Dissertations / Theses on the topic 'Combustion air'

Around the world, vehicle emission regulations become stricter, increasing exhaust emission demands. To manage these rules and regulations, vehicle manufacturers put a lot of effort into minimizing the exhaust emissions. The three-way catalytic converter was developed, and today it is the most commonly used device to control the exhaust emissions.

To work properly the catalytic converter needs to control the air-fuel mixture with great precision. This then increases the demands on the engine management systems, causing them to become more complex. With increased complexity, the time effort of optimizing parameters has grown drastically, hence increasing development costs. In addition to this, operating conditions change due to vehicles age, requiring further optimization of the parameters while running.

To minimize development cost and to control the air-fuel mixture with great precision during an engines full life span, this master thesis proposes a self-optimized system, i.e. an adaptive system, to control the air-fuel mixture.

In the suggested method, the fuel injection to the engine is controlled with help of a linear lambda sensor, which measures the air-fuel mixture. The mapping from injection to measured air-fuel mixture forms a nonlinear system. It can be approximated as a linear function at static engine operating points, allowing the system at each static point to be modelled as a first order system with long time delay. To enable utilization over full operating area, and not only in static point, the controller uses large maps, so called gain-scheduling maps, to change control parameters.

The tested controller is model based. It uses an Otto-Smith Predictor and a feed forward connection of target air-fuel. The model parameters in the controller are updated while driving and the adaptation method used is based on a least squares algorithm.

The performance of the adapted controller and the adaptation method is tested in both simulation environment and in vehicle, showing good potential.

Doutoramento em Ciências e Engenharia do Ambiente
In Portugal, it was estimated that around 1.95 Mton/year of wood is used in residential wood burning for heating and cooking. Additionally, in the last decades, burnt forest area has also been increasing. These combustions result in high levels of toxic air pollutants and a large perturbation of atmospheric chemistry, interfere with climate and have adverse effects on health. Accurate quantification of the amounts of trace gases and particulate matter emitted from residential wood burning, agriculture and garden waste burning and forest fires on a regional and global basis is essential for various purposes, including: the investigation of several atmospheric processes, the reporting of greenhouse gas emissions, and quantification of the air pollution sources that affect human health at regional scales. In Southern Europe, data on detailed emission factors from biomass burning are rather inexistent. Emission inventories and source apportionment, photochemical and climate change models use default values obtained for US and Northern Europe biofuels. Thus, it is desirable to use more specific locally available data. The objective of this study is to characterise and quantify the contribution of biomass combustion sources to atmospheric trace gases and aerosol concentrations more representative of the national reality. Laboratory (residential wood combustion) and field (agriculture/garden waste burning and experimental wildland fires) sampling experiments were carried out. In the laboratory, after the selection of the most representative wood species and combustion equipment in Portugal, a sampling program to determine gaseous and particulate matter emission rates was set up, including organic and inorganic aerosol composition. In the field, the smoke plumes from agriculture/garden waste and experimental wildland fires were sampled. The results of this study show that the combustion equipment and biofuel type used have an important role in the emission levels and composition. Significant differences between the use of traditional combustion equipment versus modern equipments were also observed. These differences are due to higher combustion efficiency of modern equipment, reflecting the smallest amount of particulate matter, organic carbon and carbon monoxide released. With regard to experimental wildland fires in shrub dominated areas, it was observed that the largest organic fraction in the samples studied was mainly composed by vegetation pyrolysis products. The major organic components in the smoke samples were pyrolysates of vegetation cuticles, mainly comprising steradienes and sterol derivatives, carbohydrates from the breakdown of cellulose, aliphatic lipids from vegetation waxes and methoxyphenols from the lignin thermal degradation. Despite being a banned practice in our country, agriculture/garden waste burning is actually quite common. To assess the particulate matter composition, the smoke from three different agriculture/garden residues have been sampled into 3 different size fractions (PM2.5, PM2.5-10 and PM>10). Despite distribution patterns of organic compounds in particulate matter varied among residues, the amounts of phenolics (polyphenol and guaiacyl derivatives) and organic acids were always predominant over other organic compounds in the organosoluble fraction of smoke. Among biomarkers, levoglucosan, β-sitosterol and phytol were detected in appreciable amounts in the smoke of all agriculture/garden residues. In addition, inositol may be considered as an eventual tracer for the smoke from potato haulm burning. It was shown that the prevailing ambient conditions (such as high humidity in the atmosphere) likely contributed to atmospheric processes (e.g. coagulation and hygroscopic growth), which influenced the particle size characteristics of the smoke tracers, shifting their distribution to larger diameters. An assessment of household biomass consumption was also made through a national scale survey. The information obtained with the survey combined with the databases on emission factors from the laboratory and field tests allowed us to estimate the pollutant amounts emitted in each Portuguese district. In addition to a likely contribution to the improvement of emission inventories, emission factors obtained for tracer compounds in this study can be applied in receptor models to assess the contribution of biomass burning to the levels of atmospheric aerosols and their constituents obtained in monitoring campaigns in Mediterranean Europe.
Em Portugal, estima-se que 1.95 Mton/ano de lenha sejam utilizadas na queima doméstica para aquecimento e confecção de alimentos. Em simultâneo, nas últimas décadas, a área de floresta ardida também tem vindo a aumentar. Estes tipos de combustão contribuem para a libertação de quantidades elevadas de poluentes tóxicos que perturbam a química da atmosfera, interferem com o clima e possuem efeitos nefastos na saúde. A quantificação rigorosa, à escala regional e global, das emissões de gases e matéria particulada associada à queima doméstica, queima de resíduos agrícolas e fogos florestais é fundamental para vários fins, nomeadamente na investigação dos diversos processos atmosféricos, na elaboração de relatórios de emissões de gases de estufa, e na quantificação de fontes de poluição atmosférica que afectam a saúde humana. No sul da Europa, as bases de dados com factores de emissão detalhados são praticamente inexistentes. Os modelos climáticos, a modelização fotoquímica, os inventários de emissões e os estudos de identificação de fontes emissoras utilizam valores típicos obtidos para biomassa norte-americana ou do norte da Europa. Assim, é conveniente utilizar valores mais específicos obtidos localmente. Este estudo teve como principal objectivo a caracterização e quantificação dos gases e aerossóis emitidos por fontes de queima de biomassa, englobando as espécies lenhosas mais representativas da realidade nacional. Foram realizadas experiências de amostragem em laboratório (queima doméstica) e no campo (queima de resíduos agrícolas/jardim e fogos florestais controlados). Em laboratório, após selecção das espécies de biomassa e dos equipamentos de queima mais representativos em Portugal, estabeleceu-se um programa de amostragem para determinar os factores de emissão de poluentes gasosos e particulados, incluindo a composição orgânica e inorgânica dos aerossóis. Ao nível do campo, efectuou-se a amostragem das plumas de fumo resultantes da queima de resíduos agrícolas/jardim e de fogos controlados numa área dominada por espécies arbustivas. Os resultados deste estudo mostram que o tipo de equipamento de combustão e o tipo de biomassa utilizados têm um papel importante nos níveis e composição dos poluentes emitidos. Diferenças significativas entre o uso de equipamentos de combustão tradicionais versus equipamentos modernos foram observadas. Estas diferenças devem-se à maior eficiência de combustão dos equipamentos modernos, reflectindo-se na menor quantidade de matéria particulada, carbono orgânico e monóxido de carbono libertados. No que diz respeito ao fogo controlado em áreas dominadas por espécies arbustivas observou-se que a fracção orgânica estudada nas amostras de fumo é composta essencialmente por produtos resultantes da pirólise da vegetação. Estes produtos são constituídos na sua maioria por esteredienos e derivados de esteróis, hidratos de carbono resultantes da quebra das moléculas de celulose, produtos alifáticos provenientes de ceras vegetais e metoxifenóis resultantes da degradação térmica da lenhina. A queima de resíduos agrícolas e de jardim, apesar de ser uma prática proibida no nosso país, é uma realidade bastante frequente. Para avaliar a composição das emissões de alguns tipos de resíduos foram recolhidas amostras de três tamanhos diferentes (PM2.5, PM2.5-10 and PM>10). Apesar de se poder observar uma grande variabilidade em termos de compostos orgânicos dependendo do tipo de resíduo queimado, os compostos fenólicos (derivados do polifenol e guaiacil) e os ácidos orgânicos foram sempre predominantes em relação à restante fracção orgânica. O levoglucosano, o β-sitosterol e o fitol foram os traçadores de queima de biomassa detectados em quantidades mais apreciáveis na generalidade dos resíduos agrícolas e de jardim. O inositol pode ser considerado um bom traçador para as emissões resultantes da queima de rama de batata. Observou-se que as condições ambientais (tais como valores elevados de humidade relativa na atmosfera) provavelmente contribuíram para processos de coagulação e de crescimento higroscópico que influenciaram as características dos traçadores de biomassa, mudando sua distribuição para diâmetros maiores. Foi também feita a avaliação do consumo doméstico de biomassa na forma de um inquérito aplicado à escala nacional. Os resultados obtidos, conjugados com as bases de dados sobre factores de emissão obtidas nos ensaios de queima laboratoriais, permitiram estimar as quantidades emitidas de vários poluentes em cada distrito de Portugal continental. Além de contribuir significativamente para o aperfeiçoamento dos inventários de emissões, os factores de emissão obtidos para vários compostos traçadores poderão ser aplicados em modelos no receptor de forma a avaliar a contribuição da queima de biomassa para os níveis de aerossóis atmosféricas e seus constituintes obtidos em campanhas de monitorização na Europa mediterrânea.

Thesis (M.S.)--University of Nevada, Reno, 2007.
"May, 2007." Includes bibliographical references. Online version available on the World Wide Web. Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2007]. 1 microfilm reel ; 35 mm.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.
Includes bibliographical references (leaves 119-123).
The problem of thermoacoustic instability in continuous combustion systems is a major challenge in the field of propulsion and power generation. With the current environmental and political pressure that is being placed on the consumption of fossil fuels, this subject has become even more critical. In the past, the presence of combustion instability could be avoided by designing a combustor with fixed inlet conditions, where these conditions were conducive to a stable system. Today, utilities and providers of propulsion systems are under pressure to make systems that are not only more efficient and clean, but also have a greater flexibility of input fuel. In order to accomplish this, combustion engineers need an even deeper insight into what causes thermoacoustic instability and they need a wider array of tools at their disposal to suppress these instabilities. This thesis adds pieces of that deeper insight and provides another tool to tackle this difficult problem. As a first step in the further understanding of thermoacoustic instabilities, experiments were done in a premixed gas backwards facing step combustor using propane or propane/hydrogen mixture as a fuel. I fully characterized the combustion dynamics in this combustor by measuring the four defining states of the system. These states are pressure, heat release, velocity, and equivalence ratio. Once these measurements were performed I tested two novel approaches to suppressing thermoacoustic instabilities through the use of microjet air injection. This was done by building upon a previous combustor setup to allow the installation of several new diagnostic capabilities and the new microjets.
(cont.) The new diagnostics include stand-off pressure sensors to measure pressure in the hot exhaust region, a hot wire anemometer to measure velocity, a photomultiplier tube to measure the integrated heat release, an automated gas probe to measure fuel concentration profiles, and a laser absorption sensor to measure the temporal variance in equivalence ratio. The novel microjets were built into the newly designed test section. By fully characterizing the system I was able to show how both equivalence ratio oscillations and wake vortex interactions drive the thermoacoustic instabilities of the combustion. I have also shown that the stability range shifts to leaner equivalence ratios as inlet temperature or hydrogen content in the fuel is increased. This thesis demonstrates the great potential the microjet air injection has for extending the range of stability of the system.
by Duane Edward Hudgins.
S.M.

The main aim of the present work is to investigate the applicability of Large Eddy Simulations to pulverised coal combustion. The Navier-Stokes equations that describe an incompressible tur- bulent reactive flow are presented, with a source term which ac- counts for the effect of the coal particles on the gas phase. Both a Eulerian and Lagrangian approach are presented to describe the coal particles motion and their heat exchange with the gas phase. The main processes that characterise pulverised coal combustion: devolatilisation, volatile combustion and char combustion are described and the main models to represent them are presented. The performance of the numerical approximation is tested on two main experimental cases: 1) a pulverised coal jet flame surrounded by a methane pilot and 2) a 100 kWth swirling burner operating in an O2/CO2 environment. The results of the simulations are com- pared to qualitative and quantitative experimental measurements for both test cases. Finally a parametric study is performed on both test cases to understand firstly, which combustion processes are dominant and secondly to understand which models perform best for each experimental set-up. The results showed the Lagrangian approach to be more representative of the pulverised coal combustion process. The analysis for the pulverised coal jet flame, showed that the radiation and char combustion processes have almost negligible effect. Instead, the simulation results were highly sensitive to variations in the devolatilisation and volatile combustion models and model parameters. For the second test case, char combustion was dominant throughout most of the domain as the coal particles had a longer time to burn. The devolatilisation and volatile combustion processes were dominant at the initial stages of the combustion process and characterised the initial flame bhevaiour.

The work presented in this thesis is an investigation of the dynamics of unconfined hydrogen-air flames in the presence of buoyant effects and the determination of an ignition criterion for flame propagation between adjacent pockets of reactive gas separated by air. The experimental work was conducted using the soap bubble technique and visualized with high speed schlieren or large scale shadowgraph systems. A study was first conducted to determine the most suitable soap solution additive among glycerol, guar and polyethylene oxide for conducting the experiments, isolating guar as the best candidate. The soap solution was then used to study the dynamics of flames in single or multiple soap bubbles filled with reactive mixtures of different compositions. The soap bubble method was also further improved by designing a soap dispenser that can maintain a bubble indefinitely and a method to burst the soap solution prior to an experiment using timed heated wires. In the experiments with single bubbles, it was found that for sufficiently lean hydrogen-air mixtures, buoyancy effects become important at small scales. The critical radius of hemispherical flames that will rise due to buoyancy was measured and estimated using a model comparing the characteristic burning speed and the rise speed of the flame kernel. Excellent agreement was found between the model predictions and the measured critical flame radii. The experiments with multiple bubbles provided the scaling rules for flame transition between neighboring pockets of hemispherical or spherical shape separated by an inert gas. The test results demonstrated that the separation distance between the bubbles is mainly determined by the expansion ratio when the buoyancy effects are negligible, corresponding to near stoichiometric mixtures. For leaner mixtures with stronger buoyant effects, the critical separation distance was no longer governed by the expansion ratio alone, as buoyancy forces render the flame propagation across the inert gas more difficult. Visualization of the ignition dynamics confirmed that buoyancy forces tend to accelerate the first kernel up before ignition of the second kernel can be achieved.

L'enrichissement des hydrocarbures par l'hydrogène permet d'améliorer les performances de la combustion pauvre (augmentation de la réactivité, résistance à l'étirement, stabilité, réduction des polluants, ...). Il est primordial de connaitre les caractéristiques de la combustion de ces combustibles hybrides dans différentes conditions, afin de pouvoir les utiliser d'une manière sûre et efficace dans les installations pratiques. L'approche expérimentale reste coûteuse et limitée à certaines conditions opératoires. Cependant, le calcul numérique peut constituer la solution la plus adaptée, compte tenu du progrès réalisé dans le domaine de l'informatique et de la modélisation. Dans ce contexte, ce travail que nous avons effectué à l'ICARE (Institut de Combustion, Aérothermique et Réactivité, CNRS Orléans) vise à compléter les résultats des essais expérimentaux. Les effets de la richesse du mélange et l'ajout de l'hydrogène sur la structure et la formation des polluants sont étudiés dans ce travail. L'augmentation de la richesse du combustible permet de stabiliser la flamme, mais augmente la température et produit plus de CO, CO2 et NOx. Par contre, l'addition de H2 augmente l'efficacité du mélange, stabilise la flamme avec une légère élévation de la température maximale et une diminution des fractions massiques de CO, CO2 et NOx. Le remplacement d'une fraction de 10% où même 20% du gaz principal par l'hydrogène améliore les performances des installations et ne nécessite aucune modification sur les systèmes de combustion.

In this study, combustion performances and emission characteristics of olive cake and olive cake+coal mixture are investigated in a bubbling fluidized bed of 102 mm inside diameter and 900 mm height. The average particle sizes of coal and olive cake used in the experiments were 1.57 mm and 1.52 mm, respectively. Flue gas concentrations of O2, CO, SO2, NOx, and total hydrocarbons (CmHn) were measured during combustion experiments. Operational parameters (excess air ratio, secondary air injection) were changed and variation of pollutant concentrations and combustion efficiency with these operational parameters were studied. The temperature profiles measured along the combustor column was found higher in the freeboard for olive cake than coal due to combustion of hydrocarbons mostly in the freeboard. The location of the maximum temperature in the freeboard shifted to the upper part of the column, as the volatile matter content in the fuel mixture increased. Combustion efficiencies in the range of 83.6-90.1% were obtained for olive cake with the excess air ratio of 1.12-2.30. The corresponding combustion efficiency for coal was 98.4-99.7% under the same conditions. As the CO and hydrocarbon concentration in the flue gas increased, the combustion efficiency decreased. Also co-combustion experiments of olive cake and coal for various mixing ratios were carried out. As the amount of olive cake in the fuel mixture increased, SO2 emissions decreased because of the very low sulfur content of olive cake. In order to increase the combustion efficiency, secondary air was injected into the freeboard which was a good solution to decrease the CO and hydrocarbon emissions, and to increase the combustion efficiency. For the setup used in this study, the optimum operating conditions with respect to NOx and SO2 emissions were found as 1.35 for excess air ratio, and 30 L/min for secondary air flowrate for the combustion of 75 wt% olive cake and 25 wt% coal mixture. Highest combustion efficiency of 99.8% was obtained with an excess air ratio of 1.7, secondary air flow rate of 40 L/min for the combustion of 25 wt% olive cake and 75 wt% coal mixture.

Two mathematical models have been developed to simulate two-dimensional, premixed, laminar, stationary, axisymmetric methane-air flames, and successfully validated with non-intrusive Coherent Anti-Stokes Raman Spectroscopy (CARS) temperature measurements. With the first model, the heat releaser ate model, volumetric heat release rate was generalised from one-dimensional computations. This approximation greatly simplified the set of governing equations that need to be solved. However, it cannot describe the effects of high stretch rates or of negative stretch rate. The second model made use of a number of reduced chemical kinetic schemes, with realistic elementary reactions. These were drawn from the literature and realistic transport properties have been included. With this model, based on the work of Peters (1985), the effects of stretch are automatically accounted for. Practical experimental validation was obtained with a multiple slot burner, supplied by the collaborating body, British Gas p1c. Temperature fields, obtained with the CARS technique, partially validated the reduced chemical kinetic scheme model. Some uncertainty arose in the prediction of heat loss to the burner tube. A numerical algorithm based upon the SUVIPLE method was employed,with a fully staggered grid. Various discretisation schemes were examined with the heat release model. Based on these tests, the hybrid scheme was selected for use in the reduced model. With this approach, a few reduced kinetic schemes have been selected and implemented. The most successfuol ne was the Peters( 1985) scheme. This consisted of 4 global reaction steps with 18 elementary reactions and 7 non-steady chemical species. The scheme has been employed in all the detailed computations in the present study. With this scheme, two-dimensional field solutions, for methane-air mixtures with equivalence ratios of 0.75,0.84 and 1.0, with slot widths of 2 mm, and 3 mm, and mean inlet velocities ranging from 0.3 m/s to 2.8 m/s have been obtained. Detailed flame structures have been obtained for all these conditions. Under these conditions, a number of parameters, essential in burner design and stability analysis, have been investigated. These includes flame height, flame thickness, and heat loss to the burner tube. The loss can range between 3% and 32% of the chemical energy in the premixture. The computations reveal the stretch rates acting on the flame and their effects on the burning velocity. At low flow rates the base of the flame has a negative stretch rate, while the flame tip is positively stretched. These effects are reversed at high flow rates. From the localised relationships between stretch rate and burning velocity, Markstein lengths have been evaluated,for different mixtures and the values compared with those obtained experimentally by other researchers. In general, there was good agreement despite the large scatter in the experimental values. The results further showed that the effects of the two components of flame stretch, namely flame curvature and aerodynamic straining, on burning velocities were very different. It seems appropriate to introduce two Markstein lengths to correlate burning velocity and the two components of stretch and these have been evaluated. Aerodynamic straining has a significantly larger effect on burning velocity than has flame curvature.

The quest for ever stronger and tougher steels has lead to an interest in the 'Acicular Ferrite' microstructure, its chaotic and disordered morphology imparting a high degree of toughness to the steel. To date, only complex and expensive materials and manufacturing processes have formed acicular ferrite within bulk cast steel. As such, the thrust of this research is to produce a cheap steel addition, an iron - titanium oxide metal-ceramic composite, that will facilitate the formation of acicular ferrite in conventionally manufactured bulk cast steels. The Self-propagating High-temperature Synthesis (SHS) process has been utilised to manufacture the iron - titanium oxide material from compacts pressed from Fe203 + Ti powders. The fundamental reactions that occur as titanium powder and Fe203 + Ti powder compacts are heated in air and argon atmospheres have been investigated. The process’s involved are reported and have been modelled mathematically. A computer simulation of the reaction process has been developed and tested against experimental evidence. The effect of various compact parameters, the starting compact stoichiometry and other processing variables have been examined with respect to the composition of the products and their morphology.

De nombreuses études sont menées pour la compréhension et l'utilisation de plasmas hors équilibre pour les procédés industriels capables d'améliorer la combustion, de stabiliser des flammes et de réduire les polluants. En effet, dans le cadre des nouvelles normes européennes, il devient indispensable de pouvoir maîtriser la qualité de la combustion et de réduire ainsi les émissions polluantes. Même si le principe de l'allumage classique par étincelle est depuis longtemps connu et utilisé dans l'industrie automobile, ce système présente néanmoins quelques limites. En effet, le caractère localisé de l'étincelle créée réduit la probabilité de rencontre entre l'étincelle et une zone de mélange inflammable ce qui conduit à des ratés d'allumages et spécialement en mélanges pauvres. Ainsi, l'utilisation de systèmes différents reposant sur des plasmas non-thermiques fournit des avantages significatifs, dont les propriétés de forte réactivité chimique et de faible coût énergétique. L'objet principal de ce travail de thèse est l'étude de l'allumage de mélanges combustibles par un certain type de décharges pulsées nanosecondes. En effet, un des intérêts du déclenchement de combustion par décharges nanosecondes est le développement d'une zone spatiale d'allumage nettement plus étendue que celle obtenue par l'étincelle de la bougie standard. Enfin, un autre avantage des décharges nanosecondes est la création de nombreux radicaux dans le milieu combustible nécessaires à l'initiation directe des cinétiques de combustion en limitant la contribution thermique, souvent impliquées dans les pertes de rendement des allumeurs. Dans notre étude, la décharge nanoseconde pulsée utilisée est caractérisée par l'application d'une surtension très élevée donnant un pulse de tension très court (12 ns), d'amplitude très élevée (50 kV) et un front de montée très raide (2 ns). Au cours de cette étude, nous avons d'abord caractérisé la décharge nanoseconde pulsée dans des mélanges air/propane et air/heptane à pression atmosphérique. Ensuite, nous avons appliqué la décharge au déclenchement de combustion dans les mélanges air/propane et air/heptane dans les proportions stœchiométriques mais aussi en mélanges pauvres et ce toujours à pression atmosphérique, ce qui a montré la réduction des délais de combustion. De plus, les résultats en mélanges stœchiométriques montrent qu'il existe trois modes d'allumage : un ponctuel, un double et un mode cylindrique et ce en fonction de la densité d'énergie.

To advance the design of hypersonic vehicles, high-fidelity multi-physics CFD is used to characterize 3-D scramjet flow-fields in two novel streamline traced configurations. The two inlets, Jaws and Scoop, are analyzed and compared to a traditional rectangular inlet used as a baseline for on/off-design conditions. The flight trajectory conditions selected are Mach 6 and a dynamic pressure of 1,500 psf (71.82 kPa). Analysis of these hypersonic inlets is performed to investigate distortion effects downstream with multiple single cavity combustors acting as flame holders, and several fuel injection strategies. The best integrated scramjet inlet/combustor design is identified. The flow physics is investigated and the integrated performance impact of the two innovative scramjet inlet designs is quantified. Frozen and finite rate chemistry is simulated with 13 gaseous species and 20 reactions for an Ethylene/air finite-rate chemical model. In addition, URANS and LES modeling are compared to explore overall flow structure and to contrast individual numerical methods. The flow distortion in Jaws and Scoop is similar to some of the distortion in the traditional rectangular inlet, despite design differences. The baseline and Jaws performance attributes are stronger than Scoop, but Jaws accomplishes this while eradicating the cowl lip interaction, and lessening the total drag and spillage penalties. The innovative inlets work best on-design, whereas for off-design, the traditional inlet is best. Early pressure losses and flow distortions in the isolator aid the mixing of air and fuel, and improve the overall efficiency of the system. Although the trends observed with and without chemical reactions are similar, the former yields roughly 10% higher mixing efficiency and upstream reactions are present. These show a significant impact on downstream development. Unsteadiness in the combustor increases the mixing efficiency, varying the flame anchoring and combustion pressure effects upstream of the step.

Many small scale agricultural operations such as greenhouses, peanut drying and tobacco curing, use significant quantities of thermal energy. Direct combustion of biomass is a potential source of heat energy for those agricultural applications to substitute for the electricity or fossil fuels (principally LP gas) currently used. However, small scale combustion equipment often operates with low efficiency and high emissions. A prototype chunkwood combustor was installed and tested. The basis for controlling heat output, was the modulation of air supplied to the primary and secondary combustors. Exhaust gas CO and CO2 concentrations, combustor efficiency, and useful heat output were measured. The cleannest burn was achieved during a forty minute test, where 50 percent of stoichiometric air was introduced at the primary, and 170 percent at the secondary, for a total of 220 percent stoichiometric. The overall average CO/CO2 ratio for this test was 0.084, and 0.1 is considered to be an average rating for a combustion in a wood stove. Moreover, the efficiency during this test was 52 percent.
Master of Science

An engine simulation model has been developed to describe turbulent combustion of gas-air mixtures in a spark-ignition engine. The model incorporates a turbulent entrainment combustion theory proposed by Daneshyar and Hill which is based on Tennekes' model of turbulence and the vortex bursting principle of Chomiak. Flame propagation was based on turbulent entrainment. The flame was modelled as a thick spherical shell composed of burned and unburned gases. Inside the thick flame, pockets of initial size A, the Taylor microscale, are consumed at a rate of the order of the laminar burning velocity. To compare the model to experimental data, turbulence levels were measured in a motored Ricardo Hydra engine using hot wire anemometry. Combustion pressure data were measured with a piezoelectric transducer. Results indicate that the model is successful in predicting trends in overall combustion rates when the engine speed and air-fuel ratio are varied. The model also provided insight into the structure of turbulent flames in engines.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

This thesis presents an investigation into a novel method of estimating the air-fuel ratio of a gasoline-fuelled spark-ignition internal combustion engine. The measurement of the air-fuel ratio is important for controlling an engine to reduce exhaust emissions. In production vehicles, the air-fuel ratio is measured using an exhaust gas analyser and the exhaust emissions are reduced by using electronically controlled three-way catalytic converters, which are expensive and subject to operationallimitations such as, requiring the engine to operate with a stoichiometric air-fuel ratio. A micro-processor based engine management system monitors the engine performance and controls various engine parameters - the fuel pulse width, ignition timing, exhaust gas re-circulation etc. - to maintain strict control of the engine and ensure optimum engine performance. In the USA and UK the engine management system is also responsible for performing on-board diagnostics and warns the driver of any problems such as misfire, knocking combustion and failure of the catalytic converter. The method of measuring the air-fuel ratio presented in this thesis, termed Spark Voltage Characterization (SVC), uses neural networks to analyse the time varying spark voltage waveform to estimate the air-fuel ratio. The spark plug is in direct contact with the combustion itself, thus making it is an excellent candidate for use as a combustion sensor. As it is already installed in the engine, no modifications are required to the engine block itself. The method uses few external components making it cheaper to implement. Preliminary investigations on this method showed that it was possible to estimate the air-fuel ratio by neural network analysis of the spark voltage waveform. As different engines are equipped with different types of ignition systems, it is important that the sensor is independent of the ignition system thus ensuring that it is able to operate with any type of ignition system. The work presented in this thesis includes: i) an extensive review of other methods of measuring the air-fuel ratio, noting the advantages and disadvantages of each method and how the SVC sensor overcome these disadvantages; ii) a description of the theoretical operation of the sensor; iii) investigation of the effects of various engine parameters on the performance of the sensor; iv) suggestions for further work to improve the sensor performance.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
Essa dissertação apresenta um estudo comparativo de quatro diferentes modelos de cinética química detalhada que envolvem as principais espécies químicas responsáveis pelo processo de formação e oxidação da fuligem, i.e., o oxigênio molecular, o radical hidroxila, o acetileno, o propargil, benzeno, fenil e pireno. Para este fim, considera-se a combustão de misturas de etileno/ar e metao/ar. Para analisar os modelos cinéticos são utilizados um reator perfeitamente misturado (PSR) e um reator parcialmente misturado (PaSR). No caso do reator perfeitamente misturado, um estudo sistemático da influência do tempo de residência e a riqueza da mistura sobre estas espécies químicas é apresentado. São discutidas as importantes discrepâncias obtidas, para o acetileno, o propargil, o benzeno, o fenil e o pireno, entre os modelos cinéticos analisados. As espécies oxidantes exibem menores discrepâncias dentre todas as espécies analisadas. No caso do reator parcialmente misturado, a razão entre o tempo de residência e o tempo de mistura é o parâmetro de análise. De modo geral, os resultados obtidos permitem avaliar o comportamento dos mecanismos cinéticos em uma situação representativa de combustão em escoamentos turbulentos.
In this dissertation a comparative study is presented of four different detailed kinetics models involving the main chemical species responsible for the soot formation and oxidation, i.e., the molecular oxygen, the hydroxyl, the acetylene, the propargyl, the benzene and the pyrene. To this purpose is considered the combustion of ethylene/air and metane/air. To analyze the kinetic models are used a perfect stirred reactor (PSR) and a partial stirred reactor (PaSR). In the case of a perfect stirred reactor a systematic study of the influence of the residence time and of the equivalence ratio on these chemical species is presented. Are discussed the important discrepancies obtained for acetylene, propargyl, benzene, phenyl and pyrene, between the kinetic models analyzed. The oxidizing species exhibit minor discrepancies only. In the case of the partially mixed reactor, the ratio between the residence time and the mixing time is the analysis parameter. Overall, the results obtained allow to evaluate the behavior of the kinetic mechanisms in situations representative of combustion in turbulent flows.

Cette étude porte sur une flamme turbulente diphasique de laboratoire, plus particulièrement sur le mode de combustion 3P ou LPP : prévaporisée, prémélangée, pauvre. Le dispositif mis au point permet d'étudier les effets de trois paramètres sur la structure de flammes diphasiques turbulentes partiellement prémélangées et prévaporisées d'un mélange pauvre heptane-air : la richesse globale du mélange, le temps de prévaporisation et la granulométrie initiale. L'anémométrie phase Doppler (PDA) a été utilisée pour la caractérisation expérimentale des champs dynamiques et granulométriques de l'écoulement diphasique réactif. Une attention particulière a été apportée à la validation des mesures par PDA. Une étude bibliographique et une série de tests nous ont permis de déterminer la configuration la mieux adaptée à nos conditions expérimentales et de s'assurer ainsi de la fiabilité des résultats. Dans un deuxième temps, la caractérisation des champs scalaires de température et du degré d'avancement de la réaction a été obtenue respectivement à l'aide d'un thermocouple et de la fluorescence induite par un laser (PLIF). Ensuite, nous avons proposé une méthode pour déterminer localement le taux moyen de vaporisation des gouttes à partir des mesures obtenues par PDA. La connaissance simultanée du taux de vaporisation, de la température et du degré d'avancement nous ont donc permis d'étudier le taux de vaporisation moyen local des gouttes d'heptane au sein d'un brouillard en combustion. Le degré d'avancement permettant notamment de comparer entre elles des flammes ayant des hauteurs différentes de par leur richesse. Nous avons pu comparer les taux, d'une part, à ceux obtenus pour une goutte isolée en atmosphère stagnante mais à température élevée, et d'autre part, à ceux obtenus pour une goutte isolée à température ambiante et soumise à une turbulence homogène isotrope. Enfin, nous avons déterminé le régime de combustion diphasique auquel appartient chaque flamme, ce qui nous a permis d'expliquer les résultats sur les taux de vaporisation.

The objective of this thesis is to develop and validate a model of soot formation which is capable of being applied to a computational fluid dynamic (CFD) simulation of gas turbine combustion. The work follows previous research by Moss and Co-workers (Moss et al.1987, Syed 1990, Stewart et al.1991) The concept of the study is to generate a detailed set of experimental data in turbulent flames of kerosine in which the complicating factors of gas turbine combustion - that is 3D geometry and droplet combustion - are removed. This allows more confidence in the computational simulation of the flames and therefore more insight into the soot formation process. There are two components to the work: the experimental and theoretical studies. The first involves the compilation of an experimental dataset of key variables in ethylene and vaporised kerosine jet flames at elevated pressure, the second with the simulation of two of the experimentally studied flames using CFD methods. The main achievement of the study is the generation of a formidable and detailed experimental database for flames at a variety of pressures and conditions. The unexpected finding is the extremely large conversion of carbon to soot found in the flames even at low pressure. This results in high radiant heat losses and measurement difficulties. From the data, it is possible to assess the pressure dependence of soot growth in kerosine flames. Although, at the higher pressures, high soot levels created uncertainties in the measurements, in absolute terms growth rate is shown to be independent of pressure up to 6atm pressure. Above this it increases significantly. The soot model of Moss et al.1988 - originally developed in laminar e~hylene flames - was shown to give excellent agreement in turbulent situations. However, owing to the large radiant heat loss and soot levels, its application to the kerosine flames was more problematic since the assumptions that soot is a perturbation to the gaseous field and that temperature may be accurately described by a single perturbed flamelet were no longer valid. Further models to deal with such situations are proposed and tested. Aside from the obvious relevance of this study to the field of gas turbine combustion, the large radiant heat loss and high soot levels observed in the flames studied here imply a further significance for the study of fire hazards. That a laboratory scale flame maybe made to behave in a similar manner to a much larger pool fire flame is a very useful finding.

Les émissions polluantes à l’échappement des véhicules automobiles sont l'une des principales sources de pollution de l'air dans le monde d'aujourd'hui. Par conséquent, la législation a évolué afin de limiter ces émissions. L'un des aspects clés pour répondre consiste à bien maîtriser les échanges gazeux au sein du moteur à combustion interne. Cette amélioration est possible par l'optimisation de répartiteurs d'admission d'air. Dans ces répartiteurs d'admission d'air, la maitrise de l’écoulement de type tumble est une piste de progrès. Des volets sont installés à la sortie du répartiteur afin d'améliorer le rapport de tumble et donc le mélange air-carburant (VTS-Variable Tumble System). Une autre caractéristique de l'écoulement à l'intérieur des répartiteurs est l'effet des écoulements pulsés qui engendrent des fluctuations de pression assez importante. Par conséquent, le but de cette étude consiste à simuler le flux d'air pulsé à l'intérieur des répartiteurs d'admission et à identifier l'effet des pulsations de pression sur les composants actifs tels que les volets. Le travail de simulation dans la présente thèse a été effectué à partir du code open source CFD OpenFOAM. Dans un premier temps, l'effet des pulsations de pression est simulé à l'intérieur d'un tube d'acier et une méthodologie de simulation est développée. Les résultats de la simulation sont validés à partir de résultats expérimentaux obtenus sur un dispositif spécifique, le banc dynamique. Ensuite, des simulations ont été effectuées sur le répartiteur d'admission principal avec des volets. Tout d’abord, les simulations sont effectuées en régime permanent avec cinq positions d'ouverture différentes du clapet. Les forces et les moments agissant sur le volet en régime permanent sont obtenus et analysés. Puis, des simulations en régime transitoire avec des effets de pulsation de pression sont effectuées. Les résultats de la simulation instationnaire sont comparés aux résultats expérimentaux en termes de fluctuations de pression relative. Les effets des pulsations de pression sur les forces aérodynamiques et les moments agissant sur les volets sont analysés et commentés
The exhaust emissions from automobiles are one of the major sources of air pollution in today’s world. Thence,research and development is the key feature of the modern automotive industries to meet strict emission legislation. One of the key aspects to meet these requirements is to improve the gas exchange process within internal combustion engines. It is possible by the design optimization of the air intake manifolds for internal combustion engines. One of such advancement in air intake manifolds is variable tumble systems (VTS). In VTS system, tumble flaps are installed at the exit of the manifold runner in order to improve tumble ratio and hence air-fuel mixing. Another feature of the flow inside the intake manifolds is pressure pulsation effect. Therefore, the aim of the Ph.D. work is to simulate the pulsating air flow inside the air intake manifolds and to identify the effect of the pressure pulsations on the active components like tumble flaps. The simulation work in the present thesis has been carried out on open source CFD code OpenFOAM. In a first step, the effect of pressure pulsations is simulated inside a steel tube and a simulation methodology is developed. The results of the simulation are validated on a specific experimental device, the dynamic flow bench. Then,simulations have been carried out on the main intake manifold with tumble flaps. Firstly, the simulations are performed with five different opening positions of the tumble flap in a steady state configuration. The forces and moments acting on the flap in steady state are obtained and analyzed. Then, unsteady simulations with pressure pulsation effects are performed. The results of obtained from unsteady simulation are compared with the experimental results in terms of relative pressure fluctuations. The effect of the pressure pulsation on the aerodynamic forces and moments acting on the tumble flaps are analyzed and explained

The harmful effects of air pollutants on human beings and environment have been the major reason for efforts in sampling, analysis and control of their sources. The major pollutants emitted to atmosphere from stationary combustion processes are nitrogen oxides, inorganic acids, carbon dioxide, carbon monoxide, hydrocarbon and soot. In the current work two methods are developed for sampling and analysis of volatile chlorinated aromatic hydrocarbons and semi-volatile chlorinated aromatic hydrocarbons for example 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) by using solid sorbent, thermal desorption and high resolution GC-MS. The capacity of several solid sorbents is compared by breakthrough value and percentage recovery ofthe analyte from the sorbent. The thermal stability of polyvinyl chloride (PVC) and PVC in the presence of metals is studied because PVC is a polymer commonly found in solid waste derived from medical waste, car recycling and electrical cable. Harmful pollutant emissions from combustion and pyrolysis of PVC are measured using the novel method developed in this work. The main inorganic volatile is HCl while benzene is the major volatile organic formed under pyrolysis and combustion conditions. The thermal degradation of PVC produces a large number of chlorinated aromatic hydrocarbon, aromatic hydrocarbon and short chain linear gases. A study is designed for control of harmful pollutants from combustion of PVC including HCl, aromatic hydrocarbon, chlorinated aromatic hydrocarbons and soot. It is reported that the presence of metal oxides have the ability to control the level of harmful emissions by facilitating the producing of more short chain linear gases. A study is designed for control of harmful pollutants from combustion of PVC including HCl, aromatic hydrocarbon, chlorinated aromatic hydrocarbons and soot. It is reported that the presence of metal oxides have the ability to control the level of harmful emissions by facilitating the producing of more short chain linear gases. Two methods are developed for the control of soot from liquid and gas combustion process by using applied fields, Magnetic and electric fields. In this study, it is shown that an increase in applied field strength leads to an increase in flame temperature but a decrease in the length of flame. The level of soot emission was decreased in presence of an applied field. A discussion of the effect of applied fields on the combustion process is given.

Coal consumption is predicted to account for about 21% of the total global primary energy in 2040 and this continues to be a challenge for global warming and air pollution. Oxyfuel combustion is one of the leading options for carbon capture and storage (CCS) technologies to reduce the impact on the environment. Initially this technology has been studied successfully on small-scale facilities but it needs to be developed for large-scale applications. CFD has been demonstrated to be a key tool for the development and optimisation of pulverised coal combustion processes and it is still an important tool for new designs and retro-fitting of conventional power plants for oxyfuel combustion. Radiation heat transfer plays an important role, influencing the overall combustion efficiency, pollutant formation and flame ignition and propagation. This thesis focuses on the radiation properties of the particles as well as gas property models on the overall influence of the prediction of the formation of NOx pollutants in pulverised coal combustion. The radiative properties of the particles are investigated with a focus on the effect of the optical properties and approximate solutions to determine the radiative properties, with different experimental data for the optical properties and approximate solutions being employed. The effects of the radiative properties on the radiative heat transfer are investigated in three dimensional enclosures for small and large-scale furnaces and implemented on a 250 kW pilot scale combustion for both air and oxyfuel conditions. The results from the study highlights the best selection for the particle properties for simulations in small and large-scale pulverised coal furnaces and employing radiation models for the gases and particles to improve the NOx predictions in pulverised coal combustion under air and oxy-fired environments.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.
Includes bibliographical references (p. 79-80).
After the oil crisis of the 1970's, stringent government standards placed on automobile manufacturers have led the industry to explore more fuel efficient alternatives to the vehicle with a conventional internal combustion engine/transmission powertrain. This is the motivation behind Mr. David F. Moyer's hybrid internal combustion engine concept. A vehicle using this engine should attain higher fuel economy levels as a result of kinetic energy recovery and reuse (achieved by using the engine as an air compressor during braking, storing the compressed air, and then utilizing that air to turn the engine and drive the vehicle), cylinder disabling, and the elimination of idling losses. Data of transmission input power for Ford Motor Company's P2000 vehicle while driven through 1373 seconds of typical urban driving (CVS cycle) were used, combined with a model to estimate engine friction, to carry out an available energy analysis of the hybrid engine. An air processing efficiency was incorporated into the analysis to determine how irreversible the air storage/use processes were. Fuel economy was estimated for the different operating conditions of the concept by matching Ford's 1.8-litre Zetec engine to the vehicle and using the fuel consumption map for that engine. The vehicle with the baseline engine yields 32.6 mpg. Adding cylinder disabling raises this value to 36.8 mpg. Ultimately, if reversible hybrid operation is added, the best possible fuel economy this concept can achieve is 52.4 mpg, for a total maximum savings of 38% in fuel consumption. Using simple thermodynamic models of a braking and an air driving event, we predicted maximum values of 85% and 88% for the air processing efficiency in the braking and the air driving case, respectively. An overall value of 65% was chosen for the efficiency, resulting in a maximum fuel economy of 48.1 mpg and fuel savings of 32%. The analysis above led us to conclude that engine friction plays a significant role in reducing the benefit of this hybrid concept. Furthermore, fully variable valve timing and cylinder disabling improve fuel economy for a conventional engine significantly, and they are essential in minimizing the thermodynamic losses involved in hybrid operation. Therefore, we recommend that methods to reduce engine friction as well as means to implement fully variable valve timing modifications to an internal combustion engine be explored further.
by Carlos A. Herrera.
S.M.

A phenomenological model for a turbulent premixed flame in homogeneous turbulence, which incorporates the conservation of the probability distribution function (pdf) of a scalar, was developed. This was used to simulate the lean burn and misfire limits of combustion within a constant volume chamber. A one-dimensional numerical approximation of the pdf equation in spherical co-ordinates was obtained using the control volume formulation. The air-fuel premixture in the chamber was divided into particles of equal mass, which in turn were distributed among control volumes considered as spherical concentric shells. Monte-Carlo methods were applied to model the diffusion of particles between and mixing of particles within the concentric spherical shells. The chemical reaction of the mixture used a first order reaction from which a set of ordinary differential equations were solved for the evolution of the temperature and species concentration of each particle. Turbulence was modelled using the rapid distortion theory. A parametric study was conducted with the present model to show its operation in the misfire region of combustion. There has also been a comparison of mean expansion speeds with the compiled experimental combustion data of Bradley (1992). A suggestion for future research with the established model involves the adoption of the k-epsilon theory for the development of turbulence-related properties. This would allow comparison to the results obtained with the present rapid distortion theory for turbulence.