The Case for Dieselcleanefficientfast cars.docx

1、The Case for Dieselcleanefficientfast carsThe Case for Diesel: Clean, Efficient, Fast Cars (Hybrids Beware!)The dark horse of fossil fuels has cleaned up its act, allowing automakers to create cars for the U.S. that are ultraefficient and high-performance. Here comes the 75-mpg revolution.Merging wi

2、th northbound traffic on Interstate 75 just outside Auburn Hills, Mich., I punch the accelerator, quickly swing left into the passing lane and pull forcefully ahead of the cars around me. In any other ride, on any other gray morning, itd be just another Interstate moment. But this rush hour, Im behi

3、nd the wheel of a preproduction 2009 Volkswagen Jetta, which is powered by a 2.0-liter turbo-charged, direct-injected diesel engine that, even as I leave the speed limit in tatters, is averaging nearly 50 mpg. Equally important, whats coming out of the tailpipe is no dirtier than the emissions from

4、the 35-mpg econoboxes I can now see in my rearview mirror. Speed, fuel efficiency and minimal emissions? These arent characteristics usually associated with diesel-powered vehicles. But they will be. Most Americans have a bad impression of diesel cars. We think of them as loud, hard to start and fou

5、l-smelling. We sneer at them for lacking the get-up-and-go of their gasoline-powered cousins. And we dislike them for their perceived environmental sins, chiefly the polluting brew of sulfur and nitrogen compounds that they emit into the atmosphere. All those complaints were fair a generation ago, w

6、hen the twin energy crises of the 1970s propelled diesels into national popularity and kept them there for a decade. Back then, many drivers ignored diesels faults, or were unaware of them, because diesel cars ran 30 percent farther on a gallon of fuel than similar gasoline-powered cars. It felt sav

7、vy to buy a diesel, even daring. Then fuel prices dropped in the mid-1980s, and drivers abandoned their clattering, odoriferous fuel sippers. They went back to gasoline. Today, diesel powertrains are on the map again, for both car manufacturers and efficiency-minded drivers. The technology could be

8、here to stay, even if fuel prices (improbably) decline. The new cars run as well as their gasoline-powered competitors. And as for the emissions problems of the past-well, the dirty bird of fossil fuels isnt so dirty anymore. The Coming Diesel InvasionAUDI A4 SEDAN BMW 3 SERIES SEDAN CADILLAC CTS SE

9、DAN Engine: 3.0-liter V6Target Release Date: 2008This 240-hp turbocharged direct-injected engine will also be available in the full-size Audi Q7 sport utility.Engine: 3.0-liter twin-turbo inline SixTarget Release Date: 2008BMW plans to release this 3.0-liter in 5 and 6 Series models in 2008 as well.

10、 It reportedly gets more than 35 mpgEngine: 2.9-liter TDI V6Target Release Date: 2009Look for clean diesel also in the Buick Enclave, GMC Acadia and GM light-duty pickups, around 2010.FORD F-150 PICKUP HONDA ACCORD SEDAN SATURN AURA SEDAN Engine: 4.4-liter V8Target Release Date: 2009Derived from the

11、 Euro-spec 3.6-liter currently used in Land Rovers, which get around 31 mpg on the highwayEngine: 2.2-liter i-DTECTarget Release Date: 2009The British version gets 51.4 mpg in combined city/highway driving. The hybrid Civic gets 50 mpg.Engine: To be determinedTarget Release Date: 2010The Auras Euro

12、twin, the Opel Vectra, gets more TDI options in 09, which will transfer to the model coming here.The Sulfur SolutionIf you told me 10 years ago that Id be putting clean and diesel in the same sentence, Id have said you were out of your mind, says Margo Oge, director of the Office of Transportation a

13、nd Air Quality at the Environmental Protection Agency. However, in response to EPA mandates that went into effect in late 2006, oil refineries are now producing whats called ultra-low-sulfur diesel (ULSD). By definition, this clean diesel has sulfur concentrations of no more than 15 parts per millio

14、n (ppm). Thats 98.5 percent cleaner than the sludge that coursed through the fuel delivery systems in those disco-era rides, and 97 percent less sulfur than was allowed under a 500-ppm standard instituted in 1993. The cut in sulfur means that less sulfur dioxide goes into the atmosphere, where it ca

15、n combine with water to produce sulfuric acid-and thus, acid rain. There are further beneficial effects of the sulfur-light fuel, ones that could make the advent of clean diesel as environmentally momentous as the introduction of unleaded gasoline in 1974. Sulfur clogs emission-control devices in di

16、esel-powered cars the same way lead impeded catalytic converters in gasoline systems, Oge says. Removing the lead from gasoline enabled engineers to develop a new generation of emission-control technologies that helped reduce noxious exhaust emissions by 98 to 99 percent. Carmakers have already star

17、ted building exhaust-scrubbing systems for engines that burn ULSD-so that not just sulfur but a rogues gallery of other pollutants are kept out of the air. Though they differ in design, the systems share some basic components. In a Mercedes-Benz BlueTec system, for example, exhaust from the engine i

18、s first filtered through a device that lowers carbon monoxide and hydrocarbon levels. Then it runs through an apparatus that removes soot and other particulates. Finally, the remaining exhaust gas is sprayed with a urea-based substance that helps convert harmful nitrogen oxides-NOx is the shorthand

19、for this group of compounds-into harmless nitrogen gas and water vapor. According to Mercedes-Benz, the system reduces the total output of harmful emissions by 80 to 90 percent. The process even eliminates diesels bad odor. How They Work: Emission Reduction SystemsExhaust leaves the engine and passe

20、s through a diesel oxidation catalyst (DOC), which minimizes carbon monoxide and hydrocarbons. It then passes through a self-cleaning particulate filter that traps and stores soot. A urea-based solution, commercially known as AdBlue, is then sprayed into the exhaust flow. Heat from the exhaust trans

21、forms the urea into ammonia, which reacts with nitrogen oxides (NOx) in the SCR, where the mix is converted into harmless nitrogen gas and water vapor. Exhaust from the engine flows through a combination DOC (diminishing the amount of carbon monoxide and hydrocarbons) and a self-cleaning particulate

22、 filter, which removes soot. From there, it enters a new type of catalytic converter that absorbs a portion of the NOx from the exhaust gas and converts it into ammonia without the need for an organic catalyst like AdBlue. The system recombines that ammonia with the remaining NOx, converting it into

23、 harmless nitrogen and water vapor, just like the SCR system. The 250,000-Mile EngineULSD fuel and the new exhaust systems receive most of diesels accolades, but they arent the only advances to set todays diesels apart from their predecessors. Advanced electronic engine control modules regulate func

24、tions, from fuel injection to timing, more precisely than old mechanical control systems, further minimizing emissions and maximizing fuel economy. Turbochargers pump more air into the engines, helping to overcome diesels former sluggishness at higher rpm. And improved engine isolation strategies, s

25、uch as the incorporation of active mounts, has quieted the knocking noises typically associated with diesel-powered vehicles. Meanwhile, diesels core virtues remain unchanged. The fuel contains more energy per unit volume than gasoline, and diesel engines operate at higher compression ratios than ga

26、soline engines-typically 14:1 to 25:1, compared to 8:1 to 12:1. (The compression ratio is the relationship between the volume of the cylinder when the piston is at the bottom of its stroke and the volume when its at the top.) The higher the compression ratio, the more mechanical energy an engine can

27、 squeeze from its fuel/air mixture. So each time the mixture in a diesel engines cylinder ignites, the car gets a slightly bigger push than it would in a gasoline engine. That means it takes less fuel to move the car down the road. It also means that the engine generates a lot of power even when it

28、isnt cycling fast-and thats the source of the beefy low-end torque these vehicles are famous for. The high compression ratios also explain why diesel engines tend to last so long. Diesel engines need to be built stronger, explains Tony Molla, author of Chiltons Diesel Engine Service Manual. The cran

29、kshaft and connecting rods are quite a bit heavier than those in gasoline engines. And because diesel has a low coefficient of friction, it also happens to be a good lubricant that provides protection to the cylinder walls. The result? Its not unusual to see diesel engines still chugging along at 25

30、0,000 miles. The European ModelFans of diesel technology often look longingly at Europe to see how their favorite automotive fuel is faring in a friendlier environment-namely, one where gasoline costs $7 per gallon. Many European countries provide tax breaks on diesel that make it consistently cheap

31、er than gas. More than half of the vehicles sold on the continent are diesel powered, and the technologys proponents like to point out that Europes average fuel consumption is 36 mpg, compared to just 22 mpg in the United States. (To be fair, that fuel economy number is partly due to the fact that E

32、uropeans drive smaller cars, regardless of their powertrains.) Could diesel gain a similar level of acceptance here? Perhaps. A recent study by J.D. Power and Associates found that in 2007, 23 percent of U.S. car buyers were considering a clean diesel for their next purchase, up from 12 percent the year before. Ultra-low-sulfur fuel is the key to clean diesel. Shell fuel scientist Nigel Dickens displays the fruits of the lab. (Photograph by Getty Images)In the short term, those numbers wont be reflected in new-car