2009 Volkswagen Jetta TDI

Clean diesel, quiet diesel, quick diesel

Mac Demere / autoMedia.com

It’s past time to take all those negative notions about diesel-engine cars and feed them through the shredder. The 2009 Volkswagen Jetta TDI is the equal of its gasoline-fueled siblings in every area, except one: It kicks gas in fuel mileage. On the government’s highway driving cycle, the 2009 Jetta TDI gets 41 miles per gallon and 30 mpg in the city. During our test drive ng (in a TDI loaned to us by VW), which included 80-mph freeway cruising maximum-effort acceleration sprints, and a bunch of city driving, we recorded 39 mpg.

Diesel Vs. Gas

The 2009 Volkswagen Jetta TDI is a roomy, sporty, quick, economical sedan. Without being told, few will know the Jetta TDI burns diesel, not gasoline. Even if diesel were to cost as much as a dollar per gallon more than regular gas, a Jetta TDI getting 41 mpg will be cheaper to operate than a Jetta using the alternative 2.5-liter gasoline engine getting its rated 29 mpg. But how is diesel fuel on the environment? In the short term, it’s a toss-up. In the long run, diesel has a chance to be better for the environment and reduce dependence on foreign oil if “synthetic diesel” technologies can be profitably industrialized. These technologies include diesel made from non-food plants, plant waste, garbage, sewage, coal and natural gas.

Synthetic diesel burns cleaner than petro-diesel. (The net environmental and social impact of soybean- and other food-plant-based bio-diesel is arguably negative.) It’s unlikely that any type of diesel will be as cheap as gasoline. One reason: The worldwide demand for diesel is exploding. In some countries, more than half the vehicles burn diesel. Also, refiners can alter only slightly the ratio between diesel and gasoline extracted from each barrel of crude oil.

Modern Diesel

Inside the Jetta TDI, there’s essentially nothing that indicates you’re driving a diesel-fueled vehicle. There’s none of the smoke, stink or sluggishness that characterized diesels from the past. It starts immediately: No waiting for the old-time glow plugs to warm up. The only significant indicator is a small written reminder, hidden behind the turn signal stalk, to use only ultra-low sulfur diesel fuel. Since there’s none of the old indications that it’s a diesel, it’s possible someone not familiar with the car will miss the “ultra-low sulfur diesel only” warning inside the fuel door and the large-lettered “DIESEL” on the fuel cap. Putting gasoline in a diesel-engined car will be an expensive, or a very expensive, mistake.

From the outside, the TDI badge is the biggest indicator it’s a diesel. There’s none of the traditional diesel clatter. (On start-up on a cold morning we heard less than a second of that old-time clatter.) Even with your nose inches from the exhaust, there’s no hint of the diesel odor that used to be evident a block away. Sometimes there’ll be a whiff of sulfur during refueling, but that’s an unfortunate reminder of when that pump and the tanker truck carried higher-sulfur diesel.

The 2.0-liter, single-overhead cam, turbocharged four-cylinder diesel engine in the Jetta TDI provides 140 horsepower and a large 236 pound-feet of torque. It features direct-into-the-cylinder, very-high-pressure fuel injection: This is key to the engine’s low emissions and noise. The diesel’s low engine speed limit of 4,500 rpm took time to get used to as some cars today redline at almost twice that number. We bounced the manual-transmissioned Jetta TDI against the rev limiter in first gear several times.

A key to Jetta TDI’s existence is ultra-low sulfur diesel (ULSD). ULSD allows the use of diesel oxidation catalysts and selective catalytic reduction devices, both similar to catalytic converters on gasoline engines. ULSD also allows the addition of mono-nitrogen oxides (NOx) absorbers (such as that on the Jetta) and particulate traps. The result is a radical reduction in smog- and acid-rain-causing NOx, carbon monoxide and unburned hydrocarbons. Unlike some other diesels, the Jetta TDI does not require a chemical to be injected into the exhaust.