Sensitivity analysis was performed on a soot model using a partially stirred reactor (PaSR) in order to determine the effects of mixing model parameters on soot scalar values. The sensitivities of the mixture fraction zeta and progress variable C to the mixing model constant C_phi were calculated; these values were used to compute the sensitivity of water mass fraction Y_H2O to C_phi and several soot quantities to soot moments. Results were validated by evaluating the mean mixture fraction sensitivity and a long simulation time case. From the baseline case, it was noted that soot moment sensitivities tended to peak on the rich side of the stoichiometric mixture fraction zeta_st. Timestep, number of notional particles, mixing timescale tau_mix, and residence time tau_res were varied independently. Choices for timestep and notional particle count were shown to be sufficient to capture relevant scalar profiles, and did not greatly affect sensitivity calculations. Altering tau_mix or tau_res was shown to affect sensitivity to mixing, and it was concluded that the soot model is more heavily influenced by the chemistry than mixing. / text

A better understanding and control of internal combustion engine pollutants require more insightful investigation of gasoline oxidation chemistry. An oxidation study has been done on n-heptane, iso-octane, their binary mixtures (Primary Reference Fuel, (PRF)), and nine hydrocarbon mixtures which represent the second generation of gasoline surrogates (multi-component surrogates). This study aims to develop a better understanding of the combustion reaction by studying the oxidation reaction of different fuels inside a jet-stirred reactor and numerically simulating the reaction using different models under the following conditions: pressure 1 bar, temperature 500-1050K, residence time 1.0 and 2.0s, and two fuel-to-oxygen ratios (ϕ=0.5 and 1.0). Intermediate and product species mole fractions versus temperature profiles were experimentally measured using a GC (gas chromatograph). The experiment was performed within the high and low-temperature regions, where the high-temperature oxidation showed similar behavior for different compositions but the low-temperature oxidation showed significant dependence on the composition of the surrogates. Additionally, the effect of octane number on oxidation chemistry has been investigated and it was found that the low octane number surrogates were more reactive than high octane number surrogates during the low temperature regime. Furthermore, Kinetic analysis was conducted to provide insightful understanding of different factors of fuel reactivity. In addition, the pyrolysis of two TPRF, (Toluene primary reference fuels) mixtures (TPRF70 and TPRF97.5), representing low octane (research octane number 70) and high octane (research octane number 97.5) gasoline, was also studied in jet-stirred reactor coupled with gas chromatography (GC) analysis to investigate the formation of soot and polycyclic aromatic hydrocarbons (PAH) formation.

In the first part of this work, instability is correctly predicted for a Rijke tube with a new two-term acoustic forcing term derived from a one-dimensional flame dynamics model. The new two-term acoustic forcing term, which is comprised of the summation of chemical heat release rate and heat transfer due to convection, correctly predicts instability where older models of acoustic forcing based solely on chemical heat release rate incorrectly predicted stability. This stability analysis correctly predicts the inlet conditions of the instability in addition to the frequency of instability. In the second part of this work, networks of dynamic well-stirred reactors are used to model qualitative behavior observed in turbulent combustion. First a model of dynamic well-stirred reactor is derived, and then several reactors are coupled together by recirculation. The dynamics of the various models are computed and assessed. The models exhibit interesting behavior that has been viewed experimentally including hysteresis and peaking in the dynamic response. / Master of Science

A jet-stirred reactor was designed and constructed in the Clean Combustion Research Center (CCRC) at King Abdullah University of Science and Technology (KAUST); was validated with n-heptane, iso-octane oxidation and cyclohexene pyrolysis. Different configurations of the setup have been tested to achieve good agreement with results from the literature. Test results of the reactor indicated that installation of a pumping system at the downstream side in the experimental apparatus was necessary to avoid the reoccurrence of reactions in the sampling probe. Experiments in ethyl levulinate oxidation were conducted in the reactor under several equivalence ratios, from 600 to 1000 K, 1 bar and 2 s residence time. Oxygenated species detected included methyl vinyl ketone, levulinic acid and ethyl acrylate. Ethylene, methane, carbon monoxide, hydrogen, oxygen and carbon dioxide were further quantified with a gas chromatography, coupled with a flame ionization detector and a thermal conductivity detector. The ethyl levulinate chemical kinetic model was first developed by Dr. Stephen Dooley, Trinity College Dublin, and simulated under the same conditions, using the Perfect-Stirred Reactor code in Chemkin software. In comparing the simulation results with experimental data, some discrepancies were noted; predictions of ethylene production were not well matched. The kinetic model was improved by updating several classes of reactions: unimolecular decomposition, H-abstraction, C-C and C-O beta-scissions of fuel radicals. The updated model was then compared again with experimental results and good agreement was achieved, proving that the concerted eliminated reaction is crucial for the kinetic mechanism formulation of ethyl levulinate. In addition, primary reaction pathways and sensitivity analysis were performed to describe the role of molecular structure in combustion (800 and 1000 K for ethyl levulinate oxidation in the jet-stirred reactor).

Soot formation mechanisms have been a target of intense research for decades. The various stages in the soot formation mechanism have been accepted and recognized, nevertheless, the nucleation stage, which corresponds to the transition from gas phase polycyclic aromatic hydrocarbons (PAH) to condensed particles, is controversial. Pyrene dimerization is considered by many models to be the first step in soot nucleation. In this work, a jet-stirred reactor (JSR) in the temperature range of 700 – 1200 K was used to perform pyrene pyrolysis and to study the various dimerization Nascent particles were chemically analyzed using Fourier-transform ion cyclotron resonance high resolution mass spectrometry (FT-ICR MS) with a laser desorption ionization (LDI) source. Simulations were realized based on a simple kinetic model using CHEMKIN-PRO, which addressed three different dimerization pathways: 1) physical dimerization of two pyrene molecules (P-DIM), 2) physical dimerization between a pyrene molecule and a pyrenyl radical (PR-DIM), and/or 3) chemical dimerization between two pyrenyl radicals (C-DIM). The detected species presented 202 and 402 Da masses in the mass spectra with different intensities. At higher temperatures, the formation rate was enhanced due to the sensibility of particle formation to the reaction temperature. The first temperature regime was identified at 700 – 900 K, where the detected species contained only pyrene molecules, stacked by Van der Waals forces (P-DIM). In the 900–1100 K range, the formation of pyrenyl radicals was considered, and the production of PR-DIM was favored. In the higher temperature range (1100–1200 K), the greater species' mass were located and related to the dimerization of two pyrenyl radicals (C-DIM). The temperature increase was reflected in the production of higher concentrations of the pyrenyl radical, resulting in the dominance of the chemical dimerization pathway at 1200 K. The use of different initial concentrations of pyrene in the simulations did not significantly affect the outcome. Results of the experiment were reflected in the simulations, based on the model used, revealing the tendency of the three dimerization pathways, the decreased survival rate of physically-formed dimers, and the enhanced production of chemically-linked dimers at high temperatures.

Rapid consumption of energy storage and serious environmental pollution demand more advanced combustion strategies and more renewable fuels. Development of chemical kinetic models and suitable selection of fuels are key factors in evolving and optimizing new engine and combustion concepts. Alkenes are typical composition of gasoline as well as typical intermediates in the oxidation of larger alkanes and alcohol, while isoprene is one of the important alkenes impacting both the atmospheric pollution and energy depletion. Isoprene is one of the most important species in the atmosphere chemistry, dominating the carbon flux emitted by vegetation and accounting for forty percent of non-methane biogenic emissions globally. Isoprene has been recognized not only as a noteworthy precursor to polycyclic aromatic hydrocarbons but also as a promising fuel additive. Isoprene has been extensively investigated in the atmosphere chemistry, but its role as a critical diolefin in combustion chemistry has received less attention. Only A few researchers studied isoprene chemistry by carrying out pyrolysis experiments and theoretical calculations. To better understand the combustion chemistry of isoprene, this work presents a detailed experimental and kinetic modeling investigation. This study explored the chemical kinetics of isoprene oxidation in ignition delay times and speciation measurements. Our shock tube experiments for ignition delay times covered the temperatures of 680 – 1470 K, pressures of 1 – 30 bar, and equivalence ratios of 0.5 – 2. We measured laser-based time-resolved CO speciation in a low-pressure shock tube at temperatures of 900 – 1470 K, pressures of 1 and 4 bar, and equivalence ratios of 0.5 and 1. Major species concentrations were measured in a jet-stirred reactor at 680 – 1280 K, 1 bar, and φ = 0.5 – 2. Afterwards, we used 1,3-butadiene as a basis to develop fuel-specific isoprene sub-mechanism and coupled it with a C0-C5 core sub-mechanism. Finally we developed a comprehensive kinetic model including 1585 species and 6884 reactions and achieved a good agreement between the model’s predictions and the experiments. To our knowledge, this study is the first comprehensive effort to describe the process and provides valuable insights into isoprene oxidation. The work reported in the thesis also facilitates the better understanding of combustion chemistry of diolefins.

No description available.

No description available.

Pour faire face à l’épuisement des combustibles fossiles conventionnels et aux préoccupationsenvironnementales dont le réchauffement climatique, de nouveaux carburants issus de la biomasse sontutilisés purs ou comme co-carburants ; d’autres sont envisagés pour le futur. Une meilleure connaissance dela cinétique chimique d’oxydation des composés présents dans ces carburants alternatifs est indispensable.L’objectif de cette thèse est donc d’obtenir de nouvelles bases de données expérimentales et d’élaborer desmécanismes cinétiques d’oxydation des constituants de ces nouveaux carburants. Des molécules de deuxfamilles chimiques, à savoir les esters méthyliques et les alcools, ont été sélectionnées. L’oxydation de cescomposés purs ou en mélanges a été étudiée en réacteur auto-agité à haute pression (10 atm) et dans un largedomaine de températures (530-1250 K) et de richesses (ca. 0,3-4). Les profils de concentration des réactifs,produits et principaux intermédiaires stables ont été obtenus par spectroscopie d’absorption infrarouge àtransformée de Fourier (IRTF) et chromatographie en phase gazeuse (GC-FID-TCD-MS). Les résultatsobtenus ont permis de proposer des modèles cinétiques permettant de simuler avec un bon accord une grandepartie des résultats expérimentaux obtenus au cours de cette thèse. Les analyses cinétiques ont permis dedéterminer les principales voies de consommation de ces composés (principalement des mécanismes deperoxydation-isomérisation à basse température et de métathèse puis décomposition par β-scission à hautetempérature). Elles ont permis d’identifier les réactions les plus influentes (réactions de métathèse etréactions impliquant particulièrement les composés de la base C0-C2). / To overcome the problems of conventional fossil fuels depletion and environmental issues includingglobal warming, new fuels derived from biomass are used pure or in blends; others are proposed for thefuture. A good knowledge of the chemical kinetics of oxidation of components present in these alternativefuels is necessary. The aim of this work is to obtain a new experimental database and to build a chemicalkinetic reaction mechanism for the combustion of these new fuels. Molecules of two functional groups werechosen: methyl esters and alcohols. The kinetics of oxidation of these compounds were studied in a Jet-Stirred Reactor at high-pressure (10 atm), over the temperature range 530-1250 K, for several equivalencesratios (ca. 0.3-4) Concentration profiles of reactants, products and main stable intermediates were obtainedby probe sampling and FTIR (Fourier transform infrared spectroscopy) and GC-FID-TCD-MS analyses. Theresults allowed proposing detailed kinetics models that successfully simulate concentration profilesdetermined by Jet-Stirred Reactor method. The kinetic analyses allowed delineating the main oxidation pathsof consumption (peroxidation-isomerisation at low temperature and beyond, metathesis followed by betascissiondecomposition), and identifying the most influencing reactions for the oxidation rate of the fuels, i.e.metathesis reactions with C0-C2 species.

In an effort to reduce NOX emissions both in the landing and take-off (LTO) cycle as well as in cruise, significant research has been conducted on novel aero-engine low emissions combustor design concepts. Preliminary combustor design and emissions prediction software tools are becoming increasingly important during the conceptual design phase of aero-engine combustors. They allow a large number of designs to be explored, in a relatively short amount of time, thereby identifying the most promising designs to consider for further development. There are three methods for NOX emission prediction; correlations, stirred reactor models and CFD models. Correlation methods are derived from experimental results and are therefore only applicable for combustors for which data is available. The stirred reactor modelling approach provides a reasonably good compromise with respect to computational time and robustness relative to correlation and CFD based methods. The stirred reactor method assumes finite rate chemistry inside the combustor using simplified chemical kinetic models. The basic concept of the reactor-based method is to split the combustor into a number of reactors (perfectly or partially stirred) to compute the overall emissions. The primary objective of this doctoral research was to assess the suitability and limitations of the stirred reactor modelling approach to predict NOX emissions of a Rich-Burn Quick-Quench and Lean-Burn (RQL) combustor concept. The geometry of the RQL combustor and the model constraints were assumed from a NASA test rig experiment. The stirred reactor emission prediction model developed was verified using this test data. The results suggest that, based on the modelling assumptions made, the stirred reactor modelling approach is able to capture the trends of emissions (with changing boundary conditions) even though there are discrepancies in the absolute values. This suggests that the stirred reactor model is a useful tool during the preliminary design phase to quantify the impact of changes in boundary conditions/design parameters on changes in NOX emissions.