Diesel is no longer a dirty word

We probably have about 50 years of "cheap" oil left. By cheap oil, I mean oil that's cheap enough--plentiful enough, really--to be used in private cars. After that, its use will likely be restricted to commercial transportation, military applications and emergency vehicles. Maybe licensed, classic-car collectors will be allowed to buy 1,000 gallons a year, but other than that, unregulated consumption of oil and its prized distillate, gasoline, just isn't fathomable.

But that's off in the distance. Most people reading this today will have had their driver's license yanked due to senility long before such restrictions kick in. We are instead concerned about how much we spend today on a gallon of gas, not when it will run out, how much it pollutes or what kind of global tensions it creates. Aside from a few Prius owners, we want cars that save us money, don't look stupid, don't require us to learn new procedures for auto ownership, and don't cost more than what we drive today.

Bottom line: You and I stand in the way of advanced powertrain vehicles, just as much as any oil company conspiracy or automaker's backwardness. We stand in the way by virtue of our attitudes, as evidenced by our responses to the carmakers' armies of market researchers who have relentlessly probed us. That's why I get excited about diesels. They can make a big difference and they aren't strange.

In fact, diesels are hot. The new Golf TDI turbo diesel I just hammered across the French countryside was imminently fun and livable. After crossing the Swiss frontier into Geneva, I immediately looked into buying one and shipping it home. Luckily they couldn't do that for me as I would have had a nasty surprise when I tried to register it back in California. (More on that later.)

I was left with memories of great, lugubrious gobs of torque coupled with a fuel-tank range that was almost goofy. In four days of hare-and-hound driving, I was never the one slowing traffic: The Golf was always willing to hunker down its little rump and breathlessly keep pace with anything else on the road.

And that Golf TDI was not alone. Car and Driver is smitten with BMW's 330d, the turbo diesel version of the familiar 330i gas engine sedan. The reviewers laud it because it "feels faster than a 330i" (its gas-powered sibling), gets 44 percent better mileage, and has so much midrange torque that you practically forget about downshifts.

Ditto for the Jaguar XJ with the brand new 2.7 Diesel V6 powertrain, which delighted The Times of London with its fabulous torque and fuel economy around 35 mpg--in a big Jag, no less.

See the pattern? Economy, sporty, luxury. Diesel is proving to be a winner in all kinds of cars. But there are two hurdles for diesels in the United States: image and emissions.

The former is due largely to General Motors' miserable forays into diesel engines in the late '70s and early '80s. As I recall, these were basically re-engineered gas engines that came apart in all kinds of unpleasant ways. Even if the cam stayed in the block, they were horrible, noisy, filthy things that made a mockery of the big, supposedly elegant cars into which they were shoved. (At least GM made a run at it; Ford mostly piddled around with oddities like the Lincoln Mark VII with optional BMW Turbo diesel engine.)

With its diesel clunkers, GM single-handedly undid all Mercedes and Volkswagen had accomplished with their excellent diesels in the S-Class and the Golf. Those well-received oil-burners from Germany weren't as fast or quiet as our modern common rail, turbo diesels today, but they were well-built. You have a good chance of pulling up next to one at a stoplight today.

The other problem with diesels is nitrogen-oxide emissions, the unburned particulate exhaust that is perhaps the greatest contributor to visible smog. This is the diesel's dirty Achilles' heel. These engines run at high compression ratios and therefore high temperatures, which creates a high level of nitrogen oxide from the sulfur in diesel fuel. As of 2007, new U.S. emissions laws will actually be a lot stricter than European regulations, which means that even if a carmaker has a thriving diesel lineup over there, it won't be certifiable for sale in the U.S.--not even close.

Here's how we'll sort this out: First, the new stringent diesel sulfur regulations will make diesel fuel 33 times cleaner than it is today and must be used in all car models beginning with 2007. Then, a combination of particulate filters already being used on European diesel exhaust systems, along with an "after-scrubber" technology (BMW has been vocal about urea injection, while Mercedes offers their BlueTec system) cleans the exhaust even further. We should see 50-state-approved diesel cars starting as soon as the 2008 model year, and really kicking in through the end of this decade.

Frankly, the public perception feels like a bigger problem than the emissions issue.

Which brings me to the last and perhaps most appealing prospect: the diesel hybrid. Coupling a diesel with an electric motor makes an accepted "alternative" engine even better. A diesel can be an even smaller and lighter partner to the electric motor while continuing a torque-fest beyond its optimal RPM range.

This is a formula for a car that can pull stumps out of the ground in almost every driving scenario and use damn little fuel doing it. Hermann Scholl, chairman of Robert Bosch, fully expects diesel hybrids in the U.S. before the end of the decade.

The stinky, noisy, gutless diesel of the past is gone. Today it's an engine that can offer roughly 45 percent better fuel economy as a drop-in replacement for a gasoline equivalent while offering much more of the kind of torque that makes real-world driving enjoyable. We have a fueling infrastructure in place that can be easily tilted more toward diesel, and there's no learning curve when you drive a diesel car: Turn the key and press the pedal on the right.

Kick in the diesel hybrids in a few years, and we're really onto something. No, diesels don't move us off oil, but they do use less of it and reduce refining effort, which has proved to be almost as big of a factor in gas prices as the cost of crude. And I'm not even factoring in the use of biodiesel.

The modern diesel engine is a path to frugality that doesn't have to feel like one, a form of motive power that is a joy to drive with, and can be cleaned up and ready in the very near future. The biggest problem is its image.