While you weren't paying attention, an alternative fuel trend has been gaining momentum. And it's not electric, fuel cell, or pedal-powered cars. It's a return to the once-shunned, viscous, under-toned petroleum distillate known as diesel.\r\nRising from the ruins of their belching forebears, which clogged roads and darkened skies in the Seventies and Eighties, diesel-powered vehicles are one of the fastest-growing segments of the domestic automotive market. (Though still a small percentage overall.) Helping this rising popularity is the falling price of diesel fuel, which is projected to decrease in price per gallon significantly over the next two years. New diesel vehicles also use advanced exhaust scrubbing technology for clean and quiet operation that does nothing to diminish the instant-on torquiness that gives them a thrusty potency. And it doesn't hurt that diesel engines routinely achieve 20 percent to 40 percent better fuel economy than their gasoline-powered brethren.\r\nIn order to serve that increasing demand, American-based car companies are developing diesel engines – or importing them from Europe, where they power more than half of vehicle sales – and stuffing them into an increasingly wide range of autos. The Chicago Auto Show – which opened for press previews on February 6 – saw the unveiling of two new notable diesel vehicles, BMW's 740LD xDrive and Nissan's Frontier Diesel Runner, giving us occasion to reflect on some of our other favorite available diesel models in a variety of categories.