ISBN 9783843926683

978-3-8439-2668-3, Reihe Ingenieurwissenschaften

Lukas Schäfer
Modeling and Simulation of Spark Ignition in Turbocharged Direct Injection Spark Ignition Engines

143 Seiten, Dissertation Technische Universität Bergakademie Freiberg (Sachsen) (2016), Softcover, A5

Zusammenfassung / Abstract

In this work the advanced Curved Arc Diffusion Ignition Model for gasoline engines is presented, which considers the influence of spark curvature, diffusion and detailed chemical kinetics.

In the advanced Curved Arc Diffusion Ignition Model the spark-channel is represented by Lagrangian marker particles, which track the convection of the spark-channel by the local flow field. The high local energy input during the ignition phase leads to steep gradients in the area of the spark-channel, which causes temperature and species diffusion normal to the spark-channel. To account for these diffusion processes, the governing equations for temperature and species are solved on a separate high-resolved grid normal to the spark surface, considering additional terms for the curvature of the spark.

In these governing equations additional source terms that contribute for the electrical spark energy and the chemical source appear. Detailed chemical kinetics are incorporated by employing an iso-octane mechanism with 222 species and more than 1400 reactions.

Beside the boundary conditions such as incylinder pressure, temperature and mixture fraction, respectively, diffusion influences the ignition delay and the first flame kernel development.

The diffusion from the hot spark-channel center towards the surrounding is additionally influenced by the curvature of the spark-channel.

For validation purposes, 3D-CFD simulations of a turbocharged direct injection spark ignition engine including gas exchange, mixture formation and combustion were carried out. The ignition process was simulated using the advanced Curved Arc Diffusion Ignition Model and was validated with experimental results. For this reason extensive experimental investigations were carried out using the optical measurement systems Visio-Tomo, Visio-Flame and high speed endoscopy.

Furthermore the results of the advanced Curved Arc Diffusion Ignition Model were compared with the standard ignition model of ANSYS CFX. The results show the significant importance of curvature and diffusion effects on the ignition process and the need of a finer mesh to resolve these phenomena compared to the CFD mesh grid. Simulating these effects the Advanced Curved Arc Diffusion Ignition Model considerably improves the quality of the combustion simulation and is an important step in achieving a predictive and parameter-less simulation methodology.