A utilização de combustíveis fósseis é percebida, cada vez mais, de forma negativa, visto seus elevados níveis de emissão de gases de efeito estufa. Por conta disso, busca-se a ampliação do uso de combustíveis de origem renovável de forma a diminuir o impacto ambiental. Dentre esses, o etanol se destaca pelas excelentes características físico-químicas. Ao se reduzir o nível de pureza (diluição em agua) durante o processo de destilação desse combustível, obtém-se um sensível decréscimo da energia dispendida na sua produção. Isso se deve ao crescimento exponencial do consumo energético para obtenção de misturas com teor de etanol superiores à 80% v/v. Assim, a possível utilização de misturas superhidratadas, mesmo que apresentem menor poder calorífico, resultam em uma economia direta de energia no processo de obtenção. Dessa forma, esse trabalho avalia o impacto da utilização de misturas de etanol com elevadas concentrações de água em um motor monocilíndrico de testes, com volume deslocado de 0,668 L, injeção de combustível no coletor de admissão, e ignição por centelha. Inicialmente, avaliou-se via testes de bancada o efeito da substituição direta do etanol comercial por misturas com maior hidratação nos parâmetros de desempenho e emissões. Em seguida, buscou-se explorar as características anti-detonantes da água através do aumento da razão de compressão visando ao aumento de eficiência indicada do motor. Por fim, estudos numéricos foram conduzidos de forma a verificar o efeito da concentração de água sobre os valores de velocidade de chama e temperatura adiabática em uma chama livre unidimensional. Foram também determinados os valores de tempo de indução para condições de temperatura e pressão experimentais. Com isso, observou-se a possibilidade de operação com elevadas razões de compressão para maiores percentuais de água com sensível aumento da eficiência indicada e nível de emissões semelhantes ao etanol comercial. O aumento de água causou uma diminuição na velocidade de queima e na temperatura adiabática de chama, enquanto que o tempo de indução possuiu efeitos opostos dependentes da condição de operação. / The use of fossil fuels have faced several restrictions due its higher greenhouse gas emissions during the combustion process in internal combustion engines. Thus, there is an urge aiming to diversify the number of renewable fuels in order to decrease the environmental impact. Among them, ethanol is notorious, presenting excellent physico-chemical properties. Decreasing the ethanol level on ethanol-in-water mixtures after the distillation process, a lower energy expense can be achieved. This is related to the exponential growing in the energy consumption to obtain mixtures containing ethanol in water concentrations higher than 80% v/v. Therefore, the use of highly hydrated mixtures, despite the decrease in heat values, results in energy savings during its production process. This work evaluates the impact of using mixtures containing high water concentrations in a single cylinder engine, 0.668L, with port fuel injection, and spark ignition combustion. The direct replace of commercial ethanol by highly hydrated mixtures was evaluated through dynamometer tests, so performance and emissions parameters were obtained. After this, it was explored the knock resistance increase due to water addition by increasing the compression ratio, aiming at reaching higher indicated efficiency values. Finally, numerical studies were conducted in order to verify the effect of water concentration increase on laminar flame speed and adiabatic flame temperatures in a one dimensional free flame simulation software. In addition, the induction time for temperature and pressure conditions obtained from experimental results was assessed. As conclusions, the increase in water concentration enabled the use of high compression ratios resulting in higher indicated efficiency values than for commercial ethanol with the same exhaust emission concentrations. Higher water volumes resulted in lower laminar flame speeds and adiabatic flame temperatures. In addition, the induction time values presented two different behavior according to the operating conditions.

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / Microfiche copy available in Archives and Engineering. / Vita. / Bibliography: leaves 80-81. / by Guido A. Danieli. / Ph.D.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Mohamad Metghalchi. / Sc.D.

This thesis proposes that internal combustion piston engines can help clear the way for a transformation in the energy, chemical, and refining industries that is akin to the transition computer technology experienced with the shift from large mainframes to small personal computers and large farms of individually small, modular processing units. This thesis provides a mathematical foundation, multi-dimensional optimizations, experimental results, an engine model, and a techno-economic assessment, all working towards quantifying the value of repurposing internal combustion piston engines for new applications in modular, small-scale technologies, particularly for energy and chemical engineering systems. Many chemical engineering and power generation industries have focused on increasing individual unit sizes and centralizing production. This "bigger is better" concept makes it difficult to evolve and incorporate change. Large systems are often designed with long lifetimes, incorporate innovation slowly, and necessitate high upfront investment costs. Breaking away from this cycle is essential for promoting change, especially change happening quickly in the energy and chemical engineering industries. The ability to evolve during a system's lifetime provides a competitive advantage in a field dominated by large and often very old equipment that cannot respond to technology change. This thesis specifically highlights the value of small, mass-manufactured internal combustion piston engines retrofitted to participate in non-automotive system designs. The applications are unconventional and stem first from the observation that, when normalized by power output, internal combustion engines are one hundred times less expensive than conventional, large power plants. This cost disparity motivated a look at scaling laws to determine if scaling across both individual unit size and number of units produced would predict the two order of magnitude difference seen here. For the first time, this thesis provides a mathematical analysis of scaling with a combination of both changing individual unit size and varying the total number of units produced. Different paths to meet a particular cumulative capacity are analyzed and show that total costs are path dependent and vary as a function of the unit size and number of units produced. The path dependence identified is fairly weak, however, and for all practical applications, the underlying scaling laws seem unaffected. This analysis continues to support the interest in pursuing designs built around small, modular infrastructure. Building on the observation that internal combustion engines are an inexpensive power-producing unit, the first optimization in this thesis focuses on quantifying the value of engine capacity committing to deliver power in the day-ahead electricity and reserve markets, specifically based on pricing from the New York Independent System Operator (NYISO). An optimization was written in Python to determine, based on engine cost, fuel cost, engine wear, engine lifetime, and electricity prices, when and how much of an engine's power should be committed to a particular energy market. The optimization aimed to maximize profit for the engine and generator (engine genset) system acting as a price-taker. The result is an annual profit on the order of \$30 per kilowatt. The most value in the engine genset is in its commitments to the spinning reserve market, where power is often committed but not always called on to deliver. This analysis highlights the benefits of modularity in energy generation and provides one example where the system is so inexpensive and short-lived, that the optimization views the engine replacement cost as a consumable operating expense rather than a capital cost. Having the opportunity to incorporate incremental technological improvements in a system's infrastructure throughout its lifetime allows introduction of new technology with higher efficiencies and better designs. An alternative to traditionally large infrastructure that locks in a design and today's state-of-the-art technology for the next 50 - 70 years, is a system designed to incorporate new technology in a modular fashion. The modular engine genset system used for power generation is one example of how this works in practice. The largest single component of this thesis is modeling, designing, retrofitting, and testing a reciprocating piston engine used as a compressor. Motivated again by the low cost of an internal combustion engine, this work looks at how an engine (which is, in its conventional form, essentially a reciprocating compressor) can be cost-effectively retrofitted to perform as a small-scale gas compressor. In the laboratory, an engine compressor was built by retrofitting a one-cylinder, 79 cc engine. Various retrofitting techniques were incorporated into the system design, and the engine compressor performance was quantified in each iteration. Because the retrofitted engine is now a power consumer rather than a power-producing unit, the engine compressor is driven in the laboratory with an electric motor. Experimentally, compressed air engine exhaust (starting at elevated inlet pressures) surpassed 650 psia (about 45 bar), which makes this system very attractive for many applications in chemical engineering and refining industries. A model of the engine compressor system was written in Python and incorporates experimentally-derived parameters to quantify gas leakage, engine friction, and flow (including backflow) through valves. The model as a whole was calibrated and verified with experimental data and is used to explore engine retrofits beyond what was tested in the laboratory. Along with the experimental and modeling work, a techno-economic assessment is included to compare the engine compressor system with state-of-the-art, commercially-available compressors. Included in the financial analysis is a case study where an engine compressor system is modeled to achieve specific compression needs. The result of the assessment is that, indeed, the low engine cost, even with the necessary retrofits, provides a cost advantage over incumbent compression technologies. Lastly, this thesis provides an algorithm and case study for another application of small-scale units in energy infrastructure, specifically in energy storage. This study focuses on quantifying the value of small-scale, onsite energy storage in shaving peak power demands. This case study focuses on university-level power demands. The analysis finds that, because peak power is so costly, even small amounts of energy storage, when dispatched optimally, can provide significant cost reductions. This provides another example of the value of small-scale implementations, particularly in energy infrastructure. While the study focuses on flywheels and batteries as the energy storage medium, engine gensets could also be used to deliver power and shave peak power demands. The overarching goal of this thesis is to introduce small-scale, modular infrastructure, with a particular focus on the opportunity to retrofit and repurpose inexpensive, mass-manufactured internal combustion engines in new and unconventional applications. The modeling and experimental work presented in this dissertation show very compelling results for engines incorporated into both energy generation infrastructure and chemical engineering industries via compression technologies. The low engine cost provides an opportunity to add retrofits whilst remaining cost competitive with the incumbent technology. This work supports the claim that modular infrastructure, built on the indivisible unit of an internal combustion engine, can revolutionize many industries by providing a low-cost mechanism for rapid change and promoting small-scale designs.

Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / M.S.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

This thesis deals with turbulent mixing processes occurring in internal combustion engines, when applying exhaust gas recirculation (EGR). EGR is a very efficient way to reduce emissions of nitrogen oxides (NOx) in internal combustion engines. Exhaust gases are recirculated and mixed with the fresh intake air, reducing the oxygen con- centration of the combustion gas and thus the peak combustion temperatures. This temperature decrease results in a reduction of NOx emissions. When applying EGR, one is often faced with non-uniform distribution of exhaust among and inside the cylinders, deteriorating the emission performance. The mixing of exhaust gases and air is governed by the flow in the engine intake manifold, which is characterized by unsteadiness due to turbulence and engine pulsations. Moreover, the density cannot be assumed to be constant due to the presence of large temperature variations.Different flow cases having these characteristics are computed by compressible Large Eddy Simulations (LES). First, the stationary flows in two T-junction type geometries are investigated. The method is validated by comparison with experimental data and the accuracy of the simulations is confirmed by grid sensitivity studies. The flow structures and the unsteady flow modes are described for a range of mass flow ratios between the main and the branch inlet. A comparison to RANS computations showed qualitatively different flow fields.Thereafter, pulsating inflow conditions are prescribed on the branch inlet in or- der to mimic the large pulsations occurring in the EGR loop. The flow modes are investigated using Dynamical Mode Decomposition (DMD).After having established the simulation tool, the flow in a six-cylinder engine is simulated. The flow is studied by Proper Orthogonal Decomposition (POD) and DMD. The mixing quality is studied in terms of cylinder-to-cylinder non-uniformity and temporal and spatial variances. It was found that cycle-averaging of the concentration may give misleading results. A sensitivity study with respect to changes in the boundary conditions showed that the EGR pulsations, have large influence on the results. This could also be shown by POD of the concentration field showing the significance of the pulses for the maldistribution of exhaust gases.Finally, the flow in an intake manifold of a four-cylinder engine is investigated in terms of EGR distribution. For this geometry, pipe bends upstream of the EGR inlet were found to be responsible for the maldistribution. / <p>QC 20130207</p>

Originally presented as the author's Thesis--Universität Hamburg, 2007. / Includes bibliographical references.

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.

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