Steps towards the fuel-cell engine

Earlier sections of this chapter, contributed by Roger Booth, have dealt with process engineering of the fuel-cell stack. Hereafter the steps leading to the development of viable fuel-cell engines are considered. While hybrid drive vehicles, using conventional battery-electric and thermal-engine power sources, provide improved fuel economy and a viable solution for urban operation, the fuel-cell powered vehicle is now seen as the long-term option. Already it is realized that thermal-engine driven vehicles can never provide the necessary fuel economy and emissions control required by world governments, primarily because the thermal engine is running at 10% of its total power potential for most of its time and there is no known way of eliminating CO₂ emissions from it.

Over the next 20 years, people using HC vehicles are going to face increasing fuel scarcity, increasing fuel cost and ever increasing restrictions on use and size of vehicles, because of the emissions they produce. The high operating efficiency and zero emission characteristic of the fuel-cell vehicle are strong arguments for its adoption. But the passage into the period of the hydrogen-fuel economy has to be a gradual and peaceful one, requiring considerable changes in attitude by the motoring publics worldwide.

4.6.1 FUEL CELLS: TOWARDS A PAINLESS TRANSITION

The only way to break out of the cycle of increasing fuel costs and heavier restrictions is for motorists to accept the necessity to move over to a hydrogen-fuel economy in the shorter term and to lessen its impact by replacing their current vehicles, when the time comes, with much more fuel-efficient types. There are two advantages to the hydrogen economy: if early hydrogen-fuelled vehicles are not very efficient it does not matter because pollution-wise they have zero emissions, and more importantly, the existing cost of expensive exhaust after-treatment is removed.

The publication by the OECD International Energy Agency in 1998 of ‘World Energy Outlook’, a year after the Kyoto Earth Summit, was a pivotal point in understanding world energy and pollution problems. The basic message was that, as people now live longer, energy usage and pollution rise exponentially and a ‘brick-wall situation threatening in ten years’ time means that we cannot stay as we are’. It was also from this point that the major G7 economies took global warming seriously. China, too, takes it seriously, realizing that nine-tenths of its population live in its southeastern corner delta region, which could be subject to flooding if global warming is not seriously addressed. World oil supply is expected to peak in 2010 and then tail off; this is unless the cost can be met of tapping into the vast oil deposits beneath the polar icecaps. But North American motorists remain blissfully unaware of these threatening situations. While the UK and Europe pay what gasoline and diesel actually costs, in total, US users have an enormous effective subsidy which hides the governmental costs, and keeps them oblivious to the problems involved.

Fuel/vehicle taxes in the UK pay for road building, health care related to accidents, also defence costs relating to naval protection of oil rigs, whereas in the USA the petrol price paid at the pumps

Fig. 4.6 GM Precept PNGV car.

is the direct cost of the fuel at world market prices. Even the cost of the US fleet in the Middle East is reckoned by some to be equivalent to a subsidy of $1/gallon and of course there is no contribution to the health-care costs associated with exhaust pollution. In the US such costs are covered by road tolls and other forms of local/central taxation. It is considered that Americans pay pump prices which cover only one-third of the real costs, the other two-thirds being borne by the state and, in the USA, local oil extraction has been declining since 1975 to the point where nowadays some 70% is imported.

4.6.2 FUEL-EFFICIENT VEHICLES

The US PNGV programme described later in this chapter is an effort to provide the technology for very low fuel consumption vehicles which industry could adopt if motorists accept the need.

Researchers such as Lovins at the Rocky Mountain Institute have shown that 500 mpg hypercars are possible, paving the way for some intermediate value to the 30 mpg average consumption vehicle typical in America. The 10 kW absorbed at 60 mph alone could be halved by the adoption of underfloor aerodynamics. In combination with an aerodynamic superstructure, double-acting brake cylinders and low rolling-resistance tyres, it could be cut to one-third.

In the deal that was struck after the Kyoto summit in 1997 hydrogen is to become available one day at filling stations; both Shell and Esso are already committed in Europe and Japan, and will start operating only when they consider the fuel markets are operated on an orderly basis. On the other hand, in America they are operated on a subsidized basis. In Europe, too, at least one manufacturer, VW, has shown with the Lupo that a 1.3 litre 80 mpg car can be built to USA PNGV requirements. This uses a high technology diesel engine with common rail fuel injection and is an instant starter without the use of glow-plugs or comparable devices. It has top speed of over 100 mph and nippy accelerative performance. But this performance could not be achieved on larger cars typical in the American market, that is not without hybrid drive technology as now made available on the Toyota Prius, which has interior accommodation comparable with some American cars. The US version has a 21 kW battery to improve acceleration and features full air-conditioning.

In 2000, this car sells at $18 000 compared with $10 000 for an American ‘base model’ car. So far some 40 000 are in use worldwide but the UK version is two-thirds dearer at £18 000, for a much higher performance vehicle required in this market.

Such fuel-efficient vehicles should permit an increase in gasoline prices that would allow oil extraction from the polar regions, permit other fuels to compete with gasoline and permit other transport systems to compete with cars and aeroplanes. The GM Precept (Fig. 4.6) is the corporation’s PNGV car and similar ones have been developed by Ford and Chrysler. GM also intends to make the vehicle in hybrid and fuel-cell versions. It is important to note that it is an ultra-low weight vehicle made primarily in aluminium alloy with underbody streamlining, a TV camera in lieu of wing mirrors, low rolling-drag tyres and double-acting brake pistons. The latter

Fig. 4.7 GM’s PEM fuel-cell stack capable of powering a 1500 kg vehicle.

overcome the problem of drag due to brake hang-on with conventional systems when the single-acting piston fails to withdraw, and some 2 kW can typically be lost at motorway speeds. Of course, hydro-mechanical brakes only operate rarely on EVs, which can rely on regenerative braking for light-duty work. The Precept is an order-of-magnitude change in technology compared with ordinary American-produced vehicles, but of course would cost considerably more than the

$10 000 dollars now charged.

4.6.3 FUEL-CELL VEHICLE PROSPECTS

The real future is with fuel-cell cars because the Precept version so fitted will have a fuel-cell stack volume of just 1.3 ft³ and produce 70 kW continuously, 95 V at 750 A, Fig. 4.7. Plate current density is 2 A/cm²; the cell is currently world leader in PEM-stack design and if used intelligently has higher power density than a thermal engine. This is, then, the turning point, and it is underlined by Mercedes whose work on the Necar IV is showing that 38% efficiency is obtained from hydrogen in the fuel tank to power at the road wheels. This compares 13–15% for a standard thermal-engine car. With this three times improvement in fuel economy GM believes that they are going to develop fuel-cell vehicles. The major challenge over the next five years is making it at a low enough cost to be attractive.

4.6.4 BATTERY ELECTRICS/HYBRIDS IN THE INTERIM

EV technology will be needed for the future fuel-cell car but currently it cannot be proven with current traction batteries which are too heavy, too expensive and made from materials that are not in plentiful enough supply. Most good quality batteries are based on nickel technology and the reason for being in this difficulty is not because the battery research

programme was a failure, but rather the reverse. The outcome is that people are using batteries for communications, camcorders and computers; they pay far more for their batteries than car manufacturers could sensibly afford. The ‘3Cs’ are prepared to pay three times what the EV builder can pay.

A better alternative to nickel technology is aluminium. This is because the nickel–metal hydride battery, to give 80 kWh needed for a 3–400 mile range (on a PNVG car), would weigh 850 kg and cost $25 000, at year 2000 prices from Ovonic. The same 80 kWh can be obtained at a weight of 250 kg with aluminium, and at a cost of just $5000; and of course the material from which it is made is the most abundant on earth, next to hydrogen. The electric car is not a failure from a performance point of view but merely waiting for its time to come when high performance batteries can be produced economically. Energy density is not the problem with aluminium, rather it is the corrosion problem which causes aluminium batteries to degrade rapidly because of the formation of aluminium hydroxide jelly. However, two years ago scientists in Finland put forward a raft of patents which overcame some of the problems; these were revealed at the 2000 ISATA conference.

For the PNVG programme, Dr Alan Rudd built an aluminium battery for the US government;

this was a pump-storage one, that was totally successful apart from the above-mentioned corrosion problem – the factor which persuaded the Americans to discontinue development. The technical committees took the decision to ignore the lower voltage couples on the grounds that the higher voltage couples were sold on the basis of having fewer cells in series. This gave the lightest batteries for portable power applications but the materials involved could never be cheap enough for an electric car.

A key advantage of the aluminium battery is its ability to operate at temperatures down to –80^oC, overcoming the disadvantage of many existing types. The corrosion problem is now thought to be soluble and effective EV batteries are foreseen in 5 years’ time. It is considered best therefore to hold back on battery electrics, while hybrids hold the fort, until such time as the most cost-effective high performance solution is found. If the current European development programme is successful EV makers will have D-cells (like torch batteries), each handling 150 Ah at 1.5 V DC and able to be discharged at about 500 A maximum.

Batteries will be formed from matrices of such cells, as discussed in Chapter 2. This is the most effective solution to the battery-electric vehicle problem. Existing technology batteries are going to be used for energy stores in hybrid-drive vehicles where the capacity needed will be less than 5 kWh.

4.6.5 POLLUTION CONTROL MEASURES

Hybrid drive cars present an early stepping point to fuel-efficient cars but very few car makers have produced the full gamut of drag-reducing measures that could transform fuel economy, and hence CO₂ emissions, with existing thermal-engine technology cars. To do so could give huge improvements at modest cost, with immediate fuel saving and emission control benefits.

The other big potential benefit would be catalytic converters for diesel engines. Such engines produce as much pollution now as petrol engines did in the 1960s and are the worse by far for PM10 particulates. Converters would dramatically cut diesel engine emissions and it is only their poisoning by sulphur in conventional diesel fuel that has prevented their widespread use.

Now that clean ‘City Diesel’ is beginning to be seen at filling stations there is real hope for a positive step forward. This new fuel has around 10 ppm sulphur instead of 250 ppm with conventional fuel. The final stage in pollution control is, of course, the zero emission vehicle, the main contender being fuel-celled vehicles which GM intends to introduce in 2004.

4.6.6 OVERALL ENERGY POLICY

The global perspective is that over the next 20 years, road vehicles and aircraft will switch to hydrogen fuel. The exact time will depend on how consumers react to the problems outlined above. Should consumers adopt a helpful attitude and accept the certain introduction of fuel-efficient cars soon? This would allow fuel prices to rise sufficiently for the extraction of polar oil deposits, then gasoline could still be used in 100 years’ time. Conversely by doing nothing, and continuing to drive 30 mpg cars, we shall be subject to a crash introduction of the hydrogen economy in ten years’ time. From an industry and cost perspective it would obviously be better to have a gradual transition; a sudden transition could have an economic effect similar to that of a world war. It is really vital that the G7 economies, at least, introduce fuel-efficient cars within the next five years. By staying with conventional HC fuels, and avoiding the hydrogen transition, will only lead to more regulation, slow strangulation and severe restrictions – which would be very hard to impose on the US market, for example.

When the transition does occur hydrogen will be produced first from the reformation of natural gas and then by the electrolysis of water using electricity from fusion reactors. In 2010 it is estimated there will be dual-fuel aircraft with paraffin in the wing tanks and liquefied hydrogen in tanks over the passenger compartment. Over the next 20 years, many airlines will prefer to transfer directly to hydrogen solely, as they gain major operational benefits. They will, at a stroke, double range or payload and thus be prepared to pay a higher price for hydrogen. The fuel will be supplied as a liquid at –180^oC and 20 bar pressure for the aerospace market and thus high quality hydrogen will also be available in quantity for road vehicles. The reformation of natural gas will be carried out in central facilities (much more efficiently than in on-board installations) with the important proviso that energy must be extracted from the carbon in the methane, as well as from the hydrogen molecules, since there is three times the energy in carbon over hydrogen. Something like an Engelhard ion–thermal catalytic process is thus required. It is also important that after the carbon has been burnt out it should be in the form of a carbonate or a carbide (and not in the form of CO₂ which would revert to the atmosphere). Although energy is released in this way during the conversion, overall, energy is consumed during the process. Some 90% of the initial energy is retained in the form of pure clean hydrogen fuel. From the point of production hydrogen can be distributed as a gas through existing natural gas pipelines. This is the likely scenario until 2050 when the exhaustion of natural gas will dictate the need for fusion reactors.