Numerical analysis of the passive pre-chamber ignition concept for light duty applications

Abstract

The use of advanced ignition concepts and enhanced combustion strategies is being widely studied for modern engine applications. In this framework, the passive pre-chamber ignition system is gaining popularity for its mechanical simplicity. However, in order to implement this ignition system in passenger car vehicles, the concept must be able to operate in the whole engine map. Numerous experimental investigations in the literature have found that the concept operates suitably at high load/speed conditions but has several problems operating at low engine load/speeds. However, not many investigation conducted to date have focused on comparing and understanding the underlying physics of this ignition strategy in different engine load/speed conditions. Therefore, in this investigation, a numerical study is carried out using a state of the art 3D-CFD model, to analyze the performance of the passive pre-chamber ignition system in three relevant operating conditions of the engine map. A novel methodology is developed to analyze the fundamentals of the passive pre-chamber concept in terms of internal flow field characteristics, combustion and energy conversion. The model is validated with experiments performed previously by the authors. In particular, the low load/speed operating point, representative of idle conditions, was deeply analyzed to asses the issues reported in the literature. Results have shown that the inherent deterioration of the flow field properties inside the pre-chamber as the engine load/speed decreases, compromises the operation at low load/speed conditions. The energy conversion in the pre-chamber is also worsened when operating at lower load/speeds, hindering the generation of suitable jets for igniting the main chamber charge. Moreover, the position of the pre-chamber in the cylinder head has a significant impact on the energy distribution in the main chamber. The results also revealed that a higher amount of non-reacting/cold flow is ejected from the pre-chamber as the spark is pushed from MBT conditions towards the top dead center (TDC), and the gap between the triggering of the spark and the onset of main chamber combustion increases. The findings of this article have allowed to close the knowledge gap between the physical characteristics of the passive pre-chamber concept and the experimental trends found in other researches on this topic.