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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.

Fuel cell vehicles powered using Hydrogen/air fuel cells have received a lot of attention recently as possible alternatives to internal combustion engine. However, the combined problems of on-board Hydrogen storage and the lack of Hydrogen infrastructure represent major impediments to their wide scale adoption as replacements for IC engine vehicles. On board fuel processors that generate hydrogen from on-board liquid methanol (and other hydrocarbons) have been proposed as possible alternative sources of Hydrogen needed by the fuel cell. This paper focuses on a methanol fuel processor using steam reformation of methanol to generate the Hydrogen required for the fuel cell stack. Since the steam reformation is an endothermic process the thermal energy required is supplied by a catalytic burner.

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.

Vehicle manufacturers claim that fuel cell vehicles are significantly more fuel-efficient and emit fewer emissions than conventional internal combustion engine vehicles /1/. A computer model can help to explore and understand the underlying reasons for this potential improvement. In previous published work, the UC Davis Vehicle Model for the case of a load-following Indirect Methanol Fuel Cell Vehicle (IMFCV) has been introduced and discussed in detail /2/. Because of possible technical barriers with load following vehicles, as well as near term cost issues, hybrid fuel cell vehicle concepts are widely discussed as another fuel cell vehicle option. For load following vehicles, the questions of fast start up and fuel processor dynamics in extreme transient situations, (e.g., during phases of hard acceleration) are not totally resolved at this time. For both of these performance issues, a hybrid design could offer at least an interim solution.

This 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 setup 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.

This paper deals with system level analysis of a methanol fuel processor for an indirect hydrogen-Air based Fuel Cell Vehicle (FCV) based on a Proton Exchange Membrane (PEM) fuel cell stack. This analysis focuses on the performance of the fuel processor from the viewpoint of efficiency and the requirements placed on it by the Fuel Cell Vehicle. It is widely accepted that hydrogen supply is an important issue in PEM-FC vehicle systems. The lack of a well-entrenched hydrogen infrastructure and the nascent state of hydrogen storage technology has led to development of on-board hydrogen generation systems to meet the fuel cell hydrogen demand. The primary fuel is typically a Hydrocarbon (methanol, gasoline) which is then “reformed” in a fuel processor to generate the hydrogen needed by the fuel cell stack. A great deal of effort has been expended in developing fuel processors that would satisfy the rigorous demands of automotive applications.

This paper examines the impacts of fuel cell system parameters and control strategies on the dynamic response of an indirect-methanol fuel cell vehicle (FCV). An indirect-methanol fuel cell system model is introduced and explained, and then the effect of parameter variations on the vehicle acceleration from 0-60 mph (ca. 0-100 kph) is analyzed. Varied parameters are the fuel processor response time, the utilization rate and the fuel cell system size (qualitatively). In addition two different fuel cell system control strategies are introduced and are compared with respect to their impact on vehicle acceleration. If poor fuel processor dynamics are the limiting factor, the vehicle acceleration can be improved adopting an alternative control strategy -- without major changes in hardware but accepting a lower fuel economy.