On post-breakdown initialization for ignition models

Abstract

An accurate evaluation of the processes taking place from the spark onset until the flame self-propagates in spark ignition internal combustion engines would be very beneficial. It would provide engine designers with more reliable criteria, and this in turn would help lower harmful emissions and achieve improved energy utilization. In order to be computationally affordable, combustion codes contain models which simplify specific tasks. Particularly, the ignition process is very demanding in terms of computational cost, so ignition models are normally resorted to. Their accuracy heavily relies on the knowledge of the physics of the process and their simplifying hypothesis. Currently widely used low-dimensional models are perceived to oversimplify some essential features, perhaps being the most important the role of plasma hydrodynamics, which eventually defines the kernel shape. In this work the effect some fundamental parameters have on the whole process, such as electrode and spark gap dimensions, amount of discharged energy and initial chamber pressure and temperature, is simulated. A qualitative and quantitative analysis allows the assessment of a recently proposed low-dimensional thermodynamic model devised for fast discharges, and to establish its range of validity. Some modifications to this model are introduced in order to improve its predictive capabilities and to extend its range of applicability. Additionally, the effect of a further arc or glow discharge and the influence of electrode configuration asymmetry are simulated, providing a methodology to treat both cases.