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.

Energetic materials encompass a wide range of chemical compounds all associated with a significant risk of fire and explosion. They include explosives, fireworks, pyrotechnics, powders, propellants and other unsteady chemicals. These materials store a high level of chemical energy and are able to release it rapidly without external contribution of oxygen or any other oxidizer. The behaviour of these materials in case of explosive detonations is relatively wellknown from empirical and practical points of view. However, fundamental scientific questions remain unanswered related to the mechanisms of heat release. The current understanding of these mechanisms lacks appropriate thermochemical characterisation. The aim of the study is the analysis of thermal and chemical characteristics of energetic materials under conditions that exclude detonations. Detonation is excluded in order to better isolate the thermal and chemical mechanisms involved in the burning process. The experimental work has been conducted using the FM Global Fire Propagation Apparatus (FPA) [ASTM E2058‐03]. One of the benefits of using this experimental apparatus rather than the Cone Calorimeter is that it allows controlling the feed of heat and oxidizer to the reaction zone. The material chosen to conduct experiments on is a ternary smoke powder based on a mixture of starch and lactose as fuel components and potassium nitrate as oxidizer. This product is currently used by fire brigades to assess smoke venting systems efficiency of buildings. The kinetics associated with the combustion of the material was assessed slow enough to allow measuring instruments to capture the thermal and chemical evolution during combustion reaction. Thermal analysis has first been carried out by means of DSC, TGA, DTA, MS and FTIR data in order to understand the decomposition of the material and its energetic evolution when undergoing heating. However, if the latter methods help defining the decomposing path of the material, they do not provide an integral view of its combustion behaviour, in particular, the emissions of toxics which are kinetic path dependent. Subsequently, combustion tests have been carried out using the FPA. Its ability to capture the evolution of gases emissions formed during the reaction has been proved. The influence of two configuration parameters on the combustion behaviour and on the gaseous emissions of the material has been investigated. The proportion fuel/oxidizer has been varied as well as the composition of the reacting atmosphere. Results shows that the quantity of oxidizer in the material affects the kinetics of the reactions taking place in the condense phase. Increasing the concentration of potassium nitrate in the mixture enhanced the reaction rate of the smouldering combustion. Higher quantity of volatiles is released which favoured the initiation of a diffusion flame regime in the gaseous phase, above the sample. While the kinetics of the condense phase is governed by the oxidizer concentration, experiments show that the flaming regime is influenced by the concentration of oxygen (O2) in the reacting atmosphere. A transition from diffusion to premixed flame is found when the concentration of O2 surrounding the sample is reduced below 18%. An analytical model has been used to explain the existence of a transition for a critical O2 concentration. Finally, thermal and combustion analyses have allowed to characterise the behaviour of the material under critical conditions, in terms of decomposition taking place in the condense phase but also potential toxic emissions that can be released. Toxicity, kinetics, temperature evolution do not provide a complete view of the combustion phenomenon. Beside these elements that characterise the behaviour of a material for given conditions as well as also the degree of fire hazard encountered, the energetic issue holds as an essential feature that cannot be neglected. The heat release rate (HRR) is a critical parameter that defines a fire. It does not constitute an intrinsic material property but it describes the energetic response of the couple formed by the material and its environment. Oxygen Consumption calorimetry (OC) and Carbon Dioxide Generation calorimetry (CDG) are widespread methods to calculate the HRR resulting from a combustion reaction. Apparatuses such as the FPA or the cone calorimeter have already proved their potential to qualify the burning behaviour of common fuels in addition to polymers when their data are combined with an adapted calorimetric procedure. The same approach has been applied to energetic materials. However, prior to using these techniques, it is fundamental to have identified their restrictions. These techniques provide approximate estimations of the HRR. Results are affected by the propagation of uncertainties. Several sources of uncertainties can be found. One can cite: 1. Uncertainties associated with the sample material; 2. Uncertainties associated with the test conditions; 3. Uncertainties associated with the measurements; 4. Uncertainties associated with calculation assumptions. If uncertainties cannot always be estimated, the three first sources cited have received attention in the past from the scientific community, alike the last one. The restrictions associated with the assumptions developed for using the OC and CDG principles have to be clarified. The limits of validity of the hypotheses have to be clearly defined. In particular, the present dissertation questions the relevance of the energy constants that have been specified for OC and CDG as well as their related uncertainties. One of the purposes of the research deals with the ability to estimate accurate error bars for the calculation of the HRR. Once uncertainties related to the calorimetric methods are assessed, a method adapted from the basic OC and CDG principles is introduced that allows estimating the HRR of energetic materials. The approach is based on considering the chemical decomposition of the burning compound and defining a fictitious molecule for which energy coefficients can be calculated. Nevertheless, it requires the material to be known. Finally, the question of the advantage brought by these techniques over others, in terms of accuracy, is discussed within the framework of unconventional products, such as energetic materials or compounds whose composition is ignored. The results from this work will contribute to the development of fireanalysis methodologies and validate their use with energetic materials.

Biodiesel is an alternative fuel that can be produced from a variety of lipid feedstocks. It has a number of perceived advantages over conventional petroleum diesel and as a result world production of biodiesel has increased dramatically since the turn of the century. Amongst its reported disadvantages is a widely observed increase in emissions of oxides of nitrogen, or NOx. Several explanations have been proposed for this phenomenon; in reality it is likely to be due to a combination of factors. The interplay of multiple factors affecting NOx emissions means that the increase in NOx when fuelling on biodiesel is not consistent or ubiquitous, but is instead dependent upon operating conditions and the specifics of the fuels being compared. The work documented in this thesis explores the nature and causes of the change in NOx emissions associated with biodiesel. The intention was that, by adjusting operating conditions, and using a wide range of fuels, doped with additives to achieve an even broader range of combustion characteristics, the impact of important variables would be made clearer, making it possible to reduce the problem to its lowest common denominators. In early experiments it was found that NOx emissions from biodiesel tended to be lower than those of petrodiesel under conditions where combustion was relatively highly premixed, but higher under more conventional diesel conditions where diffusion combustion constituted a larger proportion of heat release. The main experimental set revealed a definite increase in NOx emissions when fuelling on biodiesel, for a fixed start of combustion and equivalent degree of premixing. The addition of an oxygenate to petrodiesel elicited comparable NOx emissions to biodiesel, as a function of fuel-bound oxygen content; the data implies that the like-for-like biodiesel NOx increase may be a direct result of fuelbound oxygen. However, the like-for-like biodiesel NOx increase varies dependent upon operating conditions. In part, this may be related to higher apparent heat release rate (AHRR) through the diffusion burn phase when fuelling on biodiesel. This may result from the extended biodiesel injection duration. Across operating conditions, the extent to which smoke emissions when fuelling on petrodiesel exceeded those when fuelling on biodiesel was generally correlated with the magnitude of the biodiesel NOx increase; where the difference in smoke emissions was small, the biodiesel NOx increase was small, and where the difference in smoke emissions was more substantial, so was the difference in NOx emissions. This suggests a possible connection to changes in mixture stoichiometry. When differentiating between fuels, increased cetane number reduces NOx, and increased oxygen content increases NOx. Biodiesel does not necessarily have higher NOx emissions than petrodiesel: the biodiesel NOx increase exists where the difference in cetane number is insuffi cient to counteract the effects of fuel-bound oxygen content.

É analisado o desempenho de um motor de ignição por compressão turboalimentado por uma mistura temária de combustíveis (diesel, biodiesel e etanol) através do comportamento do motor operando com um combustível principal, o qual poderá ser o diesel ou biodiesel ou misturas destes dois, com e sem sua substituição parcial por etanol no coletor de admissão. A análise do desempenho é feita através das curvas de torque, potência, rendimento térmico e consumo específico de combustível. A combustão do motor é estudada através de um programa simulador que utiliza um modelo zero-dimensional, que avalia a taxa de liberação de calor durante a combustão e tem como dado de entrada a curva de evolução da pressão dentro do cilindro. Faz-se a identificação e quantificação do fenômeno da detonação utilizando análise espectral, através do sinal de pressão da câmara de combustão, para o motor operando com diversas misturas combustíveis. São analisadas também as emissões gasosas do motor com as misturas, e a viabilidade técnica do uso de biodiesel em motores de ignição por compressão, além de um estudo geral sobre o uso do éster de óleo vegetal. / The performance of a three-fuel system (diesel, biodiesel and ethanol) turbocharged compression-ignition engine is analyzed, through the engine behavior supplied by mixtures of diesel or biodiesel or mixtures of these fuels with ethanol in the intake manifold. The performance analysis is made by torque, power, specific fuel consumption and thermal efficiency curves. The engine combustion is studied by a simulator program that uses a zero-dimensional model, that evaluate the heat release rate during the combustion and it has as input data the pressure evolution curves inside the cylinder. The knocking phenomenon is studied by spectral analysis. The pollutant gases emissions and the technical viability of the utilization of biodiesel also are analyzed, beyond a general study about of vegetal oil ester.

É analisado o desempenho de um motor de ignição por compressão turboalimentado por uma mistura temária de combustíveis (diesel, biodiesel e etanol) através do comportamento do motor operando com um combustível principal, o qual poderá ser o diesel ou biodiesel ou misturas destes dois, com e sem sua substituição parcial por etanol no coletor de admissão. A análise do desempenho é feita através das curvas de torque, potência, rendimento térmico e consumo específico de combustível. A combustão do motor é estudada através de um programa simulador que utiliza um modelo zero-dimensional, que avalia a taxa de liberação de calor durante a combustão e tem como dado de entrada a curva de evolução da pressão dentro do cilindro. Faz-se a identificação e quantificação do fenômeno da detonação utilizando análise espectral, através do sinal de pressão da câmara de combustão, para o motor operando com diversas misturas combustíveis. São analisadas também as emissões gasosas do motor com as misturas, e a viabilidade técnica do uso de biodiesel em motores de ignição por compressão, além de um estudo geral sobre o uso do éster de óleo vegetal. / The performance of a three-fuel system (diesel, biodiesel and ethanol) turbocharged compression-ignition engine is analyzed, through the engine behavior supplied by mixtures of diesel or biodiesel or mixtures of these fuels with ethanol in the intake manifold. The performance analysis is made by torque, power, specific fuel consumption and thermal efficiency curves. The engine combustion is studied by a simulator program that uses a zero-dimensional model, that evaluate the heat release rate during the combustion and it has as input data the pressure evolution curves inside the cylinder. The knocking phenomenon is studied by spectral analysis. The pollutant gases emissions and the technical viability of the utilization of biodiesel also are analyzed, beyond a general study about of vegetal oil ester.

Cylinder pressure modeling and heat release analysis are today important and standard tools for engineers and researchers, when developing and tuning new engines. Being able to accurately model and extract information from the cylinder pressure is important for the interpretation and validity of the result. The first part of the thesis treats single-zone cylinder pressure modeling, where the specific heat ratio model constitutes a key part. This model component is therefore investigated more thoroughly. For the purpose of reference, the specific heat ratio is calculated for burned and unburned gases, assuming that the unburned mixture is frozen and that the burned mixture is at chemical equilibrium. Use of the reference model in heat release analysis is too time consuming and therefore a set of simpler models, both existing and newly developed, are compared to the reference model. A two-zone mean temperature model and the Vibe function are used to parameterize the mass fraction burned. The mass fraction burned is used to interpolate the specific heats for the unburned and burned mixture, and to form the specific heat ratio, which renders a cylinder pressure modeling error in the same order as the measurement noise, and fifteen times smaller than the model originally suggested in Gatowski et al. (1984). The computational time is increased with 40 % compared to the original setting, but reduced by a factor 70 compared to precomputed tables from the full equilibrium program. The specific heats for the unburned mixture are captured within 0.2 % by linear functions, and the specific heats for the burned mixture are captured within 1 % by higher-order polynomials for the major operating range of a spark ignited (SI) engine. In the second part, four methods for compression ratio estimation based on cylinder pressure traces are developed and evaluated for both simulated and experimental cycles. Three methods rely upon a model of polytropic compression for the cylinder pressure. It is shown that they give a good estimate of the compression ratio at low compression ratios, although the estimates are biased. A method based on a variable projection algorithm with a logarithmic norm of the cylinder pressure yields the smallest confidence intervals and shortest computational time for these three methods. This method is recommended when computational time is an important issue. The polytropic pressure model lacks information about heat transfer and therefore the estimation bias increases with the compression ratio. The fourth method includes heat transfer, crevice effects, and a commonly used heat release model for firing cycles. This method estimates the compression ratio more accurately in terms of bias and variance. The method is more computationally demanding and thus recommended when estimation accuracy is the most important property. In order to estimate the compression ratio as accurately as possible, motored cycles with as high initial pressure as possible should be used. The objective in part 3 is to develop an estimation tool for heat release analysis that is accurate, systematic and efficient. Two methods that incorporate prior knowledge of the parameter nominal value and uncertainty in a systematic manner are presented and evaluated. Method 1 is based on using a singular value decomposition of the estimated hessian, to reduce the number of estimated parameters one-by-one. Then the suggested number of parameters to use is found as the one minimizing the Akaike final prediction error. Method 2 uses a regularization technique to include the prior knowledge in the criterion function. Method 2 gives more accurate estimates than method 1. For method 2, prior knowledge with individually set parameter uncertainties yields more accurate and robust estimates. Once a choice of parameter uncertainty has been done, no user interaction is needed. Method 2 is then formulated for three different versions, which differ in how they determine how strong the regularization should be. The quickest version is based on ad-hoc tuning and should be used when computational time is important. Another version is more accurate and flexible to changing operating conditions, but is more computationally demanding.

Flexible polyurethane foam (PUF) is a very versatile material ever created. The material is used for various applications and consumer end-use products such as upholstered furniture and mattresses. The increased use of these polymeric materials causes fire safety concerns. This has led to the development of various regulations and flammability test standards aimed at addressing the hazards associated with polyurethane foam fires. Several fire protection engineering correlations and thermal models have also been developed for the simulation of fire growth behaviour of polyurethane foams. Thus, the overall objective of this research project is to investigate the laboratory test behaviour of this material and then use finer modeling techniques to predict the heat release rate of the specimens, based on information obtained from cone calorimeter tests.<p> Full-scale fire tests of 10 cm thick polyurethane foams of different sizes were conducted using center and edge-ignition locations. Flame spread and heat release rates were compared. For specimens of the same size, center-ignition tests produced flame areas and peak heat release rates which were respectively 10 and 20% larger compared to edge-ignition tests. Average flame spread rates for horizontal and vertical spread were determined, and results showed excellent agreement with literature. Cone calorimeter tests of the specimens were performed using steel edge frame and open durarock board. Results indicate that different test arrangements and heat sources have significant effects on the fire behaviour of the specimens.<p> Predictions using the integral convolution model and other fire protection engineering correlations were compared with the full-scale tests results. Results show that the model was more efficient in predicting the heat release rates for edge-ignition tests than the center-ignition tests. The model also was more successful in predicting the heat release rates during the early part of the growth phase than during the later stages of the fire. The predicted and measured peak heat release rates and total heat release were within 10-15% of one another. Flame spread and t-squared fire models also gave satisfactory predictions of the full-scale fire behaviour of the specimens.

Flexible polyurethane foam (PUF) is a very versatile material ever created. The material is used for various applications and consumer end-use products such as upholstered furniture and mattresses. The increased use of these polymeric materials causes fire safety concerns. This has led to the development of various regulations and flammability test standards aimed at addressing the hazards associated with polyurethane foam fires. Several fire protection engineering correlations and thermal models have also been developed for the simulation of fire growth behaviour of polyurethane foams. Thus, the overall objective of this research project is to investigate the laboratory test behaviour of this material and then use finer modeling techniques to predict the heat release rate of the specimens, based on information obtained from cone calorimeter tests.<p> Full-scale fire tests of 10 cm thick polyurethane foams of different sizes were conducted using center and edge-ignition locations. Flame spread and heat release rates were compared. For specimens of the same size, center-ignition tests produced flame areas and peak heat release rates which were respectively 10 and 20% larger compared to edge-ignition tests. Average flame spread rates for horizontal and vertical spread were determined, and results showed excellent agreement with literature. Cone calorimeter tests of the specimens were performed using steel edge frame and open durarock board. Results indicate that different test arrangements and heat sources have significant effects on the fire behaviour of the specimens.<p> Predictions using the integral convolution model and other fire protection engineering correlations were compared with the full-scale tests results. Results show that the model was more efficient in predicting the heat release rates for edge-ignition tests than the center-ignition tests. The model also was more successful in predicting the heat release rates during the early part of the growth phase than during the later stages of the fire. The predicted and measured peak heat release rates and total heat release were within 10-15% of one another. Flame spread and t-squared fire models also gave satisfactory predictions of the full-scale fire behaviour of the specimens.

Modeling the Response of Premixed Flames to Flow Disturbances Preetham 178 pages Directed by Dr. Tim Lieuwen Low emissions combustion systems for land based gas turbines rely on a premixed or partially premixed combustion process. These systems are exceptionally prone to combustion instabilities which are destructive to hardware and adversely affect performance and emissions. The success of dynamics prediction codes is critically dependent on the heat release model which couples the flame dynamics to the system acoustics. So the principal objective of the current research work is to predict the heat release response of premixed flames and to isolate the key non-dimensional parameters which characterize its linear and nonlinear dynamics. Explicit analytical solutions of the G- equation are derived in the linear and weakly nonlinear regime using the Small Perturbation Method (SPM). For the fully nonlinear case, the flame-flow interaction effects are captured by developing an unsteady, compressible, coupled Euler-G-equation solver with a Ghost Fluid Method (GFM) module for applying the jump conditions across the flame. The flame s nonlinear response is shown to exhibit two qualitatively different behaviors. Depending on the operating conditions and the disturbance field characteristics, it is shown that a combustor may exhibit supercritical bifurcations leading to a single stable limit cycle amplitude or exhibit sub-critical bifurcations wherein multiple stable solutions for the instability amplitude are possible. In addition, this study presents the first analytical model which captures the effects of unsteady flame stretch on the heat release response and thus extends the applicability of current models to high frequency instabilities, such as occurring during screech. It is shown that unsteady stretch effects, negligible at low frequencies (100 s of Hz) become significant at screeching frequencies (1000 s of Hz). Furthermore, the analysis also yields insight into the significant spatial dependence of the mean and perturbation velocity field induced by the coupling between the flame and the flow field. In order to meaningfully compare the heat release response across different flame configurations, this study has identified that the reference velocity (for defining the transfer function) should be based on the effective normal velocity perturbing the flame and the Strouhal number should be based on the effective residence time of the flame wrinkles.

Uma maneira ecologicamente correta de manejar os recursos energéticos disponíveis e reduzir as emissões de gases de efeito estufa é utilizar biocombustíveis ao invés de combustíveis de origem fóssil em motores de combustão interna. Entretanto, o preço mais alto dos biocombustíveis pode ser um fator limitante para o aumento e viabilização do seu uso. Em relação ao etanol, para se obter misturas com mais de 80% de etanol em água o custo de produção cresce exponencialmente. Assim, se misturas de etanol com alto percentual de água, de menor custo, puderem ser utilizadas em motores de combustão interna com sucesso, esse combustível pode se tornar mais atrativo e mais amplamente utilizado. Este trabalho analisa o desempenho de um motor de ignição por centelha operando com etanol em diferentes percentuais de hidratação, através de simulações computacionais e procedimentos experimentais. Foi utilizado um motor monocilíndrico de 0,668L e naturalmente aspirado, com relação de compressão de 19:1 e injeção direta em pré-câmara, ciclo Diesel, foi modificado para operação em ciclo Otto - injeção de combustível no duto de admissão e relação de compressão de 12:1. Testes em dinamômetro foram conduzidos com o etanol hidratado comercial (95% de etanol e 5% de água) e com misturas de etanol e água com maiores percentuais de hidratação (conteúdo volumétrico de até 60% de etanol e 40% de água). Simulação computacional através de software de volumes finitos unidimensional foi utilizada para realizar a análise da combustão. Foi possível alcançar operação estável com misturas de até 40% de água em etanol e ocorreu aumento de eficiência térmica para misturas de até 30% de água. / An environmentally friendly way to manage the available energetic resources and to reduce greenhouse gas emissions is to use bio instead of fossil fuels in internal combustion engines. However, the sometimes higher prices of biofuels can be a limiting factor for their widespread and viable use. Concerning ethanol and its production costs, to obtain above 80% ethanol-in-water mixtures demands an exponentially increasing energy supply. Hence, if a low-cost high water content ethanol could be successfully burned in internal combustion engines it would be even more attractive and extensively used. This work analyzes the performance of a spark ignition engine running with ethanol with different percentages of hydration through numeric and experimental simulations. To achieve this goal, a 0,668L naturally aspirated single cylinder engine, with compression ratio of 19:1 and pre-chamber direct injection, operating at Diesel cycle was modified to operate in Otto cycle - port fuel injection, with a compression ratio of 12:1. Dynamometer tests were carried out with commercial hydrous ethanol (95% ethanol and 5% water) and water-in-ethanol blends with higher hydration levels (volumetric content up to 60% ethanol and 40% water). Computer simulation through one-dimensional finite volume software was carried out to perform a heat release analysis. It was possible to achieve stable operation with up to 40% water-in-ethanol blends and thermal efficiency increase was achieved for blends with up to 30% of water.