Variable Valve Actuation and Split Injection to Enhance the Gas Exchange of a Passive Pre-chamber Igniter

Pre-chambers, in general, represent an established technology for combustion acceleration by increasing the available ignition energy. Realizing rapid fuel conversion facilitates mixture dilution extension with satisfying combustion stability. More importantly, knock-induced spark retarding can be circumvented, thus reducing emissions and increasing efficiency at high engine loads. Adapted valve actuation and split injections were investigated for this study to enhance the gas exchange of a passive pre-chamber igniter in a single-cylinder engine. The findings support the development of passive pre-chamber ignition systems operable over the whole engine map for passenger vehicles. There are two configurations of pre-chamber igniters: passive pre-chambers and scavenged pre-chambers. This study focuses on the passive design, incorporating an additional small volume around the spark plug into the cylinder head. Hot jets exit this volume after the ignition onset through several orifices. These jets ignite the mixture in the main chamber, surpassing the ignition energy delivered by a spark plug. However, the major challenge for such igniters is the replacement of the residual gases during engine gas exchange. The combustion products of the previous working cycle need to be replaced by a fresh air-fuel mixture to facilitate the subsequent ignition. Controlling the pre-chamber gas exchange is decisive for series applications. The geometrical design of the pre-chamber influences its gas exchange. However, additional measures that are adaptable during engine operation must be identified to ensure stable engine operation. For this study, the adaptation of the intake valve actuation was investigated, and the cyclic variation was successfully reduced. Splitting the fuel injection into two separate events further enhanced combustion stability. Comprehensive measurements of the exhaust gas composition underlined the effectiveness of the introduced parameters to enhance passive pre-chamber ignition. Furthermore, analysis of the pressure traces in the main and pre-chamber provides insight into pre-chamber gas exchange and combustion initiation.