Academic literature on the topic 'Poppet valve two-stroke engine'

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.

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.

[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.<br>[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.<br>[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.<br>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<br>TESIS

The master´s thesis deals with the design of two-stroke uniflow scavenged motorcycle engine according to patent František Pudil (PV 7018-80) 216305. The engine has been designed for using in off-road sport motorcycles. The objective of this thesis is to design the engine of this conception and to reveal benefits and defects of this concept by using this method. In this thesis the emphasis is put on design of the construction groups which are directly related to unconventional concept of engine. On the other hand, the parts which can be designed conventionally were solved marginally or were not solved at all. In the first part of the thesis there are thoroughly dicsussed expected benefits and disadvantages of this concept. Computational part focuses on valvetrain and porting of engine. Last part deals with design of engine parts.