Transient Drive Cycle Modeling of Supercharged Powertrains for Medium and Heavy Duty On-Highway Diesel Applications 2012-01-1962

The problem with traditional drive cycle fuel economy analysis is that kinematic (backward looking) models do not account for transient differences in charge air handling systems. Therefore, dynamic (forward looking) 1D performance simulation models were created to predict drive cycle fuel economy which encompass all the transient elements of fully detailed engine and vehicle models. The transient-capable technology of primary interest was mechanical supercharging which has the benefit of improved boost response and "time to torque." The benefits of a supercharger clutch have also been evaluated.

The current US class 6-8 commercial vehicle market exclusively uses turbocharged diesel engines. Three vehicles and baseline powertrains were selected based on a high-level review of vehicle sales and the used truck marketplace. Fuel economy over drive cycles was the principal output of the simulation work. All powertrains are based on EPA 2010 emission regulations. Two methodologies for NO_x reduction were also included: high percentage EGR only (for in-cylinder NO_x reduction) and low percentage EGR + SCR aftertreatment catalyst. - Class 6 Delivery truck, mid-6L displacement, FTP72 drive cycle, - Class 8 Vocational truck, 13L engine, HD-UDDS drive cycle, and Class 8 Line haul, 15L engine, HHDDT Cruise drive cycle.

Two new modeling methodologies using GT-Suite were developed in the process. Detailed dynamic models are more CPU intensive but provided output that cannot be accounted for with faster running steady state or kinematic models. The improved boost response of supercharged configurations exhibited improved vehicle performance without increasing the rated power/torque levels. Various levels of downspeeding are applied which allow either improved performance or improved fuel economy, or both, compared to the baseline turbocharged powertrain. Supercharger sizing, supercharger placement (pre- or post-compressor in a series-boosted configuration), and EGR loop configuration were also evaluated. A fuel economy improvement has been realized in all three vehicle applications.