Lean Miller Cycle System Development for Light-Duty Vehicles (Final Report)

Abstract

This report summarizes activities conducted in support of the project “Lean Miller Cycle System Development for Light-Duty Vehicles” under Cooperative Agreement Number DE-EE0006853. In order to accomplish the government objective of achieving breakthrough thermal efficiencies while meeting U.S. EPA emission standards, this project focused on combining two enabling technologies in a gasoline engine: lean combustion and “Miller Cycle.” Lean combustion is thermodynamically more efficient than stoichiometric combustion but requires a more complex exhaust aftertreatment system compared to a traditional three-way catalyst system. The “Miller Cycle” concept increases expansion of combustion gases to extract additional work, reduces pumping losses, and increases efficiency. The objective of the project was to research, develop, and demonstrate the new Lean Miller Cycle (LMC) combustion concept to achieve a 35% improvement in fuel economy over a 2010 production baseline vehicle. The baseline vehicle chosen was a Chevrolet Impala equipped with a 3.5L V6 port-fuel injected naturally-aspirated engine, a four-speed automatic transmission with a peak-power and -torque of 157 kW and 290 N-m respectively. The enabling technologies were developed and demonstrated on a single cylinder engine and then integrated into a multicylinder engine and aftertreatment system. Along with achieving the efficiency targets, the downsized boosted LMC engine system was projected to achieve a peak-power and –torque of 172 kW at 354 Nm respectively exceeding the baseline engine performance. The multicylinder engine was optimized and calibrated over a set of steady-state operating points on an engine dynamometer. The target of the project was a 35% improvement in combined city/highway fuel economy at SULEV30 tailpipe emissions over the baseline vehicle. The project achieved a projected 42.4% from the vehicle drive cycle analysis assuming no penalty for management of the lean-aftertreatment system. This penalty was projected to fall within the fuel economy margin achieved and include control and calibration compromises for catalyst heating, NH3 formation for lean-NOx SCR and drive quality. A final vehicle demonstration was planned where emissions, drivability and performance were to be confirmed. Four decision gates were set up annually with deliverables to assess progress and determine whether status to deliverables warranted project continuation through the final vehicle demonstration. The project was closed in June 2019 at the end of budget period three after not passing the third decision gate due to projected system costs prohibiting economic feasibility in the light-duty vehicle industry landscape. However, the project’s efficiency targets were achieved by validation through steady-state dynamometer testing of the multicylinder engine.