Lean, clean and mean
Once known as smelly, noisy, polluting dirt-bins, diesel cars have made great strides in cleaning up their act. During the past decade, advanced technologies, such as electronically controlled common-rail and unit pump-injector systems, have enabled diesels to run smoother, quieter and cleaner. What's more, diesel engines are roughly 30% more fuel-efficient than their petrol equivalents, and produce about 20% less carbon dioxide—the gas most responsible for the greenhouse effect.
Clean diesels have become Europe's choice in fighting global warming and saving money on fuel‚ and now account for 45% of all new car sales in Europe. The most economic model—the Volkswagen Lupo—sips a mere three litres per 100 kilometres (95 miles per imperial gallon) and is at the top of the table for climate-friendly cars.
But the competition isn't standing still. Petrol-electric hybrids, powered by both a standard internal-combustion engine and an electric motor, are catching up in terms of fuel economy and carbon emissions. The Honda Insight, a two-seater available in Japan and America, burns a frugal 3.7 litres per 100km. The Honda Civic and the Toyota Prius, currently the only two hybrids widely available in Europe, are both family-sized. All of them use a clever technology in which the electric motor acts as a generator that captures energy during braking (normally lost as heat) and converts it to electricity to re-charge the batteries. But unlike the Hondas, the Toyota Prius is also able to operate in a purely electric mode at low speeds.
In America, the Prius has already gained a celebrity following—Leonardo DiCaprio and Cameron Diaz drive them. Completely redesigned as a five-door hatchback for 2004, the second-generation Prius is larger than its predecessor but burns about 15% less fuel, having a consumption figure of 4.3 litres per 100km. That is roughly half what a similar-sized petrol-engined car would consume. Its already low carbon dioxide emission level has been reduced still further—to a mere 104 grams per kilometre—and now compares with the best of the new breed of diesels.
Better still, unlike a diesel, the new Prius's petrol engine doesn't produce particulate matter—the nasty soot that can cause respiratory problems. And its catalytic converter largely eliminates smog-forming nitrogen oxides. So far, only a handful of carmakers—notably Ford, Volkswagen and DaimlerChrysler—has begun to equip their larger diesel models with particulate traps. Ironically, that is why small diesels often end up spewing out more soot than their hefty siblings. PSA Peugeot Citroën is an exception. The French company fits most of its diesel cars with traps.
Besides being among the cleanest and most fuel-efficient cars for its size, the Prius has a lot of other things going for it. Its electric motor offers 50% more power than its predecessor, allowing the car to do a 0-100km/h (0-62mph) dash in about ten seconds. Known for its reliability, the car comes with an eight-year/ 160,000km (100,000 miles) warranty for all its hybrid components.
Consumers have responded enthusiastically to the hybrid. Toyota has sold more than 180,000 of its Prius models worldwide, and recently announced it is increasing production for America to 47,000 vehicles this year. This may not sound like a lot compared with some of the manufacturer's more popular models. But it signiﬁes the willingness of consumers to buy hybrids for whatever reason, despite the fact that the cost-saving argument may not look so great when the extra cost of the vehicle's electric motor, control system and additional batteries is factored into the equation.
That has not dulled Toyota's enthusiasm for hybrids. Next comes the Lexus RX hybrid, an SUV (sports-utility vehicle) that will reach European and American dealerships later this year, followed by another hybrid SUV for the American market, the Toyota Highlander, in early 2005. Both pack 270 horsepower engines and battery systems that are almost twice as powerful as the Prius's. Also available will be an optional four-wheel drive which saves space by replacing the bulky drive axle of conventional all-wheel drives with a high-voltage cable that delivers electricity to an electric rear motor—a set-up that should provide even further fuel savings. According to Walter McManus of J.D. Power and Associates, a market research company, Toyota is four years ahead of its rivals in developing hybrid technology.
Other manufacturers are scurrying to catch up. Ford, which recently licensed hybrid technology from Toyota, is planning to release a hybrid version of its Escape SUV this summer. The car is expected to get 6.3 litres per 100km (38 miles per American gallon) for city driving. At the same time, Honda will round out its hybrid selection by offering a third model based on the Accord. General Motors and DaimlerChrysler are expected to follow suit with pick-up trucks. Initially, however, none of these will be available in Europe.
Because of all the extra components, hybrids cost around $3,500 more than their petrol equivalents. That is double the additional cost most manufacturers charge for diesel versions of their cars. But hybrids are still in their infancy, and the cost of their components is set to come down. Ricardo, a British engine-design consultancy, reckons that the total cost of owning a hybrid could eventually be as cheap as a diesel.
So why no diesel hybrids? The answer is, they're working on it. Recently, Ricardo joined forces with Peugeot Citroën and QinetiQ, a technology solutions provider, to build a prototype for a family-sized diesel hybrid. Based on a Citroën Berlingo, the car seeks to achieve fuel economy of 3.3 litres per 100km and a carbon dioxide emission of no more than 90 grams per kilometre. It is hoped that the endeavour will help the industry develop an ultra-low-carbon car with the potential for being mass-produced.
Despite much publicity, hydrogen cars won't compete with hybrids for a long time.
Earlier this year, DaimlerChrysler presented a vehicle for a possible future Mercedes line, known as the Vision Grand Sports Tourer, at the North American International Auto Show in Detroit. The model, a cross between a luxury station wagon and an SUV, was also shown as a diesel hybrid with a 250-horsepower engine and 50-kilowatt electric motor capable of 0-100km/h in 6.6 seconds while consuming no more than 7.8 litres per 100km—20% less than a comparable diesel model.
Hydrogen-powered vehicles would, of course, be the cleanest form of transport, eliminating harmful emissions. But despite much publicity, hydrogen cars won't compete with hybrids for a long time. In fact, experts disagree wildly on when (if ever) the transition to the so-called “hydrogen economy” will take place. Estimates range from ten years to many decades. For one thing, the production of sufficient hydrogen creates an environmental challenge all by itself, since it is costly and energy-intensive to extract from natural gas, water and other sources. Even before distributing it, producing the hydrogen would generate a lot of pollution. Next is the hurdle of storing adequate amounts of hydrogen, plus the absence of a worldwide infrastructure for refuelling stations. Joseph Romm, director of the Centre for Energy and Climate Solutions in Arlington, Virginia, believes it will take at least 20 years before hydrogen cars can compete with hybrids.
Until then, consumers will have to rely on clean diesel technologies and hybrids to cut down on greenhouse emissions. Alan Lloyd, chairman of the powerful California Air Resources Board, which has enforced some of the toughest air quality rules in the world, agrees. While diesel cars are currently unable to pass the board's stringent limits on nitrogen oxides, Dr Lloyd has been impressed by the new breed of European diesels—and believes they will become as clean as petrol-engined cars.
Anne Schukat is a technology and science writer based in California.