I’m all for clean air regulations, but sometimes they don’t make very much sense. Case in point: California, along with four Northeastern states, has imposed strict limits on the type of pollutants coming out of the tailpipe of a car. There’s only one problem: these regulations make diesel engines illegal, since even the most modern diesel engines emit slightly too much NOx (nitrides of oxygen). Fancy diesel engines (like the Mercedes Bluetec) go to great lengths to reduce their NOx emissions, such as injecting ammonia-rich urea into the exhaust stream. But it’s still not clear that they will be able to pass the regulatory hurdle.
So why should we be encouraging diesel engines? For one thing, they are much more fuel efficient than conventional engines. The modern diesel engine tends to get anywhere from 25 percent to 45 percent better mileage than a comparable gas engine. (The price premium for a diesel engine is also significantly less than for a hybrid, even after the hefty tax breaks are factored in.) Diesels also are the ideal partner for the hybrid cars of the future (like the Chevy Volt), in which a fossil fuel engine drives an electric generator.
For more, read Dan Neil on the latest Mercedes Diesel.