Jostling for sales against cars equipped with gasoline or hybrid powertrains, the modern diesel finds itself needing to show off a little -- something sexier than, say, a promise to last a quarter-million miles.
That's why automakers are pushing diesel engines to extremes, pressing for more power and greater fuel efficiency. Factory-sponsored racing prototypes are sweeping the world's toughest endurance contests, while limited-production demonstration projects are showing that triple-digit fuel economy is no longer theoretical.
Sometimes, horsepower and fuel efficiency are just two sides of the same coin. Case in point: Audi kicked off a game-changing win streak in 2006 when its purpose-built R10 TDI became the first diesel racecar to take the checkered flag at the 24 Hours of Le Mans. The R10 covered a record-setting 3,223 miles over the 24 hours, averaging 134 m.p.h.
The R10's output -- 650 horsepower, according to Audi -- set the pace on the track, but its fuel efficiency was also a crucial part of the team's winning strategy. As gasoline competitors stopped to refuel, wasting precious seconds, the R10 kept lapping the track.
A Mazda 6 powered by the Japanese automaker's new Skyactiv-D diesel arrives in showrooms this year. To establish its zoom-zoom credentials, production-based Mazda 6 sedans are competing this year in the Rolex Grand-Am series. At Road Atlanta in April, Mazda scored the first-ever diesel class victory in Grand-Am and followed up with three more consecutive wins.
At the slow-but-steady end of the spectrum, the production-destined Volkswagen XL1 takes 12.5 seconds to reach 60 m.p.h. But it dusts all rivals in the efficiency race: VW bills the XL1 as the world's first "1-liter car." That refers not to engine displacement, but to its ability to travel 100 kilometers (or 62 miles) on one liter of fuel -- the equivalent of 261 miles per gallon.
On that basis, the XL1 could theoretically drive from New York to Los Angeles on 10 gallons of fuel. Such frugality requires a plug-in hybrid system with a tiny 600 cc 3-cylinder diesel engine. It also demands extreme aerodynamic efficiency and lightness. The two-passenger carbon-fiber XL1 weighs just 1,850 pounds.
VW plans to offer very limited numbers of XL1s in Europe beginning this year, but it will not bring the car to America.
Such combinations of technology remain expensive. Volvo's V60 wagon, which the company says will be Europe's first diesel plug-in hybrid, costs nearly £44,000 in Britain, or $67,000 -- even after a government grant. Yet demand has been unexpectedly high; Volvo plans to build 10,000 in 2013.
Audi has also melded the diesel and hybrid technologies in its latest winner.
The R18 E-tron quattro, which won Le Mans last month, combines a downsized diesel V-6 with a regenerative hybrid system that captures kinetic energy and stores it in a flywheel accumulator rather than as electrical energy in batteries. The spinning flywheel then delivers a jolt of power to electric motors at the front wheels -- providing short bursts of acceleration, and all-wheel drive, in the process. "The fact that our diesel cars get incredible mileage, without sacrificing performance, turns people's heads," said an Audi spokesman, Mark Dahncke. "And racing underlines that fact."
This article originally appeared in The New York Times.