A Multi Dimensional Flamelet Model For Ignition In Multi Feed Combustion Systems
Download A Multi Dimensional Flamelet Model For Ignition In Multi Feed Combustion Systems PDF/ePub or read online books in Mobi eBooks. Click Download or Read Online button to get A Multi Dimensional Flamelet Model For Ignition In Multi Feed Combustion Systems book now. This website allows unlimited access to, at the time of writing, more than 1.5 million titles, including hundreds of thousands of titles in various foreign languages.
A Multi-dimensional Flamelet Model for Ignition in Multi-feed Combustion Systems
This work develops a computational framework for modeling turbulent combustion in multi-feed systems that can be applied to internal combustion engines with multiple injections. In the first part of this work, the laminar flamelet equations are extended to two dimensions to enable the representation of a three-feed system that can be characterized by two mixture fractions. A coupling between the resulting equations and the turbulent flow field that enables the use of this method in unsteady simulations is then introduced. Models are developed to describe the scalar dissipation rates of each mixture fraction, which are the parameters that determine the influence of turbulent mixing on the flame structure. Furthermore, a new understanding of the function of the joint dissipation rate of both mixture fractions is discussed. Next, the extended flamelet equations are validated using Direct Numerical Simulations (DNS) of multi-stream ignition that employ detailed finite-rate chemistry. The results demonstrate that the ignition of the overall mixture is influenced by heat and mass transfer between the fuel streams and that this interaction is manifested as a front propagation in two-dimensional mixture fraction space. The flamelet model is shown to capture this behavior well and is therefore able to accurately describe the ignition process of each mixture. To provide closure between the flamelet chemistry and the turbulent flow field, information about the joint statistics of the two mixture fractions is required. An investigation of the joint probability density function (PDF) was carried out using DNS of two scalars mixing in stationary isotropic turbulence. It was found that available models for the joint PDF lack the ability to conserve all second-order moments necessary for an adequate description of the mixing field. A new five parameter bivariate beta distribution was therefore developed and shown to describe the joint PDF more accurately throughout the entire mixing time and for a wide range of initial conditions. Finally, the proposed model framework is applied in the simulation of a split-injection diesel engine and compared with experimental results. A range of operating points and different injection strategies are investigated. Comparisons with the experimental pressure traces show that the model is able to predict the ignition delay of each injection and the overall combustion process with good accuracy. These results indicate that the model is applicable to the range of regimes found in diesel combustion.
A Multi-dimensional Flamelet Model for Ignition in Multi-feed Combustion Systems
This work develops a computational framework for modeling turbulent combustion in multi-feed systems that can be applied to internal combustion engines with multiple injections. In the first part of this work, the laminar flamelet equations are extended to two dimensions to enable the representation of a three-feed system that can be characterized by two mixture fractions. A coupling between the resulting equations and the turbulent flow field that enables the use of this method in unsteady simulations is then introduced. Models are developed to describe the scalar dissipation rates of each mixture fraction, which are the parameters that determine the influence of turbulent mixing on the flame structure. Furthermore, a new understanding of the function of the joint dissipation rate of both mixture fractions is discussed. Next, the extended flamelet equations are validated using Direct Numerical Simulations (DNS) of multi-stream ignition that employ detailed finite-rate chemistry. The results demonstrate that the ignition of the overall mixture is influenced by heat and mass transfer between the fuel streams and that this interaction is manifested as a front propagation in two-dimensional mixture fraction space. The flamelet model is shown to capture this behavior well and is therefore able to accurately describe the ignition process of each mixture. To provide closure between the flamelet chemistry and the turbulent flow field, information about the joint statistics of the two mixture fractions is required. An investigation of the joint probability density function (PDF) was carried out using DNS of two scalars mixing in stationary isotropic turbulence. It was found that available models for the joint PDF lack the ability to conserve all second-order moments necessary for an adequate description of the mixing field. A new five parameter bivariate beta distribution was therefore developed and shown to describe the joint PDF more accurately throughout the entire mixing time and for a wide range of initial conditions. Finally, the proposed model framework is applied in the simulation of a split-injection diesel engine and compared with experimental results. A range of operating points and different injection strategies are investigated. Comparisons with the experimental pressure traces show that the model is able to predict the ignition delay of each injection and the overall combustion process with good accuracy. These results indicate that the model is applicable to the range of regimes found in diesel combustion.
3D-CFD-Simulation der Gemischbildung, Verbrennung und Emissionsentstehung eines Hochdruck-Gas-Diesel-Brennverfahrens
Author: Alexandros Hatzipanagiotou
language: de
Publisher: Logos Verlag Berlin GmbH
Release Date: 2018-09-15
Die Arbeit behandelt die Gemischbildung, Verbrennung und Emissionsentstehung eines Hochdruck-Gas-Diesel-Brennverfahrens mittels der 3D-CFD-Simulation. Als Basis dient eine Prozesskette zur Simulation der dieselmotorischen Verbrennung, welche für die Simulation des Hochdruck-Gas-Diesel-Brennverfahrens erweitert wird. Hierbei wird die Einblasung von Erdgas unter Hochdruck in den Brennraum sowie die Zündung, Verbrennung und Rußbildung von parallel vorliegendem Diesel und Erdgas modelliert. Darüber hinaus erfolgt eine im Vergleich zum Stand der Technik detailliertere Beschreibung der Strahl-Wand-Interaktion, um die Gemischbildung nach Auftreten der Gasstrahlen auf die Brennraumwand besser abzubilden. Die entwickelte Modellkette wird durch einen Vergleich mit Einzylindermessungen thermodynamisch validiert. Darüber hinaus findet eine lokale Validierung durch Vergleich mit Aufnahmen an einem optisch zugänglichen Einzylinderaggregat statt. Es zeigt sich, dass die Zündorte sowie Zündzeitpunkte der Gasstrahlen durch die Simulation unter allen betrachteten motorischen Randbedingungen sehr gut wiedergegeben werden können. Insbesondere ist die Simulation in der Lage, den Einfluss des Abstands zwischen Dieselvoreinspritzung und Gaseinblasung auf die Zündverzugszeit abzubilden. Darüber hinaus wird die Wirkung der Zündverzugszeit auf die Intensität der Vormischverbrennung für alle betrachteten Betriebspunkte gut vorhergesagt. Mit der entwickelten und validierten Simulationsmethodik kann kann die hohe Anzahl der Freiheitsgrade bei der Entwicklung des Hochdruck-Gas-Diesel-Brennverfahrens für minimalen Verbrauch und geringste Emission in einem sehr frühen Entwicklungsstadium optimiert werden.