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Dynamic Diesels

Driven by economic and environmental concerns, diesel-engine cars are gaining traction in Europe. Will the mania for compression ignition make a comeback in America?
| By Paul A. Eisenstein | From Tom Selleck, Nov/Dec 2007

Two new BMWs sit idling under the broiling Spanish sun. My first thought is simply to get inside, out of the heat. But I'm here for a test drive, not a siesta, so I jump into the nearest sedan, shift into gear and tear out of the parking lot that serves as our preview headquarters. Racing onto the Autovia, I nail the throttle and watch as the speedometer soars to 225 kmh, then ease back before turning off the freeway onto some winding local roads.

"I'm impressed," I tell the German engineer, who has tagged along as my copilot. "Yes," he says smugly. Then, with a curious grin, he adds, "But I was surprised you picked this car, since this version isn't coming to the U.S."

After nearly 30 years covering the auto industry, I pride myself on my instincts. Maybe I'm just an idiot savant, but I normally can spot and identify individual models from a half-mile away, at night, simply by their taillights. But this time, I've been surprisingly oblivious. Rather than grabbing a 330i, I've spent the last hour riding around in a 335d. That's "d," as in diesel, a name that doesn't generally sit well with American motorists. And for good reason.

Following the twin energy shocks of the 1970s, U.S. motorists were desperate to slash their fast-rising fuel bills. While some manufacturers turned to downsizing—replacing their big sedans and V-8s with pint-sized econoboxes—other makers, especially those from Europe, tried another approach. With diesels, marques like Mercedes-Benz could continue offering the large, lavishly equipped products their customers expected, while delivering significantly better fuel economy. By the mid-1980s, diesels powered more than two out of every three cars the German company sold in the States. Not surprisingly, other brands jumped onto the diesel bandwagon, including General Motors' then-formidable Oldsmobile.

Things didn't work out as planned. To shave costs and slash development time, Olds engineers tried to convert a gasoline engine to run on diesel, a disastrous decision due to the enormous compression generated inside an "oil burner." Even the best diesels of the day were slow, rough-riding and foul-smelling, but when thousands of Olds engines began failing catastrophically, the damage was done, and the U.S. diesel market went into a fast decline. Today, these high-mileage engines account for little more than an asterisk on the American automotive sales charts.

Not so in Europe, which is in the midst of a full-blown diesel revolution. From econocars to the most luxurious vehicles, a new generation of oil burners now accounts for more than half the market. In some countries, such as Austria and France, that share is closer to 70 percent—and growing. Of course, the new 335d isn't your father's Oldsmobile, which is why it's not surprising—I hope—that even an automotive expert might be fooled by the latest diesel technology. And why a fleet of new diesel vehicles will soon be arriving in U.S. showrooms.

Clean Fuel, Clean Air
In his most recent State of the Union address, President George W. Bush called on the country to "make our air significantly cleaner" and to become "much less dependent on foreign sources of energy." Achievement of those dual goals, he asserted, would require "technology and innovation."

Perhaps nowhere in the automotive world have engineers achieved so successful a technological transformation than with the diesel engine. Sure, there's plenty of talk about gasoline-electric hybrids. And if the futurists are to be believed, we'll someday drive to the grocery store in hydrogen-powered fuel cell vehicles or even battery cars. But in the nearer term, diesels are yielding dramatic improvements in fuel economy—often up to 40 percent more mileage than comparable gasoline engines—while avoiding their past drawbacks. As I discovered behind the wheel of BMW's 335d, they can be quick, smooth and amazingly clean.

It helps to start with cleaner diesel fuel. That means ridding it of sulfur—the stuff the ancients called brimstone and likened to the noxious odors of hell. Much like the lead that once was found in our gasoline, sulfur poisons the latest pollution control hardware. Until a few years ago, it wasn't unusual to find sulfur concentrations as high as 2,000 parts per million at U.S. pumps. By comparison, European refiners were required to ship diesel with 50 ppm of the devil's element. Federal regulators finally acted, last year, requiring that the vast bulk of the fuel sold in the U.S. meet new "ultra-low" standards. That translates into a maximum 15 ppm, a figure even tomorrow's more advanced emissions systems can live with. "This is the enabler of future diesel technology," declares Jens Mueller-Belau, technical manager for the Dutch energy giant Shell.

To compare Mercedes' new Bluetec power train with the diesels the maker used a quarter-century ago would be akin to pitting an open hearth against a Viking grill. Of course, it also helps to understand how fire is started in the first place.

Like the gasoline power trains in most U.S. cars, diesels are part of the bigger family known as internal combustion engines. A mixture of fuel and air, pumped into a cylinder and then ignited, creates the explosive energy that drives a piston and, ultimately, turns the wheels. With gas, that combustive mixture is touched off with a spark. In a diesel, ignition occurs when the mix is compressed to the point at which it fires spontaneously. The science is all about controlling the eruption within a compression-ignition engine.

There's much debate over who came up with the concept first. In 1890, two British engineers, Herbert Akroyd Stuart and Charles Richard Binney, obtained a patent for "Improvements in Engines Operated by the Explosion of Mixtures of Combustible Vapour or Gas and Air." A year later, they had a working prototype running in Bletchley, England. But historians generally credit—as the name would suggest—German Rudolf Diesel, who got his own patent in 1892, then took another five years to get his invention to work in the laboratory. The technology found quick application in the industrial world. By 1898, the brewer Anheuser-Busch had installed a design by Rudolf Diesel in St. Louis. Soon, the engines were powering everything from generators to U-boats. Surprisingly, it took until the 1920s to fit a diesel into a truck, and Citro&oml;n only launched the Rosalie, the world's first diesel-powered passenger car, in 1933.

Technological Revolution
For decades, astoundingly few real changes were made to the technology. Until relatively recently, the engines relied on mechanical pumps and injectors that led to wide variations in the amount of fuel supplied to each cylinder. Fuel and air didn't always mix well, leaving loads of unburnt hydrocarbons, along with foul-smelling sulfur compounds that spewed out of the exhaust.

Over the last decade or so, change has come at a rapid pace, driven largely by demand in Europe, where motorists are now paying as much as $6 a gallon for gasoline. With the advent of lower-sulfur fuels, manufacturers were able to tinker with more sophisticated ways to stabilize the combustion process, improving mileage and lowering emissions, while also adding the means to enhance performance.

Start with Common Rail technology, which can compress fuel to as much as 29,000 pounds a square inch, then deliver it into a cylinder through the latest in computer-controlled injectors. The newest of these rely on piezoelectric crystals, rather than magnetic solenoids, to further improve accuracy. At the front of the engine, there's the turbocharger, which boosts the pressure, or "charge" of the air flowing into the engine. The latest innovations not only yield dramatic improvements in horsepower and torque—the twisting power that we associate with a car's fast takeoff—but eliminate "turbo lag," that annoying hesitation when you stomp on the accelerator. At the back end, particulate filters and other, electronically regulated systems scrub out most of the soot and other noxious exhaust products.

And since the amount of global-warming carbon dioxide an engine produces is inextricably linked to its fuel consumption, diesels have an inherent advantage over less efficient gasoline power trains. That's why the diesel is the darling of the European environmental movement.

So why do so many U.S. "greenies" see diesel technology as public enemy number one? There are two culprits: inherently high levels of NOx, otherwise known as nitrogen oxides, and particulates, those micro-fine bits of soot that studies have linked to serious respiratory ailments. Over the years, federal regulators have steadily ratcheted up their Clean Air rules, something that has, until recently, been difficult for diesels to meet. Then there are the even more stringent California standards, which, until now, diesels simply couldn't overcome. So most current models, such as the Mercedes E320 CDI, cannot be sold in California and a number of other states, such as New York, that have adopted its stricter guidelines. That accounts for more than a quarter of the potential American market, leading many carmakers to simply abandon diesel technology.

But that's about to change, with the widespread availability of ultra-low-sulfur diesel fuel, and the new emissions systems that this permits. Earlier this year, the Environmental Protection Agency approved the automotive use of urea. A simple, nitrogen-based liquid, similar to ammonia, urea is the fix the diesel has been waiting for. Injected, in microscopic amounts, into the exhaust stream, it can all but eliminate smog-causing NOx. And other sophisticated control systems are on line to cut particulates down to size as well.

Urea-based Selective Catalytic Reduction, or SCR, systems will be used on larger diesel engines, typically about 2.0 liters and up, by manufacturers who include Volkswagen and Mercedes, which has dubbed the technology Bluetec. Honda, VW and several other makers have an alternative for small diesels. In a sophisticated sleight of hand, they convert NOx to ammonia, which, in turn, breaks down more nitrogen oxide, much like urea.

Diesel Comeback
Current diesel technology already carries a premium over gasoline power, typically in the range of several thousand dollars. Tomorrow's environmentally friendly diesels could double that penalty again. But considering the current cost of fuel, the money saved by an increase in mileage will quickly make up for the higher price tag at the dealership. It's notable that diesels deliver that mileage in real-world applications, unlike hybrids, which work best only in the worst stop-and-go environments, such as Los Angeles and New York and its inner suburbs.

In a world increasingly focused on global warming, ultra-clean, high-efficiency diesels are suddenly winning new friends, including Steve Albu, assistant division chief with California's powerful Air Resources Board, which has long blocked the use of diesels in the smoggy state. In a recent, unexpectedly upbeat interview, Albu declared that diesels "can address global warming issues" without other, unacceptable environmental trade-offs.

The question is whether consumers will embrace diesels as well. And that's another matter of ongoing debate. George Peterson, director of the consulting firm AutoPacific, is skeptical about demand, while J.D. Power analyst Kevin Riddell contends, "We're looking for the diesel market to more than double by 2012Éand perhaps double again."

Of course, the best technology is worthless if consumers can't find it on the market. And right now, there aren't many diesels available, especially in California. But that's about to change.

As regular readers know, Cigar Aficionado recently declared the Mercedes E320 Bluetec its Best Green Vehicle (in a tie with the ultra-luxurious Lexus LS600h hybrid sedan). But for the Bluetec badge, a casual observer would have a hard time telling the difference between the E320 and gasoline-powered versions of the big sedan. With a diesel's amazing torque, the E320 will match the performance of a bigger gas engine. Look for the German maker to upgrade the diesels in its ML and larger GL sport-utility vehicles, in the very near future. While it's unlikely the high-mileage technology will ever match the penetration it had in the mid-'80s, it is certain to become an established part of Mercedes' future lineup.

Indeed, diesel will be commonplace among the German imports. VW has had the most popular—and most affordable—diesels on the road in recent years, and while existing models are being phased out, look for an assortment of new ones using the marque's latest Clean Diesel TDI technology. It will arrive under the hood of the Jetta sedan and Jetta SportWagen, sometime during the first quarter of 2008. The massive, V-10-powered diesel Touareg SUV goes away at the end of the coming model year, but reliable sources confirm that the engine will shortly after be replaced by a V-6 Clean Diesel.

Then there's Audi, which arguably has done more for the image of the modern diesel than anyone, with its R10 race car. The most successful—albeit one of the few truly competitive—diesel race cars in history, Audi's 2,000-pound entry pumps out 650-horsepower from its twin-turbo, 5.5-liter V-12. The car is eerily silent, sneaking up on competitors like a cat stalking its prey; and since the R10 uses emissions controls, a rarity on the track, it's cleaner than most other race cars. But what matters most is that since its unveiling, in December 2005, the R10 has overwhelmed everything in its class, sweeping to two consecutive victories at the 24 Hours of Le Mans and dominating the American Le Mans endurance series. One diesel powerhouse that is built for pure velocity, the JCB Dieselmax, keeps setting new land speed records for diesel cars at the Bonneville Salt Flats with velocities that are now well over 300 mph.

How much of the R10's technology will ultimately migrate from the track to the street is uncertain, but Audi's commitment to both is clear. During the second half of 2008, look for a new, 3.0-liter clean diesel to start powering up the Q7 SUV, "our most thirsty vehicle," notes spokesman Patrick Hespen. He hints that if customer demand is there, the twin-turbo diesel could readily be transplanted to virtually any other model in the Audi lineup, from the A4 to the A8.

The line of other import makers looking at their diesel options is growing fast. Look for news from BMW, Toyota and Honda. Industry observers expect a diesel-powered version of the latter brand, its newly updated Accord, to debut perhaps as early as 2009.

And the Big Three? So far, they've limited their offerings to light trucks, such as the big Ford F-Series pickup, Chrysler Ram truck and Jeep Liberty SUV. Of the domestic makers, Chrysler has the most aggressive plans—at least those that have been made public. Among other things, look for a Bluetec version of the Grand Cherokee SUV, using technology developed by Chrysler's former German partner, Mercedes. Meanwhile, GM has begun work, at its Turin, Italy, power train center, on an advanced V-6 package that should arrive in the States by late 2009.

Diesel's Future
There are still those who believe the diesel to be no more than a niche player, at least anywhere but in Europe. Future versions of the hybrid, such as the so-called two-mode system, which is being developed in a GM/Chrysler/Mercedes/BMW partnership, could prove efficient enough to eliminate all competition. Or maybe not. Next year, the French siblings, Peugeot and Citroën, will launch production of the world's first diesel-electric hybrid, which could make Toyota's current mileage champ, the Prius, look like a veritable gas-guzzler.

And there are other breakthroughs on the horizon. The Fischer-Tropsch process—used extensively by petroleum-poor Germany, during the Second World War—can transform a wide range of feed stocks, as well as coal, into low-polluting substitutes for today's diesel fuel. Then there's bio-diesel, which is rapidly becoming a cult favorite around the United States, where it can be produced from leftover fast-food cooking oils, among other things. Willie Nelson, an active proponent, has set up his own production and distribution network. All this should sound appropriate to those familiar with the life of Rudolf Diesel, who originally hoped to fuel his invention with some form of bio-fuel, in part to help German farmers.

How much demand for the diesel will grow remains uncertain, but the days of exile are over. And the more fuel prices rise, the better a case can be made by manufacturers and consumers alike. Of course, price alone won't revive the diesel. But with the latest engines delivering great performance, unexpected comfort and few of the pollutants associated with diesels of the past, the future looks upbeat.

Contributing editor Paul A. Eisenstein publishes a magazine on automotives at on the Internet.