No description available.

No description available.

No description available.

No description available.

Diesel engine combustion has been studied during the last decades by researchers in terms of improving the performance of the engine. In order to improve the analysis of the diesel engine combustion, dimensionless parameters were used in this study. It was concluded that the newly introduced dimensionless parameters developed in this study facilitate understanding of diesel engine combustion process. A new method has been proposed to determine the values of the form factor (m) and efficiency factors (a) of the Wiebe equation. This is achieved by developing a modified form of Wiebe equation with only one constant. The modified version of Wiebe equation facilitates the determination of constants accurately, which enhances the accuracy of evaluating the burn fraction. The error induced on the burn fraction f with respect to the values of constants a and m obtained through different methods is discussed and compared. The form factor affects the burn fraction significantly compared to the efficiency factor. A new non-dimensional parameter ‘combustion burn factor (Ci)’ has been identified in the modified Wiebe equation. The burn fraction f was found to be a function of Ci only, thus the benefits of expressing heat release rate with respect to Ci have been presented. The errors associated with the determination of apparent heat release rate (AHRR) and the cumulative heat release (Cum.Hrr) from the measured cylinder pressure data and the assumed specific heat ratio (γ) was determined and compared. The γ affected the calculated AHRR more than the cylinder pressure. Overestimation of γ resulted in an underestimation of the peak value of the AHRR and vice versa, this occurred without any shift in the combustion phasing. A new methodology has been proposed to determine the instantaneous and mean value of γ for a given combustion. A two litre Ford puma Zetec diesel engine, four cylinder and 16 valves was employed to carry out this investigation. This new methodology has been applied to determine γ for a wide range of injection pressure (800 bar to 1200 bar), injection timing (9 deg BTDC to -2 deg BTDC) and engine loads at 2.7 BMEP and 5 BMEP. Standard ultra-low sulphur diesel fuel and two bio-diesels (Rapeseed Methyl Ester and Jatropha Methyl Ester) were studied in this investigation. Ignition delay is one the most important parameter that characterises the combustion and performance of diesel engines. The relation between ignition delay and combustion performance in terms of efficiency and emission was revealed by researchers. Ignition delay period measurements in diesel engine combustion along with the most used correlation for calculating ignition delay are discussed in this work. The effect of constants on accuracy in the correlation were discussed, and induced error on calculated ignition delay periods with respect to constants were calculated and compared. New techniques were proposed to calculate the constant values directly by using the experimental data. It was found that the calculated values for ignition delay using the new techniques matched well with the experimental data. These techniques can improve the accuracy of the ignition delay correlation. Also a new correlation without any constants was introduced in this work. This correlation can be used to predict ignition delay directly by using engine parameters only. The introduced correlation provides better results compared to Arrhenius type correlation presented by Wolfer. This new correlation can be used for feedback control engine combustion process.

This thesis considers the effect of compression ratio on the performance of a direct injection diesel engine. One aspect of engine performance is considered in great detail, namely the combustion performance at increased clearance volume. This aspect was of particular interest because variable compression ratio (VCR) systems normally operate by varying the clearance volume. The investigation relied upon results obtained both from experimental and computer simulating models. The experimental tests were carried out using a single-cylinder direct-injection diesel engine, under simulated turbocharged conditions at a reduced compression ratio. A number of one-dimensional computer models were developed; these simulate the induction and compression strokes, and the fuel spray trajectories in the presence of air swirl. The major objectives of the investigation were: to assess the benefits of VCR in terms of improvements in output power and fuel economy; to assess the effects on combustion of increased clearance volume, and investigate methods for ameliorating resulting problems; develop computational models which could aid understanding of the combustion process under varying clearance volume conditions. It was concluded that at the reduced compression ratio of 12.9:1 (compared to the standard value of 17.4:1 for the naturally-aspirated engine), brake mean effective pressure (BMEP) could be increased by more than 50%, and the brake specific fuel consumption (BSFC) could be reduced by more than 20%. These improvements were achieved without the maximum cylinder pressure or engine temperatures exceeding the highest values for the standard engine. Combustion performance deteriorated markedly, but certain modifications to the injection system proved successful in ameliorating the problems. These included: increase in the number of injector nozzle holes from 3 to 4, increase in injection rate by about 28%, advancing injection timing by about 6°CA. In addition, operation with weaker air fuel ratio, in the range of 30 to 40:1 reduced smoke emissions and improved BSFC. Use of intercooling under VCR conditions provided only modest gains in performance. The NO emission was found to be insensitive to engine operating conditions (fixed compression ratio of 12.9:1), as long as the peak cylinder pressure was maintained constant. Engine test results were used in order to assess the accuracy of four published correlations for predicting ignition delay. The best prediction of ignition delay with these correlations deviated by up to 50% from the measured values. The computer simulation models provided useful insights into the fuel distribution within the engine cylinder. It also became possible to quantify the interaction between the swirling air and the fuel sprays, using two parameters: the crosswind and impingement velocities of the fuel spray when it impinges on the piston-bowl walls. Tentative trends were identified which showed that high crosswind velocity coincided with lower smoke emissions and lower BSFC.

Orientador: Waldir Antonio Bizzo / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T09:38:07Z (GMT). No. of bitstreams: 1 Moretti_RicardoRoquetto_M.pdf: 3138518 bytes, checksum: 3ee2db245fb6caad13e782dc3c9072a2 (MD5) Previous issue date: 2013 / Resumo: A emissão de poluentes por veículos automotores é um dos grandes problemas ambientais enfrentados na atualidade. Para resolver o problema de emissão de poluentes à modificação da matriz energética foi o caminho adotado, e para isso realizaram-se investimentos em tecnologias para fabricação de motores com melhor eficiência térmica e capazes de operar com biocombustíveis. No Brasil etanol foi o combustível objeto de estudo para realizar a mudança na matriz energética, por ser um produto produzido em larga escala no Brasil. Durante o estudo realizou-se uma revisão bibliográfica sobre os processos de produção de etanol, biodiesel e óleos vegetais. Avaliou-se a viabilidade técnica e financeira de se utilizar uma mistura de combustível óleo diesel, biodiesel versus o desempenho da mistura óleo diesel, biodiesel e etanol anidro em um motor de ignição por compressão visando não acarretar perda de performance no motor. Para a avaliação do desempenho global do motor utilizou-se um motor ciclo diesel comercial, operando com 95% de óleo diesel e 5% biodiesel e comparou-se esse mesmo motor utilizando uma mistura de 92,15% de óleo diesel, 4,85% de biodiesel e 3% de etanol anidro / Abstract: This work investigated the feasibility of using a blend of standard Brazilian diesel (which contains 5% biodiesel) and up to 5% ethanol. We characterized the mixture as fuel and measured the performance of a diesel engine operating with a blend containing 3% anhydrous ethanol, the maximum percentage of ethanol that did not reduce the cetane number of the fuel below that specified in Brazilian legislation (ANP Resolution 42). The presence of anhydrous ethanol in the mixture did not cause a significant impact on engine performance as measured by brake power, brake torque and brake specific fuel consumption tests. The thermal efficiency of the engine used in the tests was slightly higher with standard diesel than with the diesel-biodiesel-ethanol blend / Mestrado / Termica e Fluidos / Mestre em Engenharia Mecânica

<div>The continued advancement of gas turbine combustion technology for power generation and propulsion applications requires novel techniques to increase the overall engine cycle efficiency and improved methods for mitigating combustion instabilities. To help address these problems, high-speed optical diagnostics were applied to two different experiments that replicate relevant physics in gas turbine combustors. The focus of the measurements was to elucidate the effect of various operating parameters on combustion dynamics occurring over a wide range of spatio-temporal flow and chemical scales. The first experiment, VIPER-M, enabled the investigation of coupling mechanisms for transverse instabilities in a multi-element, premixed combustor that maintains key similarities with gas turbine combustors for land based power generation. The second experiment, COMRAD, facilitated the study of the effect of fuel heating on the combustion performance and dynamics in a liquid-fueled, piloted swirl flame typical of aviation engine combustors. </div><div> </div><div><br></div><div>Two different injector lengths were tested in the VIPER-M experiment, and high-speed CH* chemiluminescence imaging and an array of high-frequency pressure transducers were used to characterize the overall combustor dynamics. For all conditions tested, the longer injector length configuration exhibited high-amplitude instabilities, with pressure fluctuations greater than 100% of the mean chamber pressure. This was due to the excitation of the fundamental transverse mode, with a frequency around 1800 Hz, as well as multiple harmonics. Shortening the injector length significantly lowered the instability amplitudes at all conditions and excited an additional mode near 1550 Hz for lower equivalence ratio cases. The delineating feature controlling the growth of the instabilities in the two injector configurations was shown to be the coupling between the transverse modes in the chamber and axial pressure fluctuations in the injectors.</div><div> </div><div><br></div><div>Heated fuels were introduced into the COMRAD experiment, and simultaneous 10 kHz stereoscopic particle image velocimetry and OH* chemiluminescence imaging were performed over a range of equivalence ratios and combustor pressures to study the influence of fuel temperature on the flow and flame structure. The main flame was found to move upstream as the fuel was heated, while no changes in the pilot flame location were observed in the field of view at the exit of the injector. The upstream shift of the main flame corresponded to a local increase in the axial velocity, which caused the shear layer between the pilot/main flames and the central recirculation zone to move downstream. Direct comparison of the mean velocity fields relative to the mean flame location showed that heating the fuel caused the velocity normal to the flame front to increase, which is indicative of an increase in flame speed. The changes to the fuel injection and chemical kinetics help explain the local changes to the flow and flame structure, which contribute to an overall increase in combustion efficiency as well as NO_x emissions.</div><div> </div><div><br></div><div>Lastly, the effect of fuel injection temperature on the presence of an 800 Hz combustion instability in the COMRAD experiment was investigated. High-frequency pressure and high-speed chemiluminescence measurements revealed a decrease in the instability amplitude as the fuel was heated. The coupling between the fuel flow and the unsteady heat release was studied using independent 10 kHz stereoscopic particle image velocimetry and 10 kHz Mie scattering measurements. The variations in the fuel flow entering the combustor over the acoustic cycle decreased as the instability amplitude weakened. 100 kHz burst-mode, two-component particle image velocimetry was then applied to the unstable condition with ambient temperature fuel. This measurement was capable of resolving both the large-scale changes to the structure of the inner recirculation zone occurring at 800 Hz as well as the time-evolution of small-scale vortex structures. The vortices were shown to correspond to a characteristic frequency in the range of 4-5.5 kHz, and the strength of the vortex structures fluctuated with the global 800 Hz combustion dynamics. These results highlight the importance of performing measurements capable of resolving the wide range of scales present in the flow-fields typical of gas turbine combustors to improve current understanding of flame-flow coupling mechanisms.</div>

O biodiesel pode ser obtido a partir de óleos vegetais, gorduras animais ou óleos residuais por meio de reação com etanol ou metanol e destaca-se entre as fontes renováveis de energia apontadas como solução para aumentar a segurança no suprimento de energia e minimizar alguns problemas ambientais decorrentes do uso de combustíveis derivados do petróleo.Torna-se necessário então, avaliar as propriedades dos diferentes tipos de biodiesel obtidos a partir de diferentes matérias-primas e processos que convergem ou divergem das especificações requeridas, quais são as desvantagens do ponto de vista ambiental e de desempenho do motor e suas possíveis soluções. Este trabalho teve por objetivo estudar os aspectos técnicos e ambientais relacionados ao seu uso em motores de combustão. / The Biodiesel can be produced from vegetal oils, animal fats or residual oils by means of reaction with ethanol or methanol and is detached among the renewable sources of energy as a solution to increase the security in the energy suppliment and to minimize some decurrent environment problems from the use of fossie fuels. Thus, it?s necessary to evaluate the trends for the specifications of fuels, which properties of biodiesel converge or not of the required specifications, which are the disadvantages of the environment and performance engine and its possible solutions. The object of this work had been to study the technical and environment aspects related about its use in combustion engine.

O biodiesel pode ser obtido a partir de óleos vegetais, gorduras animais ou óleos residuais por meio de reação com etanol ou metanol e destaca-se entre as fontes renováveis de energia apontadas como solução para aumentar a segurança no suprimento de energia e minimizar alguns problemas ambientais decorrentes do uso de combustíveis derivados do petróleo.Torna-se necessário então, avaliar as propriedades dos diferentes tipos de biodiesel obtidos a partir de diferentes matérias-primas e processos que convergem ou divergem das especificações requeridas, quais são as desvantagens do ponto de vista ambiental e de desempenho do motor e suas possíveis soluções. Este trabalho teve por objetivo estudar os aspectos técnicos e ambientais relacionados ao seu uso em motores de combustão. / The Biodiesel can be produced from vegetal oils, animal fats or residual oils by means of reaction with ethanol or methanol and is detached among the renewable sources of energy as a solution to increase the security in the energy suppliment and to minimize some decurrent environment problems from the use of fossie fuels. Thus, it?s necessary to evaluate the trends for the specifications of fuels, which properties of biodiesel converge or not of the required specifications, which are the disadvantages of the environment and performance engine and its possible solutions. The object of this work had been to study the technical and environment aspects related about its use in combustion engine.