Clean Diesel: A New Era of Green Cars

Enlarge Image Image Gallery The green transportation horizon is even brighter thanks to new clean diesel vehicles. Compared with a similar-sized gasoline engine, a diesel engine delivers about 30 percent better fuel economy, which also means roughly 30 percent less carbon dioxide emissions. RAFA IRUSTA/FOTOLIA

Whatever notions you have about diesel cars, forget them. Long gone are the days of smelly, black plumes of smoke, noisy engines, slow acceleration, and sometimes-finicky operation. Diesel technology has evolved significantly in recent years, making diesel cars a strong green transportation option.

Modern diesel powertrains are quiet, clean, smooth, reliable, powerful, durable and economical. A diesel vehicle will usually cost more than a comparable gasoline vehicle, but the diesel engine’s more robust design means that, with proper maintenance, it should last considerably longer. Plus, some clean diesel cars qualify for a federal tax credit. For more information, see 2010 Clean Diesel Cars, Trucks and SUVs, and visit www.fueleconomy.gov.

For generations, diesel power has been the best choice for work-intensive applications, with no other engine delivering as much stump-pulling power. What’s evolved is how the engine compresses and ignites the fuel to propel the vehicle — a change that has capitalized on diesel’s inherent advantages while virtually eliminating the traits that previously made diesel dirty.

Diesel enthusiasts now contend that a diesel car delivers fuel economy on par with that of a gasoline-electric hybrid, and also offers a better driving experience. (See Clean Diesel: Greener Than the Prius? to find out how clean diesel vehicles measure up with gasoline and hybrid vehicles in mpg, price, greenhouse gas emissions, annual fuel cost, and more.)

How Diesels Are Different

Aside from using diesel fuel rather than gasoline, diesel engines operate in a fundamentally different way than gasoline engines. A diesel engine doesn’t have a spark plug to ignite the fuel/air mixture in the engine. Instead, a diesel engine ignites its fuel via the heat created when the fuel/air mixture inside the cylinder is compressed sufficiently. These high-compression engines are controlled by the timing and duration of the fuel injection events rather than by the firing of spark plugs, as with gas engines.

It used to be that you could tell the difference between a gasoline engine and a diesel engine just by the sound. But the latest clean diesel cars — even those with four-cylinder engines — are quiet and smooth, with only a hint of the old telltale diesel clatter when they’re driven at certain speeds or under certain conditions. Luxury diesel models are nearly silent.