Once and for all, will the U.S. use diesel engines in its passenger vehicles, and at least start to parallel Europe's breakneck acceptance of the once-derided diesel?

Equally important, can auto makers exploit significant numbers of diesels in the U.S., given the regulatory and marketing challenges even the most passionate proponents admit diesels face?

The answer — according to participants at the Society of Automotive Engineers “Diesels and Their Future in the U.S.” Executive Management Briefing in Troy, MI — is an unequivocal “probably.”

The swelling momentum behind the diesel has become almost palpable — and now, some say, irresistible — as auto makers press to align North American consumers' powertrain tastes with the Western European model that's seen diesel penetration leap from 14% of the light-vehicle market in 1990 to 40% in 2002 (see chart).

Even regulatory and environmental interests, once ardently opposed to the diesel, are warming to its promise to quickly and drastically reverse the steadily declining fuel economy of the U.S. light-vehicle fleet. Others welcome the diesel's potential to reduce the nation's reliance on foreign energy.

That's not to say there aren't plenty of reservations. Reginald Modlin, Daimler-Chrysler Corp.'s director-environmental and energy planning, sees Europe's embrace of diesel as emblematic of the differences between European and U.S. cultures and history — and the U.S. addiction to cheap energy.

“Sound energy policy will drive diesel penetration in the U.S.,” he adds, but “the U.S. lacks a national energy policy.” Because of Europe's war-driven periods of energy scarcity, Modlin says, its practice is to heavily tax fuel, which in turn spurs conservation. The U.S. places more emphasis on health-based initiatives tilted toward reducing vehicle emissions, particularly smog-forming oxides of nitrogen (NOx).

Diesels emit markedly more NOx than do gasoline engines — which causes U.S. regulatory and political machines to favor lower-emitting gasoline engines over diesel's 30% better fuel efficiency, Modlin says.

He says if DC's U.S. diesel market penetration mirrored Europe's, the company's corporate average fuel economy figure would improve by 3 mpg (1 km/L) — and if the nation's diesel penetration reached the 40%-plus of Europe, the U.S. would save 800 million gallons (3 billion L) of oil annually (that's less than two days worth of U.S. oil consumption at current rates).

Although Modlin says the policy change is necessary for diesels to flourish in the U.S., several presenters say significant technical advances also must happen — and likely are achievable.

The larger problem, they say, is cost. Graham Hoare, Ford Motor Co.'s director — powertrain research and advanced engineering, presents figures that show advanced diesels, when fitted with expensive exhaust aftertreatment systems to enable compliance with emissions standards, will by 2010 cost OEMs nearly twice as much as today's diesels (see chart).

“Everybody wants to make exciting products,” says Hoare, who adds the diesel's high-torque at-tributes will win U.S. buyers, “but we'd like to make money doing it.”

Patrick Charbonneau, chief technical officer of International Truck and Engine Corp.'s engine group, is counting on improvements in five areas to make the diesel ready for prime time:

  • Fuel-injection systems will continue to improve, employing higher pressures and other advances to ensure higher fuel economy, lower emissions and more refinement.

  • A new generation of turbochargers will be faster-acting, enhance transient response and cost less. Charbonneau points to new features such as variable-vane/variable-nozzle designs and electrically accelerated turbines.

  • Increased knowledge of combustion will enhance fuel economy, reduce emissions and cut the amount of expensive precious metals in aftertreatment systems.

  • Advanced electronics will afford a higher level of control over the entire diesel system.

  • High-tech aftertreatment will cut NOx to mandated levels and reduce particulate-matter (PM) emissions to nothing.

Siemens VDO Automotive's Johann Warga, CEO of diesel systems, agrees foreseeable innovations will satisfy the need to improve diesel's performance and emissions profile. He promises a sophisticated new generation of fuel injection and control systems that improve fuel economy and refinement, cut emissions and increase power.

Auto makers also must convince customers, many of whom remember the famously ill-developed diesels of the 1970s, that compression ignition is a viable — let alone premium — engine choice.

Kenneth Moriarty, Volkswagen of America Inc.'s executive director-corporate strategy, says, “There was a time when you had to be a believer. But over time, diesels have gotten better and better.” VW cleverly avoids the “diesel” moniker altogether for its products, opting instead for “TDI,” an acronym for Turbo Direct Injection.

If customers understand new-age diesels and potential early adopters are presented with a chance to experience the diesels' unique performance, the job will be done, says Kevin DeHart, vice president — diesel fuel systems at Robert Bosch Corp. He says 40% of all new-vehicle buyers in the U.S. already opt for an engine upgrade — without any fuel economy benefit.

Moreover, DeHart adds, auto makers should warm to diesel's potential to realign their eroding CAFE positions. Diesels could be an expeditious fix to get everyone, particularly Detroit's Big Three, in compliance with the recently mandated increase for light-truck CAFE of 22.2 mpg (10.6L/100 km) for the '07 model year.

Light-truck CAFE for the Big Three currently hovers around 20.5 mpg (11.5L/100 km), and truck customers have yet to begin asking for less-powerful engines.