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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.

In a previous study, a wide range of gasolines with RON∼90 were tested in a single cylinder engine operated in HCCI mode using negative valve overlap, and all were found to have very similar behavior near the low-load limit. Here we broaden the range of gasolines to include PRF90 and PRF60. At high engine speed, both PRF60 and PRF90 behave similarly to all the other gasolines tested. However, at 1000 RPM, PRF90 is very different from all the other gasolines: it ignites very late, and the engine cannot be operated at low load. Simulations using a popular fuel chemistry model cannot distinguish PRF60 and PRF90 under these conditions. However, a new fuel chemistry model correctly shows the onset of fuel sensitivity at low engine speed. Sensitivity analyses indicate the low-load limit at low engine speed strongly depend on both the chemistry parameters and on the heat-transfer parameters.