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.

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.

The diploma thesis introduces a design of a construction alteration whose aim is to increase the injection efficiency of the given two-stroke engine. The first chapter deals with a construction solution of the replacement of cylinder charge. The following chapters focus on the procedure of creating a 3D model of a cylinder unit through reverse engineering. Furthermore, the thesis contains a CFD simulation of the fluid flow including the evaluation of the results and experimental measurement on an aerodynamic track.

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.

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.

[ES] El transporte terrestre es uno de los principales contribuyentes a las emisiones y tiene un impacto en los cambios climáticos y los peligros para la salud. Para abordar estos problemas, la industria automotriz se está movien- do hacia la movilidad sostenible, donde se están evaluando nuevas tecnologías como vehículos híbridos y vehículos eléctricos. Sin embargo, dado la falta de competencia en alternativas libres de combustibles fósiles para la producción de electricidad, se está abordando la dependencia de motores de combustión interna (ICEs) para ser utilizados como extensores de autonomía y producción de electricidad. Estos extensores de autonomía son generalmente motores de dos tiempos. Debido a su diseño y rango de operación, estos ICE pueden ser compactos, tener una gran reducción de tamaño y producir menos emisiones. Por lo tanto, es esencial comprender el rendimiento de estos nuevos conceptos de ICE, mostrar beneficios potenciales y ayudar en mejoras adicionales. Con el objetivo anterior en este trabajo de tesis, se evalúa un concepto de motor de dos tiempos de barrido uniflow. Se obtienen datos experimentales de una celda de prueba de motor utilizando dos disposiciones de escape, tres velocidades de motor y dos condiciones de carga. Se desarrolla y valida un modelo gasodinámico 1D con respecto a todos los puntos probados. Se mo- dela una réplica en 3D del motor y se utiliza en una simulación CFD en 3D. Los resultados del modelo 1D validados fluidodinámicamente se utilizan como condiciones iniciales y de contorno para evaluar las métricas térmicas y de barrido de este motor en particular. Al comparar los resultados 1D y CFD, se observó que la temperatura y el cortocircuito de aire no se capturaron bien utilizando modelos de transferencia de calor y barrido de última generación durante el proceso de barrido. Esto llevó a la propuesta de un nuevo modelo de transferencia de calor y una curva sintética de barrido. La transferencia de calor en el cilindro es un fenómeno que afecta la tem- peratura de los gases quemados y el aire fresco en un motor de combustión interna. En comparación con las unidades de cuatro tiempos, esta influencia es más crítica en los motores de dos tiempos durante el proceso de barrido, ya que el campo de velocidad del gas dentro del cilindro evoluciona rápidamente en el espacio y el tiempo. Este estudio propone un nuevo modelo de coeficiente de transferencia de calor convectivo más allá de aquellos basados en el cálculo del número de Reynolds con la velocidad media del pistón. El modelo utiliza ecuaciones semiempíricas con números adimensionales ya que debe integrarse en el marco de un modelo físico de motor, donde las propiedades termo y fluidodinámicas de los gases dentro del motor se resuelven mediante enfoques 0D o 1D. En esta aplicación particular, la desviación de temperatura llevó a una predicción deficiente de la masa atrapada en el cilindro. El coeficiente propuesto se calcula utilizando una pseudo-velocidad de los gases dentro del cilindro basada en las tasas de flujo de masa en los puertos de admisión y escape durante el barrido. El barrido en un motor de dos tiempos presenta un proceso complejo, dis- tinto del ciclo de cuatro tiempos, ya que los procesos de admisión y escape ocurren simultáneamente durante una parte significativa del período de inter- cambio de gases. Debido a esta naturaleza superpuesta y a la duración más corta del intercambio de gases en comparación con un motor de cuatro tiempos, modelar con precisión la dinámica de gas dentro del cilindro se vuelve crucial. Este proceso de modelado tiene como objetivo garantizar la retención efectiva de la carga fresca suministrada y la extracción eficiente de los gases residuales del ciclo de motor anterior durante la fase de intercambio de ga- ses. Este modelado es particularmente crucial en motores avanzados de dos tiempos para obtener estimaciones confiables de la composición de la mezcla atrapada y predecir con precisi. / [CA] El transport terrestre és un dels principals contribuents a les emissions i té un impacte en els canvis climàtics i els riscos per a la salut. Per abordar aquests problemes, la indústria automobilística es mou cap a la mobilitat sos- tenible, on s'estan avaluant noves tecnologies com ara vehicles híbrids i vehicles elèctrics. No obstant això, donada la manca de competència en alternatives lliures de combustibles fòssils per a la producció d'electricitat, s'està abordant la dependència dels motors de combustió interna (ICEs) per ser utilitzats com a extensors d'autonomia i producció d'electricitat. Aquests extensors d'auto- nomia són normalment motors de dos temps. A causa del seu disseny i rang operatiu, aquests ICEs poden ser compactes, força reduïts de mida, i emetre menys. Per tant, és essencial entendre les actuacions d'aquests nous conceptes de ICE, mostrar els beneficis potencials, i ajudar en millores addicionals. Amb l'objectiu anterior en aquest treball de tesi, es valora un concepte de motor de dos temps de flux uniflow. S'obtenen dades experimentals d'una cel·la de prova de motor utilitzant dues disposicions d'escapament, tres velo- citats de motor i dues condicions de càrrega. Es desenvolupa i valida un model gasodinàmic 1D amb tots els punts provats. Es modela una rèplica en 3D del motor i s'utilitza en una simulació CFD en 3D. Els resultats del model 1D va- lidats fluidodinàmicament s'utilitzen com a condicions inicials i de contorn per avaluar les mètriques tèrmiques i de flux de gas d'aquest motor en particular. En comparar els resultats 1D i CFD, es va observar que la temperatura i el tall-circuit d'aire no es van capturar bé utilitzant models de transferència de calor i flux de gas de última generació durant el procés de flux. Això va portar a la proposta d'un nou model de transferència de calor i una corba sintètica de flux. La transferència de calor al cilindre és un fenomen que afecta la tempera- tura dels gasos cremats i l'aire fresc en un motor de combustió interna. En comparació amb les unitats de quatre temps, aquesta influència és més crítica en els motors de dos temps durant el procés de flux, ja que el camp de velocitat del gas dins del cilindre evoluciona ràpidament en l'espai i el temps. Aquest estudi proposa un nou model de coeficient de transferència de calor convectiu més enllà dels basats en el càlcul del número de Reynolds amb la velocitat mitjana del pistó. El model utilitza equacions semiempíriques amb nombres no-dimensionals ja que ha de ser integrat dins del marc d'un model físic de motor, on les propietats termo i fluidodinàmiques dels gasos dins del motores resolen mitjançant enfocaments 0D o 1D. En aquesta aplicació particular, la desviació de temperatura va portar a una predicció deficient de la massa atrapada al cilindre. El coeficient de transferència de calor convectiu proposat es calcula utilitzant una pseudo-velocitat dels gasos dins del cilindre basada en les taxes de flux de massa en els ports d'entrada i d'escapament durant el flux. El flux en un motor de dos temps presenta un procés complex, diferent del cicle de quatre temps, ja que els processos d'admissió i d'escapament ocorren simultàniament durant una part significativa del període d'intercanvi de ga- sos. A causa d'aquesta naturalesa superposada i de la durada més curta de l'intercanvi de gasos en comparació amb un motor de quatre temps, modelar amb precisió la dinàmica del gas dins del cilindre es torna crucial. Aquest procés de modelatge té com a objectiu assegurar la retenció efectiva de la càr- rega fresca lliurada i l'extracció eficient dels gasos residuals del cicle de motor anterior durant la fase d'intercanvi de gasos. Aquest modelatge és particular- ment crucial en motors avançats de dos temps per obtenir estimacions fiables de la composició de la mescla atrapada i predir amb precisió el rendiment del motor. / [EN] Transportation on land is one of the major contributors to emissions and has an impact on climatic changes and health hazards. To address these is- sues, the automotive industry is moving toward sustainable mobility, where new technologies such as hybrid vehicles and electric vehicles are being assessed. However, given the lack of competence in fossil fuel-free alternatives for electricity production, dependence on internal combustion engines (ICEs) to be used as range extenders and electricity production is being addressed. These range extenders are usually two-stroke engines. Due to their design and operating range, these ICEs can be compact, be heavily downsized, and have fewer emissions. Hence it is essential to understand the performances of these new ICE concepts, showcase potential benefits, and aid in further improvements. Aiming towards the above objective in this thesis work a two-stroke uniflow scavenged engine concept is assessed. Experimental data from an engine test cell using two exhaust layouts, three engine speeds, and two load conditions is obtained. A 1D gas dynamic model is developed and validated against all tested points. A 3D replica of the engine is modeled and used in 3D CFD simulation. Fluid dynamically validated 1D model results are used as initial and boundary conditions to assess the thermal and scavenging metrics of this particular engine. On comparing 1D and CFD results, it was observed that temperature and short-circuiting of air were not well captured using state-of- the-art heat transfer and scavenging models during the scavenging process. This led to the proposal of a new heat transfer model and a synthetic scavenging curve. In-cylinder heat transfer is a phenomenon that affects the temperature of burnt gases and fresh air in an internal combustion engine. Compared to the four-stroke units, this influence is more critical in two-stroke engines during the scavenging process since gas velocity filed inside the cylinder evolves rapidly in space and time. This study proposes a new convective heat transfer coefficient model beyond those based on Reynolds number calculation with the piston mean velocity. The model uses semi-empirical equations with non-dimensional numbers since it has to be integrated within the frame of a physical engine model, where thermo and fluid dynamic properties of the gases inside the engine are solved using 0D or 1D approaches. In this particular application, the temperature deviation led to a poor prediction of trapped mass in the cylinder. The proposed convective heat transfer coefficient is calculated using a pseudo-velocity of the gases inside the cylinder based on the mass flow rates in the intake and exhaust ports during scavenging. Scavenging in a two-stroke engine presents a complex process, distinct from the four-stroke cycle, as the intake and exhaust processes occur simultaneously for a significant portion of the gas exchange period. Due to this overlapping nature and shorter gas exchange duration compared to a four-stroke engine, accurately modeling the in-cylinder gas dynamics becomes crucial. This modeling process aims to ensure the effective retention of the fresh charge delivered and the efficient extraction of residual gases from the previous engine cycle during the gas exchange phase. Such modeling is particularly crucial in advanced two-stroke engines to obtain reliable estimations of the trapped mixture composition and predict engine performance accurately. / I would like to thank Universitat Politècnica de València for their support with FPI grant with reference FPI-2020-S2-21414 / Darbhamalla, A. (2024). Analysis of the Internal Thermofluid-Dynamics in a Uniflow Scavenged Engine [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/204641

This paper deals with the problem of two-stroke engine pre-ignition controller with the use of microcontroller for single-cylinder engine and double-cylinder engine. The mechanical design is drawn for motorcycles JAWA and ČZ and for engines of the same mechanical type. The establishment uses non-contact status analysis of engine with non-electric sensor. The very important thing for the design is the simplicity of the establishment. The other important thing is the minimisation of mechanical arrangement of engine and the vehicle as a whole. The importance of this establishment is non-contact switching and the possibility of changing pre-ignition maps depending on the number of rotations per minute, the temperature and the load of the engine.

This thesis deals with two-stroke engine design modifications to enhance its performance parameters. The introduction summarizes the various solutions of two-stroke engines. The next part deals with design modifications of the engine power, their implementation and subsequent modification. The work includes strain and stress analysis of the piston, which includes a complete indication of pressures in two-stroke engine. The achieved results of FEM analysis were used to design better piston geometry.

The present diploma thesis deals with innovation of built-up crankshaft of Blata minibikes. Minibike is the type of a small two-stroke motorcycle equipped with an internal combustion engine of the volume 40 or 50 cm3. The machine is designed for racing circuits; not only for young riders but also for seniors. The innovation is in the design and verification of pressed connections in the imposition of major pins in the arms of the crankshaft. Pressed connections are designed on the basis of the analysis of force interaction on the crankshaft at maximum revolutions. The proposed solutions are verified by FEM calculations. Based on the results, the best option is selected. For the selected option, the impact of force interaction at maximum machine performance is studied. Finally, on the basis of these facts, designing, technological and economic analysis of feasibility of new production technology is carried out.

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.