Engine Knock Detection Methods for Spark Ignition and Prechamber Combustion Systems in a High-Performance Gasoline Direct Injection Engine

Knock has historically been one of the main limitations on spark ignition (SI) engine compression ratio and hence efficiency. The trend to downsizing or rightsizing in recent years, driven by everreducing carbon dioxide (CO2) targets, has increased the relevance of the knock limit for typical engine operating conditions. Even for scenarios where an engine is run on carbon-neutral fuel, thermal efficiency will always be fundamental in terms of best use of scarce resources. Knock, therefore, remains a relevant topic for current and future research. Knock is typically quantified through analysis of high-pass-filtered cylinder pressure signals. For SI engines, this is relatively unproblematic. A promising technology for further combustion engine efficiency gains, however, is prechamber ignition. It has been noted that prechamber combustion systems result in significant high-frequency content on the cylinder pressure trace in the bandwidth of interest for knock. It is therefore more difficult to accurately determine the knock limit for such engines, which is necessary in order to make a fair comparison to traditional SI systems. There is relatively little detail on this key topic in the existing literature. Accordingly, this study compares knocking experimental data from the same high-performance single-cylinder research engine with both SI and prechamber combustion systems. Established and new approaches of interpreting the knocking data are examined, applying both high-frequency and low-frequency techniques to cylinder pressure signals, complemented by statistical methods. The analysis conducted demonstrates that for knocking prechamber combustion, three distinct combustion stages are detected. The high-frequency content of the prechamber pressure signal is also more complex and is analyzed in detail. A significant gain in knock-limited (KL) combustion phasing is thus confirmed for the prechamber igniter, at appropriate levels of knock, in comparison to the standard spark plug (SP) system.