The aim of this study is to advance the present capability for modelling soot production and thermal radiation from turbulent jet diffusion flames. Turbulent methane / air jet diffusion flames at atmospheric and elevated pressure are studied experimentally to provide data for subsequent model development and validation. Methane is only lightly sooting at atmospheric pressure whereas at elevated pressure the soot yield increases greatly. This allows the creation of an optically thick, highly radiating flame within a laboratory scale rig. Essential flame properties needed for model validation are measured at 1 and 3 atm. These are mean mixture fraction, mean temperature, mean soot volume fraction, and mean and instantaneous spectrally resolved radiation intensity. These two flames are modelled using the parabolic CFD code GENMIX. The combustion/turbulence interaction is modelled using the conserved scalar/laminar flamelet approach. The chemistry of methane combustion is modelled using a detailed chemistry laminar flame code. The combustion model accommodates the non-adiabatic nature of the flames through the use of multiple flamelets for each scalar. The flamelets are differentiated by the amount of radiative heat loss that is included. Flamelet selection is carried out through the solution of a balance equation for enthalpy, which includes a source term for the radiative heat loss. A new soot model has been developed and calibrated by application to a laminar flame calculation. Within the turbulent flame calculations the soot production is fully coupled to the radiative loss. This is achieved through the use of multiple flamelets for the soot source terms and the inclusion of the radiative loss from the soot (as well as the gases) in the enthalpy source. Spectral radiative emission from the flames has been modelled using the RADCAL code. Mean flame properties from the GENMIX calculations are used as an input to RADCAL.

Currently there is unprecedented social and political pressure to minimise anthropogenic environmental change. It is a result of the paradoxical nature of emissions reduction that lean-burn technology has become the most likely agent by which future emission targets may be met. However, the inclusion of lean-burn technology requires that the flametube depth is increased, to maintain an acceptable level of pressure drop and sufficient residence time. The injector too must increase in diameter as the admission of air via the fuel nozzle is increased. Maintaining traditional dump style architecture and employing these changes creates a number of additional problems. Most notable is the increased non-uniformity which is inherited by the injector flow as a result of the mismatch between the injector and upstream feed. Injector non-uniformity is a parameter symbiotic with emissions performance and it is therefore imperative to minimise the degree of injector non-uniformity if the ambition of the lean-burn system is to be realised.

abstract: Gas turbine engine for aircraft propulsion represents one of the most physics-complex and safety-critical systems in the world. Its failure diagnostic is challenging due to the complexity of the model system, difficulty involved in practical testing and the infeasibility of creating homogeneous diagnostic performance evaluation criteria for the diverse engine makes. NASA has designed and publicized a standard benchmark problem for propulsion engine gas path diagnostic that enables comparisons among different engine diagnostic approaches. Some traditional model-based approaches and novel purely data-driven approaches such as machine learning, have been applied to this problem. This study focuses on a different machine learning approach to the diagnostic problem. Some most common machine learning techniques, such as support vector machine, multi-layer perceptron, and self-organizing map are used to help gain insight into the different engine failure modes from the perspective of big data. They are organically integrated to achieve good performance based on a good understanding of the complex dataset. The study presents a new hierarchical machine learning structure to enhance classification accuracy in NASA's engine diagnostic benchmark problem. The designed hierarchical structure produces an average diagnostic accuracy of 73.6%, which outperforms comparable studies that were most recently published. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2015

abstract: Hydrogen fuel cells have been previously investigated as a viable replacement to traditional gas turbine auxiliary power unit onboard fixed wing commercial jets. However, so far no study has attempted to extend their applicability to rotary wing aircrafts. To aid in the advancement of such innovative technologies, a holistic technical approach is required to ensure risk reduction and cost effectiveness throughout the product lifecycle. This paper will evaluate the feasibility of replacing a gas turbine auxiliary power unit on a helicopter with a direct hydrogen, air breathing, proton exchange membrane fuel cell, all while emphasizing a system engineering approach that utilize a specialized set of tools and artifacts. / Dissertation/Thesis / Masters Thesis Engineering 2016

No description available.

As usinas termelétricas a ciclo combinado empregadas na geração de energia elétrica são compostas basicamente por três elementos ou sistemas: a Turbina a Gás, a Caldeira de Recuperação e a Turbina a Vapor. A Turbina a Gás é responsável pela transformação da energia química do combustível em energia mecânica para acionar os geradores, e os gases de escapamento com alta temperatura são responsáveis pela geração de vapor para as turbinas de vapor nas caldeiras de recuperação. É por estes motivos que é importante manter disponível a Turbina a Gás. A disponibilidade de um sistema está relacionada com a confiabilidade dos seus componentes e com as políticas de manutenção associadas aos mesmos, que não só influenciam no tempo de retorno à operação após uma ação de manutenção programada ou não programada, como também na degradação da confiabilidade do sistema. Este trabalho apresenta um método de análise empregado para a estimativa da confiabilidade e disponibilidade de Turbinas a Gás empregadas em usinas termelétricas a ciclo combinado, baseado nos conceitos de Confiabilidade e Manutenção Centrada em Confiabilidade. O método baseia-se na avaliação dos tempos entre falhas das causas destas falhas, e dos tempos de reparo associados a cada uma das intervenções de operação associadas à ocorrência de falhas. Adicionalmente, apresenta-se uma aplicação deste método para Turbinas a Gás de grande porte, com potência nominal de 150MW instaladas em uma Usina Termelétrica com capacidade de geração superior a 500MW. Verifica-se a existência da diferencia na disponibilidade das duas turbinas instaladas na usina obtendo um valor de 99,35% e 96%, considerando um período de operação de 8760 horas. Finalmente, apresentam-se as principais conclusões do trabalho e uma discussão sobre a viabilidade de aplicação do método proposto. / The combined cycle thermoelectric power station presents three main equipments: the Gas Turbine, the Heat Recovery Steam Generator and the Steam Turbine. The Gas Turbine transforms the chemical energy generated by combustion in mechanical energy unit to rotate the generator\'s shaft and the exhaust gas in high temperature is used to heat water at the Heat Recovery Steam Generator to generate steam for the Steam Turbine. Taking in view the great importance of the gas turbine for power generation, its availability should be carefully evaluated to guarantee the power station full operational availability. The availability of a system is strongly associated with the parts reliability and their maintenance policy. That policy not only has influence on the parts repair time but also on the parts reliability, affecting the system degradation and availability. This study presents a method for reliability and availability evaluation of gas turbines installed in a combined cycle thermoelectric power station, based on system Reliability concepts and Reliability-Centered Maintenance. The methodology depended on time between failures, failure modes and time to repair associated to each failure that operation interruption. The method is applied on the analysis of a gas turbine with more than 150MW nominal output installed in a 500MW power plant. A difference between the gas turbines availability are identified. The calculator values are 99,35 % and 96 % for 8760 hours operation period. Finally, the main conclusions and a discussion about feasibility of application of the considered method are present at the end of the study.

This thesis reports the results of a detailed programme of research on airblast atomization carried out using a specially designed atomizer in which the liquid is first spread into a thin sheet and then exposed on both sides to high velocity air. The primary aim of the investigation was to examine the influence of air and liquid properties on atomization quality. The work was divided into four main phases:- (1) The first phase was confined to the effects of liquid properties, namely viscosity, surface tension and density on mean drop size. Special liquids were produced to study the separate effect of each property on atomization quality. They presented a range of values of viscosity from 1.0 to 124 centipoise, while surface tension and density were varied between 26 and 73.5 dynes/cm and 0.8 and 1.8 gm/cm3 respectively. Atomizing air velocities covered the range of practical interest to the designers of continuous combustion systems and varied between 60 and 125 m/sec.(2) To obtain experimental data on the influence of air properties, notably air density, on mean drop size, the air temperature was varied between 23 and 151°C at atmospheric pressure in one series of experiments, while a separate study on the effect of air pressure on atomization quality was undertaken, where tests were conducted at constant levels of air velocity and temperature, using a range of liquid flows from 5 to 30 gm/sec, at various levels of air pressure between 1 and 8.5 atm. (3) In order to provide a comprehensive picture of airb1ast atomizer performance over a wide range of conditions the separate effects of varying air velocity, liquid flow rate, and hence atomizing air/liquid mass ratio on SMD were examined. This study enabled a better understanding of the effects of changes in operation on the atomizer's performance. (4) In all three phases above, velotities of both inner and outer atomizing air streams were kept equal. This last phase was aimed at studying the effect of varying the velocity between the inner and outer air streams. Best atomization quality was achieved when 65% of the total atomizing air was flowing through the outer stream. A detailed description of the light-scattering technique for drop size measurement is included. A discussion on the importance of the results obtained and their direct relevance to the design of airblast atomizers is given. A dimensional analysis and inspection of all the data obtained on the effects of air and liquid properties on atomization quality showed that over the following range of conditions: Liquid viscosity 1.0 to 44 centipoise Liquid surface tension 26 to 73.5 dynes/cm Liquid density 0.78 to 1.5 gm/cm³ Air velocity 70 to 125 m/sec Air temperature 20 to 151 °c Air pressure 1.0 to 8.5 kgf/cm².

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No description available.

No description available.