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

Multiple measures were investigated for this study to enhance a passive pre-chamber igniter’ gas exchange 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. 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 emission and increasing efficiency at high engine loads. There are two configurations of pre-chamber igniters: firstly, passive pre-chambers, secondly, scavenged pre-chamber. The focus of this study is 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 gases inside it during engine charge exchange. The combustion products of the last working cycle need to be replaced by a fresh air-fuel mixture for the next ignition. Controlling the pre-chamber gas exchange is decisive for potential series applications. The pre-chamber’s geometrical design is crucial for the gas exchange, albeit not adaptable under engine operation. There is a need to discover such parameters to ensure stable engine operation. Candidates for this study were adapted valve actuation and split injections, both established technologies in spark ignition engines. Analysis of the pressure traces in main and pre-chamber provide insight to pre-chamber gas exchange and combustion initiation. Measurements of the exhaust gas composition and visualization of the ignition via an endoscopic optical access to the combustion chamber underline the effectiveness of the introduced parameters to enhance passive pre-chamber ignition.