Another step forward for diesels: Tenneco's exhaust particulate trap is cookin' on PSA vehicles today. It's the start of another clean-diesel technology

Automotive Industries, Nov, 2001 by Lindsay Brooke

Before you get too excited about the prospects of diesel, uh, compression-ignition engines becoming the predominant automotive powerplant, consider one of the remaining roadblocks in their path: particulate emissions, the tiny specks of grit that are blasted out of the combustion chamber with each exhaust stroke. Particulates make your eyes water in diesel-thick traffic, are nasty to breathe, and are deemed to be dangerous to human health -- carcinogenic even, according to the most virulent diesel detractors.

Particulate reduction is one of the toughest bogies facing product planners at the light passenger vehicle and heavy-truck makers. The latest rounds of worldwide emissions regulations, led by U.S. Federal Tier 2, California LEV2, Euro5 and various Class 8 standards, call for drastic cuts in diesel particulates in the 2006-08 timeframe -- meaning vehicles and engines now entering development. For automakers and suppliers, it's a call to arms.

"And it's a challenge we strongly believe can be solved," asserts Tim Jackson, senior VP for global technology at Tenneco Automotive in Lake Forest, III. As Jackson notes, France's PSA Group last year became the first automaker to install modern regenerative particulate-filter systems on its diesel cars -- the Peugeot 406 and Citroen C5. (Over a decade ago, Mercedes fitted a relatively unsophisticated particulate trap on its California-market 300TD, a system which proved to be problematic in use.) The pioneering PSA system, developed by and sourced from Tenneco, is a masterpiece of simple, robust design and serviceability. It's basically a diesel heated catalyst combined with a filter section, explains Jackson.

"The system is self sensing," he tells Automotive Industries. "During operation it heats up to 1,000 degrees Celsius for 10 to 12 minutes, cooking the collected particulates into a fine ash." The residual material resides in the filter side of the unit for a recommended 50,000 miles. At that interval, the vehicle is taken to a PSA service center, the filter section unbolted by a technician, dumped, and the filter is replaced.

Jackson adds that the particulate trap actually increases in efficiency as it ages and the size of the ash cake grows. That allows it to filter out smaller and smaller particles.

Tenneco is developing a second-generation system aimed at boosting the trap's efficiency and reducing cost. It's based on a new type of catalyst (Tenneco's OEM catalyst partners include Johnson-Matthey, OMG and Engelhard) that's installed closer to the exhaust ports and operates at higher temperatures. The system also includes Tenneco's 900/2 thin-wall cans and the company's Tubular Integrated Converter (TIC) technology. Currently used on the Peugeot/Citroen particulate-trap system, the hydroformed TIC offers up to a 25-percent cost savings over conventional fabrication methods due to lower cost tooling developed by Tenneco. Other claimed benefits include lighter weight, greater catalyst volume modularity, a weld-free housing and shorter lead times.

The issue of particle size remains a sticking point in the current technology and in how even the most advanced diesels are viewed by critics, the most vocal of whom are in California. Jackson admits that the PSA system is "nearly 100 percent efficient" but does not entirely eliminate particulate. It's what ultimately escapes the trap and leaves the tailpipe that makes regulators tighten the diesel noose with each round of emission standards.

Jackson says the system is scalable and can be upsized (and fitted in pairs) to accomodate 6.0L to 7.0L V-8 diesels, the type used on North American light trucks and SUVs.

For large diesels, Tenneco is developing a particulate filter/de-N0x catalyst. Now in the validation phase, the first production application will be a European Class 8 diesel launched in 2004. Jackson says per-vehicle cost is in the $1,200 to $1,700 range. He predicts the technology will also be adopted in North America, spearheaded as it is in the passenger vehicle arena, by stricter federal and state regulations.