Experimental Studies on the Occurrence of Low-Speed Pre-Ignition in Turbocharged GDI Engines

In the present paper the results of a set of experimental investigations on LSPI are discussed. The ignition system of a test engine was modified to enable random spark advance in one of the four cylinders. LSPI sequences were successfully triggered and exhibited similar characteristics compared to regularly occurring pre-ignition. Optical investigations applying a high speed camera system enabling a visualization of the combustion process were performed. In a second engine the influence of the physical properties of the considered lubricant on the LSPI frequency was analyzed. In addition different piston ring assemblies have been tested. Moreover an online acquisition of the unburned hydrocarbon emissions in the exhaust gas was performed.

The combination of these experimental techniques in the present study provided further insights on the development of LSPI sequences. In particular strong evidence enabling the identification of the fundamental trigger of premature, local auto-ignitions has been found. The results of the optical investigations reveal that pre-ignition is initiated in the immediate vicinity of glowing solid particles. The particles either result from the flaking of deposits or as a consequence of the contamination of the combustion chamber subsequent to a pre-ignition event.