Load-Exchange Optimization for a Passive Pre-Chamber Ignition System

Increasing ignition energy by replacing standard spark igniters with pre-chambers is an established combustion accelerator. With rapid combustion on the one hand, mixture dilution can be extended while maintaining the combustion stability at adequate levels. On the other hand, accelerated combustion reduces the need for knock-induced spark retarding, thus facilitating emission reduction and increases in efficiency simultaneously. A newly developed pre-chamber ignition system is introduced in this work. The influence of the system on combustion is investigated in a single-cylinder research engine. The findings can support the development of future ignition technology for passenger-vehicle-sized engines. There are two basic configurations of pre-chamber igniters: the first is known as passive pre-chamber, the second as scavenged pre-chamber. The first configuration can be realized as a simple replacement for standard spark plugs. While additional costs are minimized, the air-fuel ratio inside the pre-chamber cannot be influenced independently of the main chamber. Consequently, the major challenge for passive pre-chamber igniters is operating in engine map areas suffering from deteriorated pre-chamber load exchange at low engine load, for example. The second configuration allows precise air-fuel ratio control inside the pre-chamber to circumvent those issues by employing a dedicated pre-chamber injector. However, the overall system cost and complexity increase drastically. Solving these issues is decisive for potential series applications. Geometrical design and adapted valve timing are considered remedies in this publication. As preparation for experimental investigations at a single-cylinder testbench, 3D-CFD simulations were employed to determine promising pre-chamber geometries in the first place. Different pre-chamber geometries have subsequently been investigated with an engine testbench to validate the findings from the simulations. Analysis of the pressure traces in the main and pre-chamber provide insight into the quality of pre-chamber load exchange and combustion initiation. Adaptive valve actuation strategies supported the pre-chamber load exchange, consequently leading to optimized engine behavior.