GENERAL MOTORS ZAFIRA PROJECTS

GM and its Opel subsidiary are aiming at a compact fuel-cell driven vehicle by 2004, Fig. 5.23.

By 2010, up to 10% of total sales are expected to be taken by this category. The efficiency of cells tested by the company is over 60% and CO₂ emissions, produced during the reformation of methanol to obtain hydrogen, are about half that of an equivalent powered IC engine. Fuel cells have already been successfully exploited in power generation, at Westervoort in the Netherlands, and experimental versions have been shown to successfully power lap-top computers. According to GM, in principle four basic fuels are suitable: sulphur-free modified gasoline, a synthetic fuel, methanol or pure hydrogen. Modified gasoline is preferred because of the existing distribution infrastructure but CO₂ emission in reforming is higher than with methanol. Synthetic

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Fig. 5.23 GM fuel-cell developments: (a) Zafira conversion package; (b) under-bonnet power-pack; (c) reformer and cells; (d) flow diagram; (e) latest package with on-board hydrogen storage.

(a)

(b) (c)

(d)

1 battery; 2 drive motor; 3 con-verter; 4 air intake; 5 fuel-cell stack;

6 humidifier; 7 compressor; 8 cool-ing water circuit; 9 reformer.

(c)

(e)

Propulsion

Electric motor

Fuel Cell unit

Reformer

Fuel tank

Methanol

Catalytic burner

Residues Gas from anode

Gas from cathode

Heat

Water CH₃OH

H2O CO

2

H₂ CO₂, CO Air

fuel and methanol can be obtained from some primary energy sources including natural gas.

Transportation and storage of hydrogen is still at the development stage for commercial viability, Liquefying by low temperature and/or pressure being seen as the only means of on-vehicle storage.

Currently GM engineers are working on a fuel-cell drive version of the Zafira van (a) in which electric motor, battery and controller are accommodated in the former engine compartment (b).

The ‘cold combustion’ of the fuel-cell reaction, hydrogen combining with oxygen to form water, takes place at 80–90^oC and a single cell develops 0.6–0.8 V. Sufficient cells are combined to power a 50 kW asynchronous motor driving the front wheels through a fixed gear reduction. The cell comprises fuel anode, electrolyte and oxygen cathode. Protons migrate through the electrolyte towards the cathode, to form water, and in doing so produce electric current. Prospects for operating efficiencies above 60% are in view, pending successful waste heat utilization and optimization of gas paths within the system. The reforming process involved in producing hydrogen from the fuel involves no special safety measures for handling methanol and the long-term goal is to produce no more than 90 g/km of CO₂. In the final version it is hoped to miniaturize the reformer, which now takes up most of the load space, (c), and part of the passenger area, so that it also fits within the former engine compartment. Rate of production of hydrogen in the reformer, and rate of current production in the fuel cell, both have to be accelerated to obtain acceptable throttle response times – the flow diagram is seen at (d). The 20 second start-up time also has to be reduced to 2 seconds, while tolerating outside temperatures of −30°C.

Currently GM Opel are reportedly working in the jointly operated Global Alternative Propulsion Centre (GAPC) on a version of their fuel-celled MPV which is now seen as close to a production design. A 55 kW (75 hp) 3 phase synchronous traction motor drives the front wheels through fixed gearing, with the complete electromechanical package weighing only 68 kg (150 lb). With a maximum torque of 251 Nm (181 lb ft) at all times it accelerates the Zafira to 100 km/h (62 mph) in 16 seconds, and gives a top speed of 140 km/h (85 mph). Range is about 400 km (240 miles).

In contrast to the earlier vehicle fuelled by a chemical hydride system for on-board hydrogen storage, this car uses liquid hydrogen. Up to 75 litres (20 gallons) is stored at a temperature of

−253°C, just short of absolute zero, in a stainless steel cylinder 1 metre (39 in) long and 400 mm (15.7 in) in diameter. This cryostat is lined with special fibre glass matting said to provide insulating properties equal to several metres of polystyrene. It is stowed under the elevated rear passenger seat, and has been shown to withstand an impact force of up to 30 g. Crash behaviour in several computer simulations also been tested.

Fuel cells as well as the drive motor are in the normal engine compartment. In the 6 months since mid-2000 the ‘stack’ generating electricity by the reaction of hydrogen and oxygen now consists of a block of 195 single fuel cells, a reduction to just half the bulk. Running at a process temperature of about 80°C, it has a maximum output of 80 kW. Cold-start tests at ambient temperatures down to −40°C have been successfully conducted.

GAPC has created strong alliances with several major petroleum companies to investigate the creation of the national infrastructures needed to support a reasonable number of hydrogen-fuelled vehicles once they reach the market, possibly in 5 years’ time. Fuel cost is another critical factor.

Although hydrogen is readily available on a commercial basis from various industrial processes, its cost in terms of energy density presents a real problem for the many auto-makers who research both fuel cells and direct combustion.

According to one calculation based on current market prices, the energy content of hydrogen generated by electrolysis using solar radiation with photovoltaic cells equals gasoline at roughly

$10 a gallon.

5.7.2 FORD P2000

Mounting most of the fuel-cell installation beneath the vehicle floor has been achieved on Ford’s FC5, seen as a static display in 1999, with the result of space for five passengers in a medium-sized package. Their aim is to achieve an efficiency twice that of an IC engine. The company point out that very little alteration is required to a petrol-distributing infrastructure to distribute methanol which can also be obtained from a variety of biomass sources. Oxygen is supplied in the form of compressed air and fed to the Ballard fuel-cell stack alongside reformed hydrogen. Ford use an AC drive motor, requiring conversion of the fuel cell’s DC output. Even the boot is accessible on the 5-door hatchback so much miniaturization has already been done to the propulsion system.

The vehicle also uses an advanced lighting system involving HID headlamps, with fibre-optic transmission of light in low beam, and tail-lights using high efficiency LED blade manifold optics.

The company’s running P2000 demonstrator, Fig. 5.24, uses fuel in the form of pure gaseous hydrogen in a system developed with Proton Energy Systems.

5.7.3 LIQUID HYDROGEN OR FUEL REFORMATION, FIG. 5.25

Renault and five European partners have produced a Laguna conversion with a 250 mile range using fuel-cell propulsion. The 135 cell stack produces 30 kW at a voltage of 90 V, which is transformed up to 250 V for powering the synchronous electric motor, at a 92% transformer efficiency and 90–92% motor efficiency. Nickel–metal hydride batteries are used to start up the fuel cell auxiliary systems and for braking energy regeneration. Some 8 kg of liquid hydrogen is stored in an on-board cryogenic container, (a), at −253°C to achieve the excellent range. Renault insist that an on-board reformer would emit only 15% less CO₂ than an IC engine against the 50%

reduction they obtain by on-board liquid hydrogen storage.

According to Arthur D. Little consultants, who have developed a petrol reforming system, a fuel-cell vehicle thus fitted can realize 80 mpg fuel economy with near zero exhaust emissions.

The Cambridge subsidiary Epyx is developing the system which can also reform methanol and ethanol. It uses hybrid partial oxidation and carbon monoxide clean-up technologies to give it a claimed advantage over existing reformers. The view at (b) shows how the fuel is first vaporized (1) using waste energy from the fuel cell and vaporized fuel is burnt with a small amount of air in a partial oxidation reactor (2) which produces CO and O₂. Sulphur compounds are removed from

Fig. 5.24 Ford P2000 fuel cell platform with two 35 kW Ballard stacks.

the fuel (3) and a catalytic reactor (4) is used with steam to turn the CO into H₂ and CO₂. The remaining CO is burnt over the catalyst (5) to reduce CO₂ concentration down to 10 ppm before passing to the fuel cell (6).