Diesel has gotten a bad rep in the U.S. over the past few decades, but Volkswagen is looking to change that with their latest Jetta TDI, a clean diesel vehicle. Think about all the old problems with diesels, and the new Jetta TDI has an answer. There’s tons of black smoke coming out the tailpipe! The 2009 Jetta TDI meets or beats the emissions standards for gasoline vehicles in all 50 U.S. states. They put out too much carbon dioxide! The TDI has less CO2 emissions than the regular Jetta SE. They’re slow and horrible to drive! Not by a long shot.
Let’s start off with the power. The Jetta SE, which is the most comparable model to the TDI, is powered by a 2.5-liter inline five-cylinder engine. It puts out 170 horsepower and 177 lb-ft of torque. Respectable numbers for a small car. The Jetta TDI has a 2.0-liter turbocharged diesel engine that puts out 140 horsepower (so the SE wins there), but a whopping 236 lb-ft of torque. When it comes to off the line acceleration, the TDI wins, hands down. And here’s another enticing figure: the Jetta SE has a combined EPA fuel economy of 25 mpg; the Jett TDI has a combined 35.5 mpg.
The torque of the TDI eliminates any complaints that a diesel car can’t be fun to drive. Diesel fuel has more potential energy per volume than does gasoline. That means that you have to burn less of it in order to get the same amount of power you’d get from a gasoline engine. So, you can jump off the line and accelerate to your heart’s content, and still be getting better mileage than even cautious hypermiling drivers in gasoline cars. That more energy per volume figure also come into play when calculating the CO2 emissions. The Jetta SE puts out 0.81 pounds of carbon dioxide for every mile traveled. Because the TDI model has to burn less fuel in order to cover that same mile, the output is only 0.65 pounds per mile.
At this point, you’re probably wondering how they do this. The answer is in the exhaust. Older diesel designs did put out a lot of emissions, requiring that they be fitted with extra exhaust components. Until recently, those extra components were filled with urea, an organic compound that absorbs hazardous emissions. The problem was, you would have to bring your diesel car to a service station to have the contaminated urea removed and replaced with fresh stuff every so often. The process was time-consuming and expensive.
The new TDI design uses a variety of solid catalysts and particulate filters in the exhaust system that catch most of the hazardous emissions materials and stores them, much like the urea system did. However, instead of bringing the car to have them physically removed, every 500 miles or so, the onboard computer in the car will push a lot of extra heat into the catalyst to burn off the pollutants. This may seem counter-intuitive, after all, those pollutants were generated from burning diesel, but the science is sound. Under normal engine operation, not all of the fuel burns (whether it be gasoline or diesel). By applying steady and intense heat to the catalyst, the TDI’s system ensures a complete burn. So, those NOx gases are broken down into harmless nitrogen and oxygen (which together comprise about 99% of the atmosphere). There are similar breakdowns for other pollutants.
Okay, enough of the science. How does the 2009 Jetta TDI drive? Incredibly well, and incredibly smooth. The steering and handling characteristics that you’d expect from a German sedan are intact in the TDI model, so there’s no surprise there. Where you really notice the difference is on the highway. A gasoline-powered Jetta, or most any gasoline vehicle for that matter, usually cruises at highway speeds with the engine turning at about 3,000-4,500 RPM. The Jetta TDI does it at about 1,800 RPM due to the energy per volume of diesel fuel we mentioned earlier. It simply doesn’t have to work hard in order to produce the power needed to maintain a speed of 70 mph.
And that’s really the genius of this car: it doesn’t work hard. Worried about long term ownership? Well, since the TDI’s engine doesn’t work all that hard, it doesn’t get worn down as quickly as a gasoline engine would, so don’t be surprised to see a 2009 Jetta TDI cruising down roads 20 years from now with an original engine that has logged 300,000 miles. Obviously, components like brakes, suspension, and all that other stuff that is pretty much borrowed from the regular Jetta will wear down, but that’s the same on every car. And, a recent survey by Internet auto market tracker Intellichoice.com determined that the overall cost savings of owning a Jetta TDI over a five-year period versus the Jetta SE worked out to be about $6,000 (this figure incorporates all scheduled maintenance and federal tax rebates to offset the higher initial upfront cost of the TDI model). The 2009 Jetta TDI, and the other Volkswagen family vehicles that will adapt the same powerplant (there’s an Audi A3 set for next year that uses the same engine), could really change the public perception of diesel as a viable fuel for the everyday driver.