Gas turbine combustion chambers were traditionally designed through trial and error which was unfortunately a time-consuming and expensive process. The development of computers, however, contributed a great deal to the development of combustion chambers, enabling one to model such systems more accurately in less time. Traditionally, preliminary combustor designs were conducted with the use of one-dimensional codes to assist in the prediction of flow distributions and pressure losses across the combustion chamber mainly due to their rapid execution times and ease of use. The results are generally used as boundary conditions in three- dimensional models to predict the internal flow field of the combustor. More recent studies solve the entire flow field from prediffuser to combustor exit. This approach is, however, a computationally expensive procedure and can only be used if adequate computer resources are available. The purpose of this study is two-fold; (1) to develop a one-dimensional incompressible code, incorporating an empirical-based combustion model, to assist a one-dimensional network solver in predicting flow- and temperature distributions, as well as pressure losses. This is done due to the lack of a combustion model in the network solver that was used. An incompressible solution of flow splits, pressure losses, and temperature distributions is also obtained and compared with the compressible solution obtained by the network solver; (2) to utilise the data, obtained from the network solver, as boundary conditions to a three-dimensional numerical model to investigate possible modifications to the dome wall of a standard T56 combustion chamber. A numerical base case model is validated against experimental exit temperature data, and based upon that comparison, the remaining numerical models are compared with the numerical base case. The effect of the modification on the dome wall temperature is therefore apparent when the modified numerical model is compared with the numerical base case. A second empirical code was developed to design the geometry of axial straight vane swirlers with different swirl angles. To maintain overall engine efficiency, the pressure loss that was determined from the network analysis, of the base case model, is used during the design of the different swirlers. The pressure loss across the modified combustion chamber will therefore remain similar to that of the original design. Hence, to maintain a constant pressure loss across the modified combustion chambers, the network solver is used to determine how many existing hole features should be closed for the pressure loss to remain similar. The hole features are closed, virtually, in such a manner as not to influence the equivalence ratio in each zone significantly, therefore maintaining combustion performance similar to that of the original design. Although the equivalence ratios in each combustion zone will be more or less unaffected, the addition of a swirler will influence the emission levels obtained from the system due to enhanced air-fuel mixing. A purely numerical parametric analysis was conducted to investigate the influence of different swirler geometries on the dome wall temperature while maintaining an acceptable exit temperature distribution. The data is compared against the data obtained from an experimentally validated base case model. The investigation concerns the replacement of the existing splash-cooling devices on the dome wall with that of a single swirler. A number of swirler parameters such as blade angle, mass flow rate, and number of blades were varied during the study, investigating its influence on the dome wall temperature distribution. Results showed that the swirlers with approximately the same mass flow as the existing splash-cooling devices had almost no impact on the dome wall temperatures but maintained the exit temperature profile. An investigation of swirlers with an increased mass flow rate was also done and results showed that these swirlers had a better impact on the dome wall temperatures. However, due to the increased mass flow rate, stable combustion is not guaranteed since the air/fuel ratio in the primary combustion zone was altered. The conclusion that was drawn from the study, was that by simply adding an axial air swirler might reduce high-temperature gradients on the dome but will not guarantee stable combustion during off-design operating conditions. Therefore, a complete new hole layout design might be necessary to ensure good combustion performance across a wide operating range. / Dissertation (MEng (Mechanical))--University of Pretoria, 2008. / Mechanical and Aeronautical Engineering / MEng / unrestricted

The abilities of Scramjets and Ramjets, in their respective operating ranges, are partially bridged by dual-mode Scramjets. The limitations of operation are due to making a static motor that is designed to function in both modes resulting in low and high speed restrictions. This study covers the analysis into the ability of morphing the combustor in a Scramjet to allow for expanded operational capacities through simple mechanisms. Through the restriction and expansion of combustor cavity volume, operational capabilities of the engine can, therefore, be modified to best match scenario requirements. Due to the engine's ability to match a wide variety of scenarios the limitations seen in that of the dual-mode Scramjet are avoided through the usage of a morphing combustor. From initial findings using the quasi-1D Canonical REactor Scramjet Simulation (CReSS) solver, progress was made to confirm results through the usage of Computational Fluid Dynamics (CFD). Prior analysis of the momentum balance between stages two and four of the simulated Scramjet engines, the results showed that the variable geometry matched or outperformed the baseline HiFiRE geometry. The analysis revealed points of Mach and altitude where certain combustor volumes demonstrated greater performance. This greater performance is only gained by the ability to tune the engine in flight to react to external factors as there is no dominant geometry for a given range of Machs and altitudes. This tuning allows for the usage of performance mapping to extract the greatest performance possible over a variety of conditions. Further, it allows for the project to be continuously expanded into mapping appropriate reactions to other initial conditions and stimuli. Using CFD modeling to perform a parametric study on the prior work allows for finer control and analysis of said initial conditions and the resulting flow paths in the variety of tested combustor volumes. From this a discussion is made in regards to the effectiveness of the prior CReSS based analysis of the novel approach. / Master of Science / The abilities of Scramjets and Ramjets (engines which contain no moving parts as the compression of the incoming air is accomplished by the speed at which they operate with the separating factor being that the scramjets internal flow does not go below supersonic speeds), in their respective operating ranges, are partially bridged by dual-mode Scramjets. Dual-mode Scramjets are scramjets which can function with both sub- and super-sonic internal flow speeds. This being below or above Mach 1 (343 m/s, 767.3 mph) respectively. The limitations of operation are due to making a static motor where the geometry does not change that is designed to function in both modes resulting in low and high speed restrictions. This study continues the analysis into the ability of morphing the combustor, the volume in which the air fuel mixture combusts, in a Scramjet to allow for expanded operational capacities through simple mechanisms. Through the restriction and expansion of combustor volume, operational capabilities of the engine can, therefore, be modified to best match scenario requirements. Due to the engine's ability to match a wide variety of scenarios the limitations seen in that of the dual-mode Scramjet are avoided through the usage of a morphing combustor where morphing in this case is a simple volume change equivalent to that of a slide whistle. From initial findings using the quasi-1D Canonical REactor Scramjet Simulation (CReSS) solver, progress was made to confirm results through the usage of Computational Fluid Dynamics (CFD). Prior analysis of the momentum balance between stages two and four of the simulated Scramjet engines, the results showed that the variable geometry matched or outperformed the baseline HiFiRE geometry. The analysis revealed points of Mach and altitude where certain combustor volumes demonstrated greater performance. This greater performance is only gained by the ability to tune the engine in flight to react to external factors as there is no dominant geometry for a given range of Machs and altitudes. This tuning allows for the usage of performance mapping to extract the greatest performance possible over a variety of conditions. Further, it allows for the project to be continuously expanded into mapping appropriate reactions to other initial conditions and stimuli. Using CFD modeling to perform a parametric study on the prior work allows for finer control and analysis of said initial conditions and the resulting flow paths in the variety of tested combustor volumes. From this a discussion is made in regards to the effectiveness of the prior CReSS based analysis of the novel approach.

Cooling combustor chambers for gas turbine engines is challenging because of the complex flow fields inherent to this engine component. This complexity, in part, arises from the interaction of high momentum dilution jets required to mix the fuel with effusion film cooling jets that are intended to cool the combustor walls. The dilution and film cooling flow have different performance criteria, often resulting in conflicting flow mechanisms. The purpose of this study is to evaluate the influence that the dilution jets have on the film cooling effectiveness and how the flow and thermal patterns in the cooling layer are affected by both the dilution flow and the closely spaced film cooling holes. This study also intends to characterize the development of the flow field created by effusion cooling injection without dilution injection. This work is unique because it allows insight into how the full-coverage discrete film cooling layer is interrupted by high momentum dilution jets and how the surface cooling is affected. The film cooling flow was disrupted along the combustor walls in the vicinity of the high momentum dilution jets and the surface cooling effectiveness was reduced with increased dilution jet momentum. This was due to the secondary flows that were intensified by the increased jet momentum. High turbulence levels were generated at the dilution jet shear layer resulting in efficient mixing. The film cooling flow field was affected by the freestream turbulence and complex flow fields created by the combined dilution and effusion cooling flows both in the near dilution jet region as well as downstream of the jets. Effusion cooling holes inclined at 20Ë created lower coolant layer turbulence levels and higher surface cooling effectiveness than 30Ë cooling holes. Results showed an insensitivity of the coolant penetration height to the diameter and angle of the cooling hole in the region downstream of the dilution mixing jets. When high momentum dilution jets were injected into crossflow, a localized region in the flow of high vorticity and high streamwise velocity was created. When film cooling air was injected the inlet flow field and the dilution jet wake were fundamentally changed and the vortex diminished significantly. The temperature field downstream of the dilution jet showed evidence of a hot region which was moderated appreciably by film cooling flow. Differences in the temperature fields were nominal compared to the large mass flow increase of the coolant. A study of streamwise oriented effusion film cooling flow without dilution injection revealed unique and scaleable velocity profiles created by the closely spaced effusion holes. The effusion cooling considered in these tests resulted in streamwise velocity and turbulence level profiles that scaled well with blowing ratio which is a finding that allows the profile shape and magnitude to be readily determined at these test conditions. Results from a study of compound angle effusion cooling injection showed significant differences between the flow field created with and without crossflow. It was found from the angle of the flow field velocity vectors that the cooling film layer grew nearly linearly in the streamwise direction. The absence of crossflow resulted in higher turbulence levels because there was a larger shear stress due to a larger velocity difference between the coolant and crossflow. The penetration height of the coolant was relatively independent of the film cooling momentum flux ratio for both streamwise oriented and compound angle cooling jets. / Ph. D.

Made available in DSpace on 2014-06-12T18:07:23Z (GMT). No. of bitstreams: 2 arquivo7932_1.pdf: 1883283 bytes, checksum: afaf20da65b732cf3c87aa82e363af33 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2004 / A modelagem dinâmica de um combustor de gás natural em leito fluidizado foi estudada. Simulações foram realizadas para o caso do leito de partículas inertes, através de diferentes modelos matemáticos para o combustor. Modelos baseados na teoria das duas fases e um modelo baseado na teoria fluidodinâmica da fluidização foram empregados na simulação do comportamento do sistema. O sistema foi considerado isotérmico e os balanços de massa e momento permitiram boa predição dos perfis de composição dos gases ao longo do leito. A resposta dinâmica do processo foi verificada através de perturbações aplicadas à entrada do sistema. A resolução numérica do sistema de equações diferenciais parciais não-lineares resultantes foi efetuada através do método das diferenças finitas para os modelos unidimensionais e através do código MFIX para o modelo fluidodinâmico. A importância do estudo desta tecnologia é justificada pelos baixos níveis de produção de NOx em sistemas de leito fluidizado

Cette thèse décrit l'étude d'une chambre de combustion innovante de type Trapped Vortex Combustor (TVC): ce concept utilise des cavités de gaz chauds pour stabiliser des flammes prémélangées pauvres. A partir d'une étude globale d'un point de fonctionnement instable, l'approche scientifique vise à différencier l'impact des différents mécanismes physiques. La structure de l'écoulement inerte est étudiée finement avant de mener une étude spatio-Temporelle sur un point de fonctionnement instable, en conditions réactives. L'analyse permet de comprendre les interactions entre la structure de la flamme, la topologie de l'écoulement et l'acoustique du brûleur. Différents mécanismes pilotant l'apparition d'instabilités de combustion sont mis en évidence, et des recommandations sont fournies afin de les supprimer. Un vérification a posteriori permet de valider l'importance de ces mécanismes, notamment grâce à la détermination de diagrammes de stabilité de flamme. / This thesis describes the investigation of an innovative trapped vortex combustor (TVC): this concept uses recirculating hot gas flow trapped in cavities to stabilize lean main flames. Based on a global investigation of an unstable operating condition, the scientific strategy aims to treat separately the different physical mechanisms. The inert flow structure is analyzed prior to leading a spatio-Temporal study on an unstable mode. This investigation aims to understand the flaine-Flow-Acoustic interactions in the combustor. Several mechanisms piloting combustion instabilities are highlighted, and recommandations are provided in order to suppress them. An a posteriori check validate the preponderance of these mechanisms, in particular with the determination of stability flaine diagrams.

In this study, the response of a liquid-fueled resonant pulse combustor to changes in liquid fuel composition was investigated. Experiments were performed with gasoline- ethanol, gasoline-diesel, and gasoline-heptane mixtures selected to produce meaningful variations in the ignition delay time. A review of ignition quality tester (IQT) data provided an expected increase in the overall delay for gasoline-ethanol mixtures with increasing ethanol concentrations, and a decrease for gasoline-diesel mixtures with increasing diesel concentrations in the mixture. By taking the phase of the ion signal as an indicator of heat release timing, the experimental results showed an agreement of gasoline-ethanol cases with the IQT data with a near linear increase with increasing ethanol concentrations. However, for gasoline-diesel, there exit no linear relation with the IQT data. For the case of gasoline-heptane mixtures, the results showed a linear decrease in delay with increasing heptane concentrations. Furthermore, it was shown that small changes in the physical properties of the fuel can significantly in sequence the cold-start operation of the combustor and alter the coupling between the unsteady heat release and resonant acoustic pressure wave during resonant operation. Dynamic combustion chamber pressure, stagnation temperature and pressure are recorded after a fixed warm-up time to characterize the performance and operation of the device. Results are interpreted in the context of fuel sensitivity and performance optimization of a resonant pulse combustor for pressure gain turbine applications.

<P> The design, and construction of a combustion chamber was undertaken, and the basic considerations, design steps and calculations are described. The preliminary testing consisted of measurements of flame temperature, flame tube wall temperature, and flame tube exit plane temperature. A comparison was made between the experimental and theoretical flame temperatures. The uniformity of air flow in the annulus between the flame tube and outer casing was investigated. Tests were made to ascertain the effect of the gas nozzle position on the condition of the combustion gases. </p> / Thesis / Master of Engineering (MEngr)

This thesis describes the coincident prediction and observation of thermo-acoustic instabilities in a turbulent, swirl-stabilized research combustor using a stability model constructed from validated reduced-order component models. The component models included the acoustic response to flame heat release rate at various locations in the combustor, the turbulent diffusion of uneven fuel-air mixing, and the flame's response to perturbations in both inlet velocity and equivalence ratio. These elements are closed in a system-level model to reflect their natural dynamic coupling and assessed with linear stability criteria. The results include the empirical validation of each of the component models and limited validation of the total closed-loop model with a lean premixed gaseous fuel combustor not dissimilar to an industrial burner. The degree of agreement between the predictions and the measurements encourages the conclusion that the reduced-order technique described herein not only includes the relevant physics, but has characterized them with sufficient acuracy to be the basis for design techniques for the passive avoidance of thermo-acoustic instabilities. / Master of Science

It is widely accepted that climate change is a very serious environmental concern. Levels of carbon dioxide (CO2) and other emissions in the global atmosphere have increased substantially since the industrial revolution and now increasing faster than ever before. There is a thought that this has already led to dangerous warming in the Earth’s atmosphere and relevant changes around. Emissions legislations are going to be stringent as the years will pass. Hydro carbon fuel cost is also increasing substantially; more over this is non- renewable source of energy. There is an urgent need for novel combustor technologies for reducing emission as well as exploring alternative renewable fuels without effecting combustor performance. Development of novel combustors needs comprehensive understanding of conventional combustors. The design and development of gas turbine combustors is a crucial but uncertain part of an engine development process. At present, the design process relies upon a wealth of experimental data and correlations. Some major engine manufacturers have addressed the above problem by developing computer programs based on tests and empirical data to assist combustor designers, but such programs are proprietary. There is a need of developing design methodologies for combustors which would lead to substantial contribution to knowledge in field of combustors. Developed design methodologies would be useful for researchers for preliminary design assessments of a gas turbine combustor. In this study, step by step design methodologies of dual annular radial and axial combustor, triple annular combustor and reverse flow combustor have been developed. Design methodologies developed could be used to carry out preliminary design along with performance analysis for conventional combustion chambers. In this study the author has also proposed and undertaken preliminary studies of some novel combustor concepts. A novel concept of a dilution zone less combustor has been proposed in this study. According to this concept dilution air would be introduced through nozzle guide vanes to provide an optimum temperature traverse for turbine blades. Preliminary study on novel dilution zone less combustor predicts that the length of this combustor would be shorter compared to conventional case, resulting in reduced weight, fuel burn and vibrations. Reduced fuel burn eventually leads to lower emissions. Another novel concept of combustor with hydrogen synthesis from kerosene reformation has been proposed and a preliminary studies has been undertaken in this work. Addition of hydrogen as an additive in gas turbine combustor shows large benefits to the performance of gas turbine engines in addition to reduction in NOx levels. The novel combustor would have two stages, combustion of ~5% of the hydrocarbon fuel would occur in the first stage at higher equivalence ratios in the presence of a catalyst, which would eventually lead to the formation of hydrogen rich flue gases. In the subsequent stage the hydrogen rich flue gases from the first stage would act as an additive to combustion of the hydrocarbon fuel. It has been preliminary estimated that the mixture of the hydrocarbon fuel and air could subsequently be burned at much lower equivalence ratios than conventional cases, giving better temperature profiles, flame stability limits and lower NOx emissions. The effect of different geometrical parameters on the performance of vortex controlled hybrid diffuser has also been studied. It has been predicted that vortex chamber in vortex controlled hybrid diffuser does not play any role in altering the performance of diffuser. The overall contribution to knowledge of this study is development of combustor preliminary design methodologies with different variants. The other contribution to knowledge is related to novel combustors with a capability to produce low emissions. Study on novel combustor and diffuser has yielded application of two patent applications with several other publications which has resulted in a contribution to knowledge. A list of research articles, two patents, awards and achievements are presented in Appendix C.

O carvão mineral nacional representa uma alternativa atraente para a solução do problema energético do Brasil. Os maiores problemas técnicos associados à queima dos carvões minerais brasileiros referem-se à emissões de gases poluentes de enxofre e nitrogênio e a problemas causados por fusão de cinzas. Por outro lado, a queima eficiente e limpa de biomassa e resíduos industriais entre outros materiais combustíveis, pode trazer benefícios ambientais consideráveis. O processo de combustão em leito fluidizado é reconhecidamente flexível quanto ao uso de combustível, trabalha com baixas temperaturas que evitam a fusão de cinzas e diminuem a emissão de NOx e permite a remoção de SOx ainda dentro do leito, por meio da adição de calcário o que dispensa tratamento adicional para este gás. Considerando o exposto acima, uma planta piloto de combustão em leito fluidizado foi projetada e construída no NETeF da EESC/USP e utilizada inicialmente para testes de remoção de SO2 durante a queima de carvão. A concepção e construção do reator e de seus periféricos são discutidas e os resultados são apresentados. Na absorção de SO2 duas variáveis foram consideradas; a relação molar Ca/S e o excesso de ar de combustão. Os resultados mostram eficiência de remoção de SO2 de até 94% para relação Ca/S = 4 e excesso de ar de 21%. Para a relação Ca/S = 1, a mais baixa utilizada neste trabalho e que representa a condição estequiométrica, este valor cai para 55%. O excesso de ar mostrou um papel claro, porém mais modesto. A redução do excesso de ar de 21% para a condição estequiométrica levou a eficiência de 94 para 84%. / The utilization of coal is an attractive way to reduce some of the energy problems in Brazil. Major problems associated with coal combustion are polutant emissions, mainly SOx and NOx and ash fusion. Additionally, the efficient combustion of biomass and industrial hazardous wastes, among other fuels, can bring a significant environmental benefit. Fluidized bed combustion is recognized to be flexible in the use of fuel, produce low temperature that avoid ash fusion and reduce NOx emissions, and allow SOx absorption by limestone inside the bed, what makes unnecessary additional gas treatment for this pollutant. Considering that, a fluidized bed combustion pilot plant was projected and built in NETeF at EESC/USP and initially used for investigations of the SO2 absorption by limestone during coal combustion. The concept and construction of the plant are presented and discussed and the results are shown. Regarding the absorption of SO2, two variables were investigated, namely the molar ratio Ca/S and the excess of combustion air. An absorption efficiency of up to 94% was achieved with Ca/S = 4 and excess air of 21%. When Ca/S = 1 was used - what represents the stoichiometric ratio and was the lowest used in this work, this efficiency dropped to 55%. Excess air showed a clear but more modest role. The decrease of excess air from 21% to the stoichiometric condition decreased the efficiency from 94 to 84%.