Hydrogen fuel cell power train

Fig. 6.27 Experimental results obtained on the fuel cell power train in hard hybrid configuration for the R47 driving cycle a battery, input electric drive, and output DC-DC converter powers versus cycle length, b hydrogen, input and output DC-DC converter powers versus cycle length, c battery state of charge versus cycle length...

Froeschle, P. and Wind, J. (2010) Fuel cell power trains, in Hydrogen and Fuel Cells (ed. D. Stolten.), Wiley-VCH Verlag GmbH, Weinheim, pp. 793-810. 

It is because hydrogen fuel cells might one day meet all of the requirements for the automotive power train of the future that they have become such a focus of government and industry initiatives. 

A conventional FPS, shown in Fig. 14.2, includes a reformer, two WGS reactors, and two Preferential Oxidation (PrOx) reactors, located downstream of the WGS. For PEM fuel cells, it is a necessity to assure < 10 ppm of CO in the cell stack. These reactors form a considerable fraction of the FPS weight, volume, and cost. Replacing this train by an integrated hydrogen permeation selective membrane on the water gas shift reactor, shown in Fig. 14.3, results in a considerable reduction in the number of components, cost, and volume of the FPS. This will make fuel cell power plants practical and affordable for power generation in a wide range of applications, especially for residential and transportation. Numerous published works [8, 9] in the area of catalytic membrane reactors can be quoted in the experimental [10] and numerical [11, 12] domains. 

The most attractive feature of the fuel cell technology is probably its superior energy efficiency as a part of a hydrogen-fuel cell-electro-motor power-train, that is, in the tank-to-wheel (TtW) part of the fuel chain. On the other hand, the energy loss in hydrogen production, that is, in the well-to-tank (WtT) part of the fuel chain, is considerable. The total well-to-wheel (WtW) efficiency is potentially superior to even advanced ICVs or hybrid solutions. 

Today, the power train costs of fuel-cell vehicles are still far from being competitive. They have the largest influence on the economic efficiency of hydrogen use in the transport sector and the greatest challenge is to drastically reduce fuel-cell costs from currently more than 2000/kW to less than 100/kW for passenger cars. On the other hand, fuel-cell drive systems offer totally new design opportunities for... 

The DMFC, based on a polymer electrolyte fuel cell (PEFC), uses methanol directly for electric power generation and promises technical advantages for power trains. The fuel can be delivered to the fuel cell in a gaseous or liquid form. The actual power densities of a DMFC are clearly lower than those of a conventional hydrogen-fed polymer electrolyte fuel cell. In addition, methanol permeates through the electrolyte and oxidizes at the cathode. This results in a mixed potential at the cathode (Hohlein et al., 2000). 

Many fuel cell systems have been developed since the first discovery of Sir William Grove. Fuel cell systems can produce electricity from several fuels (hydrogen, natural gas, alcohols, etc.) for many applications stationary power plants, power train sources, APU, and electronic portable devices, with nearly the same energy efficiency (around 40% in electric energy), irrespective of their size (from tens of MW for power plants to a few W for portable electronics). 

In recent years the concept of a fuel cell propulsion system has gained in attention as a result of the need to reduce the fossil fuel consumption and greenhouse gas emissions. Since the fuel cells suitable for vehicle application (polymeric electrolyte membrane fuel cells) are fuelled by hydrogen, and deliver power as long as fuel and air are supplied, they potentially can provide the range capabilities of an internal combustion engine when used in a power system, but with clean and quiet operation. Therefore, the fundamental benefit of this type of propulsion consists in the possibility to adopt pollution-free electric drive-trains, without the drive range limitations typical of traditional electric vehicles. 

The analysis of the main aspects to be faced in design and realization of a fuel cell system as power source of an electric drive train is described in Chap. 4. Here the problems connected to the choice of auxiliary components, their energy consumption and integration in the overall system are discussed, paying particular attention to the management of membrane humidification, hydrogen purge and air supply as a way to optimize system efficiency and reliability. 

---