Detailed Investigation of Knocking Combustion in Spark Ignited Engines by CFD Methods

Within the development of the combustion system of spark ignited engines one of the most limiting factors is the appearance of untypical combustion like knocking. This paper introduces an improved workflow of how to utilize CFD methods for the investigation of knocking processes. The approach uses a new type of combustion model, which has been combined with a statistical method for the description of pre- and post-flame reactions.
The particle based calculation of the pre-flame chemistry allows in this context to draw conclusions about the statistical behavior of the knocking combustion. The Flame-Tracking-Particle Model (FTPM), which provides the basis of the new tool is a numerical algorithm to simulate the kinetics of the premixed and partially premixed flame represented by a distinct surface. The method is based on a wellbalanced combination between a Lagrangian and an Eulerian approach. From the Lagrangian formulation, it takes advantage of obtaining the detailed evolution of surface movement based on flame speed and local flow velocity. From the Eulerian approach, heuristic numerical stability is achieved and it is possible to compute a smooth surface normal vector field from the Lagrangian particles, which is crucial in order to include all effects of turbulent combustion as accurate as possible. The model utilizes well known correlations for the turbulent flame speed, which connect the fuel property of the laminar flame speed with local turbulence intensities.