Understanding the buzzwords of alternative powertrains and fuels can be hard. Especially when the language used by equipment and vehicle manufacturers — keen to talk up their exciting new technologies — is sometimes light on reality. We hope that, when you emerge from reading this page, you will be able to face the subject head-on without being distracted by — dare we say it — hot air.
Daimler Citaro fuel cell bus during road trials in London.
A significant problem with talking about alternative fuels is that it’s usually impossible to make genuine comparisons between the effectiveness of different technologies. And that, of course, is what everyone wants to do. Reliable data are just not available to compare — for example — the overall carbon efficiency of one fuel against another, from the oil well (or sugar cane) to the wheel. How much energy is required to produce a particular type of fuel? Can that energy be generated using renewables? How hard is it to store and transport the fuel? There are too many variables. So we hope you will understand that, in not providing you with a neatly packaged and presented clear-cut answer to the world’s big transport questions, we’re not being indecisive. Our intention is that you will be able to read future articles about alternative fuels with enough insight to fish the few morsels of solid information out of the PR chaff.
This page, then, is an introduction to alternative fuels and drivetrains, and to how they work in practice. It’s not an engineer’s monograph — not least because the technologies used in alternative drivetrains are developing very quickly, and there’s a lot of recently-patented equipment out there which the press are not cordially invited to dismantle.
Although the technologies of alternative powertrains are moving and evolving rapidly, it will be many years yet before we see a major shift in the types of cars that buyers actually drive home from the showroom. The reasons are simple. The new technologies that already work — hybrids, for example — are complex and expensive, while the more radical developments are still at the prototype stage. Where is your local hydrogen filling-station, or the nearest charging point for your electric car? There are some around, but it will be a while before we can tour the country in a car powered by electricity or hydrogen.
Last autumn, Volkswagen published a document called Update on the Future: Technologies on the roadmap to the world of tomorrow. Its authors are in no doubt about the pace of change. ‘Bold promises are being made which suggest that future technologies — especially electric cars — are already production-mature for the mass market today. That is incorrect. Because the path to the emissions-free car is a long one. Consequently, the Volkswagen Group is following a Powertrain and Fuel Strategy that is laid out for the long term yet will still culminate in the reinvention of the automobile.’
There are two phrases here that stand out. ‘Long term.’ And, ‘Reinvention of the automobile.’
But maybe Volkswagen is being cautious. In November, Guillaume Faury, Executive Vice President, Manufacturing and Components at Peugeot-CitroŽn, announced that the Group would be devoting more than half of its R&D expenditure for the 2010-2012 period to new technologies aimed at cutting CO2 and other emissions.
The pursuit of new powertrains is serious business.
What are the alternatives?
The most familiar type of alternative fuel vehicle is the hybrid. In fact, this is actually not a single technology at all, but a general term for a vehicle that uses more than one form of motive power. The best-known hybrid vehicle Toyota’s Prius, which uses a petrol engine and an electric motor.
Confusingly (and incorrectly), Toyota uses the word ‘hybrid’ to describe its fuel cell car, which is actually not a hybrid at all because it has only one source of power. A fuel cell vehicle uses (usually) hydrogen gas as a fuel, producing electricity to drive a traction motor.
We are all familiar with traditional electric vehicles that run on battery power alone, recharged at charging stations or from the domestic supply. They have a long history — as have straightforward piston engines fed on non-hydrocarbon fuels. In the 1970s, the Brazilians began running Fiat 147s on ethanol produced from the sugar cane that grows easily in that country, and ethanol is a major fuel for cars and light commercials in Brazil today. In Europe, hydrogen is also seen as a fuel to watch for combustion engines.
Ethanol is not the only bio-fuel. We have all heard about biodiesel, originally produced from rapeseed oil. Although seed oils are not now seen as a useful way forward for making fuel, there are new production systems for biodiesel that are attracting interest. Given that diesel engines are thermodynamically efficient, and non-fossil fuels have the potential to be produced to a high degree of purity, this type of fuel certainly has a future.
Biofuels: ethanol & biodiesel
Most of the engine designs that we are already using can be modified to run on biofuels. Bioiesel can be made successfully from biomass — mulched or chipped plant material — while anhydrous ethanol produced from sugarcane can be mixed with petrol. In Brazil, all fuel for petrol-engined vehicles must be at least 22 per cent. ethanol.
Fiat 147: the first Brazilian to consume alcohol.
Earlier this year, the U.S. Environmental Protection Agency designated Brazilian sugarcane ethanol as an ‘advanced biofuel’ due to its 61 per cent. reduction of total life cycle greenhouse gas emissions. This is good, of course, but when the alcohol is mixed with ordinary petrol, the advantages tend to be diluted. Specifically, ethanol has a lower energy density than petrol, so even a vehicle running on a blend of 85 per cent. ethanol with petrol — known as E85 — will produce only marginally less CO2 than it does with raw petrol, because it will be considerably thirstier overall. This is not the end of the world, though, because spark-ignition engines can be designed to run on pure hydrated ethanol, or E100. The Brazilians have been doing it for 30 years.
Biodiesel can also be blended easily with mineral fuel. There are some potential pitfalls that need to be answered with recognised standards — for example, the lubricity of the fuel needs to be adequate to prevent the engine’s fuel injectors destroying themselves. Similarly, the purity of biofuels needs to be subject to mandatory standards.
If we can produce bio-mineral blends that conform to the same performance and quality standards as current fuels, they can be offered as direct substitutes using existing infrastructure. The need to develop new infrastructure will slow down the introduction of any novel fuel, even if the public is keen to buy a car that runs on it.
Care needs to be taken in auditing whole-cycle CO2 for any new biofuel plant or process, because an advantage over mineral fuels is not guaranteed. It can be substantial, but it can be nothing — or worse. According to Volkswagen, ‘Depending upon the raw material and process, the CO2 benefits can fluctuate wildly, even with the same product — in the case of ethanol, between 0 and 90 per cent.’
And as the environmental lobby has pointed out, there is a danger that the pressures placed on land for the production of biofuels could have serious environmental and social consequences.
Synthetic hydrocarbon fuels
Making synthetic fuels is a great way to achieve very high standards of purity, consistency from day-to-day, and self-consistency in the range of carbon chain lengths in the fuel. Like purity, chain-length influences the quality and consistency of combustion. This means cleaner local emissions, better power and better fuel economy.
Synthesising fuels also opens up the possibility of designing new types of combusion engine, using tailored fuels that don’t fit into our existing categories. This is particularly significant because of the increasingly blurred dictinction between diesel and petrol engines. The adoption of direct fuelling for engines running on petrol means that these engines are no longer carburated: fuel is injected at the point where combustion is required to start, just like a diesel. Combustion is triggered by a combination of a spark and the temperature and pressure conditions in the combustion chamber — not just the latter, as is the case with a diesel engine, but it’s worth bearing in mind that conventional petrol is blended specifically to resist compression ignition.
Traditionally, synthetic hydrocarbons have been made from natural gas. Clearly this gives no CO2 advantage over ordinary fuels, but biomass can easily be used as a raw material to produce the feedstock for synthetic fuel production.
Plug-in electric vehicles
The single major potential drawback of a plug-in electric vehicle is that the electricity you feed it could well be generated using fossil fuels. That being the case, it is far more efficient to run a small diesel engine — perhaps as part of a hybrid powertrain — and convert the chemical energy in the fuel directly into motion. But of course, there’s always the potential to generate electricity using renewables, and that’s why plug-in technology is important for the future.
Peugeot’s all-electric Ion will be available for rent by the end of 2010.
Lithium-ion battery technology has worked wonders for the range and performance of plug-in electric vehicles (and also for the electric range of hybrids). These batteries have a higher power density than NiMH packs
and are less prone to lose efficiency as a result of repeated part-charging or deep-cycling.
Lithium-ion battery packs have been under development for cars since the early ’90s. The latest versions use manganese anodes and a planar, laminated structure, instead of the more traditional cylindrical design. The laminated form is cost-effective as well as giving a long life and good cooling performance. It also uses fewer components than earlier types. At the same time, the laminated construction has boosted power by 150 per cent. while halving the physical size of the complete battery pack. And as if that weren’t enough, the new design is also twice as efficient as a conventional cylindrical Li-Ion battery, even after five years or 100,000km of continuous usage.
CitroŽn’s C4 HDi Hybride was presented at Geneva four years ago. It has a layout similar to most other series-parallel hybrids. The nickel hydride battery packs (coloured red) are at the rear; the high-voltage inverter/converter is at the front coloured blue. Behind it is a 12V battery (red). The electric motor is in the drivetrain between the clutch and the automated six-speed gearbox.