GET READY FOR FLOWER POWER
Practical hydrogen- powered cars are still decades away from reality. But you could be putting in your tank before then
KEITH HOWARD
If all the talking-up of fuel cells in recent years has left you imagining you'll be driving a hydrogen-powered car in a few years, think again. The truth is that the technology isn't yet good enough or cheap enough, and establishing the infrastructure to manufacture and distribute hydrogen in the required quantities will be a massive undertaking.
``Fuel cell vehicles, ultimately powered by renewably generated hydrogen, are the best long-term vision anyone has articulated to date,'' says BP's future fuels manager, Chris Wilks. ``Technology challenges still face us, both with the cost and performance of the fuel-cell vehicles and with the costs of distributing hydrogen.
Our view is that hydrogen is a long-term solution and is unlikely to become economical for a further 15-20 years, and not a significant percentage of the transport mix until after 2030. There will be continuing trials before then, but we don't think that fuel-cell vehicles will be a substandard part of the mix in the short or medium term.''
Even Iceland, which has committed itself to being a hydrogen economy and is unusually well placed to achieve it _ it has copious hydroelectric and geothermal power, and an enthusiastic population _ doesn't reckon to complete the project until 2050.
IF NOT HYDROGEN THEN WHAT?
So what fuels will we be using in our cars in the interim? There is a broad consensus within both the oil companies and the car industry that diesel and petrol will continue to be the most important automotive fuels for the foreseeable future.
Diversification will not occur within the range of fuels we use so much as in the feedstocks that are used to create them.
There are three drivers of this change. First, there is a widespread if not universal recognition that carbon dioxide (CO2) emissions must be substantially reduced before global warming spirals out of control. Second, many countries wish to reduce their dependence on petroleum for strategic reasons, particularly as future supply is increasingly dependent on the Middle East. Third, there is continuing concern about `local' emissions _ particularly nitrogen oxide (NOx), hydrocarbons and particulates _ and their effect on human health.
``The priorities around these three drivers are very different region by region, and are likely to change over time,'' says Wilks.
``Tackling greenhouse gas emissions is probably the biggest challenge in the long term. Meeting the challenges around local air quality is particularly important in the developing world, although technological solutions already exist to tackle this. The issue is how quickly these can be deployed in developing markets.''
In Europe the principal concern is to rein in CO2 emissions, with the increased use of fuels derived from renewable resources playing a part in this. Bio-diesel, containing five percent FAME (fatty acid methyl ester) produced from vegetable oils, is the most obvious example of current fuel diversification in Europe.
Although most modern diesel engines are compatible with much higher proportions of FAME _ PSA Peugeot-Citroen, for instance, permits the use of up to 30% in fleet contexts _ just achieving a universal five percent in European diesel fuels is considered challenging. To offset the higher production costs, tax incentives will be needed to achieve it.
Gasohol (gasoline-ethanol) blends are widely used in Brazil and some US states, and may come to Europe as a means of levering some renewables-derived content into petrol. Ethanol is already in use in Sweden, where a version of the Saab 9-5 which can use any blend of ethanol and petrol is available, and by 2008 a quarter of Swedish filling stations will offer it . But there is no clear EU policy on ethanol as yet, and it is unclear whether blended bio-ethanol would be preferred to the use of octane-enhancing ETBE (ethyl tertiary butyl ether), which can also be derived from the fermentation of agricultural crops or crop waste.
``We would prefer the bio-ETBE option,'' says Dr Wolfgang Steiger, director of powertrain at VW's Group Research division, ``because this doesn't create any engine problems. A five percent ethanol blend is acceptable to our current engines but around the world a 10% blend seems to be becoming the standard. This could cause problems with older engines, so if we have a fuel with 10 percent ethanol it would have to be clearly marked, and we'd have to sell standard petrol alongside it for at least the next 10 years.''
AND IF WE CAN'T USE PLANTS?
Looking further into the future, synthetic fuels _ particularly synthetic diesel _ promise to play an increasingly important role. Synthetic fuel is manufactured by subjecting oxygen and syngas _ a mixture of carbon monoxide and hydrogen _ to a high-temperature catalytic process called Fischer-Tropsch synthesis. Hydrocracking (processing with hydrogen gas and a catalyst) the resulting liquid hydrocarbon mixture produces a range of fuels, including synthetic gasoline (petrol) and diesel.
The syngas for this process can be derived from a variety of feedstocks: natural gas (which produces so-called GTL, or gas-to-liquid fuels), coal (CTL fuels) and biomass (BTL fuels). Diesel fuels with GTL content are already on sale in various countries, although their use is currently limited by supply-side restrictions.
Shell has manufactured limited quantities of GTL in Malaysia since 1993 and will open a much larger, 2.72bn facility in Qatar in 2009, producing 140,000 barrels a day. Other oil companies are active in this area, too.
GTL is particularly attractive to oil companies which are sitting on large ``stranded'' natural gas reserves that cannot be economically exploited in other ways. Car makers are enthusiastic about them because synthetic diesel is virtually free of sulphur and aromatic hydrocarbons and has a very high cetane number (the diesel equivalent of octane), all of which makes for dramatic improvements in exhaust emissions.
In 2003, VW conducted a fleet trial with Shell GTL fuel in Berlin and achieved reductions of six percent in NOx emissions, 63% in hydrocarbons and 26% in particulates.
``If you look at US emissions legislation, particularly in California, the properties of GTL would be very useful in reaching those goals,'' says Dr Steiger. ``What we would need as a minimum is a 50% blend, because our tests show that 50% GTL gives us 80% of the benefits. The best option would be to use pure GTL, but this will take a long time to achieve because the availability of GTL fuels will be limited initially.
``To cover the whole of Europe with a 50:50 blend wouldn't be possible for the next 10 or 15 years. Starting in 2008/9 when larger GTL facilities come on line, we may calculate a 10% blend for Europe, but not more. In the meantime new emissions requirements will have to be met with other technologies, like particulate traps and NOx traps, and these create a lot of difficulties.''
One of these difficulties, ironically, is an increase in CO2 emissions. ``From a Euro 1 (emissions regulations compliant ) to a Euro 4 engine we lose roughly 12 percent efficiency because we have to use extremely late injection timing,'' explains Dr Steiger. ``A synthetic fuel allows us to claw as much as eight percent of this back.''
Although synthetic gasoline fuels can also be made, their advantages are less significant.
``Most of the benefit we can get with synthetic fuels is from diesel combustion, where most of the emissions are created by the stratified charge and lean burn process,'' says Dr Steiger.
``The exhaust gas after-treatment is also very limited, so the effect of a high quality fuel is much higher on the diesel side.''
GTL, though, does relatively little to lower carbon dioxide emissions, and coal-to-liquid _ which is likely to be favoured in countries with large coal deposits, like China _ generates excess CO2 in production. So the supreme prize is to make synthetic fuels renewably, or almost renewably, from biomass (vegetable matter).
Like the much-vaunted hydrogen-powered cars, this prospect is a long way off, but one day your car could run on plants. |
