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M. Heiß, B. Geringer, T. Lauer:
"A Detailed Analysis of Engine Knock Initiation by Means of a Stochastic Reactor Model";
Talk: 6th European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2012), University of Vienna; 2012-09-10 - 2012-09-14; in: "CD-ROM Proceedings of the 6th European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2012), September 10-14, 2012, Vienna, Austria", (2012), 8 pages.

The operating range of supercharged spark ignited engines with highest efficiency is mostly constrained by the knocking combustion that can lead to severe engine damage.
Therefore, the responsible initiation mechanism is still subject of extensive research work.
Experiments at low speed at the knock limit on a SIDI test engine were the basis for numerical investigations. A multi-cycle analysis of gas-exchange and combustion showed that important charge properties like the charge temperature at inlet valve closing or the internal residual gas fraction were within a narrow range over all cycles. Furthermore it could be shown that the 2 % burn duration correlated with cycles showing autoignition. All cycles with an accelerated early flame development were showing an irregular heat release later on during combustion.
To analyse the initiation mechanism for an autoigniting cycle a detailed modelling of this behaviour was carried out in a stochastic reactor model that included the full chemistry of low and high temperature oxidation. Finally, it was possible to reconstruct a reported knocking cycle with early combustion. It could be shown that only with an initial reactor temperature distribution according to the CFD simulation that included hot regions, the autoignition set in as early as in the measurement. The crank angle resolved heating process of knock critical regions leading to autoignition could be shown.
Most theoretical investigations on abnormal combustion are based on a simplified approach considering the mean cycle for a given operating point. However, abnormal combustion never
occurred for the mean cycle but rather for a very early cycle. For that reason, this work focused especially on a detailed reconstruction of a knocking cycle with reaction kinetics to
describe the mechanism for knock initiation what is a new and innovative approach.

Reaction Kinetics, Cyclic Variations, Knocking, Autoignition