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We present simulated fuel economy and emissions of city transit buses powered by conventional diesel engines and diesel-hybrid electric powertrains of varying size. Six representative city drive cycles were included in the study. In addition, we included previously published aftertreatment device models for control of CO, HC, NOx, and particulate matter (PM) emissions. Our results reveal that bus hybridization can significantly enhance fuel economy by reducing engine idling time, reducing demands for accessory loads, exploiting regenerative braking, and shifting engine operation to speeds and loads with higher fuel efficiency. Increased hybridization also tends to monotonically reduce engine-out emissions, but tailpipe (post-aftertreatment) emissions are affected by complex interactions between engine load and the transient catalyst temperatures, and the emissions results were found to depend significantly on motor size and details of each drive cycle.

The University of Tennessee, Knoxville's (UTK) EcoCAR 2 team developed a Series-Parallel Plug-In Hybrid Electric Vehicle (PHEV) that utilizes E85 fuel. The vehicle was developed and modeled in Year One of the EcoCAR 2 competition. The team has spent Year Two refining the theoretical design from Year One and implementing the design into a working mule vehicle. The developed architecture has been integrated into a 2013 Chevrolet Malibu, which was donated by General Motors. The team focused on strengthening the replacement and modified components, integrating the new vehicle components, bench testing the vehicle controller and implementing the entire design into a working vehicle.

We compare the simulated fuel economy and emissions for both conventional and hybrid class 8 heavy-duty diesel trucks operating over multiple urban and highway driving cycles. Both light and heavy freight loads were considered, and all simulations included full aftertreatment for NOx and particulate emissions controls. The aftertreatment components included a diesel oxidation catalyst (DOC), urea-selective catalytic NOx reduction (SCR), and a catalyzed diesel particulate filter (DPF). Our simulated hybrid powertrain was configured with a pre-transmission parallel drive, with a single electric motor between the clutch and gearbox. A conventional heavy duty (HD) truck with equivalent diesel engine and aftertreatment was also simulated for comparison. Our results indicate that hybridization can significantly increase HD fuel economy and improve emissions control in city driving. However, there is less potential benefit for HD hybrid vehicles during highway driving.

We summarize results from comparative simulations of hybrid electric vehicles with either stoichiometric gasoline or diesel engines. Our simulations utilize previously published models of transient engine-out emissions and models of aftertreatment devices for both stoichiometric and lean exhaust. Fuel consumption and emissions were estimated for comparable gasoline and diesel light-duty hybrid electric vehicles operating over single and multiple urban drive cycles. Comparisons between the gasoline and diesel vehicle fuel consumptions and emissions were used to identify potential advantages and technical barriers for diesel hybrids.

The University of Tennessee, Knoxville's (UTK) EcoCAR 2 team chose to develop a Plug-In Series-Parallel Hybrid Electric Vehicle that will utilize E-85 fuel. The architecture will be integrated into a 2013 Chevrolet Malibu, donated by General Motors. Throughout the first year of the competition, Tennessee implemented the EcoCAR 2 Vehicle Development Process. The team focused on the development of the supervisory controller through software simulations and Hardware-in-the-Loop (HIL) simulations. Simultaneously, packaging studies were performed via Computer Aided Design (CAD) for powertrain components, as well as the development of the energy storage system, and finite-element analysis (FEA) of modified vehicle components.

Due to increasing interest in the emissions-producing characteristics of today's automobiles, emissions testing procedures have come under close scrutiny. In addition, development of procedures to measure emissions of vehicles operating in “on-road” conditions have been proposed to gain knowledge of the instantaneous mass flow rates of various legislated gaseous emissions. The problem with the measurement of these instantaneous flow rates is that the responses of modern emissions analyzers to transients are too slow for reliable results. Therefore, a method for improving the dynamic response of these instruments is needed. A method is described which utilizes generalized predictive control theory concepts in conjunction with system identification techniques to produce a software “filter” which reconstructs the distorted output of these analyzers.

A methodology for developing modal vehicle emissions and fuel consumption models is described. These models, in the form of look-up tables for fuel consumption and emissions as functions of vehicle speed and acceleration, are designed for simulations such as the Federal Highway Administration's TRAF-series of models. These traffic models are used to evaluate the impacts of roadway design on emissions and fuel consumption. Vehicles are tested on-road and on a chassis dynamometer to characterize the entire operating range of each vehicle. As a verification exercise the models were used to predict cycle emissions and fuel consumption, and the results were compared to certification-type tests on a different population of vehicles. Results of the verification exercise show that the developed models can generally predict cycle emissions and fuel consumption with error comparable to the variability of repeat dynamometer tests.