The Impact of Engine Operating Conditions on Reformate Production in a D-EGR Engine

Dedicated EGR has shown promise for achieving high efficiency with low emissions [1]. For the present study, a 4-cylinder turbocharged GDI engine which was modified to a D-EGR configuration was used to investigate the impact of valve phasing and different injection strategies on the reformate production in the dedicated cylinder. Various levels of positive valve overlap were used in conjunction with different approaches for dedicated cylinder over fueling using PFI and DI fuel systems. Three speed-load combinations were studied, 2000 rpm 4 bar IMEP_g, 2000 rpm 12 bar IMEP_g, and 4000 rpm 12 bar IMEP_g. The primary investigation was conducted to map out the dedicated cylinders' performance at the operating limits of intake and exhaust cam phasing. In this case, the limits were defined as conditions that yielded either no reformate benefit or led to instability in the dedicated cylinder. Based on the result of cam timing sweeps for both PFI and a DI strategy, valve timing strategies were developed to maximize reformate production. Further, a detailed sweep of dedicated cylinder equivalence ratio (Φ) was conducted at near optimum valve phasing to study the differences between various fuel injection strategies at each speed-load combination.