Fuel Economy Benefits and Aftertreatment Requirements of a Naturally Aspirated HCCI-SI Engine System

This vehicle simulation study estimates the fuel economy benefits of an HCCI engine system and assesses the NOx, HC and CO aftertreatment performance required for compliance with emissions regulations on U.S. and European regulatory driving cycles. The four driving cycles considered are the New European Driving Cycle, EPA City Driving Cycle, EPA Highway Driving Cycle, and US06 Driving Cycle. For each driving cycle, the following influences on vehicle fuel economy were examined: power-to-weight ratio, HCCI combustion mode operating range, driving cycle characteristics, requirements for transitions out of HCCI mode when engine speeds and loads are within the HCCI operating range, fuel consumption and emissions penalties for transitions into and out of HCCI mode, aftertreatment system performance and tailpipe emissions regulations. A key result of this work is that development priorities for attaining maximum fuel economy during urban driving cycles in the U.S. and Europe differ greatly due to the emissions regulations. Compliance with U.S. Tier 2 Bin 2 regulations requires lean NOx aftertreatment system conversion efficiencies that approach those of a three-way catalyst.