<p>A novel two-loop estimation and control strategy is proposed to reduce the natural gas (NG) spark-ignition (SI) engine tail pipe emissions, with focus on the outer loop development. In the outer loop, an fractional oxidation state (FOS) estimator consisting of a three-way catalyst (TWC) model and an extended Kalman-filter is used to estimate the real-time TWC's FOS, and a robust controller is used to control the first-half TWC's FOS by manipulating the desired engine lambda (i.e., air–fuel equivalence ratio; lambda=1 at stoichiometry). The outer loop estimator and controller are combined with an industry-production baseline inner loop controller, which controls the engine $\lambda$ based on the desired lambda value. This novel two-loop control strategy reduces more CH4 and NOx emissions over no-outer-loop control strategy and the conventional two-loop control strategies through simulation. </p> <p><br></p> <p>Engine with and without fuel cut-off are both investigated. Although fuel cut-off brings better fuel economy, it also over-oxidizes the TWC during fuel cut events, which makes the FOS-based controller's competence in NOx reduction over non-FOS-based controllers less significant. By comparing simulation results with and without fuel cut-off, it shows huge potential for much better emission result if fuel cut-off's side effect can be alleviated. Considering that fuel cut-off generally being cutting engine fueling during zero load periods and introducing unreacted oxygen into the after-treatment system, the best way of dealing with the issue is to cut off or reduce the oxygen input to the TWC during those events. Several advanced engine technologies such as cylinder deactivation and exhaust gas re-circulation are good candidates to approach this issue. </p> <p><br></p> <p>An industry-production Cummins B6.7N natural gas SI engine was installed in the Ray W. Herrick Laboratories for study of variable valve actuation (VVA) technology, for the purpose of evaluating/improving SI engine's fuel efficiency, emission reduction, and engine knock resistance. A one-dimensional, physics-based natural gas SI engine model was investigated and calibrated in GT-Power software. To calculate the burn rates in the cylinder, three different pressure analysis methods were investigated and implemented. It is observed that all six cylinders' pressure curves are different, which in turn render different burn rates cylinder-to-cylinder. Cylinder with a higher peak cylinder pressure has a faster burn rate. Each operating condition has its unique pressure curve, and their burn rates are different under different operating conditions. Considering that the burn rate profile can vary cylinder-to-cylinder and operation-to-operation, to make the GT combustion model work for a larger range of loads, a fixed burn rate model may help in the preliminary research phase, but a predictive combustion model is more preferable.</p> <p><br></p> <p>The GT-Power model's VVA capability is investigated, where intake valve closure (IVC) modulation and cylinder de-activation (CDA) are built and analyzed. To mitigate TWC's over-oxidation issue during engine's fuel cut-off events, the CDA is implemented and simulated to demonstrate its benefit on further emission and fuel consumption reductions.</p>

Bioenergy contributes significantly towards the share of renewable energies, in Europe and worldwide. Besides solid and liquid biofuels, gaseous biofuels, such as biogas or upgraded biogas (biomethane), are an established renewable fuel in Europe. Although many studies consider biomethane technologies, feedstock potentials, or sustainability issues, the literature on the required legislative framework for market introduction is limited. Therefore, this research aims at identifying the market and legislative framework conditions in the three leading biomethane markets in Europe and compare them to the framework conditions of the top six non-European biomethane markets. This study shows the global status and national differences in promoting this renewable energy carrier. For the cross-country comparison, a systematic and iterative literature review is conducted. The results show the top three European biomethane markets (Germany, United Kingdom, Sweden) and the six non-European biomethane markets (Brazil, Canada, China, Japan, South Korea, and the United States of America), pursuing different promotion approaches and framework conditions. Noteworthy cross-national findings are the role of state-level incentives, the tendency to utilise biomethane as vehicular fuel and the focus on residues and waste as feedstock for biomethane production. Presenting a cross-country comparison, this study supports cross-country learning for the promotion of renewable energies like biomethane and gives a pertinent overview of the work.

A key factor for driving the shift towards sustainable transportation systems is alternative fuels, where compressed natural gas (CNG) is a beneficial alternative to the conventional fossil fuels with respect to greenhouse gas emissions. A fuel system is needed for heavy-duty natural gas vehicles, in order to transport the highly pressurized gas from the fuel tanks to the internal combustion engine. The fuel system can be contaminated from several different sources – carry-over compressor oil from refuelling stations, water already present in the gas, manufacturing residuals and road dust entering the fuel system via the receptacle valve. The contaminants can induce fuel system failure modes, leading to poor engine performance, increased emissions or gas pressures above component pressure ratings. The objective of this thesis was to develop an accelerated test method to evaluate CNG fuel system robustness against contamination, to be able to prevent CNG fuel system failures and to ensure a high-quality product. The experimental setup was developed to be installed on a truck in order to utilize already present surrounding systems. The setup enables performance testing of six out of nine components belonging to the fuel system, which can be tested individually or combined in an arbitrary way. The setup induces premature failure modes primarily through excessive contamination in a controlled manner. An experimental procedure has been developed as a complement. Validation of metrics through testing is needed before the test method can be considered finalized. / En nyckelfaktor för att driva omställning mot hållbara transportsystem är alternativa bränslen, varpå naturgas (CNG) är ett slagkraftigt alternativ till konventionella fossila bränslen med avseende på utsläpp av växthusgaser. För att kunna transportera den högt trycksatta gasen från bränsletankarna till förbränningsmotorn krävs ett bränslesystem för tunga naturgasfordon. Bränslesystemet kan kontamineras genom ett flertal olika källor – överförd kompressorolja från tankstationer, vatten som redan finns i gasen, tillverkningsrester och vägdamm eller grus som tar sig in i systemet genom bränslepåfyllningsventilen. Kontamineringen kan ge upphov till felmoder i bränslesystemet, vilket leder till låg motorpresentanda, ökade utsläpp eller övertryck i systemet. Syftet med examensarbetet var att utveckla en accelererad testmetod för att utvärdera CNG-bränslesystems robusthet mot kontaminering, för att kunna förebygga systemfel och säkerställa en högkvalitativ produkt. Den experimentella uppställningen utvecklades för att monteras på lastbil, för att på så vis nyttja de kringliggande befintliga systemen. Uppställningen möjliggör prestandaprovning av sex av nio komponenter som tillhör bränslesystemet, som kan testas individuellt eller kombineras på ett godtyckligt sätt. Uppställningen framkallar tidiga felmoder, huvudsakligen genom excessiv kontaminering på ett kontrollerat vis. En metodbeskrivning har utvecklats som ett komplement till den experimentella uppställningen. Validering av metrik genom testning är nödvändigt för att finna testmetoden färdigställd.

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[pt] Na exploração de campos offshore, é frequente a necessidade transportar óleo e gás por dutos de produção ou de transferência que percorrem grandes distâncias no leito submarino. Em relação aos gasodutos, podem ocorrer a formação de condensado ao longo desses, o que afeta drasticamente a capacidade de entrega e a modalidade operacional, sendo a remoção do condensado realizada por pigs. Além disso, devido a existência de condições extremas como baixas temperaturas e altas pressões, pode ocorrer a formação de plug de hidrato nos gasodutos. Nesse caso, são previstas operações especiais para a remoção do plug de hidrato, onde, durante o procedimento, pode ser gerado condensado. Dessa forma, é importante que essas operações sejam simuladas durante a fase de projeto e de operação para avaliar a efetividade dos procedimentos e os valores das variáveis de processo de forma a garantir a segurança operacional do sistema. O objetivo deste estudo é investigar numericamente o processo de deslocamento de pigs e de plugs de hidrato ao longo de tubulações, na presença de condensado. A formação de condensado é obtida através de um modelo de equilíbrio de fases, que utiliza a equação de Peng-Robinson para o cálculo das propriedades termodinâmicas para ambas as fases. O escoamento bifásico é modelado como unidimensional. A solução das equações de conservação de massa, quantidade de movimento linear e energia, acopladas ao balanço de forças para prever o deslocamento do pig/plug são resolvidas utilizando o método numérico de diferenças finitas. A modelagem do escoamento e do modelo termodinâmico, englobando o equilíbrio de fases e as propriedades termodinâmicas, foram validadas com soluções analíticas e dados da literatura. Estudos de casos de deslocamento de pig e de plug de hidrato na presença de condensado foram realizados e os resultados obtidos foram bastante satisfatórios, permitindo concluir que os modelos desenvolvidos podem ser utilizados para a análise e previsão das operações de passagem de pig e de remoção de plugs de hidrato na presença de condensado. / [en] In offshore oilfield exploration, gas is often transported through long-distance transfer pipelines or production pipelines on the seabed. Along the pipeline, condensate may be formed, which dramatically affect the delivery capacity and the operational mode, requiring condensate removal employing pigs. Further, due to the presence of extreme conditions encountered in these pipelines, such as low temperatures and high pressures, hydrate plug can also be formed inside the gas pipelines. In this case, special procedures are foreseen to remove the hydrate plug, during which condensate may be generated. Thus, it is essential that these operations should be simulated throughout the design and operation stages to evaluate the efficacy of these procedures and the process variable values in order to guarantee the system s operational safety. The purpose of this study is to investigate numerically the process of displacement of pigs and hydrate plugs along pipelines, in the presence of condensate. The condensate formation is obtained through a phase behavior model (FLASH), which employs the Peng-Robinson equation to calculate the thermodynamic properties for both phases. Two-phase flow is modeled as one-dimensional. The conservation equations of mass, linear momentum and energy, coupled with the force balance to predict the displacement of the pig/plug are solved, using the numerical method of finite differences. The flow and thermodynamic models were validated with analytical solutions and literature data. The validation of the thermodynamic model included the phase equilibrium and thermodynamic properties. Case studies of displacement of pig and hydrate plug in the presence of condensate were performed and the results obtained were very satisfactory, allowing to conclude that the developed models can be used for the analysis and prediction of the pigging operations and removal of hydrate plugs in the presence of condensate.

[pt] O gás natural liquefeito (GNL) tem importante papel na cadeia de suprimento de gás natural e energia elétrica no país. No Brasil, o produto importado visa prioritariamente o atendimento da demanda termelétrica para este insumo. O modelo de geração termelétrico é flexível e a característica principal deste modelo é a necessidade de se garantir uma oferta de combustível flexível para usinas que deverão suprir uma demanda termelétrica igualmente flexível. O objetivo deste trabalho é modelar e avaliar o desempenho de um modelo causal de regressão dinâmica em previsões de demandas de GNL, de longo prazo, para o atendimento das usinas termo-elétricas a gás natural e comparar a capacidade preditiva com modelos tradicionais univariados, vastamente discutidos na literatura, como o ARIMA e o amortecimento exponencial. Foram estabelecidos cenários da variável explicativa a fim de avaliar como tais cenários influenciam a demanda do GNL. O produto desenvolvido nessa dissertação mostrou a viabilidade dos modelos causais serem utilizados como ferramenta para a simulação da demanda de GNL considerando cenários das variáveis causais What if analysis. / [en] Liquefied natural gas (LNG) plays an important role in the country s natural gas and electricity supply chain. In Brazil, the imported product primarily targets the supply of thermoelectric demand for this input. The thermoelectric generation model is flexible and the main characteristic of this model is the need to guarantee a flexible fuel supply for plants that must meet an equally flexible thermoelectric demand. The objective of this work is modeling and evaluate the performance of a causal dynamic regression model in long-term LNG demand forecasts, for supplying of natural gas thermoelectric plants and to compare the predictive capacity with traditional models widely discussed in the literature, such as the ARIMA and the dynamic regression model. Scenarios of the explanatory variable were established in order to evaluate how the explanatory variables influences LNG demand. The product developed in this dissertation showed the viability of causal models to be used as a tool for the simulation of LNG demand considering scenarios of the causal variables. What if analysis.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo do presente trabalho é apresentar um estudo sobre o equilíbrio de fases sólido-líquido-vapor para hidratos de metano. A análise do equilíbrio trifásico sólido-líquido-vapor tem encontrado diversas aplicações para sistemas hidrocarboneto-água, uma vez que permite, por exemplo, a determinação da região de estabilidade de hidratos de metano e hidratos de gás natural. Inicialmente foi feita uma pesquisa sobre o estado da arte no que diz respeito ao comportamento termodinâmico e equilíbrio de fases de hidratos. Foram implementados os modelos apresentados por Ballard (2002) e Zhang et al. (2005). A proposta de Zhang et al. (2005) é aplicável para equilíbrios de fases a temperaturas abaixo de 300 K. Sua abordagem combinou a teoria de van der Waals e Platteeuw para a fase hidrato com a equação do estado de Peng-Robinson (1976) modificada por Stryjek e Vera (1986) para ambas as fases fluidas (fase vapor e fase aquosa). A abordagem de Ballard (2000) considerou a distorção do hidrato do seu estado padrão, o que fornece uma exata composição do hidrato e melhora a previsão da formação dos hidratos a altas pressões. Ao esclarecer a mudança de volume no hidrato, o raio da gaiola do hidrato é uma função do seu volume. Com isso, Ballard propôs uma nova abordagem considerando tal variação de volume e gerou um equilíbrio de fases em uma rotina de flash multifásico através da minimização da energia livre de Gibbs. Assim, o presente trabalho apresenta as abordagens de Zhang et al. (2005) e Ballard (2002) para o comportamento termodinâmico de hidratos e faz uma análise e comparação entre eles. Para resolver o problema do flash computacionalmente, foi utilizada a ferramenta lsqnonlin (built-in do software MATLAB). O lsqnonlin é um algoritmo baseado no método de Levenberg-Marquadt. / The objective of the present work is to present a study of solid-vapor-liquid three-phase equilibrium for methane hydrates. The analysis of three-phase equilibrium has several applications for water-hydrocarbon systems, since it permits, for example, determination of stability region for methane hydrates and natural gas hydrates. We have started seeking in literature about the state-of-art for thermodynamic behaviour and phase equilibrium for hydrates. And then the models proposed by Ballard (2002) and Zhang et al. (2005) were implemented. Zhang et al. (2005) have proposed a phase equilibrium for single-guest gas hydrates at temperatures below 300 K. Their approach has combined the van der WaalsPlatteeuw theory for the hydrate phase and the PengRobinson equation of state for both fluid phases (vapor and aqueous phase) (1976) modified by Stryjek and Vera (1986). Ballards (2000) approach has allowed the hydrate distortion from its standard state and has gave a more accurate composition of the hydrate and has improved hydrate formation predictions at high pressures. As a direct result of accounting for a changing hydrate volume, the cage radii were functions of the hydrate volume. Thus, Ballard have proposed the hydrate phase equilibrium by Gibbs energy minimization in a multi-phase flash routine. Thus, this work presents the Zhang et al. (2005) and Ballards (2002) approaches for hydrate thermodynamic behavior and makes an analysis and comparison of them. To compute the flash problem, we use the tool lsqnonlin (built-in of MATLAB software). The algorithm lsqnonlin is based on the Levenberg-Marquadt method.