Dissertations / Theses on the topic 'Two-stroke engines performance'

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.

Un modelo de simulación presenta muchas ventajas en el campo del desarrollo de motores de combustión interna alternativos. Su utilidad es doble. Por un lado, para entender la naturaleza de los fenómenos físicos que suceden en el interior del motor, y por otro, con el fin de optimizar el diseño de los sistemas que integran el mismo. El principal objetivo de esta tesis es desarrollar un modelo de un motor de dos tiempos de 125 cc de altas prestaciones para caracterizar la fluidodinámica interna en los sistemas de admisión, cilindro y escape. Para la construcción del modelo unidimensional del motor es imprescindible conocer información experimental. Por tanto, se han caracterizado de forma experimental los elementos que forman el motor. Por una parte, se ha usado un banco de impulsos para la caracterización dinámica. Por otra parte, se ha empleado un banco de flujo para caracterizar las pérdidas de presión en los elementos. Además, en banco motor, se ha analizado el proceso de combustión, con el objetivo de determinar la ley de liberación de calor. En relación a las tareas de modelado, se ha usado un modelo de diagnóstico para caracterizar del proceso de combustión, experimentando 37 condiciones de operación modificando el régimen de giro, el avance del encendido y usando cinco sistemas de escape. Asimismo, con el fin de poder reproducir el fenómeno de propagación de ondas en el interior del sistema de escape se ha propuesto un modelo de transmisión de calor ya que los modelos convencionales usados en motores de 4T no proporcionan resultados precisos al no contemplar los fenómenos físicos que suceden en el proceso de escape espontáneo de un motor de 2T de estas características. Para ello, se ha caracterizado experimentalmente el fenómeno de propagación de ondas en el interior del sistema de escape midiendo con diversos transductores de presión a lo largo de: un escape de diámetro constante y recto, y varios sistemas de escape derivados del original del motor. El primero se usó para proceder al necesario ajuste de las constantes del modelo mientras que los segundos para realizar la validación del mismo. Para el desarrollo del modelo de transmisión de calor se han contemplado las fluctuaciones de la velocidad instantánea del fluido y la disipación de la turbulencia con una longitud de entrada. Una vez es construido el modelo unidimensional del motor con capacidad de reproducir los complejos fenómenos ondulatorios que existen en el interior de los sistemas de admisión, cilindro y escape, es necesario desarrollar correlaciones para los parámetros que definen la función de Wiebe, usada como ley de liberación de calor en el cilindro. Se ha correlacionado la variación de estos parámetros (en particular, la duración de la combustión y el parámetro de forma) con variables de funcionamiento del motor: régimen de giro y avance del encendido, y variables que se calculan en el modelo: fracción de residuales y densidad de la carga. De esta forma se dispone de un modelo predictivo de las prestaciones del motor si se conoce una correlación para las pérdidas mecánicas, que también ha sido obtenida. El uso del modelo de transmisión de calor propuesto en este trabajo reproduce con precisión la fase y amplitud de la presión de escape con valores inferiores al 1% al comparar el coeficiente de admisión medido y modelado. Las diferencias pueden alcanzar el 7% si se emplean otros modelos encontrados en la literatura. Por otra parte, los resultados obtenidos al usar las correlaciones para la combustión se traducen en: diferencias inferiores al 1.5% entre potencia medida y modelada para todas las condiciones de funcionamiento del motor si el proceso de combustión presenta un coeficiente de variación en la presión del cilindro inferior al 2.5%. Cuando el coeficiente de variación aumenta, debido a la dispersión cíclica, las diferencias entre potencia medida y modelada pueden alcanzar el 4%. Palabras clave: Motores de Combustión Interna Alternativos, Motor de Dos Tiempos, Altas Prestaciones, Instalaciones Experimentales y Medición, Modelado Unidimensional, Modelo de Acción de Ondas, Proceso de Combustión, Transmisión de Calor.
Jiménez Macedo, VD. (2013). Contribución al modelado unidimensional en motores de dos tiempos de altas prestaciones [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/30773
TESIS

It is standard practice in one-dimensional gasdynamic simulations of high performance two-stroke engines to model the exhaust tail pipe entry as an area change using an algorithm similar to the area change of the reverse cone. In the reverse cone the area continually steps down while at the tail pipe entry it changes from stepping down to constant area. At this point a vena contracta can form that effects the flow resistance of the tail pipe. In an effort to improve the accuracy of the gasdynamic simulations the area change algorithm at the tail pipe entry was replaced with a restriction algorithm that incorporates a coefficient of discharge and allows an increase in entropy on the expansion side. The coefficient of discharge is defined as the actual measured mass flow divided by the mass flow predicted by the restriction algorithm. An experimental set up was designed and constructed to measure mass flows for a variety of tail pipe entry geometries at a range of pressures covering the pressure ratios encountered in a real engine. From the mass flow results the coefficients of discharge for a range of pressure and area ratios and reverse cone angles could be calculated and arranged into matrix form to define Cd-maps. The Cd-maps were incorporated into the simulation software and tested to ensure that it functioned correctly. Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2006.
Mechanical and Aeronautical Engineering
unrestricted

碩士
國立中興大學
機械工程學系
86
ABSTRACTAs the LPG vehicles have lower emissions than the gasoline vehicles, the LPG vehicles have the potential to improve the metropolitan air pollution. In Taiwan, the pollution problem of motorbikes is more serious than that of automobiles. However, applications of LPG just are concentrated on automobiles only. The research of LPG motorbikes has not begun yet.This is a preliminary study on the LPG motorbike engine. Two studies were conducted in this project. The first one is to study the influence of engine design parameters and the fuel system design parameters on the power and exhaust emission of LPG motorbike engines. The LPG vaporizer temperature, the air-fuel ratio, the spark ignition timing, and the compression ratio were considered in this study. In the second part of study, the performance as well as the emission characteristics were compared with thResults of experiments show that increasing the compression ratio can improve the engine performance. However, the spark timing did not have significant effect on engine performance. In changing the A/F, the engine performance as well as the engine emissions were affected. As for the effect of vaporizer temperature, no conclusive results can be obtained.Results of measured data showed that the unburned hydrocarbon is still very high for the LPG engine. This is because the unburned HC is caused by the fuel short circuit, which can not be eliminated by changing fuel to LPG. Besides, the LPG engine output torque is 20-30﹪lower than that of gasoline engine. There are two reasons for the deficiency of engine torque. One is that the gaseous fuel would replace some of the volume of air such that in inlet air flow rate is reduced. The other reason is that the

碩士
國立臺灣科技大學
機械工程系
88
The characteristics of the scavenge and exhaust system of a 50cc motorcycle two-stroke engine are experimentally studied. Based on the experimental and computational results, convenient design procedures for port dimensions and exhaust tuning pipes are developed. The port dimensions and timing are firstly obtained via semi-empirical formula. Variations around the initial design are tested. Optimized dimension and timing designs are finally obtained. The exhaust tuning pipes altered in length. The histograms of the pressure wave propagating in the engine cylinder and at the exhaust port are simultaneously recorded via high speed pressure transducers. The differences of the phases and intensities between the pressure waves in the cylinder and at the exhaust port are analyzed with the assistance of the measured results of engine performance to extract the information imbedded in the system. Various tuning pipe designs fitted to different exhaust port opening are investigated. The wave propagation speed as well as the optimal length of the tuning pipes are of great use to the design and performance improvement of the exhaust system of the 50cc two-stroke engine.

碩士
國立臺灣科技大學
機械工程研究所
83
The design criteria of the transfer and exhaust ports of the loop scavenge two stroke engines were developed . Both computer simulation and experimental methods were employed to implant a formal procedure for design process. The port demensions and timing were firstly botained via semi-empirical formula, and successively corrected by using a computer engine simulation program. The port ngles were firstly designed according to semi- empirical criteria, and subsequently modified with Jante test method. The Helmholtz resonator was designed and installed to the inlet of the engine . An immediate promotion in the engine power was observed. The systematic survey of the different designs of the Helmholtz resonator results in an optimized engine performance.

Thesis (M.S.)--University of Wisconsin--Madison, 1997.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 79-85).

Student Number : 9707408V - MSc(Eng) research report - School of Mechanical, Industrial and Aeronautical Engineering - Faculty of Engineering and the Built Environment
This research is an investigation into the performance and combustion characteristics of a two-cylinder, four-stroke compression ignition engine fuelled on diesel and then on dimethyl ether (DME). Baseline tests were performed using diesel. The tests were then repeated for dimethyl ether fuelling. All DME tests were performed at an injection opening pressure of 210 bar, as recommended for diesel fuelling. The tests were all carried out at constant torque with incremental increases in speed and an improved method of measuring the DME flow rate was devised. It was found that the engine’s performance characteristics were very similar, regardless of whether the engine was fuelled on diesel or DME. Brake power, indicated power and cylinder pressure, during the highest loading condition of 55 Nm, were virtually identical for diesel and DME fuelling, with the most significant finding being that the engine was more efficient when fuelled on DME than when fuelled with diesel. Another interesting finding was that the energy release of diesel decreases with increasing load, whilst the energy release of DME increases with increasing load. At the highest loading condition of 55 Nm, the energy release of DME was approximately 210 joules higher than that of diesel. This investigation concluded that DME may definitely be a suitable substitute fuel for diesel.