The diesel engine market has been rapidly changing in recent years. Higher fuel prices and changes in emission regulations have brought about a whole new generation of clean diesel engines in both the light- and heavy-duty truck markets.

According to the Diesel Technology Forum (www.dieselforum.org), particulate emissions from new on-highway diesel engines have been reduced 83% since 1988. Nitrogen oxide (NOx) emissions are down 83% over the same time period. With the latest low sulfur diesel fuel and exhaust particulate traps, diesel emissions will be reduced up to 90%.

Because of their higher fuel efficiency (typically 20-40% better than a gasoline engine with the same displacement), diesel engines power most heavy-duty trucks, transit buses and emergency vehicles. Diesel engines also power most farm machinery as well as a majority of school buses and medium-duty trucks, and they are a popular option in many pickup trucks. But Volkswagen has been the only vehicle manufacturer to sell diesel-powered cars in the U.S. in recent years, and in 2007 they didn't offer any because of changes in diesel emission regulations.

In Europe, where fuel prices are considerably higher than in the U.S., and emission regulations are more diesel-friendly, 50-60% of passenger cars are now powered by diesel engines. Many experts predict that the number of diesel-powered passenger cars in the U.S. will increase dramatically over th...