"Clean Diesel" in the U.S.

Chicago Tribune
Published March 19, 2006
No diesel in your future?
Because they are noisy, smelly and belch smoke?
Because you remember the 1980s when General Motors sold diesel-powered cars whose engines had the durability of papier-mache?
Because diesel fuel, of late, has cost more than premium gasoline?
Because diesel engines are among the biggest polluters on the highway?
All of the above?
It may be time for an attitude adjustment. And here are a few jumping off points:
Though diesel costs more than gasoline, drop for drop, it contains more energy. That's why fuel mileage is better in a diesel vehicle. Diesel is the most efficient fuel used in internal combustion engines.
With the advent of "clean diesel" in the U.S., that could bring big changes.
Clean diesel has been mandated by the federal government for use starting in fall. As its name implies, it burns cleaner because nearly all of the sulfur is removed That allows carmakers to install emission control systems that won't get ruined by the sulfur. Today's diesel-powered cars have no systems to control oxides of nitrogen.
But even before cleanup devices are added, diesel engines spew fewer of some pollutants than gas ones. Of the five most common emissions--carbon monoxide (CO), carbon dioxide (CO {-2} ), hydrocarbons (HC), particulates (smoke) and oxides of nitrogen (NOx)--diesels emit fewer of the first three. The big nasty has been NOx.
Smoke is controlled by particulate traps on trucks. The traps use catalytic converters or heating elements to snag those bits of carbon smoke. But NOx has been tricky to eliminate because the technology to do so relies on low sulfur fuel. That fuel also reduces particulates.
Most of new diesel technology has been applied to trucks, the biggest users of diesel fuel in America. But this year, DaimlerChrysler will begin selling diesel vehicles with advanced technology that will meet emissions standards in all 50 states.
Two are Mercedes-Benz sedans: The E-320 Bluetec and the GL-320 Bluetec.
The two Mercedes cars will go on sale in the fall, when clean diesel fuel is available across the country. The Bluetec technology, in use in Europe for a couple years, needs the fuel, which contains less than 15 parts per million sulfur.
Bluetec uses an oxidizing catalytic converter, that turns carbon monoxide and hydrocarbons into carbon dioxide and water. A particulate filter downstream removes 98 percent of the particulates to meet EPA rules. And the Bluetec converter turns NOx into harmless nitrogen plus water vapor. Gas-powered cars have one three-way cat to clean up emissions.
That Bluetec converter is the ticket. It uses ammonia, in the form of urea, to reduce the NOx into nitrogen and water vapor. Unlike other converters, where the catalyst causes a reaction, the urea gets used up and must be replaced. That makes it a reagent, technically speaking.
The process is based on the injection of a reducing agent, which the company calls AdBlue, into the exhaust gas stream. AdBlue is a water-based urea solution carried in a separate tank. When AdBlue is injected into the exhaust gas, ammonia (NH {-3} ) is released, causing the nitrogen oxides to turn into nitrogen and water. AdBlue must be precisely metered into the exhaust to work properly.
Owners of Bluetec equipped vehicles will have to return to the dealership to have the urea replaced with every oil change. That could change as independent shops gain access to the product. In Europe, there are 1,500 stations where trucks can top off their AdBlue tanks.
Registrations of new diesel passenger cars in Western Europe totaled 7.2 million last year, so every second customer opted for a diesel. Light-duty diesels are expected to grow from 3 percent of the U.S. automotive fleet to 14 to 15 percent by 2012.
Considering the fact that diesel engines get 20 to 40 percent better mileage than their gas counterparts, the higher cost of fuel and added cost of the reagent, may very well be offset.