Technology Status of Hydrogen Road Vehicles

Wetzel (1996) gives a comprehensive summary of the special facility operating in Germany since 1991,
dedicated to the improvement of LH 2 handling at refueling stations. All operations in the three main refueling
phases (connect--cool down, filling proper, depressurize--disconnect) are automatic, except the relatively
simple ones of connect and disconnect. Total refueling times are now down to 8.6 or 5.2 minutes depending
on the coupling used, and LH 2 releases (which are largely recuperable) are correspondingly down to 14.2 or
8.0 liters, respectively. These improvements are valid for the BMW test car (Item 1 Table 1) which was
frequently refueled at the facility. Hettinger et al. (1996) describe more qualitatively a mobile filling station
for refueling cars and buses with LH 2.
Yamane and Furuhama (1996) is a parameter study concerning on-board hydrogen storage, showing the effect
of total weight of fuel and fuel tank on the main parameters that affect car performance; it concludes by stating
that only LH 2 offers the accustomed performance.
4.0 Vehicle Power Units and Drives
When conventional vehicles were introduced at the end of the last century, several approaches to the
fundamental choices of engine and drive were taken, but the winner--the ICE with geared drive--quickly
emerged and has remained dominant for most of this century. This is not likely to happen with hydrogen
vehicles in the foreseeable future.
As discussed, the choice of fuel storage has a strong influence on system layout, and can directly affect the
choice of prime mover. For example, only LH 2 today seems capable of giving a hydrogen ICE a range
comparable to conventional fuels, at least for cars with limited space; on the other hand, an FC with its much
higher efficiency confers greater flexibility on the choice of fuel storage.
More fundamentally, enough progress has been made during the past 5 years to reinforce the conviction,
already tentative in DeLuchi’s 1989 report, that FCs are a more natural partner for hydrogen in whatever form,
and possess the potential of lower life-cycle costs than the ICE. It is still too early for definite conclusions,
and indeed there is good reason to think that the ICE and a successful FC can coexist for many decades.
The proliferation underway in prime mover research, development, and demonstration can be conveniently
grouped in three broad categories:
! The ICE, usually reciprocating but including the rotary version
! FCs, especially the two types most indicated today for mobile applications
! Hybrids, which re-dimension the prime mover (ICE or FC) size down to average running loads, and cover
transients with energy-storage devices such as batteries, capacitors, or flywheels.
A fourth category could include more speculative concepts; e.g., the external combustion engine--the Stirling
engine is being re-examined because of its adaptability to H 2. They are not included because of lack of
information.
Lund (1996) illustrates an innovative type of hydrogen vehicle that is emerging from the classic electric
vehicle. Instead of traditional lead-acid batteries, Toyota and Panasonic envision upgrading their innovative
Ni-metal hydride batteries to vehicle size, thereby improving energy density and reducing vehicle weight.
4.1 Internal Combustion Engines
The ICE is highly optimized for conventional fuels, but is an awkward partner for hydrogen. This is surprising
at first glance, perhaps because of hydrogen’s excellent combustion characteristics. The problem is that the
7