Abstract
Keywords - fuel economy, variable valve actuation, direct-injection, stratified-charge, compression-ignition
Future powertrains are required to generate high torque and power, ultra-low emissions, and provide great fuel economy. Today, the diesel engine sets the standard for fuel economy, but faces significant emission challenges. The naturally aspirated gasoline engine generates good power with low emissions potential when using highly efficient three-way aftertreatment, but needs further development to improve fuel economy. Current high-volume production gasoline engines are port-fuel-injected (PFI) and calibrated with internal or external EGR, providing some additional fuel economy with lower engine-out NOx emissions. The PFI engine is being replaced with the spark-ignition-direct-injection (SIDI) engine to provide better fuel economy along with better idle quality, cold-start emissions, and wideopen- throttle (WOT) performance. Variable intake-valve lift and duration mechanisms are being introduced to unthrottle the engine for better fuel economy. The homogeneous-charge engine can also be calibrated lean of stoichiometry to improve fuel economy with the added challenge of managing lean NOx emissions. The stratified-charge and homogeneous-chargecompression- ignition (HCCI) gasoline engines offer the highest fuel economy potential along with significant emission and control challenges. This paper provides a comparison of these gasoline engine technologies, focusing on the fuel consumption potential during normal driving conditions. A breakdown of the individual mechanisms including reduced pumping work and improved indicated efficiency is provided with the intention to explore synergies between the various technologies. To illustrate the feasibility of successfully transferring steady-state multi-cylinder engine performance to the vehicle, a fuel economy analysis along with measured vehicle fuel consumption is provided for one stratified-charge engine concept.