variation and unacceptable engine behavior characteristics. Hydrogen-enhancement can suppress the undesirable consequences of lean operation by accelerating the combustion process, thereby extending the "lean limit." Hydrogen can be produced onboard the vehicle with a plasmatron fuel reformer device. Combustion optimization experiments focused on three key areas: the ignition system, charge motion in the inlet ports, and mixture preparation. The ignition system tests compared a standard inductive coil scheme against high-energy discharge systems. Charge motion experiments focused on the impact of turbulence patterns generated by conventional restrictor plates as well as novel inlet flow modification cones. The turbulent motion of each configuration was characterized using swirl and tumble flow benches. Mixture preparation tests compared a standard single-hole pintle injector against a fine atomizing 12-hole injector. Lastly, a further series of trials was also run to investigate the impact of high exhaust gas recirculation (EGR) dilution rates on combustion stability. Results indicate that optimizations of the combustion system in conjunction with hydrogen-enhancement can extend the lean limit of operation by roughly 25% compared against the baseline configuration. Nearly half of this improvement may be attributed to improvements in the combustion system.
(cont.) An inductive ignition system in conjunction with a high tumble-motion inlet configuration leads to the highest levels of combustion performance. Furthermore, hydrogen enhancement affects a nearly constant absolute improvement in the lean misfire limit regardless of baseline combustion behavior. Conversely, the amount of improvement in the point of peak engine NIMEP output is inversely related to the level of baseline performance.
by Joshua A. Goldwitz.
S.M.

This thesis describes an experimental investigation into ignition systems, their effects on the combustion process, and how the discharge is affected by the prevailing pressure, temperature and flow. The work is divided into four main areas, a comprehensive literature review, engine testing for ignition system suitability, non-flow rig testing (including erosion) and flow rig testing. The literature review concluded that the most practical ignition system for lean burn gas engines will continue to be based on the spark plug, but in the medium to long term, laser ignition may become viable. The measurement of the HT voltage and current is not straightforward, and appropriate methods have been identified. Capacitive and inductive ignition system types were compared in lean and diluted conditions on a single cylinder research engine of modern design at different engine loads and speeds. It was found that the most beneficial ignition system was an inductive ignition system, although that for some conditions, capacitive systems induced better engine performance with a fraction of the stored energy of the inductive alternative. Non flow tests showed that the early part of the spark discharge is sensitive to pressure and temperature effects, and as a consequence, the latter stages of the discharge are also affected. A correlation has been developed, for use with conventional nickel electrode spark plugs, to predict breakdown voltage as a function of pressure, temperature and gap. Experiments were carried out at elevated pressures in a stream of flowing air with capacitive and inductive ignition systems. Different electrode designs and orientations were also compared. It was shown that when exposed to a flow field, the discharge can be stretched which results in a shortened spark duration; in some cases the electrode can shield the discharge from flow field effects. This work showed that flow through the spark gap is a hindrance to the spark process, especially for longer duration systems. However for flame kernel growth, the literature review identified that flow is beneficial, serving to convect the kernel away from the electrodes, reducing the heat transfer from the flame. Analysis of the glow voltage history in the pressurised flow rig has been used to develop a correlation relating the voltage, current, flow velocity, pressure and time. This correlation was used to analyse the velocity records from the spark plug in a firing engine. The predicted velocities and turbulence intensity were in agreement with independent measurements.

Natural gas is currently an attractive substitute for diesel fuel in the Heavy-Duty (HD) diesel transportation sector. This is primarily attributed to its cost effectiveness, but also its ability to reduce the amount of CO2 and harmful engine pollutants emitted into the atmosphere. Lean-burn dual-fuel engines substitute natural gas in place of diesel but typically suffer from high engine-out methane (CH4) emissions, particularly under low load operation. In response to this issue, this work set out to improve upon the efficiency and emissions of a lean-burn dual-fuel combustion system in an HD diesel/natural gas engine. Thermodynamic experimental engine testing was performed at various steady-state operating points in order to identify the most effective methods and technologies for improving emissions and efficiency. Low Temperature Combustion (LTC) along with several valvetrain and injection strategies were evaluated for benefits, with special attention paid to low load operating conditions. LTC was proven to be a useful method for decreasing methane emissions while simultaneously improving engine efficiency. The benefits of LTC were a function of load with the greatest advantages experienced under medium load operation. Additionally, the low load strategies tested were determined to be effective techniques for reducing methane emissions and could possibly extend the dual-fuel operating regime to lighter load conditions. Overall, no operating condition tested throughout the engine map resulted in a brake engine-out methane emissions level of less than 0.5 g/kWh at gas substitutions greater than approximately 75%. It is suggested that the limits of this particular lean-burn dual-fuel design were reached, and that it would likely require improvements to either the combustion system or exhaust after-treatment if Euro VI emissions levels for methane were to be achieved.

La ricerca nel campo dei motori a combustione interna è sempre più rivolta ad identificare una soluzione alternativa all’utilizzo dei combustibili derivati dal petrolio, per ragioni di carattere ambientale, politico ed economico. Il gas naturale (NG) è un combustibile ideale per motori a combustione interna, essendo caratterizzato da basso impatto ambientale e consumi ridotti rispetto ai combustibili convenzionali (benzina e gasolio). Inoltre esso è particolarmente adatto ad essere utilizzato in motori ad elevato rapporto di compressione volumetrico, ed è caratterizzato da un ampio campo di infiammabilità. Quest’ultimo aspetto promuove la combustione magra di miscele di aria e NG, ottenendo un ulteriore incremento di rendimento ed un’ulteriore diminuzione dei consumi. I motori dual-fuel NG/diesel permettono di estendere il limite magro d’infiammabilità rispetto ai motori ad accensione comandata alimentati a NG, ed allo stesso tempo consentono di ridurre il trade-off NOX-PM di cui soffrono i motori diesel. Tale tecnologia consiste nell’introduzione del NG come combustibile principale in un motore diesel. Una certa quantità di gasolio viene ancora iniettata, ed agisce come sorgente d’accensione per la miscela di aria e NG. La facilità di conversione rende la tecnologia dual-fuel particolarmente allettante come retrofit di motori diesel già esistenti che in futuro si troverebbero a non soddisfare i sempre più stringenti limiti sulle emissioni inquinanti. Nel presente lavoro, la combustione dual-fuel, con la sua inerente complessità, viene analizzata seguendo un approccio misto numerico-sperimentale. L’attività sperimentale ha come obiettivo l’analisi dei vantaggi e dei problemi connessi con la conversione di un motore diesel heavy-duty al funzionamento dual-fuel, sulla base delle prestazioni e delle emissioni inquinanti. L’attività numerica è caratterizza da un approccio misto 1-D/3-D, ed è stata inizialmente condotta per la corretta comprensione del complesso meccanismo di combustione in modalità dual-fuel. L’analisi multi-dimensionale (3-D) dettagliata del sistema cilindro–pistone è stata successivamente effettuata per la corretta rappresentazione dei fenomeni termo-fluidodinamici evolventi in camera di combustione. Una tale strategia permette la completa descrizione del comportamento dell’intero sistema motore e della combustione dual-fuel nel dettaglio.
The research activity on internal combustion engines is increasingly cast to find an alternative solution to reduce the wide utilization of petroleum fuels like diesel oil and gasoline, for environmental, political and economic concerns. Natural gas (NG) is an ideal fuel to be operated in internal combustion engines, since its characteristics allow for much lower environmental impact and reduced fuel consumption with respect the conventional fuels. It also is particularly suitable to be operated under high volumetric compression ratio engines, thus providing higher efficiency, and moreover it is characterized by a wide flammability range. This latter aspect promotes the employment of a lean burn strategy, thus further increasing the engine efficiency and reducing the exhaust emissions. The dual-fuel natural gas/diesel concept allows extending the lean flammability limit of NG with respect to SI-NG operations and simultaneously reducing the NOX-PM trade-off affecting diesel combustion. Such a technology consists in introducing NG as main fuel in a conventional diesel engine. A certain amount of diesel pilot injection is preserved to act as the ignition source for the air/NG mixture. The easiness of dual-fuel conversion makes such technology rather inviting especially as a retrofit for the existing diesel vehicles, which could not meet the more and more stringent emission regulations in the future. In the present study, the dual-fuel combustion process with its inherent complexity is investigated both from an experimental and a numerical point of view. The experimental activity has the main target to analyze the problems connected with the conversion of a heavy-duty diesel engine to dual-fuel operation, and to put into evidence the influence of the main engine parameters on performance and pollutants formation. The numerical activity, characterized by a mixed 1-D/3-D approach, has been carried out with the initial target of a correct understanding of the complex dual-fuel combustion mechanism. A detailed multi-dimensional simulation of the whole working cycle of the engine has been subsequently performed, to provide for the correct representation of the fluid-dynamic effect involved in dual-fuel operations. Such an approach allows for the complete description of the engine overall behavior and the dual-fuel combustion in detail.

[EN] This research work presents the study of a low pressure EGR loop influence on a SI gasoline turbocharged direct injection engine in steady and transient testing conditions, with an optimization process of the original engine calibration in order to minimize the engine fuel consumption when cooled EGR is introduced in steady testing conditions. The cooled EGR strategy was also evaluated operating in synergy with other fuel consumption reduction strategies, such as: lean burn, multi-injection, higher coolant temperature and in-cylinder induced swirl motion. To fulfill the main objectives of this research work, firstly, a methodical process was followed, where a global methodology was first developed in order to obtain high accuracy engine tests, based on the experimental tools chosen that could comply with the requirements of the testing conditions, and the appropriate theoretical tools and procedure to post-process the tests performed. Secondly, a specific methodology was developed for each stage of the study and testing conditions, taking into account optimization processes or parametric tests in order to study the effect of a single parameter on engine's outputs or optimize an engine parameter in order to minimize the engine fuel consumption. As a first stage of the study, a basic analysis of the impact of cooled EGR on the engine combustion, performance, air management and exhaust emissions is presented. Afterwards, an optimization of the combustion phasing in order to minimize the fuel consumption was performed, and therefore the potential of cooled EGR in order to reduce the engine fuel consumption was observed for low load, part load and full load engine conditions, for two different engine speeds. In addition, a study in transient conditions of the engine operating with cooled EGR was performed. NEDC cycles were performed with different EGR valve openings and therefore a comparison of different cooled EGR rates influence on the engine performance, air management and accumulated exhaust emissions was presented. The second stage, consisted in a methodology developed to optimize the VVT setting and injection timing, for part load engine conditions, in order to maximize the cooled EGR potential to reduce engine fuel consumption. After this optimization, a synergy analysis of the optimum engine condition operating with cooled EGR and three other engine fuel consumption reduction strategies was performed. These strategies were tested to investigate and evaluate the potential of increasing the cooled EGR operational range to further decrease the engine fuel consumption. Furthermore, a basic study of the potential to reduce the engine fuel consumption and impact on combustion, air management and exhaust emissions of a lean burn strategy, in part load engine conditions, was presented as introduction of the final study of the cooled EGR strategy operating in synergy with the lean burn strategy in order to investigate the potential to control the exhaust emissions and reduce the engine fuel consumption.
[ES] El objetivo de este trabajo de investigación es estudiar la influencia de un lazo de baja presión de EGR en las prestaciones de un motor de gasolina de encendido provocado turbosobrealimentado e inyección directa, en condiciones de ensayos estacionarios y transitorios, con un proceso de optimización de la calibración original del motor para minimizar el consumo de combustible del motor. La estrategia de "cooled EGR" fue también evaluada operando en sinergia con otras estrategias usadas para reducir el consumo de combustible del motor, entre ellas: mezcla pobre, múltiples inyecciones, operación a alta temperatura del fluido refrigerante del motor y movimiento de "swirl" inducido en el cilindro. Para cumplir con los objetivos mencionados, se siguió un proceso metódico donde previamente se desarrolló una metodología global para obtener resultados de indudable calidad, basados en el uso de herramientas experimentales que cumplieran con los requerimientos de las condiciones de ensayo, y las apropiadas herramientas teóricas y procedimiento para post-procesar los ensayos realizados. En segundo lugar, se desarrolló una metodología específica para cada etapa del estudio, teniendo en cuenta los procesos de optimización o estudios paramétricos que se pudieran realizar. Como primera etapa, se presenta un estudio básico del impacto del "cooled EGR" en la combustión, prestaciones, renovación de la carga y emisiones contaminantes del motor. Seguidamente, se procedió a la optimización del centrado de la combustión con la finalidad de minimizar el consumo de combustible del motor y poder analizar el potencial del "cooled EGR" como estrategia de reducción de consumo de combustible. El estudio presentado se realizó para baja, media y alta carga del motor con dos diferentes regímenes de giro del motor. Adicionalmente, se llevó a cabo un estudio del motor operando en condiciones transitorias con "cooled EGR". Se realizaron una serie de ensayos usando el ciclo NEDC como base y se probaron diferentes estrategias sencillas de control de la apertura de la válvula de EGR para analizar la influencia del "cooled EGR" en condiciones transitorias. La segunda etapa consiste en el desarrollo de una metodología para optimizar los parámetros del diagrama de distribución (VVT) y el inicio de inyección, para cargas medias del motor, con la finalidad de maximizar el potencial de reducción de consumo de combustible de la estrategia "cooled EGR". Una vez realizada la optimización, se llevó a cabo un estudio usando la configuración óptima encontrada, operando en sinergia con otras tres estrategias usadas para reducir el consumo de combustible del motor. Estas estrategias fueron evaluadas con la finalidad de incrementar el rango de operación de la estrategia "cooled EGR" para lograr reducir aún más el consumo de combustible del motor. Adicionalmente, se llevó a cabo un estudio básico sobre la influencia de operar con mezcla pobre en la combustión, prestaciones, renovación de la carga y emisiones contaminantes del motor, como introducción al último estudio llevado a cabo sobre la posibilidad de usar la estrategia de mezcla pobre en conjunto con la estrategia de "cooled EGR", con la finalidad de analizar el potencial de controlar las emisiones contaminantes y reducir el consumo de combustible del motor al mismo tiempo.
[CAT] L'objectiu d'este treball d'investigació és estudiar la influència d'un llaç de baixa pressió d'EGR en les prestacions d'un motor de gasolina d'encesa provocat turbosobrealimentat i injecció directa, en condicions d'assajos estacionaris i transitoris, amb un procés d'optimització del calibratge original del motor per a minimitzar el consum de combustible del motor. L'estratègia de "cooled EGR" va ser també avaluada operand en sinergia amb altres estratègies usades per a reduir el consum de combustible del motor, entre elles: mescla pobra, múltiples injeccions, operació a alta temperatura del fluid refrigerant del motor i moviment de `"swirl" induït en el cilindre. Per a complir amb els objectius mencionats, es va seguir un procés metòdic on prèviament es va desenrotllar una metodologia global per a obtindre resultats d'indubtable qualitat, basats en l'ús de ferramentes experimentals que compliren amb els requeriments de les condicions d'assaig, i les apropiades ferramentes teòriques i procediment per a post- processar els assajos realitzats. En segon lloc, es va desenrotllar una metodologia específica per a cada etapa de l'estudi, tenint en compte els processos d'optimització o estudis paramètrics que es pogueren realitzar. Com a primera etapa, es presenta un estudi bàsic de l'impacte del "cooled EGR" en la combustió, prestacions, renovació de la càrrega i emissions contaminants del motor. A continuació, es va procedir a l'optimització del centrat de la combustió amb la finalitat de minimitzar el consum de combustible del motor i poder analitzar el potencial del "cooled EGR" com a estratègia de reducció de consum de combustible. L'estudi presentat es va realitzar per a baixa, mitja i alta càrrega del motor amb dos diferents règims de gir del motor. Addicionalment, es va dur a terme un estudi del motor operand en condicions transitòries amb "cooled EGR". Es van realitzar una sèrie d'assajos usant el cicle NEDC com a base i es van provar diferents estratègies senzilles de control de l'obertura de la vàlvula d'EGR per a analitzar la influència del "cooled EGR" en condicions transitòries. La segona etapa consistix en el desenrotllament d'una metodologia per a optimitzar els paràmetres del diagrama de distribució (VVT) i l'inici d'injecció, per a càrregues mitges del motor, amb la finalitat de maximitzar el potencial de reducció de consum de combustible de l'estratègia "cooled EGR". Una vegada realitzada l'optimització, es va dur a terme un estudi usant la configuració òptima trobada, operant en sinergia amb altres tres estratègies usades per a reduir el consum de combustible del motor. Estes estratègies van ser avaluades amb la finalitat d'incrementar el rang d'operació de l'estratègia "cooled EGR" per a aconseguir reduir encara més el consum de combustible del motor. Addicionalment, es va dur a terme un estudi bàsic sobre la influència d'operar amb mescla pobra en la combustió, prestacions, renovació de la càrrega i emissions contaminants del motor, com a introducció a l'últim estudi dut a terme sobre la possibilitat d'usar l'estratègia de mescla pobra en conjunt amb l'estratègia de "cooled EGR", amb la finalitat d'analitzar el potencial de controlar les emissions contaminants i reduir el consum de combustible del motor al mateix temps.
Rivas Perea, ME. (2016). Assessment of fuel consumption reduction strategies on a gasoline turbocharged direct injection engine with a cooled EGR system [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68497
TESIS

The recent limitations imposed by ICAO-CAEP towards a drastic reduction of NOx emissions is driving the development of modern aeroengines towards the implementation of lean burn concept. The increased amount of air dedicated to the combustion process (up to 70%) involves several technological issues, including a signicant reduction of coolant available for the thermal management of combustor liners. This, from a design perspective, involves the continuous research for effective cooling schemes, such as effusion cooling, and the necessity of more accurate methodologies for the estimation of metal temperature, so as to properly assess the expected duration of hot gas path components. The flame stabilization through swirler characterized by large effective area leads to extended recirculating zones, which interact considerably with the liner cooling system. As highlighted in the first part of this dissertation, the impact on the near-wall flow field makes any consideration based on a correlative approach untrustworthy, demanding for more reliable evaluations through CFD analysis. Unfortunately, the application of effusion cooling entails a huge computational effort due to the high number of film cooling holes involved, therefore many approaches have been proposed in literature with the aim of modelling the coolant injection through mass sources. This work presents SAFE (Source based effusion model), a methodology for the CFD simulation of the entire combustor, which is based on the local coolant injection through point sources and a calculation of mass flow rate according to local flow conditions. A further step in reduction in the computational effort is represented by a different methodology, called Therm3D, which involves the simulation of the flame tube, whereas the solution of the remaining part of the combustor is fulfilled through the modelling of an equivalent flow network, which provides for the estimation of flow split and cold side heat loads. Ultimately, this work introduces innovative approaches for the CFD investigation of effusion cooled combustor, with a special focus on the metal temperature prediction. A model for the film cooling injection is proposed to overcome the issues related to the necessity of meshing the perforation, nevertheless several improvable aspects have been highlighted, pointing the way for further enhancements.

Legislation limits concerning polluting emissions, for civil aircraft engines, are expected to become even more stringent in the future. To meet these targets, especially in terms of NOx, it is required to maintain the temperature in the combustion zone as low as possible. Lean burn swirl stabilized combustors represent the key technology to reduce NOx emissions. The high amount of air admitted through a lean-burn injection system is characterized by very complex flow structures such as recirculations, vortex breakdown and processing vortex core, that may deeply interact in the near wall region of the combustor liner. This interaction and its effects on the local cooling performance make the design of the cooling systems very challenging. In addition, since up to 70% of the overall air mass flow is utilized for fuel preparation and the initiation of lean combustion, the amount of air available for combustor liner cooling has to be strongly reduced with respect to the traditional diffusive combustor architectures. State-of-the-art of liner cooling technology for modern combustors is represented by the effusion cooling. Effusion cooling is a very efficient cooling strategy based on the use of multi-perforated liners, where metal temperature is lowered by the combined protective effect of coolant film and heat removal through forced convection inside each hole. Beyond that, multiperforated liners act also as passive devices to mitigate thermoacoustic phenomena which is one of the main concern regarding lean combustors operability. A large part of the activities and the achievements deriving from the Ph.D. course are collected in the present study, that deals with two experimental campaigns on effusion cooling schemes designed for aero-engine combustor liner applications. In the first part of the current research, an experimental survey has been performed for the evaluation of thermal performance, in terms of overall and adiabatic effectiveness, of seven multi-perforated planar plates representative of a portion of combustor liner, with uniform mainstream conditions. Effusion geometries were tested imposing 6 blowing ratios in the range 0.5-5, two values of density ratio and two level of mainstream turbulence. Concerning the geometrical features, different porosity levels have been considered: such values are obtained both increasing the hole diameter and pattern spacing. Then, the effect of hole inclination and aspect ratio pattern shape have been tested to assess the impact of typical cooling system features. The analysis of the data points out the impact of the main geometrical and fluid dynamics parameters on the thermal performance, proposing a possible thermal optimization strategy that seems to be promising also from the acoustic damping requirements. Results represent a wide experimental database relevant for the design of an high efficiency effusion cooling systems, even though the survey leaves the impact of the swirled gas flow on thermal performance an open issue. To enhance the TRL (Technology Readiness Level) of experiments, a planar sector test rig equipped with three AVIO Aero PERM (Partially Evaporated and Rapid Mixing) injector systems and working at atmospheric conditions has been considered in the second part of the work. The test rig allowed to reproduce a representative flow field on the gas side and to test the complete liner cooling scheme composed by a slot system, that reproduced the exhaust dome cooling mass flow, and an effusion array. The final aim of the study is the experimental characterization of the flow field and the measurement of cooling performance in terms of heat transfer coefficient and adiabatic effectiveness due to the interaction of the swirling flow coming out from the injectors and the cooling scheme. Tests were carried out imposing several realistic operating conditions, especially in terms of reduced mass flow rate and pressure drop across swirlers and effusion cooling holes.

Experimental Investigation of the effects of a modern lean burn combustor outflow on the performance of a film-cooled NGV cascade. Evaluation of chamber flow field, NGV inlet/outlet aerothermal field, turbulence decay and adiabatic effectiveness on the NGV profiles

The liquid fuel preparation has a strong impact on the combustion process and consequently on pollutant emissions. However, currently there are no validated and computational affordable methods available to predict the spray breakup process and to reliably compute the spray distribution generated after primary breakup. This research activity, carried out within the framework of the European project FIRST (Fuel Injector Research for Sustainable Transport), is aimed at developing reliable tools to be used in the industrial design process able to describe the processes involved in liquid fuel preparation in advanced injection systems based on prefilming airblast concept. A multi-coupled solver for prefilming airblast injectors which includes liquid film evolution and primary breakup was developed in the framework of OpenFOAM. The solver is aimed at improving the description of the complex physical phenomena characterizing liquid fuel preparation and spray evolution in advanced airblast injection systems within the context of typical RANS (U-RANS) industrial calculations. In this kind of injectors, gas-phase, droplet and liquid film interact with each other, thus, in order to properly predict spray evolution and fuel distribution inside the combustor, proper tools able to catch the most important interactions among the different phases are necessary. A steady-state Eulerian-Lagrangian approach was introduced in the code together with up-to-date evaporation and secondary breakup models. Particular attention was devoted to the liquid film primary breakup and to the interactions between gas-phase and liquid film. A new primary breakup model for liquid films, basically a phenomenological model which exploits liquid film and gas-phase solutions for the computation of spray characteristics after breakup, was developed and implemented in the code. Different formulations for the computation of droplet diameter after breakup were evaluated and revised on the basis of recent experimental findings. The multi-coupled solver was validated against literature test cases with detailed experimental measurements and eventually applied to the simulation of an advanced prefilming airblast injector based on the PERM concept in a tubular combustor configuration. The proposed approach allows us to better describe the fuel evolution in the injector region leading to a more comprehensive and physically consistent description of the phenomena regulating liquid fuel preparation compared to standard approaches which neglect the presence of liquid film and its interaction with both droplets and gas-phase.

The recent limitations imposed by ICAO-CAEP, regulating NOx emissions, are leading to the implementation of lean burn concept in the aero-engine framework. From a design perspective, a depth insight on lean burn combustion is required and Computational Fluid Dynamics (CFD) can be a useful tool for this purpose. Several interacting phenomena are involved and various modelling strategies, with huge differences in terms of computational costs, are available. Nevertheless, up to now few numerical tools are able to account for the effects of liquid fuel preparation inside reactive computations. Spray boundary conditions are normally determined thanks to correlative approaches that are not able to cover the wide range of operating conditions and geometrical characteristics of aero-engine burners. However, as highlighted in the first part of the dissertation, where several literature test cases are analysed through numerical calculations, the impact of liquid preparation can be extremely important. Considerations based on correlative approaches may be therefore unreliable. More trustworthy predictive methods focused on fuel atomization are required. This research activity is therefore aimed at developing a general numerical tool, to be used in an industrial design process, capable of modelling the liquid phase from its injection till the generation of a dispersed spray subject to evaporation. The ELSA (Eulerian Lagrangian Spray Atomization) model, which is based on an Eulerian approach in the dense region and a Lagrangian one in the dilute zone, has been chosen to this end. The solver is able to deal with pure liquid up to the generation of a dispersed phase and to account for the breakup process through the introduction of the liquid-gas interface density. However, several limitations of such method arise considering its application in a highly swirled reactive environment like an aero-engine burner. Therefore, particular attention has been here devoted first to the study of the turbulent liquid flux term, inside the liquid volume fraction equation. This quantity is of paramount importance for a swirled flow-field, with high slip velocities between phases. A completely innovative modelling framework together with a new second order closure for this variable is proposed and validated on a literature jet in crossflow test case. Then, to handle a reactive environment, a novel evaporation model is integrated in the code and assessed against experimental results. Finally, an alternative way to derive the Drop Size Distribution (DSD) in ELSA context for the lagrangian injection is presented and assessed by means of Direct Numerical Simulations. Ultimately, this work introduces an innovative framework towards a unified description of spray combustion in CFD investigations. The proposed approach should lead to a comprehensive description of fuel evolution in the injector region and to a proper characterization of the subsequent reacting flow-field. Several improvable aspects are also highlighted, pointing the way for further enhancements.

The transformation towards a climate-neutral civil aviation is providing significant business opportunities to the aero engine market players. To meet this target and keep competitiveness, however, groundbreaking solutions must be introduced at the product’s level in the shortest possible time. Industry lead-ers are increasingly embracing lean and digital approaches for this purpose, by applying these concepts at all company’s levels. Considerable room for im-provements can be identified in the development of complex components as, for instance, the combustor. Due to the complexity of phenomena taking place and interacting into it, there are conflicting functional requirements defined over different physical domains. This leads to a design approach that must be both multidisciplinary and multi-objective, in which the need for supporting know-how and product expertise arises with extensive and structured studies of the design space arises. Nowadays, simulation-based methodologies repre-sent a standard in evaluating multiple configurations of the system, although it may lead to heterogeneous models interacting with each other, sharing miscel-laneous information within the process. In this context, taking advantage of in-tegrated design systems has been proven to be beneficial in standardizing the simulation processes while embedding design’s best practices. The subject matter of this work is the Combustor Design System Integra-tion (DSI), an integrated methodology aimed at easing and streamlining the preliminary design phase of aero engine combustors. Its concept will be de-scribed in the first part, where the automation of low value-added tasks will be introduced together with four custom integrated tools. It is composed of a CAD generation system, a RANS-based CFD suite for reactive flow calculations, a boundary-conditions processor for 3D thermal FEA and a FE structural envi-ronment for stress and displacement estimation. Particular importance is given to the definition of cooling and quenching systems on combustor’s liners, since their prominent impact on aero-thermal and durability performance. Therefore, specific features for a detailed topological management of holes are presented in this work, providing advance patterning and arrangement capabilities which are not addressed in other design systems. Finally, it will be possible to prove the reduction of lead time for analysis, as well as the enhancement of the overall process robustness. The NEWAC combustor, a lean-burn concept developed in the context of the homonymous European research project, will be exploited as a case allowing, moreover, an assessment of the DSI modelling approach. In the second part will be presented a dedicated framework for multi-objective design optimization, comprising the DSI tools for CAD generation and CFD analysis. A fully automated and water-tight process is here implemented in order to ad-dress the combustor’s problem of dilution mixing, aimed at optimizing the temperature profiles and the emission levels at its outlet. This approach will leverage on advanced neural network algorithms for improving the overall de-sign workflow, so to ensure that the optimal combustor configuration is de-fined as a function of the product’s Critical-To-Quality. The results of the opti-mization will be shown for a rich-quench-lean combustor concept intentionally designed to support this activity, referred as to LEM-RQL. The general intention of this work, in the end, is to demonstrate how in-tegrated design systems embedded in optimization frameworks could repre-sent both a strategic asset for industry players and a relevant topic for academ-ics. Given the pervasive integration-and-automation of the process, the general-ity in processing multiple design layouts and the possibility to accommodate increasingly advanced and sophisticated optimization algorithms, the DSI pro-cedure configure itself as an ideal platform within the technology maturation process, thus enabling not only the improvement of in-service components but also the development of next-generation combustor products.