Aluminium silicon alloy has been found to be advantageous in many automobile components like pistons, cylinders, brakes and clutches. The main objective in using these alloys is to obtain lightweight and low friction at a reasonable cost without sacrificing reliability and durability. Out of all the tribological components piston skirts, piston rings and cylinder liners, have to face the most hostile of environments in an internal combustion engine. Wear mechanism of these components have been identified as abrasion, scuffing and corrosion. Narrowing down the line of interest, cylinder wear is more important than ring wear to both the engine manufacturer and the user, as cylinders are more expensive to replace than piston rings. Wear of piston ring and cylinder combination have been studied using a wide range of techniques. It is difficult to predict the tribological performance of these parts in an engine, even with the most well designed laboratory tests, due to chemical, thermal and mechanical complexities in the operating environment. Therefore, a good correlation is sought from the wear behaviour of test bed engines and laboratory tests. This should form the basis of further development particularly in terms of efficiency, weight eduction and wear life improvement of the components. Many ASTM bench-wear tests are used to study wear, some of the common tests being ball-on-disc and pin-on-disc testing. From these tests, a large database of wear information can be achieved and they offer rapid and low cost means of comparison. The only drawback is that the real components are not tested. However, since the bench tests can never simulate the engine environment completely, engine tests are always required for final verification. This thesis work reports preliminary studies of machining damage and wear in actual engine bore to set a bench mark, followed by a set of unidirectional sliding bench tests to study the wear of aluminium alloy under lubricated conditions, to classify the different wear regimes in boundary lubrication zone under different pressure conditions, and to study the effect of a surface modification technique, etching, which improves wear properties. The investigation is divided into four parts. 1. Study of subsurface damage in an actual cylinder surface as introduced by prior machining and actual worn case: A study of the microstructure of bores, processed through a range of machining variables; feed and speed, are investigated in this part of the thesis. This work suggests that the first step of rough machining may be responsible for the microstructure of the finished bore even though subsequent processing steps are intended to remove all prior damages. This also includes some observations of worn surface of an actually run engine, locating the various worn spots and studying the cause of this damage 2. Bench wear test in pin-on-disc under dry and lubricated condition with varying load and lubricant: After setting a benchmark on wear in engine using actual worn cylinder bore, a set of bench tests were carried out on aluminium alloy. Here, steel pins are slid on aluminium silicon alloy discs in the boundary lubrication regime in the presence of one drop of oil. The effect of pure hexadecane and engine oil containing additives on friction and wear are analysed and the data are discussed in terms of the formation of a mechanically mixed layer at the interface. 3. Ultra-mild Wear in Lubricated Tribology of an Aluminium Alloy: To study the different wear regimes in boundary lubrication zone, flat faces of cylindrical steel pins were slid on an eutectic aluminium silicon alloy under lubricated condition in the 1-100 MPa mean contact pressure range and 0.2 m/s sliding speed. Two transitions in wear rate were observed, at 10 MPa and 70 MPa. The wear rate in the 1-10 MPa regime was found to be very small and within the measuring instrument resolution and also insensitive to contact pressure. The regime is designated ultra-mild wear. Lack of plastic flow, minimal fragmentation of silicon particles and the presence of undistorted voids on the fractured and unfractured silicon particles in the subsurface suggest that the state of stress in the near surface region is elastic. Contact mechanical calculations demonstrate that at contact pressures less that 13.7 MPa the system is likely to shakedown to an elastic state. 4.Ball-on-disc wear tests for etched and unetched samples: In the fourth part of the thesis, comparative studies have been done between the as polished and chemically treated samples. Formation of grooves in a ball-on-disc experiment is observed on etched and unetched flats as a function of normal load and sliding distance. The groove is initially formed by plastic flow, and then expanded by micro-abrasion as the ball continues to slide on the groove. However etching causes surface hardening of the alloy, but, more importantly, creates a surface topology that reduces the peak contact pressure, which inhibits further plastic flow in the subsurface.

Nuolat brangstantis kuras, mažėjantys gamtiniai energijos šaltinių ištekliai bei didėjanti aplinkos tarša verčia ieškoti alternatyvių energijos šaltinių. Perspektyviu variklinių degalu laikomas bet kuris cheminis energijos šaltinis, kurio panaudojimas tradicinėse ar naujai kuriamose transporto priemonėse pagerina jų ekologiškumą (sumažina deginių toksiškumą, degalų išgaravimą). Darbe yra pateikti etanolio panaudojimo, kaip papildomo degalo dyzeliniame variklyje, eksperimentinių tyrimų rezultatai. Panaudojant matematinį modelį buvo simuliuojami ir vėliau bandymais patikslinti šie ekonominiai ir ekologiniai rodikliai ir jų priklausomybės nuo etanolio kiekio degiajame mišinyje: lyginamosios ir valandinės degalų sąnaudos, dūmingumas, šviesos absorbcijos koeficientas, taip pat ir prie tam tikro etanolio kiekio mišinyje išvystoma galia bei sukimo momentas ir kt. Bandymo metu nustatytas optimaliausias etanolio kiekis degiajame mišinyje, prie kurio variklio dūmingumas, šviesos absorbcijos koeficientas bei kietųjų dalelių kiekis yra minimalus. Darbą sudaro penkios dalys: įvadas, alternatyvių degalų ir etanolio panaudojimas dyzeliniame variklyje apžvalga, eksperimentiniai tyrimai, išvados, literatūros sąrašas. Darbo apimtis – 60 p. teksto be priedų, 37 iliustracija, 14 lentelės. Atskirai pridedami darbo priedai – matematinio simuliavimo metu gauti rezultatai bei parametrų priklausomybės. / All rising in price the fuel, decreasing natural stocks of energy sources and atmospheres increasing pollution forces to search for alternative kinds of fuel. Perspective fuel considers any chemical energy source which use in traditional and projected vehicles improves their ecological parametres (reduces level of emission of toxic products of combustion). In work ethanol application as addition to fuel in diesel engines, ethanol influence, depending on its concentration in a working mix, on ecological and economic indicators is considered, such as smoke issue, factor of absolute absorption of light, power and the twisting moment of the engine, the specific effective and hour expense of fuel, etc. During mathematical modelling and after tests the optimum maintenance of ethanol in a working mix is checked up and established at which issue of a smoke and factor of absolute absorption of light are minimum. Work consists of five parts: introduction, the analysis of application of ethanol and alternative kinds of fuel in the diesel engine, experimental tests, conclusions, the literature list. Work volume - 60 page without additions, 37 illustration, 14 tables. Additions to work - the received results and dependences of parametres are separately given at mathematical feigning. / Всё дорожающие топливо, уменьшающиеся природные запасы источников энергии и увеличивающиеся загрязнение атмосферы заставляет искать альтернативные виды топлива. Перспективным топливом считается любой химический источник энергии, использование которого в традиционных и проектируемых транспортных средствах у��учшает их экологические параметры (уменьшает уровень выброса токсичных продуктов сгорания) В работе рассматривается применение этанола как дополнение к топливу в дизельных двигателях, влияние этанола, в зависимости от его концентрации в рабочей смеси, на экологические и экономические показатели, такие как эмиссия дыма, коэффициент абсолютного светопоглощения, мощность и крутящий момент двигателя, удельный эффективный и часовой расход топлива и т.п. В ходе математического моделирования и позже испытаний проверено и установлено оптимальное содержание этанола в рабочей смеси при котором эмиссия дыма и коэффициент абсолютного светопоглащения минимальны. Работа состоит из пяти частей: введение, анализ применения этанола и альтернативных видов топлива в дизельном двигателе, экспериментные испытания, выводы, список литературы. Объём работы – 60 страниц без добавлений, 37 иллюстраций, 14 таблиц. Отдельно предоставлены добавления к работе – полученные результаты и зависимости параметров при математическом симулировании.

In the last decades, the focus of internal combustion engine development has moved towards more efficient and less pollutant engines. In a Diesel engine, approximately 30-40% of the energy provided by combustion is lost through the exhaust gases. The exhaust gases are hot and therefore rich of energy. Some of this energy can be recovered by recycling the exhaust gases into turbocharger. However, the energy losses in the exhaust port are highly undesired and the mechanisms driving the total pressure losses in the exhaust manifold not fully understood. Moreover, the efficiency of the turbine is highly dependent on the upstream flow conditions. Thus, a numerical study of the flow in the exhaust port geometry of a Scania heavy-duty Diesel engine is carried out mainly by using the Large Eddy Simulation (LES) approach. The purpose is to characterize the flow in the exhaust port, analyze and identify the sources of the total pressure losses. Unsteady Reynolds Averaged Navier-Stokes (URANS) simulation results are included for comparison purposes. The calculations are performed with fixed valve and stationary boundary conditions for which experimental data are available. The simulations include a verification study of the solver using different grid resolutions and different valve lift states. The calculated numerical data are compared to existent measured pressure loss data. The results show that even global parameters like total pressure losses are predicted better by LES than by URANS. The complex three-dimensional flow structures generated in the flow field are qualitatively assessed through visualization and analyzed by statistical means. The near valve region is a major source of losses. Due to the presence of the valve, an annular, jet-like flow structure is formed where the high-velocity flow follows the valve stem into the port. Flow separation occurs immediately downstream of the valve seat on the walls of the port and also on the surface of the valve body. Strong longitudinal, non-stationary secondary flow structures (i.e. in the plane normal to the main flow direction) are observed in the exhaust manifold. Such structures can degrade the efficiency of a possible turbine of a turbocharger located downstream on the exhaust manifold. The effect of the valve and piston motion has also been studied by the Large Eddy Simulation (LES) approach. Within the exhaust process, the valves open while the piston continues moving in the combustion chamber. This process is often analyzed modeling the piston and valves at fixed locations, but conserving the total mass flow. Using advanced methods, this process can be simulated numerically in a more accurate manner. Based on LES data, the discharge coefficients are calculated following the strict definition. The results show that the discharge coefficient can be overestimated (about 20 %) when using simplified experiments, e. g. flow bench. Simple cases using fixed positions for valve and piston are contrasted with cases which consider the motion of piston and/or valves. The overall flow characteristics are compared within the cases. The comparison shows it is impossible to rebuild the dynamic flow field with the simplification with fixed valves. It is better to employ LES to simulate the dynamic flow and associated losses with valve and piston motion. / <p>QC 20131204</p>

A crescente demanda de diminuição das emissões e redução do consumo dos motores de combustão interna exige a melhoria dos métodos para diagnose, em tempo real, e para melhor controle do processo de combustão. Portanto, é desejável determinar a relação ar-combustível sobre uma extensa faixa de condições de operação para obter um melhor controle do motor. Este trabalho apresenta a aplicação do Método dos Momentos para obtenção de um modelo de estimação da relação ar-combustível, através do sinal de pressão no cilindro, em um motor ciclo Otto a etanol. O modelo obtido permitirá o desenvolvimento de novos sistemas de controle utilizando como estratégia a pressão no cilindro. / The increasing demands for low emission and low fuel consumption in internal combustion engines require improved methods for diagnosis, in real-time and best possible control of the combustion process. Therefore, determining air-fuel ratio over a wide range of engine operating conditions is desirable for better engine control. This work presents the Moment Method application for obtaining air-fuel ratio estimation model, by cylinder pressure sign, in Otto cycle engine powered by ethanol. The obtained model will allow the development of new control systems, for engine powered alcohol, using as strategy the cylinder pressure.

Motor a álcool teve grande aplicação no Brasil com a implantação do Proálcool, programa lançada na década de 1970, vislumbrando reduzir a dependência externa do petróleo. Ressalta-se que avanços na tecnologia do referido motor, bem como na produção de álcool, tornaram-no técnica e economicamente viável como substituto da gasolina em algumas regiões. O presente trabalho teve por objetivo avaliar o desempenho e a emissão de um motor ciclo Otto funcionando com dois tipos de álcool, 92,8 e 75 INPM, sendo o último considerado de baixo teor alcoólico, possibilitando variar a taxa de compressão. O ensaio foi realizado em bancada dinamométrica, no laboratório de motores da EESC/USP, campus de São Carlos. Para tanto, utilizou-se de motor de 1.000 \'CM POT.3\', oito válvulas e quatro cilindros. Os resultados evidenciaram que o combustível de baixo teor alcoólico aceitou aumento na taxa de compressão de 13,5:1 para 16,2:1, ressaltando-se que, nessa condição, houve aumento de torque e da potência máxima, redução de emissão de NOx e aumentos de consumo e de emissão de hidrocarboneto. / Ethanol engines had a great application in Brazil with the implantation of Proalcool, a program launched in 1970 decade, guessing the reduction in exterior oil dependence. Progress in technology in the cited engine, as well as in ethanol production have turned this combustible into a technically and economically viable option, as an oil substitute in some regions. The present work had the aim of evaluating the performance and emission of an Otto cycle engine working with two types of ethanol, 92.8 and 75 INPM, the latter considered as a low grade alcohol, enabling a variation in the compression rate. The experiment was performed at the dynamometer testing bench in the engine laboratory of EESC/USP, campus at São Carlos. With this intent a 1,000 \'CM POT.3\' engine, eight valves and four cylinders were utilized. The results have shown that the low grade alcoholic combustible accepted an enhancement in the compression rate from 13.5 to 16.2:1, emphasizing that in this condition there was increase maximum torque and maximum power, a reduction in NOx emission and a rise in the consumption and hydrocarbon emission.

Esta dissertação analisa a viabilidade técnico-econômica de pequenas centrais de cogeração a gás natural no setor terciário do estado de São Paulo, os estudos de cogeração foram baseados em casos reais de estabelecimentos comerciais dos principais segmentos do setor terciário com demanda elétrica e térmica compatível ao balanço energético para a configuração de cogeração. A análise dos resultados inclui o fator de utilização de energia (FUE), investimentos iniciais, economia operacional (fluxo de caixa), retorno dos investimentos (Payback), taxa interna de retorno (TIR) e valor presente líquido (VPL). As tecnologias empregadas nos estudos foram gerador do tipo Motor a Combustão Interna (MCI) e Microturbina (TG), resfriador de líquido por absorção (ABS) e resfriador de líquido elétrico convencional. Foi realizada análise do potencial de mercado para aplicação de cogeração através do mapeamento dos principais segmentos do setor terciário e realizado o levantamento do estado da arte. Foram estudadas as legislações brasileiras tanto no que se refere à cogeração qualificada como geração distribuída, realizado análise de emissões com destaque ao comparativo entre emissão de CO2 das centrais de cogeração e a emissão de CO2 das termelétricas a gás natural. Foi realizado estudo do cenário energético brasileiro do ponto de vista geração e distribuição de energia elétrica, cenário da oferta de gás natural no Brasil e a sua estrutura de distribuição no estado de São Paulo e, por fim, foram destacados os benefícios e barreiras da cogeração no Brasil. Os resultados alcançados apontam para um revés na viabilidade financeira da cogeração devido aos consecutivos aumentos no preço da tarifa de gás natural, apesar de bastante racional e com benefícios diretos ao meio ambiente e ao país, fazem-se necessários incentivos específicos relacionados à tarifa do gás natural para o crescimento da aplicação de cogeração no setor terciário do estado de São Paulo. / This dissertation examines the technical and economic feasibility of small cogeneration plants powered by natural gas in the tertiary sector of the state of São Paulo. Cogeneration studies were based on real cases of commercial facilities of the main segments of the tertiary sector with electrical and thermal demands compatible for energy usage in cogeneration configuration. The analysis results include energy utilization factor (EUF), initial investments, operational savings (cash flow), return on investment (payback), internal rate of return (IRR) and net present value (NPV). The technologies investigated in the study were Internal Combustion Engine (ICE) and Microturbine (TG) generator, absorption chiller (ABS) and conventional electrical chiller. It was carried out an analysis of the potential market for application of cogeneration by mapping the main segments of the tertiary sector and conducted a survey of the state of the art. Brazilian laws were studied both with regard to qualified cogeneration and distributed generation, performed emissions analysis with emphasis on the comparative between CO2 emission from cogeneration plant and CO2 emission from power plants by natural gas. It was made a study of Brazilian energy scenario from the viewpoint of generating and distributing of electricity, scenario of supply of natural gas in Brazil and its distribution structure in the São Paulo state and, finally, it was appointed the benefits and barriers of cogeneration in Brazil. The results indicate a setback on the financial viability of cogeneration due to consecutive increases in the price of natural gas, although quite rational and with direct benefits to the environment and the country, it\'s necessary specific incentives related to the natural gas price for the growth of the application of cogeneration in the tertiary sector of the state of São Paulo.

Made available in DSpace on 2016-03-15T19:36:32Z (GMT). No. of bitstreams: 1 Valter Barragan Neto.pdf: 3036136 bytes, checksum: ab88f80ccbb35090b829c391e8f0536e (MD5) Previous issue date: 2011-09-27 / General Motors do Brasil / Automotive cylinder liners are mechanical components with the function of internal coating of the cylinder automotive engines. The liners have been made of cast iron, which meets the necessary requirements. The replacement of parts made of steel/ cast iron in aluminum alloys has been made with advantages not only in reducing weight as well as fuel consumption and emission of pollutants. This work has an objective to study the possibility to apply the cylinder liners built in aluminum and silicon alloy on engines with computer aided engineering help. The finite element method consists to generate a mathematical model with computational assistance, of geometry, representing several elements that have in common the node connection, forming the finite element, defined as a mesh. For each node the partial differential equations are solved by numerical methods. This study was aided by finite element software Hyperworks, where the mesh was generated and was exported to Abaqus where were performed the processing of input data. The starting point for the simulation of aluminum liners used in internal combustion engines was to define the format of the mesh for the engine block with less refinement, was chosen a mesh with tetrahedron elements of 4 nodes of with size ranging between 1 mm and 12 mm of edge element. The liners was designed with hexahedron elements of six nodes, which by definition are more consistent and have more accurate answers to the elements tetrahedrons and with a larger refinement, about 1 mm, both elements are first order elements with no nodes on edge s midpoint . In function of the process of manufacturing the liners to be cast by centrifugation, layers of elements were created to meet the variation in the amount of the silicon liner, which in turn affects the physical properties of the liner along the thickness of the wall. With this model it was possible to show the viability of applying these liners in engine blocks of cast iron. The analysis has shown that a prototype could be build in order to test the cylinder liners application and also test the wear of the cylinder liner. / Camisas de cilindro automotivo são componentes mecânicos com a função de revestir internamente os cilindros dos motores automotivos. As camisas de cilindros têm sido feitas de ferro fundido, que atende os requisitos necessários de desgaste e rigidez. A substituição de partes feitas em aço e ferro fundido por ligas de alumínio em veículos têm vantagens não só na diminuição de peso como também no consumo de combustível e emissão de poluentes. Este trabalho teve por objetivo estudar a viabilidade da aplicação de camisas constituídas em liga de alumínio e silício em motores com o auxilio de engenharia assistida por computador. O método de modelagem em elementos finitos consiste em gerar um modelo matemático auxiliado por computador, da geometria, constituída por vários elementos que têm em comum nós de ligação formando os elementos finitos, assim definidos por malha. Para cada um dos nós são resolvidas as equações diferenciais parciais por métodos numéricos. O estudo em elementos finitos foi auxiliado pelos softwares Hyperworks, onde foi gerada a malha e exportada para o Abaqus onde foi realizado o processamento dos dados de entrada. O ponto de partida para a simulação das camisas de alumínio aplicadas em motores de combustão interna foi definir a formato da malha para o bloco com um menor refinamento, foi então escolhida uma malha com elementos tetraédricos de quatro nós de tamanho variando entre 1 mm e 12 mm de aresta de elemento. A camisa foi elaborada com elementos hexaédricos de seis nós, que por definição são mais fiéis e possuem respostas mais precisas que os elementos tetraédricos, e com um refinamento maior, cerca de 1 mm, ambos de primeira ordem sem nós intermediários nas arestas. Em função do processo de fabricação da camisa ser a fundição por centrifugação, camadas de elementos foram criadas a fim de satisfazer a variação da quantidade de silício da camisa, que por sua vez afeta as propriedades físicas da camisa ao longo da espessura da parede. Com este modelo foi possível mostrar a viabilidade da aplicação dessas camisas em motores com blocos de ferro fundido. As análises mostraram que um protótipo poderá ser construído para testar a aplicação destas camisas e testá-las quanto ao desgaste.

The research topic of liquid drop interaction with solid surfaces is being actively pursued to gain in-depth understanding of several practical cases such as the impingement of fuel spray droplets on surfaces like combustion chamber walls and piston top of an I.C. engine, heat transfer via spray impingement, ink-jet printing, etc. In most of the cases, the physical and flow properties of the liquid drop/spray may be fixed whereas it may be possible to tune the physical and chemical properties of the solid surface thereby enabling to control the interaction process. The present work belongs to the study of liquid drop-solid surface interaction process with special focus on the physical characteristics of solid surface. The thesis reports an experimental study of the dynamics of millimetric water drops impacted onto the junction of dual-textured substrates made of stainless steel. The dual-textured substrates consisted of hydrophobic (textured) and hydrophilic (smooth) portions. The entire textured portion comprised of parallel groove-like structures separated by solid posts/pillars. Two dual-textured substrates, which differ only in the geometry of their textured portions, were employed. Surface topography features of the dual-textured substrates were characterized using scanning electron microscopy (SEM) and optical surface profilometer. The wetting behavior of the textured and smooth portions of the substrates, quantified in terms of the equilibrium, advancing, and receding contact angles adopted by a water drop on the surface portions, was characterized experimentally through the methods of sessile drop formation, captive needle volume addition, and drop evaporation under ambient conditions. Free-falling water drops were impacted from a height onto the junction between the hydrophobic (textured) and hydrophilic (smooth) portions of the dual-textured substrates. A set of twelve different impact experiments were conducted on each of the target substrates with drop impact velocity (Uo) ranging from 0.37 to 1.50 m/sec. The dynamics of drop impact were captured using a high speed camera with frame rate ranging from 3000 to 10000 frames per second. From the captured frames, the temporal variations of the impacting drop parameters were measured using a MATLAB-assisted program. A systematic analysis of experimental data revealed the existence of four distinct regimes of drop dynamics on the dual-textured substrate: (a) early inertia driven drop spreading, (b) primary drop receding, (c) secondary spreading on the hydrophilic portion, and (d) final equilibrium regimes. It is shown that the drop impact dynamics during the early inertia driven impact regime remains unaffected by the dual-texture feature of the substrate. A larger retraction speed of impacting drop liquid observed on the hydrophobic portion of the substrate makes the drop liquid on the higher wettability/hydrophilic portion to advance further (secondary drop spreading). The net horizontal drop velocity towards the hydrophilic portion of the dual-textured substrate decreases with increasing drop impact velocity. The available experimental results suggest that the movement of bulk drop liquid away from the impact point during drop impact on the dual-textured substrate is larger for the impact of low inertia drops. A semi-empirical model, based on the balance of the wettability gradient, contact angle hysteresis, and viscous forces acting on impacted drop liquid on the substrate, is formulated to predict the movement of bulk drop liquid away from the impact point (ξ). A satisfactory comparison between the model predictions and the experimental measurements is reported for the variation of ξ with Uo.

The internal combustion engine is synonyms with the automobile since its invention in late 19th century. The internal combustion engine today is far more advanced and efficient compared to its early predecessors. An intense competition exists today amongst the automotive OEMs in various countries and regions for stepping up sales and increasing market share. The pressure on automotive OEMs to reduce fuel consumption and emission is enormous which has lead to innovations of many variations in engine and engine-related technologies. However, IC engines are in existence for well more than a century and hence have already evolved to a highly refined state. Changes in IC engine are therefore largely incremental in nature. A deterrent towards development of an engine configuration that is significantly different from its predecessor is the phenomenal cost involved in prototyping. Thus, the only viable alternative in exploring new engine concepts and even optimizing designs currently in operation is through extensive use of CAE. In light of published work in the field of analysis of IC engines, current research effort is directed towards development of a rational methodology for arriving at a weight-optimized engine design, which simultaneously meets performance of various attributes such as thermal, durability, vehicle dynamics and NVH. This is in contrast to the current methodology adopted in industry, according to which separate teams work on aspects of engine design such as combustion, NVH (Noise, Vibration and Harshness), acoustics, dynamics, heat transfer and durability. Because of the involvement of heterogeneous product development groups, optimization of an engine for weight, which can have a significant impact on its power-to-weight ratio, becomes a slow process beset with manual interventions and compromise solutions. Thus, following the traditional approach, it is quite difficult to claim that an unambiguous weight-optimized design has been achieved. As a departure from the practiced approach, the present research effort is directed at the deployment of a single multi-physics explicit analysis solver, viz. LS-DYNA - generally known for its contact-impact analysis capabilities, for simultaneously evaluating a given engine design for heat transfer, mechanical and thermal loading, and vibration. It may be mentioned that only combustion analysis is carried out in an uncoupled manner, using proven phenomenological thermodynamic relations, to initially arrive at mechanical and thermal loading/boundary conditions for the coupled thermo-mechanical analysis. The proposed methodology can thus be termed as a semi-integrated technique and its efficacy is established with the case study of designing a single cylinder air-cooled diesel engine from scratch and its optimization.

In-cylinder fuel-air mixing in a compressed natural gas (CNG)-fuelled, single-cylinder, spark-ignited engine is analysed using a transient three-dimensional computational fluid dynamic model built and run using STAR-CD, a commercial CFD software. This work is motivated by the need for strategies to achieve improved performance in engines utilizing gaseous fuels such as CNG. The transient in-cylinder fuel-air mixing is evaluated for a port gas injection fuelling system and compared with that of conventional gas carburetor system. In this work pure methane is used as gaseous fuel for all the computational studies. It is observed that compared to the premixed gas carburetor system, a substantial level of in-cylinder stratification can be achieved with the port gas injection system. The difference of more than 20% in mass fraction between the rich and lean zones in the combustion chamber is observed for the port gas injection system compared to less than 1% for the conventional premixed system. The phenomenon of stratification observed is very close to the “barrel stratification” mode. A detailed parametric study is undertaken to understand the effect of various injection parameters such as injection location, injection orientation, start of injection, duration of injection and rate of injection. Furthermore, the optimum injection timing is evaluated for various load-speed conditions of the engine. It is also observed that the level of stratification is highest at 50% engine load with a reduced level at 100% load. For low engine loads, the level of stratification is observed to be very low. To analyse the effect of stratification on engine performance, the in-cylinder combustion is modeled using the extended coherent flame model(ECFM). For simulating the ignition process, the arc and kernel tracking ignition model(AKTIM) is used. The combustion model is first validated with measured in-cylinder pressure data and other derived quantities such as heat release rate and mass burn fraction. It is observed that there is a good agreement between measured and simulated values. Subsequently, this model is use to simulate both premixed and stratified cases. It is observed that there is a marginal improvement in terms of overall engine efficiency when the stoichiometric premixed case is compared with the lean stratified condition. However, a major improvement in performance is observed when the lean stratified case is compared with lean premixed condition. The stratified case shows a faster heat release rate which could potentially translate to lower cycle-to-cycle variations in actual engine operation. Also, the stratified cases show as much as 20% lower in-cylinder NOx emissions when compared with the conventional premixed case at the same engine load and speed, underscoring the potential of in-cylinder stratification to achieve improved performance and lower NOx emissions.