Computational Development of a Dual Pre-Chamber Engine Concept for Lean Burn Combustion

Pre-chambers are a means to enable lean burn combustion strategies which can increase the thermal efficiency of gasoline spark ignition internal combustion engines. A new engine concept is evaluated in this work using computational simulations of non-reacting flow. The objective of the computational study was to evaluate the feasibility of several engine design configurations combined with fuel injection strategies to create local fuel/air mixtures in the pre-chambers above the ignition and flammability limits, while maintaining lean conditions in the main combustion chamber. The current work used computational fluid dynamics to develop a novel combustion chamber geometry where the flow was evaluated through a series of six design iterations to create ignitable mixtures (based on fuel-to-air equivalence ratio, φ) using fuel injection profiles and flow control via the piston, cylinder head, and pre-chamber geometry. The desirable and undesirable features that guided the design progression are presented. Major combustion chamber design iterations involved changes to the pre-chambers position relative to the cylinder head deck plane, azimuthal orientation of the pre-chambers, and piston crown geometry. Further criteria were developed to assess the flow interaction with the nozzle connections to the pre-chambers. The modeling results indicated appropriate fueling strategies achieved near stoichiometric fuel-to-air equivalence ratios in the pre-chambers with lean fuel-to-air equivalence ratios in the main chamber. The results also demonstrated the utility of the flow-alignment and chamber filling criteria to select the nozzle design for the pre-chambers.