Diesel Revisited

Technology beat the clatter and smoke of diesel car engines. It's time for a U.S. comeback.

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During the 1980s, A diesel-powered Volkswagen Rabbit was briefly part of my household fleet. It was a particularly frigid Detroit winter, and we had to plug in the Rabbit’s engine block heater if we were parked for even an hour or it absolutely refused to start. Even on warm days, our Rabbit hesitated at the touch of the ignition key. Its lack of power necessitated long-term planning for the simplest highway passing maneuvers. The engine clattered, smoked, and smelled like a city bus. The car’s sole saving grace was that it traveled miles and miles on a single tank of fuel.

Anyone who has been to Europe recently and rented, say, a BMW 7 Series or a Mercedes-Benz S-Class, or even a Volkswagen Beetle or Ford Focus, knows that today’s diesels are far more civilized than our irascible Volkswagen Rabbit. In the past decade, diesel technology has revved ahead. It began with European consumers, who were motivated by gasoline prices at least twice those in the United States. European government officials, meanwhile, concerned about global warming, created tax breaks to encourage diesel car ownership (since diesels burn less fuel, they produce fewer of the greenhouse gases, including carbon dioxide, that contribute to climate change). Automakers responded by investing heavily in diesel research, and the new technologies that emerged have virtually eliminated the smell, noise, and power disadvantage of the diesel. Today, 35 percent of passenger vehicles sold in Europe are diesel-powered, and industry experts predict that portion will rise to 50 percent in the next decade.

In North America, however, only 2 to 3 percent of vehicles sold annually are diesel-powered, according to the Diesel Technology Forum, an industry trade group — and most of those are commercial vehicles. Diesel is an attractive option for trucks because the fuel savings on gas-guzzling 18-wheelers can be tremendous. When it comes to diesel-powered passenger cars, however, only one is available in the United States: the Volkswagen Golf TDI. That is in part because American consumers, spoiled by cheap gas prices and hampered by enduring negative perceptions, have been down on diesels. In addition, diesel emissions have been specially targeted by U.S. regulators. Diesels spew high levels of nitrogen oxides, gases believed by some experts to be carcinogenic, as well as soot (or particulates), which contribute to the formation of smog. Whereas European pollution standards focus primarily on carbon dioxide emissions and so are achievable by diesel cars, new EPA regulations about to take effect in the United States aim specifically to reduce nitrogen oxides and particulates and will be more difficult for diesel manufacturers to meet.

Nevertheless, automakers are anxious to introduce more diesel-powered models in the United States. That’s because SUVs, pickup trucks, and other vehicles that burn through gasoline have been selling so well in recent years, leaving car manufacturers struggling to meet U.S. fuel-economy standards. Those standards are calculated company-wide, which means that fuel-efficient diesels could conveniently offset the gluttony of their more wasteful brethren.

And if the strong sales of the Golf TDI and General Motors’ new diesel-powered heavy-duty pickup trucks are any indication, U.S. consumers may be ready. Customers have waited up to six months for delivery of the GM trucks, which are equipped with Duramax diesel engines, and GM is planning to increase production by 50 percent — to 150,000 diesel engines a year. A shift to diesel could be rather seamless for Detroit automakers, since they are already making diesel-powered vehicles and marketing them elsewhere. Ford, for example, sells a wide range of models abroad, including its economy-size Focus; Chrysler, meanwhile, sells diesel-powered minivans and Jeep Libertys in Europe.

The main appeal of the new diesels, industry proponents say, is that they’re not only efficient but fun to drive. “The great success of diesels in Europe comes from much more than simply the engine’s fuel economy,” says Hermann Scholl, board chairman of Robert Bosch, a German automotive supplier. “The new generation of diesel engines delivers outstanding torque and acceleration — appealing to people who love to drive.”

Rudolf Diesel, a French-born engineer, patented the idea for the diesel engine in 1892. What Diesel invented was an engine that was inherently more fuel-efficient than a gasoline engine. A gasoline engine works by taking in a mixture of gas and air, compressing it, and then igniting the mixture with a spark. A diesel engine, by contrast, takes in only air, compresses it, and then injects fuel into the compressed air. The heat of the compressed air lights the fuel spontaneously. Today’s diesels deliver up to 30 percent more fuel economy than do gasoline engines. Diesel fuel, which is heavier and oilier than gasoline, has a higher energy density: A gallon of diesel fuel produces more energy than a gallon of gasoline.

Bosch’s American subsidiary recently held a special event in Detroit for U.S. journalists called Diesel Day. On hand were about 15 diesel-powered models from Audi, BMW, DaimlerChrysler, Ford, General Motors, and Volkswagen. When I turned the key of the Mercedes-Benz S400, its powerful V8 engine started up immediately. The car propelled powerfully and smoothly through the gears as I depressed the pedal, and was nearly silent. The same was true for most of the other cars, especially the large, luxury models, which emitted virtually no smell, smoke, or noise, and delivered powerful acceleration from a dead stop to highway speeds.

What has made such diesels possible? The most significant breakthrough has been the development of the common rail, a reservoir that runs alongside the cylinder heads in which diesel fuel is stored under pressure. When the engine requires fuel for combustion, a high-pressure pump forces the fuel from the rail straight into the injectors, which quickly open and close, spraying fuel into the cylinders. In older diesel engines, by contrast, fuel had to travel from the pump to each individual cylinder in separate pipes.

The common rail enables fuel to be injected into the engine’s combustion chamber at very high pressures, so the fuel and air mix more thoroughly and burn more efficiently. And because the pump constantly replenishes the common rail with pressurized fuel, high fuel pressure is maintained throughout the engine’s range of speeds — ending the problem of hesitation on acceleration. “Common rail is the biggest single thing that has civilized the diesel engine,” says Bernard Robertson, senior vice president of engineering technologies at DaimlerChrysler.

A second recent advancement in diesel engine technology is direct fuel injection. Diesel engines of the past relied on indirect injection, a system in which fuel was sprayed into a small chamber in the cylinder head, where a glow plug sparked combustion. With direct injection, fuel is sent directly into the combustion chamber. The result is even more fuel economy and lower emissions than with a traditional diesel engine.

Engineers are striving to further refine the diesel engine. They’re developing injectors that will more precisely deliver fuel into the combustion chamber for an even more thorough burn. One intriguing new fuel injector is the piezoactuator. Launched by the German automotive supplier Siemens, it is based on technology borrowed from the company’s high-speed inkjet printers. Piezoactuators distribute fuel faster — about five times during a single combustion stroke — than a traditional solenoid valve can open and close. At Bosch, meanwhile, engineers are increasing the pressure of the fuel that’s propelled from the common rail into the injectors — they’ve recently pushed it to 23,500 pounds per square inch, up from 19,500.

It’ll still be a struggle, however, for today’s diesel engines to meet upcoming U.S. emissions regulations. The EPA is introducing restrictions known as Tier 2 that are specifically aimed at reducing nitrogen oxides and particulates, among other things. Those rules will be phased in beginning in 2004, with full compliance required by 2009. Additionally, California — a state that’s large enough to influence automakers’ planning — aims to dramatically reduce smog-forming emissions, especially in Los Angeles, with its stringent Low Emission Vehicle II regulations, which will be phased in from 2004 to 2010.

In response, auto manufacturers are working to develop special after-treatment systems for diesel exhaust. Peugeot, for instance, has introduced a particulate trap. Enabled by the common rail system, the device captures the soot particles produced by the engine and burns them to levels low enough to be practically unmeasurable, according to Peugeot. Ford, meanwhile, has developed a system in which a solution of urea, an ammonia-based compound, is held in a tank on the car. The urea, which is injected into the exhaust gases before they have finished their progression through the catalytic converter, eliminates most of the nitrogen oxides. Ford has built a research vehicle equipped with a particulate trap and the urea catalyst that it asserts meets California’s stringent new standards.

Troublesome emissions aren’t the only remaining obstacle, however. For one thing, whereas in Europe diesel fuel — often subsidized by governments — is generally cheaper than gasoline and readily available, here gas is cheaper and diesel hard to find. A second hurdle is that diesel engines cost more to manufacture than gasoline engines, in part because they require extra equipment such as the particulate traps and urea scrubbers. Unless U.S. officials institute tax breaks like the ones available in Europe, those higher prices will be prohibitive.
At this point, in fact, diesel experts assert that the political challenges are more daunting than the technological ones. I recently test drove the Volkswagen Golf to evaluate the new diesel technology, and I had to agree. The experience vividly demonstrated how far diesel engines have come since the days when I had to coax my Rabbit to start up on a cold day. Nothing about the Golf indicated to me that it was a diesel, other than the diesel fuel label on the fuel tank — and the long distances I could travel between fill-ups.

**Diesel Roars in the Baja 1000 **

Ojos Negros, Mexico — It’s mile 127 of the Baja 1000, the world’s oldest and most prestigious off-road race, and the 8,100-pound Ford Excursion I’m strapped into takes to the air, stretches its full 16 inches of suspension — and lands surprisingly gently on 37-inch wheels. Even more astonishing than the soft landing, however, is the fact that this behemoth is diesel-powered-living proof that diesel engines can match the power of their high-performance gas brethren and thereby appeal to more than the fuel-economy minded.

Racing veteran Steve Scaroni of SMD Motorsports transformed this full-sized SUV, originally designed for the Sunday mall crawl, into a dune buggy on steroids. The truck is equipped with a 60-gallon fuel tank with a firewall, off-road coolers that double the capacity of the radiator, and a so-called intercooler, made by Hypermax, which ensures that air from the turbocharger gets cooled before it reaches the engine. Other modifications include a larger turbocharger and a special fuel injector, co-developed by International Truck and Engine Corp. and Caterpillar for marine applications, that yields a 15 percent boost in flow capacity.
This monster went like spit across desert-dry lake beds, over pine-forested mountains, and through cactus fields in the November 2001 race. And no wonder: Its 7.3-liter turbocharged Power Stroke engine, made by International, pulls 400 horses and 850 pound-feet of torque from V8 stock that normally produces 235 hp and 505 lb.-ft. of torque (granted, the emissions are nasty).

The race ended early for us — in a cactus bed filled with boulders — courtesy of a steering box that clearly needs to be upgraded before next year’s event. But the Excursion accomplished its larger mission: It proved that diesel is a contender.