Karl-Heinz Hauer

A Comparison of Energy Use for a Direct-Hydrogen Hybrid Versus a Direct-Hydrogen Load-Following Fuel Cell Vehicle

Hybridizing a fuel cell vehicle has the potential to improve the vehicle efficiency largely due to the ability to recover braking energy. However, tradeoffs do exist, and the advantages (in terms of potential fuel savings) are largely dependent on the drive cycle. The tradeoffs include added energy losses associated with the DC/DC converter and the battery pack itself. Additional tradeoffs not explicitly addressed in this study include added overall complexity, additional packaging constraints, and potentially higher overall cost. This report will focus on a quantitative analysis of the performance of the direct-hydrogen (DH) hybrid and load-following fuel cell vehicles (FCVs) from the viewpoint of the energy use throughout the system. Specifically, the vehicle energy use and efficiency will be compared between the load following and hybrid vehicle platforms. Several hybrid component configurations were studied. When the DC/DC converter is placed in the path of the fuel cell stack current, there does not appear to be much benefit, in terms of energy usage, in hybridizing the DH fuel cell vehicle. Specifically, on the US EPA cycles, the load following vehicle outperformed the hybrid on the HIWAY sequence, but the hybrid had slightly better results on the FUDS cycle. However, if the DC/DC converter is placed in the battery current path only, with the fuel cell stack directly connected to the electric drive train, the benefits in terms of improved fuel economy are larger than in the first configuration. This later configuration will be the design used for this study. Overall, three main factors affect these vehicle results, all of which will be explicitly examined in this study. These factors are: vehicle weight, fuel cell system efficiency (including the battery), and regenerative braking capabilities. Specifically, the hybrid vehicle fuel economy was reduced due to a ∼10% heavier vehicle, and a lower overall system efficiency (when including the battery and DC/DC converter losses). The important factor, therefore, is the regenerative braking capability and whether this gain outweighs the added losses.

Dynamic interaction between the electric drive train and fuel cell system for the case of an indirect methanol fuel cell vehicle

This paper examines the impact of the drive system and fuel cell system characteristics as well as the dynamic interaction between the electric drive train and the fuel cell system of an indirect-methanol fuel cell vehicle (FCV) on vehicle performance. First, simple models for the electric drive train and the fuel cell system will be explained. Second the interaction of the two models is illustrated. Third the effect of parameter variations on the vehicle acceleration from 0-60 mph (ca. 0-100 kph) is analyzed. For this the sub-models for the drive train and the electric motor will be embedded in a vehicle model.

A Comparison of Energy Use for a Indirect-Hydrocarbon Hybrid versus an Indirect-Hydrocarbon Load-Following Fuel Cell Vehicle

Hybrid vehicles have been in the news quite a bit of late given the commercial introduction of a number of hybrid vehicles that sport significant improvements in fuel economy. The improved fuel efficiency of these vehicles can be directly attributable to the hybridized power train on board these internal combustion engine vehicles. Similarly, hybridization of fuel cell vehicles not only helps improve fuel economy but can also help overcome other technical barriers (start up delays, transients). For fuel cell vehicles, hybridization of on-board fuel cell systems is expected to have the potential to improve the vehicle efficiency largely due to the ability to recover braking energy and via flexibility in designing the system controls. However, the advantages can be offset by the tradeoffs due to added energy losses associated with the DC/DC converter and the battery pack itself. Additional tradeoffs not explicitly addressed in this study include added overall complexity, additional packaging constraints, and potentially higher overall cost. This report will focus on a quantitative analysis of the performance of the indirect-hydrocarbon (IH, onboard fuel processor using gasoline type fuel), hybrid and load- following fuel cell vehicles (FCVs) from the viewpoint of the energy use throughout the system. Specifically, the vehicle energy use and efficiency will be compared between the load following (non-hybrid) and hybrid vehicle platforms. Several hybrid component configurations were studied and two representative configurations were investigated in depth. The first (Configuration 1), in which the DC/DC converter is placed in the path of the fuel cell stack current, there does appear to be some benefit, in terms of energy usage, in hybridizing the IH fuel cell vehicle. Specifically, on the US EPA cycles, the hybrid vehicle outperformed the load following vehicle on the FUDS sequence but the load following vehicle had slightly better results on the HIWAY cycle. However, if the DC/DC converter is placed in the battery current path only, with the fuel cell stack directly connected to the electric drive train (Configuration 2), the benefits in terms of improved fuel economy are larger than in the first configuration. The results corresponding to both these configurations will be analyzed and discussed in this paper.

A Simulation Model for an Indirect Methanol Fuel Cell Vehicle

Author(s): Hauer, Karl-Heinz; Moore, Robert M; Ramaswamy, Sitaram | Abstract: Presented at the Future Transportation Technology Conference a Exposition, Costa Mesa, CASession: Alternative Fuels a Fuel CellsThis work focuses on the algorithms to simulate and analyze the characteristics of an indirect methanol fuel cell vehicle. The individual components of the electric drive train including transmission, the vehicle properties, such as drag, frontal area, wheel inertia etc., and the fuel cell system are modeled in a dynamic manner. Further the interaction between the individual components and a simple driver model is described. The algorithms are coded using the simulation tool Matlab/Simulink.The simulation tool is strictly set up in a modular form allowing modifications of individual component characteristics or control algorithms without the need to change the remainder of the model. For the benefit of a more in depth discussion of the applied algorithms and the setup of the model this paper focuses solely on the case of an Indirect Methanol Fuel Cell Vehicle (IMFCV) with steam reformer and without any additional energy storage. Other papers expanding this initial work and discussing various cases of hybridization (batteries, ultra capacitors, reformate gas storages or other fuel cell systems) are under preparation.It is important to notice that the focus of the paper is on the explanation of the algorithms and not the calculation of the fuel consumption or emissions associated with one specific vehicle design or technology. Therefore all quoted data are only illustrative but are not intended to serve as evaluations of the potential of a certain technology.