Hydrogen power train

Several models of HICE vehicles have been demonstrated and few are commercially available [25,28,33,38]. However, hydrogen-powered vehicles will not be available to common public until there is an adequate refueling infrastructure and trained technicians to repair and maintain these vehicles. The design of each hydrogen-powered vehicle may vary from manufacturer to manufacturer and model to model. One model may be simple in design... 

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). 

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. 

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...

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. 

Fuel cell technology provides the potential for a true local zero emission power train if hydrogen is used as the fuel in combination with higher energy densities and fast refueling. The energy density is mainly limited by the energy density of... 

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. 

As an energy carrier, hydrogen is exclusively used as the fuel for PEMFCs, the power train of the energy-efficient, enviromnentally friendly, and the most promising vehicles, FCVs. Reforming of hydrocarbons is the most economic and dominant pathway for H2 production. However the existence of trace amounts of impurities in hydrogen products is inevitable. Some impurities, such as CO, CO2, H2S, and NH3, are detrimental to the PEMFC anode, which normally operates at a low temperature and uses Pt as the catalyst. 

Tank-to-wheels efficiency Fuel ceU systems use less energy than conventional power trains, because of the intrinsic high efficiency of the stacks. Hydrogen-based FCVs exhibit significantly higher fuel economy than those employing on-board fuel processors. 

Tank to Speed Efficiency The power train working in conventional vehicles requires more energy compared to fuel cell systems. The latter have intrinsic high efficiency of the stacks. The sffidy also exhibited higher fuel economy for hydrogen-based FCVs compared to those processing fuel on board. 

The optimization of performance and efficiency needs an experimental analysis of the power train, which has to be effected in both stationary and transient conditions (including standard driving cycles). Corbo et al. (2005) have carried out such a study with a 2.5 kW PEMFC stack coupled to an electric propulsion chain of 3.7 kW. The control unit of the system allowed the main stack operative parameters (stoichiometric ratio, hydrogen and air pressure, temperature) to be varied and regulated in order to obtain optimized polarization and efficiency curves. 

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