Squeaky Clean

| December 12, 2008

The good news for 2007 engines is that maintenance and fuel costs will be affected only minimally, according to engine makers. With more time to do field testing than
for the 2002 engines, they are also confident that reliability won’t be a problem.

Achieving the huge step in lowered emissions, however, even with the help of new low-sulfur fuel, will mean a significant price increase. It also puts tremendous demands on the technology, with turbo boost pressures as high as 70 psi, says Steve Egleston, engineering leader for Flexfab, a hose manufacturer.

“The 2007 engines will run hotter, use more boost pressure, and have oil vapor and corrosive EGR gases introduced into the intake air,” Egleston says. “This means we have had to rethink the materials we use for these critical hoses.” But an exotic lining, reinforcement of the bellows and new construction methods have enabled Flexfab to do its part for the new engines, Egleston says.

Engine makers are doing much more than that to meet the stringent standards. All engines made starting Jan. 1, 2007, must drop particulate emissions to .01 grams per horsepower-hour, a tenth of present levels. At the same time, engine makers must cut nitrogen oxide in half, to 1.2 grams per horsepower-hour. In addition, any crankcase emissions will be considered part of the NOx output.

REDUCING PARTICULATE
The only way to cut particulate to required levels is to add a diesel particulate filter. This device will sit where the muffler is now and also will reduce noise levels. Its job is to collect the unburned soot and hydrocarbon particles and hold them in place until they burn off. Since diesel exhaust normally contains plenty of oxygen and heat, this will be easily done in over-the road applications.

There are three DPF challenges. The first is that diesel exhaust cools under light load because the airflow through the engine does not drop as much as the flow of fuel. Burning the accumulated soot and hydrocarbons when the engine isn’t working hard enough will require periodic heating of the exhaust. Getting the fuel to ignite and burn safely and cleanly is a minor challenge.

The second challenge is that sulfur itself is a source of particulate, and it can readily poison the DPF, too. The petroleum industry will be lowering the sulfur in diesel fuel from its present 500 parts per million to 15 ppm or less. Regulations require that 80 percent of diesel fuel be available as this ultra-low sulfur diesel by 2007.

The third DPF challenge is that exhausted ash collected in the DPF won’t burn off no matter how hot it gets. Ash is composed mainly of additives that get into the exhaust via the oil the engine consumes. The primary ingredient is the total base number additive that combats acidity in the oil. This issue will be partially dealt with through a new oil standard, tentatively called PC-10. This oil will provide adequate TBN protection with a strictly limited amount of ash. The ash that does accumulate will have to be removed through a maintenance operation.

REDUCING NOX
For the most part, NOx will be reduced via the exhaust gas recirculation designs of all 2002 engines except Caterpillar. This means more EGR for Cummins, Detroit Diesel, Volvo, Mack and, very likely, the new Class 8 engines from International. Increased EGR means higher cylinder pressures and increased heat rejection.

Hardware remains very similar for Cummins and Detroit, although Detroit mentions an “enhanced” Series 60 without giving details. Detroit will also introduce a new engine that will be available only in Freightliners and will be built in four different displacements. A 14.8-liter version will be the first. It reportedly may include some exotic new hardware.

In the case of Volvo and Mack, a new engine line will be produced. Because of higher levels of EGR, the pulse EGR system Volvo used on the VED-12 will be replaced by a variable geometry turbocharger. These engines will provide better throttle response, says Tony Greszler, vice president of Volvo Powertrain.

Caterpillar will continue its basic hardware and ACERT technology, though with tuning changes to further lower NOx. The only basic NOx-related change will be clean gas induction. Bob Keene, customer satisfaction manager at Caterpillar Engine Division, says CGI differs from EGR. For example, because ACERT technology means less NOx in the combustion chamber, the volume of recirculated exhaust will be negligible, Keene says. Also, Caterpillar will draw post-DPF exhaust, meaning the lion’s share of soot will already be removed.

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