Clean diesel engines coming to a road, and track, near you

lean diesel technology is beginning to take root. Friday at our "Future of the Car" event I drove a couple of clean diesel SUVs, an Audi Q7 and a Mercedes-Benz ML320D. In both, the powertrains were very impressive: quiet, smooth, powerful, and quick. The Q7 is a stretched cousin of the Volkswagen Touareg while the ML320D is a diesel version of the familiar ML.

Since these were just trial laps around our swoopy mile-long ride evaluation course, and not instrumented runs, I can’t tell you what the timed acceleration numbers would be. By the seat-of-the-pants feel, these SUVs felt good, and if you weren’t told, you wouldn’t guess these were diesel engines. They felt punchy and responsive and there was no clatter, no smell, and no slow-motion takeoff. They will soon be joined on American roads by diesel versions of the Mercedes R320, GL320 (with the new Bluetec technology) SUVs, and the BMW 335 and X5. The Volkswagen Jetta diesel is already available.

It’s hard to overstate the potential significance of clean-diesel technology. The superior thermal efficiency of a diesel engine promises about 30 percent more miles per gallon than an equivalent gasoline engine, right from the get-go. If a big chunk of the current American fleet switched over to diesel, the cumulative fuel-savings would be gigantic. Essentially, it would cut fuel demand by one third without sacrificing space, power, or utility. The Audi and Mercedes-Benz reps who brought these vehicles to our test track told us that the cruising range of each was about 600 miles on a  tank.

The arrival of these first few clean diesels coincides with a milestone in air-quality standards, as well. Next year marks the completion of a phase-in period when all passenger vehicles -- both cars and light trucks, gasoline or diesel powered -- must meet the same stringent emissions standards, technically known as Tier 2 regulations. The rules put strict limits on smog-forming or otherwise toxic emissions, including carbon monoxide, non-methane organic gases, hydrocarbons, and particulate matter.

Particulate matter, or soot, has been a special concern with diesels, since fine particulates have been linked to lung disease. The Tier 2 standards reduce allowable particulate matter emissions to zero.

The other emissions hurdle that diesels have had to overcome to make the grade here is on oxides of nitrogen, or NOx emissions. NOx is one of the smog-forming pollutants. Engines that run lean, meaning they run using lots of air and relatively little fuel, tend to create lots of NOx just as a result of combusting the oxygen portion of atmospheric air and the chemical reaction that creates. Part of the Bluetec system jointly developed and used by Mercedes-Benz, BMW, Chrysler, and Volkswagen/Audi have a special method for dealing with NOx emissions.

Some vehicles will use a urea-injection system that combines with catalytic action to filter out NOx, while others, such as the Jetta, use a soot and NOx trap that is periodically flushed by running the engine a little rich and catalytically burning the accumulated soot.

This technology enables the smooth, powerful diesel powertrains like those sampled at the test track. But could diesels go even further to improve vehicle fuel economy? I’ll explore that in my next blog.

—Gordon Hard

Comments

[Lingohocken]

Isn't diesel fuel in the United States taxed higher than gasoline on the assumption that it is for heavy trucks that cause exponentially greater damage to roadways?

If so, how can diesel ever be competitive with gasoline for cars, light trucks and SUVs in this country?

[Lingohocken]

I understand diesel is taxed at a higher rate than gasoline -- the opposite of what's done in the EU -- on the assumption that it is for heavy trucks that cause exponentially more damage to roadways.

If this is the case, then how can diesel become cost competitive with gasoline for cars, SUVs and light trucks in this country?

[Scott Gifford]

I've had a diesel VW New Beetle since 2002. Diesel fuel has been more expensive than gasoline for the last 2 years, but before that it was cheaper. In the last 2 years it has tended to cost about 20% more, which is made up for by 30% better fuel efficiency. So it still ends up being a good deal, and diesel prices are starting to come back down.

I'm not sure about the taxes, it would be interesting to find that out.

[Paul]

Yes, diesel fuel is taxed higher than gas. Diesel is taxed at 24.4 cents per gallon. Gas is 18.4 cents per gallon. So the federal tax is about 33% higher for diesel than gas. Keep in mind that this is just for Federal taxes.

The average State tax for diesel is 29.2 cents and for gas is 28.6 cents per gallon, although the state tax varies widely depending on the state in which you live.

Diesel prices vary over time, sometimes more expensive than gas and sometimes less. It depends a lot on how much diesel production is going on compared to gas production. If more refineries are switched to producing diesel, diesel prices decrease and gas prices increase.

[CharlesP]

Yeah, our wonderful government has it bass ackwards- if we REALLY wanted to cut our oil consumption, we could reduce the taxes on diesel, give tax credits for purchasing a diesel, and increase road taxes for trucks to offset the revenue drop. WHY DON'T WE GET IT!!!
Good grief! Here's a "technology" that WORKS, the fuel is in the pipeline, why are our lawmakers asleep at the wheel?
Oh, that's right, we have the bank "crisis"... That's why we have credit unions.
NO TO BAILOUTS.

[KD]

For diesel sales, the tax rate for autos is less than for heavy vehicles. Some pumps are set at the light vehicle rate and some for the heavy vehicle rate. Look for a sign on the pump that states "this fuel is for use in vehicles less than XXX GVW". If you do not see this sticker, then go inside and ask. Many places, but not all, will refund the tax difference. The difference in AZ is either 8 or 9 cents per gallon.

[Rayman]

Is there not a higher initial cost for a diesel as well as more expensive servicing/maintenance? Along with our love for higher powered automobiles and disdain for conservative type driving, my calculation indicate there is not clear advantage over gasoline powered motors. Even the hybrid situation shows that as GM has a Yukon hybrid that tests out at 20/20 MPG. No advantage there along with the higher initial cost. By the way, I advise all to be wary of any Audi products as poor reliability along with poor customer service makes owning and operating an Audi, any model, a liability. Audi advertises and articulates their mission well but fail to follow thru. Just check all the class action lawsuits against them. My attempts to get any response from Audi executives have failed as they seem to follow the path of American manufactures in ignoring the very source of their income: the customer.

[Clean diesel]

Yep! why diesel cost is day by day its increasing compared to gasoline it have been increased a lot and government not coming forward to reduce diesel.hope this problem may turn over soon.

[cleandiesel]

diesel engines have been frowned at because of the black soot that they produce. Noisy operation of this type of internal combustion engine is also one of the reasons why it never made a positive impact in the United States in the past decades.