A Computational Investigation of Fuel Enrichment in the Pre-Chamber on the Ignition of the Main Chamber Charge

Pre-chamber combustion (PCC) engines allow extending the lean limit of operation compared to common SI engines, thus being a candidate concept for the future clean transportation targets. To understand the fundamental mechanisms of the main chamber charge ignition in PCC engines, the effects of the composition in the pre-chamber were investigated numerically. A well-stirred reactor combustion model coupled with a methane oxidation mechanism reduced from GRI 3.0 was used. An open-cycle simulation was run with initialization at exhaust valve opening (EVO). For posterior simulations, the initial flow field was attained by mapping the field variables obtained from the full cycle simulation. The entire simulation domain (pre-chamber and main chamber) global excess air ratio (λ) was set to 1.3. As parametric variants, additional amounts of fuel were further injected into the pre-chamber to achieve a global pre-chamber λ of 0.7 and 1.0 at spark timing, thus having the pre-chamber and the main chamber with different compositions (emulating an active type pre-chamber). For the same operating conditions, the pre-chamber charge residence time after the spark ignition is mostly governed by the geometry. Therefore, by varying the air/fuel ratio (AFR) in the pre-chamber, it is possible to produce jets with various compositions and ultimately determine the impact of the pre-chamber enrichment on the main chamber response. The results show that the pre-chamber is sensitive to fuel enrichment and the results serve as a baseline guideline for subsequent studies.