Prediction of flow and combustion in IC engines remains a challenging task. Traditional Reynolds Averaged Navier Stokes (RANS) methods and emerging Large Eddy Simulation (LES) techniques are being used as reliable mathematical tools for such predictions. However, RANS models have to be further refined to make them more predictive by eliminating or reducing the requirement for application based fine tuning. LES holds a great potential for more accurate predictions in engine related unsteady combustion and associated cycle-tocycle variations. Accordingly, in the present work, new advanced CFD based flow models were developed and validated for RANS and LES modelling of turbulent premixed combustion in SI engines. In the research undertaken for RANS modelling, theoretical and experimental based modifications have been investigated, such that the Bray-Moss-Libby (BML) model can be applied to wall-bounded combustion modelling, eliminating its inherent wall flame acceleration problem. Estimation of integral length scale of turbulence has been made dynamic providing allowances for spatial inhomogeneity of turbulence. A new dynamic formulation has been proposed to evaluate the mean flame wrinkling scale based on the Kolmogorov Pertovsky Piskunow (KPP) analysis and fractal geometry. In addition, a novel empirical correlation to quantify the quenching rates in the influenced zone of the quenching region near solid boundaries has been derived based on experimentally estimated flame image data. Moreover, to model the spark ignition and early stage of flame kernel formation, an improved version of the Discrete Particle Ignition Kernel (DPIK) model was developed, accounting for local bulk flow convection effects. These models were first verified against published benchmark test cases. Subsequently, full cycle combustion in a Ricardo E6 engine for different operating conditions was simulated. An experimental programme was conducted to obtain engine data and operating conditions of the Ricardo E6 engine and the formulated model was validated using the obtained experimental data. Results show that, the present improvements have been successful in eliminating the wall flame acceleration problem, while accurately predicting the in-cylinder pressure rise and flame propagation characteristics throughout the combustion period. In the LES work carried out in this research, the KIVA-4 RANS code was modified to incorporate the LES capability. Various turbulence models were implemented and validated in engine applications. The flame surface density approach was implemented to model the combustion process. A new ignition and flame kernel formation model was also developed to simulate the early stage of flame propagation in the context of LES. A dynamic procedure was formulated, where all model coefficients were locally evaluated using the resolved and test filtered flow properties during the fully turbulent phase of combustion. A test filtering technique was adopted to use in wall bounded systems. The developed methodology was then applied to simulate the combustion and associated unsteady effects in Ricardo E6 spark ignition engine at different operating conditions. Results show that, present LES model has been able to resolve the evolution of a large number of in-cylinder flow structures, which are more influential for engine performance. Predicted heat release rates, flame propagation characteristics, in-cylinder pressure rise and their cyclic variations are also in good agreement with measurements.

Como consecuencia de las exigentes legislaciones medioambientales actualmente en vigor, como las Euro Emission Standards en Europa, los investigadores e ingenieros se ven forzados a "re-desarrollar" el proceso de combustión diésel para hacerlo menos contaminante. Uno de los principales contaminantes y más dañinos para la salud son los óxidos de nitrógeno (NOx) que están principalmente compuestos por: monóxido de nitrógeno (NO), dióxido de nitrógeno (NO2) y trióxido de dinitrógeno (N2O3). Centrándose en los NOx generados en una combustión diésel, una de las técnicas más populares para mitigar su formación es mediante la dilución de la corriente oxidante con productos de la combustión, previamente generados. De este modo, al reducir la reactividad de la corriente oxidante se consigue una disminución considerable de la temperatura de combustión y por extensión de los NOx. Sin embargo, dicha técnica causa nuevas interacciones físico-químicas entre los hidrocarburos y los NOx así como principalmente un notable cambio en la estructura del chorro diésel. Es por ello necesario considerar las diferentes vías de formación de éstos para poder predecir su generación. El hecho de considerar las diferentes vías de formación implica un incremento considerable de los recursos computacionales destinados a realizar las simulaciones, siendo en algunos casos inviable. Es por ello que el objetivo principal de esta tesis consiste en: desarrollar herramientas capaces de tener en consideración todas estas vías sin incrementar de manera considerable el coste computacional. Para ello inicialmente se realiza una exhaustiva revisión bibliográfica en donde se repasan las diferentes herramientas desarrolladas para la predicción de los NOx y se analizan sus puntos débiles. Éstos radican en simplificaciones de dudosa validez, que solamente tienen efectos positivos a altas y no a bajas temperaturas, o bien procesos demasiado tediosos y complejos para caracterizar los diferentes estados de una combustión. Posteriormente se diseña una metodología capaz de satisfacer el objetivo principal, basada en tres estudios. El primero permite profundizar en el proceso de formación de este contaminante a través de estudiar el incremento de la proporción de NO2 en los NOx debido a la recirculación masiva de estos productos. Por otro lado, los otros dos consisten en desarrollar diversas herramientas predictivas centradas exclusivamente en el NO, ya que como se dedujo del estudio anterior el NO2 se forma principalmente a partir del NO a través de un proceso de enfriamiento. La primera de estas herramientas está basada en una correlación empírica que a modo de ecuación correctiva mejora la capacidad predictiva, especialmente en condiciones de recirculación masiva, del mecanismo más implementado mundialmente, mientras que la segunda se sustenta en tabular únicamente la velocidad de formación del NO y el NO en equilibrio en función de la temperatura y de la cantidad de oxígeno disponible inicialmente para reaccionar. Finalmente para poder llevar a cabo estos estudios y cumplir con el objetivo principal se hace uso de un software comercial cinético-químico Chemkin, en su versión Professional, que sirve tanto de herramienta desarrolladora como de referencia. / Redón Lurbe, P. (2013). Modeling of the nitrogen oxides formation process applicable to several diesel combustion modes [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/33183 / TESIS

[ES] El objetivo de esta tesis es la investigación y análisis de la estructura interna de los chorros diésel reactivos y el efecto de las condiciones de contorno en los parámetros asociados a la combustión. Este objetivo se consigue por medio de la simulación numérica del chorro con modelos de turbulencia RANS y LES usando un modelo de combustión avanzado basado en el concepto flamelet. Para este estudio, se aplica una aproximación simplificada de las flamelets de difusión, conocidas en la literatura como Flamelets de Difusión Aproximadas (ADF en inglés), como fundamento del modelo de combustión. En una primera etapa, el modelo se valida con combustibles de diferente complejidad química en regímenes estacionarios y transitorios para el conjunto de posibles velocidades de deformación. Una vez se confirma su idoneidad para condiciones encontradas en chorros diésel, se aplica a la simulación del chorro A del Engine Combustion Network (ECN), representativo de chorros diésel. Para proporcionar un cuadro completo de los fenómenos subyacentes, la combustión se analiza inicialmente para condiciones homogéneas y llamas laminares para las distintas condiciones de contorno de este experimento. Después este análisis se complementa con la simulación de diferentes mecanismos químicos para determinar cómo las características del encendido predichas por el esquema de oxidación afectan a la propagación de llama. Los resultados obtenidos en esta etapa se enlazan con el análisis del chorro turbulento en el contexto de simulaciones RANS y LES para describir cómo el fenómeno de la combustión se modifica con los diferentes niveles de complejidad física. La estructura del chorro turbulento se describe profundamente para las distintas condiciones de contorno y mecanismos químicos en términos de mezcla y escalares reactivos para las fases temporales y las regiones espaciales de la llama. La satisfactoria concordancia con los resultados experimentales muestran que el concepto flamelet, y más particularmente el modelo ADF, es adecuado para las simulaciones de chorros diésel. / [CAT] L'objectiu d'esta tesi és la investigació i anàlisi de l'estructura interna dels dolls dièsel reactius i l'efecte de les condicions de contorn en els paràmetres associats a la combustió. Este objectiu s'aconsegueix per mitjà de la simulació numèrica del doll amb models de turbulència RANS i LES usant un model de combustió avançat basat en el concepte flamelet. Per a este estudi, s'aplica una aproximació simplificada de les flamelets de difusió, conegudes a la literatura com Flamelets de Difusió Aproximades (ADF en anglés), com a fonament del model de combustió. En una primera etapa, el model es valida amb combustibles de diferent complexitat química en règims estacionaris i transitoris per al conjunt de possibles velocitats de deformació. Una vegada es confirma la seua idoneïtat per a condicions trobades en dolls dièsel, s'aplica a la simulació del doll A del Engine Combustion Network (ECN), representatiu de dolls dièsel. Per a proporcionar un cuadre complet dels fenòmens subjacents, la combustió s'analitza inicialment per a condicions homogènies i flames laminars per a les distintes condicions de contorn d'aquest experiment. Després esta anàlisi es complementa amb la simulació de diferents mecanismes químics per a determinar com les característiques de l'encesa predites per l'esquema d'oxidació afecten la propagació de flama. Els resultats obtinguts en esta etapa s'enllacen amb l'anàlisi del doll turbulent en el context de simulacions RANS i LES per a descriure com el fenomen de la combustió es modifica amb els diferents nivells de complexitat física. L'estructura del doll turbulent es descriu profundament per a les distintes condicions de contorn i mecanismes químics en termes de mescla i escalars reactius per a les fases temporals i les regions espacials de la flama. La satisfactòria concordança amb els resultats experimentals mostren que el concepte flamelet, i més particularment el model ADF, és adequat per a les simulacions de dolls dièsel. / [EN] The objective of this thesis is the investigation and analysis of the internal structure of diesel-like reacting sprays and the effect of boundary conditions on combustion related parameters. This objective is achieved by means of the numerical simulation of the spray with RANS and LES turbulence models using an advanced combustion model based on the flamelet concept. For this study, a simplified approach for diffusion flamelets, known in the literature as Approximated Diffusion Flamelet (ADF), is applied as the basis of the combustion model. In a first step, this model is validated for fuels with different chemical complexity in steady and transient regimes for the whole set of possible strain rates. Once its suitability is confirmed for conditions found in diesel sprays, it is applied to the simulation of spray A from the Engine Combustion Network (ECN), representative of diesel-like sprays. In order to provide a complete picture of the underlying phenomena, combustion is initially analysed in homogeneous conditions and laminar flames for the different boundary conditions of this experiment. Later, this analysis is complemented with the simulation of different chemical mechanisms in order to determine how the ignition characteristics predicted by the oxidation scheme affect to the flame propagation. The results obtained at this stage are connected with the analysis of the turbulent spray in the context of RANS and LES simulations as a way to track how combustion phenomenon is modified at the different levels of physical complexity. The turbulent spray structure is thoroughly described for the different boundary conditions and chemical schemes in terms of mixing and reactive variables for both temporal phases and spatial flame regions. The satisfactory agreement with experimental results shows that the flamelet concept, and more particularly the ADF model, is suitable for diesel-like sprays simulations. / Pérez Sánchez, EJ. (2019). Application of a flamelet-based combustion model to diesel-like reacting sprays [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/117316 / TESIS

The accurate description of the turbulence chemistry interactions that can determine chemical conversion rates and flame stability in turbulent combustion modelling is a challenging research area. This thesis presents the development and implementation of a model for the treatment of fluctuations around the conditional mean (i.e., the auto-ignition and extinction phenomenon) of realistic turbulence-chemistry interactions in computational fluid dynamics (CFD) software. The wider objective is to apply the model to advanced combustion modelling and extend the present analysis to larger hydrocarbon fuels and particularly focus on the ability of the model to capture the effects of particulate formation such as soot. A comprehensive approach for modelling of turbulent combustion is developed in this work. A direct quadrature conditional moment closure (DQCMC) method for the treatment of realistic turbulence-chemistry interactions in computational fluid dynamics (CFD) software is described. The method which is based on the direct quadrature method of moments (DQMOM) coupled with the Conditional Moment Closure (CMC) equations is in simplified form and easily implementable in existing CMC formulation for CFD code. The observed fluctuations of scalar dissipation around the conditional mean values are captured by the treatment of a set of mixing environments, each with its pre-defined weight. In the DQCMC method the resulting equations are similar to that of the first-order CMC, and the “diffusion in the mixture fraction space” term is strictly positive and no correction factors are used. Results have been presented for two mixing environments, where the resulting matrices of the DQCMC can be inverted analytically. Initially the DQCMC is tested for a simple hydrogen flame using a multi species chemical scheme containing nine species. The effects of the fluctuations around the conditional means are captured qualitatively and the predicted results are in very good agreement with observed trends from direct numerical simulations (DNS). To extend the analysis further and validate the model for larger hydrocarbon fuel, the simulations have been performed for n-heptane flame using detailed multi species chemical scheme containing 67 species. The hydrocarbon fuel showed improved results in comparison to the simple hydrogen flame. It suggests that higher hydrocarbons are more sensitive to local scalar dissipation rate and the fluctuations around the conditional means than the hydrogen. Finally, the DQCMC is coupled with a semi-empirical soot model to study the effects of particulate formation such as soot. The modelling results show to predict qualitatively the trends from DNS and are in very good agreement with available experimental data from a shock tube concerning ignition delays time. Furthermore, the findings suggest that the DQCMC approach is a promising framework for soot modelling.

[pt] O presente trabalho tem por objetivo a realização de experimentos e simulações numéricas para estudar a interação da turbulência e da combustão em uma chama não pré-misturada de hidrogênio no ar estabilizada a jusante de um corpo rombudo. Para tanto, são utilizadas, simultaneamente, as técnicas de PIV, para a determinação de dois componentes da velocidade, e a técnica de PLIF para a determinação da intensidade de fluorecência do radical químico OH, que é um bom indicador da localização da frente de chama. São avaliados os métodos de pós processamento dos resultados do PIV com o intuito de maximizar a resolução espacial da técnica e ao mesmo tempo remover o maior número de vetores espúrios dos campos de velocidade instantâneos. Paralelamente, o queimador é modelado no software ANSYS/FLUENT e os resultados de simulação validados por comparação com os resultados experimentais. Modelos baseados nas médias de Reynolds são empregados para a caracterização da turbulência e o modelo de elementos de chama é adotado para a descrever a combustão. Os resultados experimentais indicam que, para as vazões de ar e hidrogênio adotadas, a combustão ocorre no regime de elementos de chama, onde a frente de chama apresenta algumas dobras, mas sem descontinuidades. Os resultados das simulações com combustão não obtiveram boa concordância com os resultados experimentais, indicando que a malha de cálculo precisa ser aprimorada. / [en] The aim of this work is to carry out experiments and numerical simulations to study the turbulence-combustion interaction in a nonpremixed hydrogen-air ame stabilized in a bluff body wake. For this purpose, are used a PIV technique for the determination of two velocity components and a PLIF technique to determine the uorescence intensity of the chemical species OH, which is a good indicator of the flame front location. PIV post-processing methods are evaluated in order to maximize the spatial resolution of the technique and to remove spurious instantaneous velocity vectors. In addition, the burner is modeled in ANSYS / FLUENT and the simulation results are validated by comparisons with the experimental results. Models based in the Reynolds avareges are used to characterize the turbulence and a flamelet model is adopted to describe combustion. The experimental results indicates that, for the ow rates of air and hydrogen adopted, combustion occurs in the flamelet regime, where the flame front is wrinkled, but without discontinuities. The reactive cases simulations did not agree with the experimental results, indicating that the computational mesh needs to be improved.

This thesis describes the application of the first-order Conditional Moment Closure (CMC) to the autoignition of high-pressure fuel jets, and to piloted and lifted turbulent jet flames using classical and advanced CMC submodels. A Doubly-Conditional Moment Closure (DCMC) formulation is further proposed. In the first study, CMC is applied to investigate the impact of C₂H₆, H₂ and N₂ additives on the autoignition of high-pressure CH₄ jets injected into lower pressure heated air. A wide range of pre-combustion air temperatures is considered and detailed chemical kinetics are employed. It is demonstrated that the addition of C₂H₆ and H₂ does not change the main CH₄ oxidisation pathways. The decomposition of these additives provides additional ignition-promoting radicals, and therefore leads to shorter ignition delays. N₂ additives do not alter the CH₄ oxidisation pathways, however, they reduce the amount of CH₄ available for reaction, causing delayed ignition. It is further shown that ignition always occurs in lean mixtures and at low scalar dissipation rates. The second study is concerned with the modelling of a piloted CH₄/air turbulent jet flame. A detailed assessment of several Probability Density Function (PDF), Conditional Scalar Dissipation Rate (CSDR) and Conditional Velocity (CV) submodels is first performed. The results of two β-PDF-based implementations are then presented. The two realisations differ by the modelling of the CSDR. Homogeneous (inconsistent) and inhomogeneous (consistent) closures are considered. It is shown that the levels of all reactive scalars, including minor intermediates and radicals, are better predicted when the effects of inhomogeneity are included in the modelling of the CSDR. The two following studies are focused on the consistent modelling of a lifted H₂/N₂ turbulent jet flame issuing into a vitiated coflow. Two approaches are followed to model the PDF. In the first, a presumed β-distribution is assumed, whereas in the second, the Presumed Mapping Function (PMF) approach is employed. Fully consistent CV and CSDR closures based on the β-PDF and the PMF-PDF are employed. The homogeneous versions of the CSDR closures are also considered in order to assess the effect of the spurious sources which stem from the inconsistent modelling of mixing. The flame response is analysed over a narrow range of coflow temperatures (Tc). The stabilisation mechanism is determined from the analysis of the transport budgets in mixture fraction and physical spaces, and the history of radical build-up ahead of the stabilisation height. The β-PDF realisations indicate that the flame is stabilised by autoignition irrespective of the value of Tc. On the other hand, the PMF realisations reveal that the stabilisation mechanism is susceptible to Tc. Autoignition remains the controlling stabilisation mechanism for sufficiently high Tc. However, as Tc is decreased, stabilisation is achieved by means of premixed flame propagation. The analysis of the spurious sources reveals that their effect is small but non-negligible, most notably within the flame zone. Further, the assessment of several H₂ oxidation mechanisms show that the flame is very sensitive to chemical kinetics. In the last study, a DCMC method is proposed for the treatment of fluctuations in non-premixed and partially premixed turbulent combustion. The classical CMC theory is extended by introducing a normalised Progress Variable (PV) as a second conditioning variable beside the mixture fraction. The unburnt and burnt states involved in the normalisation of the PV are specified such that they are mixture fraction-dependent. A transport equation for the normalised PV is first obtained. The doubly-conditional species, enthalpy and temperature transport equations are then derived using the decomposition approach and the primary closure hypothesis is applied. Submodels for the doubly-conditioned unclosed terms which arise from the derivation of DCMC are proposed. As a preliminary analysis, the governing equations are simplified for homogeneous turbulence and a parametric assessment is performed by varying the strain rate levels in mixture fraction and PV spaces.

This thesis describes the application of the first-order Conditional Moment Closure (CMC) to the autoignition of high-pressure fuel jets, and to piloted and lifted turbulent jet flames using classical and advanced CMC submodels. A Doubly-Conditional Moment Closure (DCMC) formulation is further proposed. In the first study, CMC is applied to investigate the impact of C₂H₆, H₂ and N₂ additives on the autoignition of high-pressure CH₄ jets injected into lower pressure heated air. A wide range of pre-combustion air temperatures is considered and detailed chemical kinetics are employed. It is demonstrated that the addition of C₂H₆ and H₂ does not change the main CH₄ oxidisation pathways. The decomposition of these additives provides additional ignition-promoting radicals, and therefore leads to shorter ignition delays. N₂ additives do not alter the CH₄ oxidisation pathways, however, they reduce the amount of CH₄ available for reaction, causing delayed ignition. It is further shown that ignition always occurs in lean mixtures and at low scalar dissipation rates. The second study is concerned with the modelling of a piloted CH₄/air turbulent jet flame. A detailed assessment of several Probability Density Function (PDF), Conditional Scalar Dissipation Rate (CSDR) and Conditional Velocity (CV) submodels is first performed. The results of two β-PDF-based implementations are then presented. The two realisations differ by the modelling of the CSDR. Homogeneous (inconsistent) and inhomogeneous (consistent) closures are considered. It is shown that the levels of all reactive scalars, including minor intermediates and radicals, are better predicted when the effects of inhomogeneity are included in the modelling of the CSDR. The two following studies are focused on the consistent modelling of a lifted H₂/N₂ turbulent jet flame issuing into a vitiated coflow. Two approaches are followed to model the PDF. In the first, a presumed β-distribution is assumed, whereas in the second, the Presumed Mapping Function (PMF) approach is employed. Fully consistent CV and CSDR closures based on the β-PDF and the PMF-PDF are employed. The homogeneous versions of the CSDR closures are also considered in order to assess the effect of the spurious sources which stem from the inconsistent modelling of mixing. The flame response is analysed over a narrow range of coflow temperatures (Tc). The stabilisation mechanism is determined from the analysis of the transport budgets in mixture fraction and physical spaces, and the history of radical build-up ahead of the stabilisation height. The β-PDF realisations indicate that the flame is stabilised by autoignition irrespective of the value of Tc. On the other hand, the PMF realisations reveal that the stabilisation mechanism is susceptible to Tc. Autoignition remains the controlling stabilisation mechanism for sufficiently high Tc. However, as Tc is decreased, stabilisation is achieved by means of premixed flame propagation. The analysis of the spurious sources reveals that their effect is small but non-negligible, most notably within the flame zone. Further, the assessment of several H₂ oxidation mechanisms show that the flame is very sensitive to chemical kinetics. In the last study, a DCMC method is proposed for the treatment of fluctuations in non-premixed and partially premixed turbulent combustion. The classical CMC theory is extended by introducing a normalised Progress Variable (PV) as a second conditioning variable beside the mixture fraction. The unburnt and burnt states involved in the normalisation of the PV are specified such that they are mixture fraction-dependent. A transport equation for the normalised PV is first obtained. The doubly-conditional species, enthalpy and temperature transport equations are then derived using the decomposition approach and the primary closure hypothesis is applied. Submodels for the doubly-conditioned unclosed terms which arise from the derivation of DCMC are proposed. As a preliminary analysis, the governing equations are simplified for homogeneous turbulence and a parametric assessment is performed by varying the strain rate levels in mixture fraction and PV spaces.

In-cylinder fuel-air mixing in a compressed natural gas (CNG)-fuelled, single-cylinder, spark-ignited engine is analysed using a transient three-dimensional computational fluid dynamic model built and run using STAR-CD, a commercial CFD software. This work is motivated by the need for strategies to achieve improved performance in engines utilizing gaseous fuels such as CNG. The transient in-cylinder fuel-air mixing is evaluated for a port gas injection fuelling system and compared with that of conventional gas carburetor system. In this work pure methane is used as gaseous fuel for all the computational studies. It is observed that compared to the premixed gas carburetor system, a substantial level of in-cylinder stratification can be achieved with the port gas injection system. The difference of more than 20% in mass fraction between the rich and lean zones in the combustion chamber is observed for the port gas injection system compared to less than 1% for the conventional premixed system. The phenomenon of stratification observed is very close to the “barrel stratification” mode. A detailed parametric study is undertaken to understand the effect of various injection parameters such as injection location, injection orientation, start of injection, duration of injection and rate of injection. Furthermore, the optimum injection timing is evaluated for various load-speed conditions of the engine. It is also observed that the level of stratification is highest at 50% engine load with a reduced level at 100% load. For low engine loads, the level of stratification is observed to be very low. To analyse the effect of stratification on engine performance, the in-cylinder combustion is modeled using the extended coherent flame model(ECFM). For simulating the ignition process, the arc and kernel tracking ignition model(AKTIM) is used. The combustion model is first validated with measured in-cylinder pressure data and other derived quantities such as heat release rate and mass burn fraction. It is observed that there is a good agreement between measured and simulated values. Subsequently, this model is use to simulate both premixed and stratified cases. It is observed that there is a marginal improvement in terms of overall engine efficiency when the stoichiometric premixed case is compared with the lean stratified condition. However, a major improvement in performance is observed when the lean stratified case is compared with lean premixed condition. The stratified case shows a faster heat release rate which could potentially translate to lower cycle-to-cycle variations in actual engine operation. Also, the stratified cases show as much as 20% lower in-cylinder NOx emissions when compared with the conventional premixed case at the same engine load and speed, underscoring the potential of in-cylinder stratification to achieve improved performance and lower NOx emissions.

Cette thèse est consacrée à l’amélioration des capacités de prédiction des émissions polluantes (CO, NOx . . . ) des foyers de combustion de turboréacteurs. L’étude, exclusivement numérique, repose sur des simulations aux grandes échelles (ou LES pour Large-Eddy Simulation) basées sur des méthodes de tabulation de la chimie détaillée. L’approche PCM-FPI (pour Presumed Conditional Moments - Flame Prolongation of ILDM) a été étendue à la chimie des oxydes d’azote via la modification de la variable d’avancement. Différentes validations sur des configurations laminaires simples puis des flammes de laboratoire (Cabra, Sandia) sont présentées. Les résultats en terme de structure de flamme et de champs d’espèces chimiques sont confrontés aux mesures expérimentales. Le rôle du formaldéhyde comme marqueur de la zone réactionnelle est illustré à l’aide de calculs de flammes laminaires puis confirmé par un calcul 3D LES. Une analyse des spécificités de l’implantation de ce type de modèle sur des machines à architecture massivement parallèle est ensuite menée. Diverses modifications de la structure de la table et des méthodes d’interpolation sont réalisées, servant de base à une étude de sensibilité de maillage appliquée à la flamme Sandia D. Les difficultés relatives à la prédiction du NO dans les flammes turbulentes sont exposées : divers modèles de sous-maille sont alors employés et comparés. / This thesis is focused on the prediction capabilities of pollution (CO, NOx especially) for numerical tools applied to aeronautical combustion chambers. The modeling work is based on Large-Eddy Simulation methods coupled with a tabulated detailed chemistry approach. The PCM-FPI model, which stands for Presumed Conditional Moments - Flame Prolongation of ILDM, has been revised to take into account nitrogen chemistry through a modification of the progress variable. Several benchmarks and test-cases (laminar and turbulent flames) are gathered in this study : Cabra and Sandia flames have been computed and satisfactory comparisons with measurements are obtained. The role of CH2O as a marker of heat release is investigated, first in the frame of laminar premixed flames and then validated through LES runs. The challenges of the implementation of tabulated chemistry methods on massively parallel machines are discussed. Modifications are proposed regarding both the table structure and the interpolation methods leading to a mesh sensitivity review applied to the Sandia D flame. Difficulties arising when dealing with NOx chemistry in turbulent flows are presented : new Sub-Grid Scale models are introduced and investigated.

Utsläpp från bilar har spelat stor roll de senaste decennierna. Detta har lett till ökad användning av Otto gasmotorer som använder naturgas som bränsle. Nya motordesigner behöver optimeras för att förbättra motorens effektivitet. Ett effektivt sätt att göra detta på är genom användningen av simuleringar för att minska ledtiden i motorutvecklingen. Verifiering och validering av simuleringarna spelar stor roll för att bygga förtroende för och förutsägbarhet hos simuleringsresultaten. Syftet med detta examensarbete är att föreslå förbränningsmodellparametrarna efter utvärdering av olika kombinationer av förbrännings- och tändmodeller för Otto förbränning, vad gäller beräkningstid och noggrannhet. In-cylindertrycksspår från simulering och mätning jämförs för att hitta den bästa kombinationen av förbrännings- och tändmodell. Inverkan av tändtid, antal motorcykler och randvillkor för simuleringsresultatet studeras också. Resultaten visar att ECFM-förbränningsmodellen förutsäger simuleringsresultaten mer exakt när man jämför med mätningarna. Effekten av tändningstiden på olika kombinationer av förbrännings- och tändningsmodell utvärderas också. Stabiliteten hos olika förbränningssimuleringsmodeller diskuteras också under körning för fler motorcykler. Jämförelse av beräkningstid görs även för olika kombinationer av förbrännings- och tändmodeller. Resultaten visar också att flamspårningsmetoden med Euler är mer känslig för cellstorlek och kvalitet hos simuleringsnätet, jämfört med övriga studerade modeller. Rekommendationer och förslag ges om nät- och simulerings-inställningar för att prediktera förbränningen på ett så bra sätt som möjligt. Några möjliga förbättringsområden ges som framtida arbete för att förbättra noggrannheten i simuleringsresultaten. / Emission from automobiles has been gaining importance for past few decades. This has gained a lot of impetus in search for alternate fuels among the automotive manufacturers. This led to the increase usage of Otto gas engine which uses natural gas as fuel. New engine designs have to be optimized for improving the engine efficiency. This led to usage of virtual simulations for reducing the lead time in the engine development. The verification and validation of actual phenomenon in the virtual simulations with respect to the physical measurements was quite important.  The aim of this master thesis is to suggest the combustion model parameters after evaluating various combination of combustion and ignition models in terms of computational time and accuracy. In-cylinder pressure trace from the simulation is compared with the measurement in order to find the nest suited combination of combustion and ignition models. The influence of ignition timing, number of engine cycles and boundary conditions on the simulation results are also studied. Results showed that ECFM combustion model predicts the simulation results more accurately when compare to the measurements. Impact of ignition timing on various combination of combustion and ignition model is also assessed. Stability of various combustion simulation models is also discussed while running for more engine cycles. Comparison of computational time is also made for various combination of combustion and ignition models. Results also showed that the flame tracking method using Euler is dependent on the mesh resolution and the mesh quality.  Recommendations and suggestions are given about the mesh and simulation settings for predicting the combustion simulation accurately. Some possible areas of improvement are given as future work for improving the accuracy of the simulation results.