Dissertations / Theses on the topic 'Two-stroke engine'

Thesis (M.S.)--West Virginia University, 1998.
Title from document title page. Document formatted into pages; contains x, 82 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 69-70).

Thesis (M.S.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains ix, 64 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 42-43).

Inside the master thesis there is represented computer simulation program of the gas flow through the two-stroke engine. The simulation program is developed in software package “Fortran” and is represented as Annex 2. The program simulates gas flow through the two-stroke engine and gives results of pressure changes and mass flow. The simulation is done by using concentrated volume method. The pressure inside the engine parts is described by pressure changes equation. The program is intended for the two-stroke engine tuning for the race. In the thesis is deeply investigated small swept volume engine used for tether model car race. Using the program is possible to do engine inlet and transfer timing optimization. The optimization results were very successful and showed that the cylinder filling with fresh air fuel mixture can be increased by 0.5%. For the numerical solution of the first order differential equations there were used Runge-Kutta IV method.
Magistriniame darbe pristatoma dvitakčio variklio modeliavimo programa, kuri apskaičiuoja dujų tekėjimą dvitakčiame variklyje. Programa sukurta naudojantis programiniu paketu „Fortran“ ir pateikta antrame priede. Programa modeliuoja dujų tekėjimą dvitakčiame variklyje ir pateikia slėgio bei debito rezultatus. Modeliavimui taikytas koncentruotų tūrių metodas. Slėgiai variklio dalyse yra aprašomi slėgio kitimo formule. Programa skirta lenktyniniams dvitakčiams varikliams, jų galiai didinti. Darbe labai smulkiai analizuojami mažo darbinio tūrio varikliai, kurie naudojami automobilių modelių greičio varžybose. Naudojant programą įmanoma atlikti variklio įsiurbimo ir prapūtimo fazių optimizavimą. Optimizavimo rezultatai rodo, kad galima pagerinti cilindro užpildymą šviežiu oro-kuro mišiniu net 0,5 % - tai yra labai geras rezultatas, kadangi dvitakčiai varikliai yra labai išvystyti. Pirmo laipsnio diferencialinėms lygtims spręsti panaudotas skaitinis Rungės-Kuto IV metodas.

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
Neste trabalho, foi desenvolvida uma simulação numérica do processo de lavagem para um motor de dois tempos, com pistão chato. O ar entra circunferencialmente no cilindro, induzindo um escoamento turbulento tri-dimensional. O problema foi modelado assumindo axissimétrico, em regime permanente, através de um cilindro com temperatura uniforme nas paredes. O regime permanente foi simulado , assumindo o pistão fizo no ponto morto inferior. Os campos de velocidade e temperatura foram obtidos utilizando o modelo de turbulência K-E. Os reultados foram comparados com dados experimentais de um escoamento que simula o processo de lavagem no interior de um cilindro em regime permanente. Observou-se uma boa concordância entre os dados. Realizou-se também, uma comparação com uma solução numérica disponível, mostrando ter o presente trabalho comportamento superior, com soluções mais próximas às experimentais. Investigou-se o efeito do número de Reynolds, dos ângulos de entrada do gás e da geometria do motor no escoamento e no processo de troca de calor. Pode-se concluir que o número de Reynolds, a razão de aspectos e a localização da saída são os principais parâmetros do processo de lavagem.
A numerical simulation of the scavenging process in a two-stroke flat-piston model engine has been developed. Air enterns the cylinder circunferentially , inducing a 3-D turbulent swirling flow. The problem was modeled as a steady state axi-symetric flow through a cylinder with uniform wall temperature. The steady state regime was simulated by assuming the piston head fized at the bottom dead center. The calculation was performed employing the K-E model of turbulence. A comparison of the results obtained for the flow field with available experimental data showed very good agreement, and a comparison with available numerical solution revealed superior results. The effect of the Reynolds number, the inlet port angles, and engine geometry on the flow and heat transfer characteristics were investigated. It can be conclude that main parameters for the scavenging process are the Reynolds number, aspect ratio and type of the outflow exit.

This thesis covers the design and prototyping of an electronic throttle control (ETC) system for a small two-stroke engine. The thesis work is being realized in collaboration between a cooperating company and KTH. The throttle control system is veried with a physical combustion engine. The development process of the control systems is being done mostly in-house in the cooperating company. The company has developed electronic control of fuel and ignition system. In addition to the ETC throttle control system this thesis work also develops a control system of the angular velocity of the combustion engine by controlling the intake air to the small two-stroke engine. Today the air supply to the engine is controlled by a valve mechanically connected to the trigger/gas pedal operated by the user. The focus of the thesis is to investigate the advantages and drawbacks of implementing an electronically controlled air supply to a small two-stroke combustion engine. This master thesis discuss the detailed system design requirement of an ETC system for a small two-stroke engine. The result of this master thesis shows that it is possible to have velocity control on a small two-stroke engine, also minor improvements in acceleration of the small combustion engine is shown when using the ETC system.
Detta examensarbete omfattar design och prototypbygge av ett elektroniskt gasreglagesystem (ETC) for en liten tvataktsmotor. Examensarbetet utfors som ett sammarbete mellan ett sammarbetande foretag och KTH. Gasreglagesystemet verieras med en fysisk forbranningsmotor. Utvecklingsprosessen av styrsystemet bedrivs mestadels internt hos det sammarbetande foretaget. Foretaget har utvecklat elektronisk styrning av bransle och tandsystem. Utover det elektroniska gasreglagesystemet har detta examensarbete ocksa behandlat utvecklingen av ett styrsystem av vinkelhastigheten hos forbranningsmotorn genom att styra insugsluften till den lilla tvataktsmotorn. Idag styrs lufttillforseln till forbranningsmotorn av ett spjall som ar mekaniskt ansluten till avtryckaren som manovreras av anvandaren. Fokus for examensarbetet ligger i att undersoka for- och nackdelar med att implementera ett elektroniskt styrt luftspjall till en liten tva-taktsmotor. Examensarbetet behandlar det detaljerade designkravet hos ett ETC system for en liten tvataktsmotor. Resultatet av detta examensarbete visar att det ar mojligt att ha hastighetsstyrning pa en liten tvataktsmotor, aven sma forbattringar i acceleration pavisas nar ETC systemet anvands.

Despite challenges with poor emissions and fuel economy, gasoline two stroke engines continue to be developed for a number of applications. The primary reasons for the choice of a gasoline two stroke engine includes its low cost, mechanical simplicity and high specific power output. Some applications for the gasoline two stroke engine include small capacity motorcycles and scooters, off road recreational vehicles, hand held power tools and unmanned aerial vehicles. New technologies, which are already mature in four stroke engines, are now being applied to two stroke engines. Such technologies include direct fuel injection, electronic engine management and exhaust gas after treatment. To implement these new technologies computation models are being continuously developed to improve the design process of engines. Multi-dimensional computational fluid dynamics modelling is now commonly applied to engine research and development, it is a powerful tool that can give great insight into the thermofluid working of an engine. Multi-dimensional tools are however computationally expensive and quasi-dimensional modelling methods are often better suited for the analysis of an engine, for example in transient engine simulation. This thesis reports the development of a new quasi-dimensional combustion model for a loop scavenged two stroke engine. The model differs from other quasi-dimensional models available in the literature as it accounts for a bulk motion of the flame front due to the tumble motion created by the loop scavenge process. In this study the tumble motion is modelled as an ellipsoid vortex and the size of the vortex is defined by the combustion chamber height and a limiting elliptical aspect ratio. The limiting aspect ratio has been observed in experimental square piston compression machines and optical engines. The new model also accounts for a wrinkled flame brush thickness and its effects on the interaction between flame front and combustion chamber. The new combustion model has been validated against experimental engine tests in which the flame front propagation was measured using ionization probes. The probes were able determine the flame front shape, the bulk movement of the flame front due to tumble and also the wrinkled flame brush thickness.

Engine knock has long been a well recognized phenomenon in the automotive industry. Detecting engine knock opens up the possibility for an indirect feedback of the engine's internal combustion without installing a pressure transducer inside the cylinder. Knock detection has mainly been used for spark advance control, making it possible to control the engine close to its knock limit in search for the optimal ignition timing. This application has to a lesser extent been applied to lightweight two-stroke engines, which is the focus of this study. The investigation features a modern chainsaw engine whose knock characteristics were first determined with a pressure transducer. The structural vibrations originating from the engine knock are filtered out of the signal from a remote located accelerometer. The knock intensity is compared with the signal from the pressure transducer which shows a correlation with an accepted extent between the two sensors. Parameters that affect the knock intensity have also been investigated. These include engine temperature, different types of fuel and ignition timings.

For any crankcase scavenged two-stroke engine, the fuel dynamics is not easily predicted. This is due to the fact that the fuel has to pass the crankcase volume before it enters the combustion chamber. This thesis is about the development of a model for fuel dynamics in the crankcase of a small crankcase scavenged two-stroke engine that gives realistic dynamic behavior. The crankcase model developed in this thesis has two parts. One part is a model for wall wetting and the other part is a model for concentration of evaporated fuel in the crankcase. Wall wetting is a phenomenon where fuel is accumulated in fuel films on the crankcase walls. The wall wetting model has two parameters that have to be tuned. One is for the fraction of fuel from the carburetor that is not directly evaporated and one parameter is for the evaporation time of the fuel film. The thesis treats tuning of these parameters by running the model with input data from measurements. Since not all input data are possible to measure, models for these inputs are also needed. Hence, development of simple models for air flows, fuel flow, gas mixing in the exhaust and the behavior of the λ-probe used for measurements are also treated in this thesis. The parameter estimation for the crankcase model made in this thesis results in parameters that corresponds to constant fraction of fuel from the carburetor that evaporates directly and a wall wetting evaporation rate that increases with increasing engine speed. The parameter estimation is made with measurements at normal operation and three specific engine speeds. The validity of the model is limited to these speeds and does not apply during engine heat-up. The model is run and compared to validation data at some different operation conditions. The model predicts dynamic behavior well, but has a bias in terms of mean level of the output λ. Since this mean value depends on the relation between input air and fuel flow, this bias is probably an effect of inaccuracy in the simple models developed for these flows.
För alla tvåtaktsmotorer med bränslematning genom vevhuset är bränsledynamiken svårpredikterad. Detta beror på att bränslet måste passera vevhusvolymen innan det når förbränningskammaren. Denna uppsats handlar om utveckling av en modell som ger realistisk dynamik för bränslet i tvåtaktsmotorers vevhus. Vevhusmodellen i denna uppsats har två delar. Den ena delen är en modell för bränslefilm på motorväggar och den andra delen är en modell för koncentration av förångat bränsle i vevhusvolymen. Bränslefilmsmodellen har två parametrar som måste trimmas. Den ena är andelen bränsle från förgasaren som inte förångas direkt och den andra är tidsåtgången för förångning av bränslefilmen. Uppsatsen behandlar trimning av dessa parametrar genom körning av modellen med indata från mätningar. Eftersom inte all indata kan mätas behövs även modeller för dessa. Därför behandlar uppsatsen även utveckling av enkla modeller för luftflöde, bränsleflöde, gasblandning i avgasvolymen och beteende hos den för mätningar använda λ-sonden. Parameterestimeringen för vevhusmodellen som är gjord i denna uppsats resulterar i parametrar som svarar mot konstant andel av bränslet från förgasaren som förångas direkt och en förångningshastighet för bränslefilmen som ökar med ökande motorhastighet. Parameterestimeringen är gjord med mätdata från normal körning vid tre olika motorhastigheter. Giltigheten för modellen är begränsad till dessa hastigheter och kan inte appliceras på körning av motorn vid kallstart. Modellen är körd och jämförd med valideringsdata från olika körfall. Modellen förutser dynamiska beteenden väl, men har ett systematiskt fel gällande medelvärdet på λ. Eftersom detta medelvärde beror på förhållandet mellan luftflöde och bränsleflöde in i vevhuset är sannolikt detta systematiska fel en effekt av osäkerhet i de enkla modeller som utvecklats för dessa flöden.

Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, December 1997.
"December 1997." Thesis advisor(s): Knox T. Millsaps, Jr. Includes bibliographical references (p. 57-58). Also available online.

Due to their ability to simultaneously reduce fuel consumption and NOx emissions, Controlled Auto Ignition (CAI) and HCCI combustion processes have been extensively researched over the last decade and adopted on prototype gasoline engines. These combustion processes were initially achieved on conventional two-stroke ported gasoline engines, but there have been significantly fewer studies carried out on the CAI combustion in two-stroke engines. This is primarily due to the inherent problems associated with conventional two-stroke engine intake and exhaust ports. Meanwhile, engine downsizing has been actively researched and developed as an effective means to improve the vehicle’s fuel economy. This is achieved by operating the engine at higher load regions of lower fuel consumption and by reducing the number of cylinders. However, aggressive downsizing of the current 4-stroke gasoline engine is limited by the knocking combustion and high peak cylinder pressure. As an alternative approach to engine downsizing, boosted two-stroke operation is being researched. In this thesis, it has been shown that the CAI combustion in the two-stroke cycle could be readily achieved at part-load conditions with significant reductions in CO and uHC emissions when compared to typical SI combustion in a single cylinder gasoline direct injection camless engine. In addition, extensive engine experiments have been performed to determine the optimum boosting for minimum fuel consumption during the two-stroke operation. In order to minimise the air short-circuiting rate, the intake and exhaust valve timings were varied and optimised. It is shown that the lean operation under boosted condition can extend the range of CAI combustion and increase combustion and thermal efficiencies as well as producing much lower CO and HC emissions. By means of the cycle-resolved in-cylinder measurements and heat release analysis, the improvement in combustion and thermal efficiencies were attributed to the improved in-cylinder mixture, optimised autoignition, and combustion phases. Finally, in view of the increased use of ethanol in gasoline engines, E15 and E85 were used and their effect on engine performance, fuel economy and exhaust emissions were investigated.

Two-stroke poppet-valved engines may combine the high power density of two - stroke engines and the low emissions of poppet-valved engines. A two-stroke diesel engine can generate the same power as a four-stroke engine of the same size, but at higher (leaner) air/fuel ratios. Diesel combustion at high air/fuel ratios generally means hydrocarbons, soot and carbon monoxide are oxidised more completely to water and carbon dioxide in the cylinder, and the opportunity to increase the rate of exhaust gas recirculation should reduce the formation of nitrogen oxides (NOx). The concept is being explored as a means of economically modifying diesel engines to make them cleaner and/or more powerful. This study details the application of two computational models to this problem. The first model is a relatively simple thermodynamic model created by the author capable of rapidly estimating the behaviour of entire engine systems. It was used to estimate near-optimum engine system parameters at single engine operating points and over a six-mode engine cycle. The second model is a detailed CFD model called KIVA-ERC. It is a hybrid of the KIVA engine modelling package developed at the Los Alamos National Laboratory and combustion and emissions subroutines developed at the University of Wisconsin-Madison Engine Research Center. It was used for detailed scavenging and combustion simulations and to provide estimates of emissions levels. Both models were calibrated and validated for four-stroke cycle operation using experimental data. The thermodynamic model was used to provide initial and boundary conditions to the KIVA-ERC model. Conversely, the combustion simulations were used to adjust zero-dimensional combustion correlations when experimental data was not available. Scavenging simulations were performed with shrouded and unshrouded intake valves. A new two-zone scavenging model was proposed and validated using multidimensional scavenging simulations. A method for predicting the behaviour of the two-stroke engine system based on four-stroke data has been proposed. The results using this method indicate that a four-stroke diesel engine with minor modifications can be converted to a two-stroke cycle and achieve substantially the same fuel efficiency as the original engine. However, emissions levels can not be predicted accurately without experimental data from a physical prototype. It is therefore recommended that such a prototype be constructed, based on design parameters obtained from the numerical models used in this study.

This thesis is a study conducted in collaboration with the engine performance group atHusqvarna AB. The study focuses on engine stability of smaller two stroke handheld enginesrunning on E10 (10% ethanol mixture in gasoline). The reason for the study is the new EUproposition that by 2020 all fuel must have 10 % renewable fuel content. To meet thisproposition Husqvarna has evaluated E10 and found that the engine stability of smaller twostroke engines are affected in a negative way by the fuel.The study focuses on events occurring prior to the combustion and mainly the carburetor. Theobjective for the thesis is to seek what contribution the events occurring prior to thecombustion have to the engine stability and find simple and implantable solution to improvethe stability with regards to the carburetor.The study has been conducted in three different work packages, system understanding to buildknowledge of how the carburetor operates, fault finding to seek potential attributes that canaffect the stability and fault mode analysis to seek why the attributes affect the stability.Furthermore, all the attributes found has been tested and validated on the engine to seek theircontribution to the stability.The conclusion made of the thesis is that with simple and implementable improvements of thecarburetor the engine stability could be increased with 40 %. A total of five differentattributes were found to affect the stability of the engine. Furthermore, a very detailedexplanation of how the carburetor operates and components inside the carburetor has beenestablished during the thesis.

Thesis (Ph. D.)--West Virginia University, 2003.
Title from document title page. Document formatted into pages; contains xxvii, 166 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 121-126).

Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.
Includes bibliographical references (p. 126).
by Shihab M. Elborai.
S.B.and M.Eng.

The restrictions imposed by CO2 emission standards in Europe and many countries have promoted the development of more efficient spark ignition engines. The reduced swept volume and number of cylinders of four-stroke engines has significantly improved fuel economy by means of lower pumping and friction losses. This approach, known as engine downsizing, has demonstrated its potential of reducing fuel consumption on its own as well as applied to hybrid vehicles where a low weight engine is desired. However, aggressive engine downsizing is currently constrained by thermal and mechanical stresses and knocking combustion. In order to overcome these limitations, the present work evaluates the application of a conventional poppet valve direct injection engine into the two-stroke cycle. Two-stroke engines have the ability to produce higher power with reduced swept volume and less weight than four-stroke engines thanks to the doubled firing frequency. These advantages, although, are sometimes offset by poorer emissions resulted from fuel short-circuiting; lower thermal efficiency resulted from short expansion process; and reduced engine durability due to lubrication issues. Therefore, in this research the four-stroke engine architecture was employed so these shortcomings could be addressed by the use of direct fuel injection, variable valve actuation and a wet crankcase, respectively. The burnt gases were scavenged during a long valve overlap by means of boosted air supplied by an external compressor. An electrohydraulic fully-variable valve train enabled the optimisation of the gas exchange process in a variety of engine operating conditions. The air-fuel mixture formation was evaluated through computational fluid dynamic simulations and correlated to experimental tests. In addition, the engine operation with ethanol was assessed in a wide range of engine loads and speeds. Finally, the engine performance, combustion process, air-fuel mixing and gas exchange results were presented, discussed and contextualised with current four-stroke engines. Keywords: Two-stroke poppet valve engine; gasoline and ethanol direct injection; engine downsizing; supercharged two-stroke cycle.

HCCI combustion engines can provide high fuel efficiencies with low NOx emissions compared to SI and CI engines due to their lean combustion, high compression ratios and low combustion temperatures. The disadvantage of HCCI is that it is inherently difficult to control. The need for an optimized fuel injection system is crucial in the design of an HCCI engine to achieve desirable and controllable performance. The aim of this thesis was to develop and optimize the fuel injection system for a 2- stroke, opposed piston gasoline engine thus continuing the development of the engine towards achieving stable HCCI combustion. The engine and the components that make up the fuel supply and injection system characteristics were analyzed using experimental and theoretical methods. The mathematical ideal mass of fuel and point of injection was found (when exhaust ports are closed). Injector delay, mass vs. electrical on-time and voltage sensitivity was found. Deflector designs used to divert the fuel flow laterally along the cylinder were studied and prototypes manufactured and tested. The engine was then run with new settings and deflector and the results analyzed. It was found that an L-cut design gave the best spray properties in this situation. An Lcut design with two internal seals gave the most favorable spray angle and atomization. A mass equation was formed that linked the mass injected to on-time in the ECU with consideration of the varying supply voltage. Using this mass equation and taking into account the delay, an ideal injection point was found. Implementing the new deflector and with improved injection timing, the engine was able to run smoothly with the theoretical mass required for λ=1 at 6000rpm and produce 0.28 kW of power. This was a noticeable improvement over previous engine tests which required more fuel mass for stable combustion. In conclusion, information was gained which allowed improvement of the injection timing and fuel control. The engine was run with much more accurate masses of fuel injected and injection times. The deflector improved atomization and optimized the spray angle. The data gained from the tests and analysis can be implemented into the engines ECU code for automated injection timing and fuel mass. This, coupled with the improved spray profile has aided in the continuing development of the engine towards stable, efficient HCCI combustion.
HCCI förbränningsmotorer kan ge hög verkningsgrad med låga NOx-utsläpp jämfört med SI och CI-motorer på grund av sin magra förbränning, högt kompressionsförhållande och låg förbränningstemperatur. Nackdelen med HCCI är att den är svår att kontrollera. Behovet av ett optimerat bränsleinsprutningssystem är avgörande för utformningen av en HCCI motor för att uppnå önskvärt och kontrollerbart resultat. Syftet med detta examensarbete var att utveckla och optimera bränsleinsprutningssystemet för en 2-takts, motkolvs bensinmotor och därmed fortsätta utvecklingen av motorn för att uppnå en stabil HCCI förbränning. Motorn och de komponenter som utgör bränsletillförseln analyserades med hjälp av experimentella och teoretiska metoder. Den matematiska ideala massan bränsle och den ideala insprutningsvinkeln bestämdes (när både insugs-och avgas portarna var stängda). Insprutningsfördröjning kontra ”electrical on-time” och spänningskänslighet bestämdes. Olika utformningar av deflektorn som används för att avleda bränsleflödet i sidled längs cylindern studerades, prototyper tillverkas och testades. Motorn kördes därefter med nya inställningar och ny deflektor och resultaten analyserades. Det visade sig att ”L-cut ”designen gav de bästa spray egenskaperna i denna situation. En ”L-cut” design med två inre tätningar gav den mest fördelaktiga sprayvinkeln och finfördelningen. En massekvation skapades som länkade den insprutade massan till ”elektrical on-time” i ECUn med hänsyn till den varierande matningsspänningen. Genom att använda massekvationen och samtidigt ta hänsyn till fördröjningen kunde en ideal insprutningsvinkel hittas. Implementering av den nya deflektorn tillsammans med förbättrad insprutningsvinkel gjorde att motorn kunde köras jämnt med den teoretiska massan som krävs för λ = 1 vid 6000rpm, och samtidigt producera effekt om 0,28 kW. Det var en märkbar förbättring jämfört med tidigare motortester som krävde dubbla bränslemängden för stabil förbränning. Sammanfattningsvis erhölls data som gjorde förbättringarna av insprutningsvinkel och bränslekontrollen möjlig. Motorn kördes med mycket mer exakt insprutad bränslemassa och insprutningsvinkel. Deflektorn förbättrade finfördelningen och optimerade sprayvinkeln. De data som insamlas från tester och analyser kan implementeras i motorns ECU kod för automatiserad insprutningstidpunkt och bränsle massa. Detta har tillsammans med den förbättrade sprayprofilen bidragit till den fortsatta utvecklingen av motorn mot en stabil, effektiv HCCI förbränning.

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This thesis compared the combustion performance of algae-based hydroprocessed renewable Diesel fuel (HRD) and HRD/F-76 blends, to that of conventional Naval Diesel fuel, F-76. The tests were conducted using a two-stroke, direct injected Detroit 3-53 Diesel engine. The cetane number (CN) of the HRD used was 78 while the CN of the F-76 used was 46. The start of injection (SOI) was measured with a strain gauge mounted on the mechanical fuel injector rocker arm. SOI was found to advance as load increased and retard as speed increased; however, SOI remained constant with the use of the different fuels HRD or F-76. Ignition delay (IGD) decreased significantly with HRD which is consistent with the much higher CN. The heat release rate analysis performed determined that the shorter IGD of HRD led to later combustion phasing, increased overall combustion duration and lower maximum rate of pressure rise. The use of HRD also resulted in lower max cylinder pressure. These results suggest that the combustion performance of HRD has no detrimental effects on the Diesel engine tested.

[EN] The research work presented on this thesis has been performed in the framework of the development and optimization of the combustion system of a novel two-stroke CI engine, with a scavenging configuration through poppet-valves, which has been specifically designed for a light-duty vehicle application. The main objective of this investigation is to improve the existing understanding about two-stroke poppet-valves engines, and assess the main relationships between the gas exchange and combustion processes in this type of architecture, with the aim of evaluating their impact on the exhaust emissions formation processes and on final engine efficiency. Then, the performance of this two-stroke engine is going to be optimized while operating in conventional diesel mixing-controlled controlled combustion; and in a second step, two advanced premixed combustion concepts will be evaluated to identify their potential for decreasing NOx and soot emissions compared to CDC as well as its main technological limitations. The methodology proposed on this thesis combines both a theoretical and experimental approach, that allows maximizing the available information about the basic phenomena involved in the various processes under study, while also keeping an efficient optimization approach to reduce as much as possible the number of necessary experimental tests. Additionally, to analyze in detail the physical relationships between the local cylinder gas conditions (such as the oxygen concentration, the combustion temperature and the equivalence ratio) and the formation of exhaust emissions, particularly NOx and soot, it was necessary to develop and setup different theoretical tools to complement and support the experimentally measured trends. To achieve these objectives, the research work has been divided in two sequential stages: first, the conventional diesel combustion is studied and optimized, based on a proper combination of engine settings that have a strong influence over the characteristics of the mixing-controlled combustion; and in a second step, two advanced combustion concepts are implemented and analyzed, the highly-premixed combustion (HPC) of diesel and the partially premixed combustion (PPC) using a fuel with higher resistance to autoignition (in this case it has been used a RON95 gasoline). In this phase of the research, special emphasis has been made to the gasoline PPC concept, since this combustion mode showed the highest potential and most promising results during the initial implementation studies. Accordingly, the last stage of the research was mainly focused on the detailed study of the effect of different injection settings over the characteristics of the gasoline PPC concept. Finally, the main results obtained with the gasoline PPC concept have been compared against the optimized points found in CDC, in regards to the final exhaust emissions levels, specific fuel consumption and indicated efficiency.
[ES] El trabajo de investigación presentado en esta tesis doctoral está enmarcado en el desarrollo y optimización del sistema de combustión de un novedoso motor de dos tiempos de encendido por compresión, que presenta una arquitectura de barrido por válvulas en culata, y que ha sido diseñado para aplicaciones de automoción dentro de la gama de coches compactos. El objetivo principal de esta investigación ha consistido en mejorar el conocimiento existente sobre los motores dos tiempos con arquitectura de barrido por válvulas, y a la vez identificar los principales vínculos entre los procesos de renovación de la carga y de combustión, con el fin de cuantificar su impacto sobre la formación de emisiones contaminantes y el rendimiento térmico del motor. Adicionalmente, se desea optimizar las prestaciones de este motor de dos tiempos operando con el proceso de combustión diésel convencional controlada por mezcla, así como evaluar el potencial de distintos conceptos avanzados de combustión de baja temperatura con fase de premezcla extendida, con el fin de reducir los niveles de emisiones contaminantes y mejorar el consumo específico de combustible del motor. La metodología utilizada en esta tesis ha sido concebida combinando un enfoque teórico-experimental, que permite maximizar la información que se puede obtener acerca de los fenómenos físicos involucrados en los diferentes procesos objeto de estudio, y a la vez conservar un enfoque de optimización eficiente reduciendo en la medida de lo posible el número de ensayos experimentales requeridos. Con la finalidad de analizar en detalle la relación que existe entre las condiciones en el cilindro (como lo es la concentración de oxígeno, la temperatura de combustión y el dosado local) y el proceso de formación de emisiones contaminantes, especialmente de NOx y hollín, se desarrollaron y utilizaron distintas herramientas teóricas para complementar y sustentar los comportamientos y tendencias observadas mediante los ensayos experimentales, tanto para el modo de combustión diésel convencional como para los conceptos avanzados de combustión. Para la consecución de dichos objetivos se ha seguido una estructura secuencial en la cual el trabajo de investigación ha sido desarrollado en dos grandes bloques: primero, se analizó y optimizó el proceso de combustión diésel convencional, mediante la combinación adecuada de parámetros de operación del motor que modifican apreciablemente las características del proceso de combustión controlada por mezcla; y segundo, se logró implementar y evaluar el desempeño de dos conceptos avanzados de combustión, específicamente el modo combustión altamente premezclado de tipo HPC utilizando diésel como combustible (acrónimo de "Highly-Premixed Combustion") y el modo de combustión parcialmente premezclada de tipo PPC ("Partially Premixed Combustion") utilizando un combustible con mayor resistencia a la auto-ignición (en este caso se utilizó gasolina de octanaje 95). En esta segunda fase, se hizo énfasis en el análisis del concepto de combustión PPC con gasolina, ya que este arrojó los resultados más prometedores durante la fase inicial de implementación. Consecuentemente, la última etapa de la investigación se centró en el estudio detallado del efecto de distintos parámetros de inyección sobre las características del proceso de combustión de tipo PPC. Finalmente, se ha comparado críticamente dicha operación en modo PPC con los resultados obtenidos operando con el modo de combustión diésel convencional, en cuanto al nivel final de emisiones contaminantes, al consumo de combustible y rendimiento indicado y al desempeño general del motor.
[CAT] El treball d'investigació presentat en esta tesi està emmarcat en el desenvolupament i optimització del sistema de combustió d'un nou motor dos temps d'encesa per compressió, amb configuració d'escombratge per vàlvules, i que ha estat dissenyat per a aplicacions d'automoció dins de la gamma de cotxes compactes. L'objectiu principal d'esta investigació ha consistit a millorar el coneixement existent sobre els motors dos temps amb configuració d'escombratge per vàlvules, així com també identificar els principals vincles entre els processos de renovació de la càrrega i de combustió, a fi de quantificar el seu impacte sobre la formació d'emissions contaminants i el rendiment tèrmic del motor. Addicionalment, es desitja optimitzar les prestacions d'este nou motor operant amb el mode convencional de combustió dièsel per difusió, així com avaluar el potencial de noves maneres de combustió de baixa temperatura amb fase de premescla extesa, per a controlar el nivell d'emissions i el consum de combustible. La metodologia utilitzada en esta tesi s'ha plantejat des d'un punt de vista teóric experimental, que permet maximitzar la informació que es pot obtindre sobre els fenòmens basics involucrats en els diferents processos objecte d'estudi, i al mateix temps conservar un enfocament d'optimització eficient reduïnt en la mesura del possible el nombre d'proves experimentals requerit. Amb la finalitat d'analitzar en detall la relació que existeix entre les condicions en el cilindre (com ho és la concentració d'oxigen, la temperatura de combustió i el dosatge local) i el procés de formació d'emissions contaminants, especialment de NOx i sutge, es van desenvolupar i van utilitzar distintes eines teòriques per a complementar i sustentar els comportaments i tendències observades per mitjà dels assajos experimentals, tant per al mode de combustió dièsel convencional com per als conceptes avançats de combustió. Per a abordar eixe objectiu, s'ha seguit una estructura seqüencial, en la qual el treball d'investigació s'ha desenvolupat en en dos grans blocs: en primer lloc, es va analitzar i va optimitzar el procés de combustió dièsel convencional, per mitjà de la combinació adequada de paràmetres d'operació del motor que modifiquen apreciablement les característiques del procés de combustió controlada per difusió; i en segon lloc, es va aconseguir implementar i avaluar les prestacions de dos conceptes avançats de combustió de baixa temperatura premesclats, específicament el mode combustió altament premesclat HPC (acrònim de "Highly-Premixed Combustion") utilitzant dièsel com a combustible i el mode de combustió parcialment premesclat PPC ("Partially Premixed Combustion") utilitzant un combustible amb major resistència a l'autoignició (en aquest cas s'ha utilitzat gasolina d'octanatge 95). En esta segona etapa, es va fer èmfasi en l'anàlisi del concepte de combustió PPC amb gasolina, ja que aquest va presentar els resultats més prometedors durant la fase inicial d'implementació. Conseqüentment, l'última etapa de la investigació es va centrar en l'estudi detallat de l'efecte de distints paràmetres d'injecció sobre les característiques del mode de combustió PPC. Finalment, s'ha comparat críticament la dita operació en mode PPC amb els resultats obtinguts operant amb el mode de combustió dièsel convencional, quant al nivell final d'emissions contaminants, al consum de combustible i rendiment indicat, i a les prestacions generals del motor.
De Lima Moradell, DA. (2016). Analysis of combustion concepts in a poppet valve two-stroke downsized compression ignition engine designed for passenger car applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68502
TESIS

This thesis deals with the construction of two-stroke motorcycle engine. Specifically, the racing engine for the Enduro class with a displacement of 250 cm3, adapted to be mounted in a chassis with extremely long swingarm according to patent of Frantisek Krnavek. The introduction briefly describes the E2 class rules and discussed design powertrain solutions of this class. Following design and calculation of required motor parameters. Further attention is devoted to detailed calculation of main bearings lifespan. The next section describes in detail the construction of the crank mechanism, cylinder head, exhaust pipe, power valve and reed valve. Conclusion deals with location of other engine parts.

This diploma thesis deals with the design of a two-stroke engine for paragliding. First of all, the different types and designs of two-stroke engines are discussed. After the design of the crank mechanism, the forces in the engine are tested, followed by the strength control of selected components. In addition, the work includes design of individual engine components, propeller reducer and 3D models of components and motor unit.

Diploma thesis deals with design of crankshaft for two stroke opposed piston diesel engine. In the theoretical research part a history, comparison with competitive engines in nowadays light aircrafts and the advantages of opposed piston engines are mentioned. In the practical part the balancing is chosen and CAD model of crankshaft is designed. Geometry of this model is than checked for fatigue damage fallout. In the final part was chosen the propeller and appropriate reduction gearbox.

The first part of this thesis describes the different systems of the refill cylinders in two-stroke engines The second part introduces the issue of motorcycling class minicross and its specifics. In the final part is presented the construction of a modern two-stroke engine, which can be used for motorcycle class minicross. In the individual chapters are sketched design of the crank mechanism, gears and automatic clutch. Detailed analytical calculations are attached in the appendices at the end of the text in source code form.

The Master's Thesis is focused on a design of motorcycle two-stroke combustion engine. This single cylinder engine of a stroke volume of 50 ccm is based on a geometry of an existing engine of Blata company that has a stroke volume of 40 ccm. The newly designed engine contains some parts that are used in 40 ccm engine as well. This thesis contains a proposal of production technology of a cylinder as well as an analysis of actuating forces on crankshaft mechanism and solidity control of a piston and piston-rod.