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Several diesel passenger car boosting systems were studied to assess their impact on vehicle performance and fuel economy. A baseline 1.5L diesel engine model with a single VGT turbocharger was obtained through Gamma Technologies' fast running model library. This model was modified to explore multiple two stage boosting systems to represent the anticipated architecture of future engines. A series sequential turbocharged configuration and a series turbocharger-supercharger configuration were evaluated. The torque curves were increased from that of the original engine model to take advantage of the increased performance offered by two stage boosting. The peak cylinder pressure for all models was limited to 180 bar. Drive cycle analysis over the WLTP was performed using these engine architectures, while assessing the sensitivity to various system parameters. These parameters include: vehicle weight and aerodynamic drag, EGR target maps, level of downspeeding, and turbocharger inertia.

In order to improve power density, the majority of diesel engines have intake manifold pressures above atmospheric conditions. This allows for the introduction of more fuel, which results in more power. Except for a few applications, these engines receive charged air from a turbocharger. The turbocharger develops boost by converting exhaust gas energy into power. This power is then used to compress the intake charge. The medium- and heavy-duty engine markets have both stringent regulatory targets and customer demand for improved fuel efficiency. Two approaches used to meet fuel efficiency targets are downspeeding and downsizing. Until now, the industry has adapted to the turbocharger lag experienced during a transient acceleration event. This performance deficiency is severely exaggerated when the displacement and speed of an engine are reduced. The solution proposed to improving fuel economy, while maintaining equivalent performance, is supercharging.

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.