The winning paper was “Assessing the low load challenge for jet ignition engine operation” written by M.P. Bunce, N.D. Peters, S.K. Pothuraju Subramanyam, H.R. Blaxill of MAHLE Powertrain LLC, USA.
Highly dilute combustion in spark ignition (SI) engines is an advanced engine operating mode that has been proven to produce significant increases in efficiency, a requirement for future engines. This operation necessitates the use of an advanced ignition concept. MAHLE Jet Ignition (MJI)® is a pre-chamber-based concept that produces high energy distributed ignition events throughout the cylinder, enabling rapid, stable combustion under highly dilute conditions.
Pre-chambers have historically had challenges at low loads such as idle and catalyst heating. This includes poor combustion stability and severely limited ability to retard spark timing. This study found that the poor performance at low loads was due to an arresting of the gas exchange process between the pre-chamber and the cylinder induced by heavy throttling. This resulted in ineffective purging of residual gases from the pre-chamber, leading to unstable pre-chamber combustion which propagated throughout the burning process in the cylinder.
The added flexibility of auxiliary fueled pre-chamber concepts such as MJI was leveraged to mitigate these challenges. The introduction of partial dilution at idle loads allowed for more effective purging of residuals. Under catalyst heating conditions, the addition of auxiliary pre-chamber fuel provided more direct control over pre-chamber mixture preparation, resulting in reduced instability in the pre-chamber combustion event. These steps, in conjunction with other optimization activities, resulted in the MJI multi-cylinder engine achieving idle and catalyst heating performance comparable to those of modern SI engines. These results represent progress in ensuring the applicability of high efficiency jet ignition concepts across the full range of operation required of modern engines.