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Large eddy simulation of spray combustion in an HSDI engine is carried out in this thesis. The implementation of the code was performed in logical steps that allowed both assessment of the performance of the existing KIVA-LES and later development. The analysis of the liquid annular jet confirmed existence of typical, annular jet exclusive structures like head vortices, stagnation point and recirculation in the inner zone. The influence of the swirl in the ambient domain was found to have profound impact on the development, penetration and radial spreading of the jet. Detailed results were reported in Jagus et al. (2008). The code was further validated by performing an extensive study of large eddy simulation of diesel fuel mixing in an engine environment. The reaction models were switched off in order to isolate the effects of both swirl and the different numerical treatment of LES. Reference RANS simulation was performed and significant differences were found. LES was found to capture much better the influence of the swirl on the liquid and vapour jets, a feature essentially absent in RANS results. Moreover, the predicted penetration of the liquid was much higher for the LES case and more in accordance with experimental measurements. Liquid penetration and subsequent evaporation are very important for prediction of heat release rates and encouraging results formed a good basis to performing a full simulation with models for ignition and combustion employed. The findings were analyzed in the paper by Jagus et al. (2009). Further modifications were introduced into the LES code, among them changes to the combustion model that was originally developed for RANS and calculation of the filter width. A new way of estimating the turbulent timescale (eddy turnover time) assured that the incompatibilities in the numerical treatment were eliminated and benefits of LES maximized. The new combustion model proved to give a very good agreement with experimental data, especially with regard to pressure and accumulated heat release rates. Both qualitative and quantitative results presented a significant improvement with respect to RANS results and old LES formulation. The new LES model was proved to give a very good performance on a spectrum of mesh resolutions. Encouraging results were obtained on a coarse mesh sets therefore proving that the new LES code is able to give good prediction even on mesh sizes more suitable for RANS. Overall, LES was found to be a worthy alternative to the well established RANS methods, surpassing it in many areas, such as liquid penetration prediction, temperature-turbulence coupling and prediction of volume-averaged data. It was also discovered that the improved LES code is capable of producing very good results on under-resolved mesh resolutions, a feature that is especially important in industrial applications and on serial code structure.

Le charbon demeure à l’heure actuelle l’un des combustibles fossiles les plus couramment employés afin de produire de l’énergie. Son utilisation accrue dans le futur devra toutefois être conciliée avec la problématique de réduction des émissions de gaz à effet de serre. Des procédés permettant de limiter les émissions de CO2 ou de faciliter son captage, à l’image de l’oxycombustion, sont de fait actuellement développés. Leur implémentation à l’échelle industrielle implique toutefois de lever un certain nombre de verrous scientifiques liés à la compréhension des mécanismes physico-chimiques d’oxydation du charbon pulvérisé sous atmosphères plus ou moins riches en oxygène. Ce travail de thèse a de fait porté sur la mise au point d’un banc d’essais de laboratoire permettant d’étudier la combustion du charbon en reproduisant des conditions de chauffe analogues à celles rencontrées industriellement. Le brûleur hybride qui a été mis au point lors de ce travail a permis d’analyser des flammes jets de combustible solide sous atmosphères O2/N2 et O2/CO2 contenant des teneurs variables en oxygène. Une caractérisation détaillée des champs de vitesse et de température dans la chambre réactionnelle a été opérée. Des mesures de température des semi-cokes dans les flammes et de concentrations d’espèces gazeuses (CO, CO2, O2, NO, NOx et SOx) ont également été réalisées tout au long de la combustion. Des prélèvements de semi-cokes à différents temps de séjour ont enfin été opérés de sorte à obtenir des profils de dévolatilisation qui ont pu être confrontés à divers modèles empiriques issus de la littérature. L’ensemble des données que nous avons obtenues nous a permis de mettre en évidence l’impact d’un enrichissement en oxygène du milieu réactionnel sur les cinétiques de dévolatilisation et sur les mécanismes de formation de polluants tels que les NOx et les SOx. Les travaux menés sous oxycombustion ont pour leur part permis de mieux appréhender les différences fondamentales entre la combustion du charbon pulvérisé sous air et sous atmosphères O2/CO2. Pour terminer, des essais préliminaires de combustion de mélanges à base de charbon et de bois ont également été menés, la co-combustion de charbon et de biomasse constituant un autre moyen de limiter les quantités nettes de CO2 émises dans l’atmosphère. / Coal is currently one of the most widely used fossil-fuel for energy production applications. Its increasing use in the near future will have to face the greenhouse gas reduction objectives. Different processes have thus been developed to reduce CO2 emissions or ease their capture as oxy-fuel combustion for instance. The implementation of such techniques at industrial scale implies fundamental works to be undertaken to better understand the physical-chemical processes involved in the oxidation of pulverized coal under oxygen enriched environments. The present work has thus focused on the development of a lab-scale test bench allowing the study of coal combustion with heating rates similar to those met in industrial combustors. The hybrid burner that has been set up allowed the analysis of different solid fuels jet-flames under O2/N2 and O2/CO2 atmospheres containing various amounts of oxygen. A detailed characterization of the velocity and temperature fields has been carried out in the combustion chamber. Char temperatures and gaseous species concentrations (CO, CO2, O2, NO, NOx and SOx) have also been monitored during the combustion. Char samples at different residence times have finally been collected to derive devolatilization profiles that have been compared to simulated data issued from various empirical models from the literature. Obtained results clearly illustrate the impact of an oxygen enrichment of the reaction medium on devolatilization kinetics and pollutants formation including NOx and SOx. Works conducted in the fields of oxy-fuel combustion allowed to better understand the fundamental differences between pulverized coal combustion under air and O2/CO2 environment. Finally, preliminary experiments have been conducted using coal and wood blends since coal co-combustion with biomass appears to be another interesting mean to reduce net CO2 emissions into the atmosphere.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master in Science in Engineering, Johannesburg September 1998 / Combustion modelling of utility furnace chambers provides a cost efficient means to extrapolate the combustion behaviour of pulverised fuel (pf) as determined from drop tube furnace (DTF) experiments to full scale plant by making use of computational fluid dynamics (CFD). The combustion model will be used to assimilate essential information for the evaluation and prediction of the effect of • changing coal feedstocks • proposed operational changes • boiler modifications. TRI comrnlssloned a DTF in 1989 which has to date been primarily used for the comparative characterisation of coals in terms of combustion behaviour. An analysis of the DTF results allows the determination of certain combustion parameters used to define a mathematical model describing the rate at which the combustion reaction takes place. This model has been incorporated into a reactor model which can simulate the processes occurring in the furnace region of a boiler, thereby allowing the extrapolation of the DTF determined combustion assessment to the full scale. This provides information about combustion conditions in the boiler which in turn are used in the evaluation of the furnace performance. Extensive furnace testwork of one of Eskom's wall fired plant (Hendrina Unit 9) during 1996, intended to validate the model for the ar plications outlined above, included the measurement {If : • gas temperatures • O2, C02, CO, NOx and S02 concentrations • residence time distributions • combustible matter in combustion residues extracted from the furnace • furnace heat fluxes. The coal used during the tests was sampled and subjected to a series of chemical and other lab-scale analyses to determine the following: • physical properties • composition • devolatilisation properties " combustion properties The same furnace was modelled using the University of Stuttgart's AIOLOS combustion code, the results of Which are compared with the measured data. A DTF derived combustion assessment of a coal sampled from the same site but from a different part of the beneficiation plant, which was found to burn differently, was subsequently used in a further simulation to assess the sensitivity of the model to char combustion rate data. The results of these predictions are compared to the predictions of the validation simulation. It was found that the model produces results that compare well with the measured data. Furthermore. the model was found to be sufficiently sensitive to reactivity parameters of the coal. The model has thereby demonstrated that it can be used in the envisaged application of extrapolating DTF reactivity assessments to full scale plant. In using the model, it has become apparent that the evaluations of furnace modifications and assessments of boiler operation lie well within the capabilities of the model. / MT2017

PhD, Faculty of Engineering and the Built Environment, 1993

Thesis presented in partial fulfillment of the requirements for the degree of Master of Technology (MTech) at Department of Chemistry, Faculty of Applied Science, Cape Peninsula University of Technology 2011 / Aromatic polyamides (PAs) are widely used as high-performance polymers in technical applications due to their unique combination of outstanding thermal, optical, mechanical and chemical properties. Although PAs are mostly utilized where strength or heat resistance is of primary concern, they also find use in other important applications such as in NOMEX membranes for desalination of brackish water or seawater. PAs do however have some disadvantages such as high melting points, high glass transition temperatures (T 9) and a limited solubility in most organic solvents, wh.ich makes their processing difficult. Polyureas (PUs) are generally known for their excellent thermal stability and high chemical resistance due to the presence of thermally stable bonds of aromatic or heterocyclic ring systems along their backbone. Both polymer systems are poorly researched when it comes*' the introduction of furan units into the chains. The same is valid for cases where two or more different diacids or diamines are incorporated. The aim of this study was therefore to investigate the influence of furan units in the polymer chains and the change in properties if the composition of starting materials is varied further. Nineteen PAs were prepared via the interfacial polymerization method and the homogeneous phase polymerization method. These polymers were prepared either with furan- or isophthalic acids in their chains and then compared with the copolymers, containing both diacids in different ratios. Products were characterized by various analytical techniques. Furanoyl-2,5-dichloride (FDC) and different amounts of isophthaloyl chloride (IPDC) - 0, 10, 30 and 50% - as the basic starting monomers were reacted individually with four diamines: m-phenylen diamine (MPD), 4,4'-diamino diphenylsulfone (DDS), 4,4'-diamino diphenylether (ODE) and 2,4-bis(4-aminophenyl)-6-phenyl-1,3,5-triazine-2,4,6-triamine (BAT) by interfacial or homogeneous polycondensation reactions. Two polyureas, starting with furanoyl-2,5-diazide (FDZ) and transformed into the diisocyanate were prepared by reaction with two diamines, namely MPD and DDS in homogeneous solution. The PAs and PUs were characterized by Fourier-Transform Infrared Spectroscopy (FTIR), Proton NMR CH), Carbon NMR C3C), Gel Permeation Chromatography (GPC), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The water up-take per polymer unit (mol water I repeat unit of the polymer) was measured. The values for 70% Relative Humidity (RH) were between 0.87 and 1 ~80 moles of water per repeat unit and for 43% RH between 0.40 and 1.35 mols.