Fuel Efficiency Estimates for Future Light Duty Vehicles, Part A: Engine Technology and Efficiency

This study evaluates powertrain technologies capable of reducing light duty vehicle fuel consumption for compliance with 2025 CAFE standards. A fully integrated GT-Power engine model with physics based sub-models was developed to capture any positive or negative synergies between the technologies. The two zone multi-cylinder engine model included typical thermodynamic subroutines, with predictive combustion, flame quench and knock models, along with map-based turbocharger models to capture key combustion and efficiency behaviors. The engine model was calibrated to data from a boosted GDI engine and exercised through one series of current and production viable technology configurations for 2025 regulations. Technologies evaluated included: dual cam phasing and discrete variable valve lift to reduce pumping work, engine friction reduction via improved lubrication, gasoline direct injection, downsized and boosted operation to reduce the relative contributions of friction and pumping losses, and the introduction of cooled EGR to mitigate knock. The results showed that the valvetrain improvements reduced pumping work and widened the low BSFC islands without impacting peak efficiency. While downsizing and boosting provided little fuel economy benefit at a constant BMEP, it provides a benefit at constant engine torque by shifting operation to higher BMEPs with improved efficiency. The introduction of cooled EGR improved efficiency slightly at constant BMEP. The impact of these engine efficiency improvements on the resulting vehicle fuel economy is studied in a companion paper.