(Photo: Nick Ferrari)As consumers clamor for cars with higher mpg numbers and with rigorous new federal fuel-economy standards on the horizon, carmakers are exploring all their options. This has largely meant improving the gasoline internal combustion engine's efficiency and offering a few hybrid and electric vehicles. Conspicuously absent from many lineups in the U.S., however, have been vehicles with diesel powerplants. And understandably so: The American public has been reluctant to embrace diesels ever since General Motors and other automakers sold noisy, dirty, and unreliable versions back in the '80s. But modern diesel systems are clean, powerful, and fuel-efficient.
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This is good news. Because diesel engines operate at a high compression ratio and the fuel has a higher energy density (about 15 percent more than gasoline), fuel economy is high and torque is abundant. With excellent thrust off the line and long cruising ranges, diesels fit the driving style of most Americans. Of course, there's a catch: Diesel vehicles come at a premium, and in the past two years diesel fuel has cost 10 to 70 cents more per gallon than gasoline. Making up the purchase- price difference in fuel economy takes tens of thousands of miles. Even so, consumers already pay extra for hybrid efficiency. For those seeking an alternative, or for people who just hate stopping to fill up, a diesel vehicle might be the perfect solution.
(Photo: Vic Kulihin)How Diesels Meet Emissions StandardsA. Engine
Diesel combustion creates two emission problems: particulate matter and nitrogen oxides (NOx ).
B. Particulate Filter
The particulate filter traps soot caused by incomplete combustion. The soot burns off eventually.
C. SCR Catalytic Converter
SCR uses an aqueous urea solution (aka diesel exhaust fluid, which is kept in an onboard tank) with a catalyst that reduces NOx to nitrogen, water, and carbon dioxide. Smaller engines can get by without SCR.
