Development of Two-Step Exhaust Rebreathing for a Low-NOx Light-Duty Gasoline Compression Ignition Engine

The global automotive industry is undergoing a significant transition as battery electric vehicles enter the market and diesel sales decline. It widely recognized that internal combustion engines (ICE) will be needed for transport years to come; however, demands on ICE fuel efficiency, emissions, cost, performance are extremely challenging. Gasoline compression ignition (GCI) one approach achieving demanding efficiency emissions targets. A key technology enabler GCI partially-premixed, (PPCI) combustion, which involves two high-pressure, late injections during stroke. Both NOx smoke greatly reduced relative diesel, this reduces aftertreatment (AT) requirements significantly. For robust low-load cold operation, two-step valvetrain system used exhaust rebreathing (RB). Exhaust reinduction of hot gases into cylinder second lift event intake stroke help promote autoignition. amount controlled by backpressure, created vanes variable nozzle turbine (VNT) turbocharger. Because higher cycle temperatures rebreathing, HC CO may significantly reduced, while robustness stability also improve. Importantly, increases in order maintain active catalysis AT ultra-low tailpipe emissions. To achieve these benefits, it important optimize rebreathe valve profile develop an RB ON→OFF (mode switch) strategy easy implement control, without engine torque fluctuation. In study, model was developed using GT-Suite conduct steady-state transient simulations process, followed tests. investigation conducted four parts. part 1, various profiles were simulated. evaluated based in-cylinder temperature, pumping work. results compared with alternative actuation (VVA) strategies such early closing (EEVC), negative overlap (NVO), positive (PVO). 2, determine appropriate load range mode switching (exhaust ON/OFF vice-versa). limits both temperature gas well external recirculation (EGR) delivery potential set criteria selection. 3, evaluate switch strategies. OFF, cooled EGR utilized goal dilution switches low most promising mode-switch produced negligible fluctuation switch. Finally, 4, tests conducted, profile, at operating conditions. experiments correlated simulation results. demonstrated simplicity approach. response, CNL, high out achieved region.