Integration of a Dual-Mode SI-HCCI Engine Into Various Vehicle Architectures

A simulation study was performed to evaluate the potential fuel economy benefits of integrating a dual-mode SI-HCCI engine into various vehicle architectures. The vehicle configurations that were considered include a conventional vehicle and a mild parallel hybrid electric vehicle. The two configurations were modeled and compared in detail for a given engine size (2.0 L) over the EPA UDDS (city) and highway cycles. The results show that the dual-mode engine in the conventional vehicle offers a modest gain in vehicle fuel economy of approximately 5-7%. The gains were modest because the baseline (the SI engine in the conventional vehicle) is relatively advanced with a six-speed automated manual transmission. The mild parallel hybrid with the SI engine achieved 32% better fuel economy than the conventional vehicle in the city, but only 6% on the highway. For the dual-mode engine in the mild parallel hybrid, a specific control strategy was used to manipulate engine operation in an attempt to minimize the number of engine mode transitions and maximize the time spent in HCCI. The parallel hybrid with the dual-mode engine and modified control strategy provides dramatic improvements of up to 48% for city driving, demonstrating that the addition of HCCI has a more significant impact with mild parallel hybrids than with conventional vehicles. Finally, a systematic study of engine sizing provides guidelines for selecting the best option for a given vehicle application.