Knock Onset Detection Methods Evaluation by In-Cylinder Direct Observation 2019-24-0233
Improvement of performance and emission of future internal combustion engine for passenger cars is mandatory during the transition period toward their substitution with electric propulsion systems. In middle time, direct injection spark ignition (DISI) engines could offer a good compromise between fuel economy and exhaust emissions. However, abnormal combustion and particularly knock and super-knock are some of the most important obstacles to the improvement of SI engines efficiency. Although knock has been studied for many years and its basic characteristics are clear, phenomena involved in its occurrence are very complex and are still worth of investigation. In particular, the definition of an absolute knock intensity and the precise determination of the knock onset are arduous and many index and methodologies has been proposed.
In this work, most used methods for knock onset detection from in-cylinder pressure analyses have been considered. Moreover, same methodologies were applied also to the ionization signal collected through the spark plug, properly instrumented. High speed imaging has been carried out in the combustion chamber of a high performance DISI engine provided with an optical window in the piston top. In this way, it has been possible to follow the entire combustion evolution almost until the cylinder borders. Particularly, the knock onset has been determine with a resolution of about 0.1 crank angle degrees. Three engine conditions were explored with different knock intensities, high medium and borderline. In this way it has possible to evaluate the real resolution of different knock onset detection methods also depending on knock severity.
Francesco Catapano, Paolo Sementa, Bianca Maria Vaglieco