Dedicated-EGR™ (D-EGR™) is a concept where the exhaust of one dedicated cylinder (D-Cyl) is routed into the intake thus producing EGR to be used by the whole engine. The D-Cyl operates rich of stochiometric which produces syngas that enhances the EGR stream permitting faster combustion and greater knock mitigation. Operating an engine using D-EGR improves the knock resistance which can permit a higher compression ratio (CR) thereby increasing efficiency. One challenge of traditional D-EGR is that the D-Cyl combustion becomes unstable operating with both rich and EGR dilute conditions. Therefore, the ‘Split Intake D-EGR’ concept seeks to resolve this problem by feeding fresh air to the D-Cyl, thus allowing even richer operation in the D-Cyl which further increases the H2 and CO yield thereby enhancing the efficiency benefits.
This concept was employed on a downsized PSA EP6CDTx 1.6 L gasoline engine with a baseline BMEP of 20 bar, a CR of 10.5:1, and a peak brake thermal efficiency (BTE) of 36%. After a careful analysis of the CR feasible for the baseline engine, the CR for the D-Cyl was increased from 10.5:1 to 12:1. Furthermore, at both part-load and knock-limited conditions, the Split Intake D-EGR strategy demonstrated better engine BTEs in comparison with the conventional D-EGR and baseline external and internal EGR systems. Proper implementation of the Split Intake D-EGR strategy led to a BTE increase to 39.64% from the baseline of 36%.
Apart from the efficiency benefits, the other advantage of running a Split Intake D-EGR system is that the dedicated cylinder could be operated independently of the main cylinders due to the additional throttle for the D-Cyl. An imbalanced IMEP approach was explored during this study where the dedicated cylinder was operated at a 40% higher IMEP compared to the main cylinders, thus producing more EGR for a given operating condition.