Engine Notebook: Mack attack

For its MP family of engines, Mack has created an all-new design from the oil pan up. The MP engines are Mack’s solution for meeting current EPA emissions standards and those that will take effect on January 1, 2007.

The 11-liter MP7 will arrive this month and meet the in-place EPA ’04 standards. The engine will be available in Mack’s new Pinnacle and Granite models, while the company’s previous solution, the ’04-compliant Application Specific Engine Technology (ASET) power plants, will continue to be offered in Vision highway and Granite vocational trucks.

Mack plans to have the second member of the MP family, the 13-liter MP8, in the market in 2007, and a 16-liter MP10 will be introduced in 2008. The MP7 and MP8 will be available in three application-specific configurations: Econodyne (typical interstate, less than load), MaxiCruise (rolling interstate, full load) and Maxidyne (high performance, severe duty, especially off highway).

Something old, something new
While the design of the MP engines is new, some of the concepts are tried and true. Cooled exhaust gas recirculation plays an integral part in the MP engines’ scheme for emissions compliance. The cooled EGR enables the MP7 to meet current standards and the more stringent ’07 regs with the addition of a catalyzed diesel particulate filter. The MP8 will start life wearing a diesel particulate filter.

Besides the conventional inline, six-cylinder layout, other examples of established technologies include electronically controlled unit injectors, a single overhead camshaft, wet cylinder liners, four valves per cylinder and steel one-piece pistons.

Other components, such as the variable geometry turbocharger (VGT) and the high performance exhaust gas recirculation system, are relatively new to the on-highway and vocational heavy-duty truck market. Turbochargers have been around for awhile but VGTs have not. According to Mack, VGTs provide the best of both worlds – the large capacity of a big turbocharger at higher engine speeds and the quick response of a smaller turbo at lower engine speeds.

The “high performance” designation of the 2007 engines’ EGR refers to its higher rate of capture of exhaust gases. In order to meet emissions standards, more exhaust gas is recycled back through the engine. This dilutes available oxygen, lowers peak combustion temperatures and reduces NOx production (contrary to the popular misperception that the recycled gases are burned again). With the higher capture rate comes greater heat rejection, so trucks with 2007 MP engines have larger cooling systems.

Benefits of clean sheets
By starting from scratch, Mack has been able to accomplish several desirable goals. Fuel consumption for the ’04-compliant MP7 is slightly better than that of the engines it replaces, and according to the company, the ’07-compliant MP7 and MP8 will bear a minimal fuel penalty even with the diesel particulate filter.

The new engines are also lightweight and compact. The MP7 is nearly 143 pounds lighter than previous Mack highway engines and 27 pounds lighter than previous vocational models. The optional rear-engine power takeoff trims 126 pounds from the engine and shortens the back by 10 inches compared to the same arrangement on a non-MP engine of similar displacement.

The MP engines sit about 6 inches lower in the frame. Mack says this lower stance improves service access. It also gives the engines more “breathing room” at the top, where heat can build up. Service intervals are up from 250 to 300 hours for construction applications and from 25,000 to 30,000 miles for highway use.

Dealing with a new filter
Servicing the diesel particulate filter on ’07 engines will occur infrequently, says David McKenna, Mack powertrain products marketing manager. “Although we don’t have a lot of real-world experience with diesel particulate filters yet, as an industry we’ve been doing extensive testing,” he says. “It appears that the diesel particulate filter will require cleaning after about the first 100,000 miles and then every 150,000 miles after that. For non-highway applications we think the service intervals will be somewhere between 18 and 24 months.”

Is this something that an owner will be able to tackle? “Getting at the filter is simple,” says McKenna. “You undo two v-clamps and the filter section comes right out. If you had a swing unit you could replace it at that point and send the dirty filter out to be cleaned. You may let your local service center do just the cleaning or you may have them do the whole job. If your fleet is big enough, you might have your own filter cleaner, which is a very high speed, high pressure vacuum.”

In everyday operation the diesel particulate filter is self-cleaning. Exhaust flowing over the catalyst creates heat sufficient to burn off soot and keep the filter clean in a process that’s called passive regeneration, says Scott Barraclough, power train sales manager. “Over time, however, passive regeneration won’t be able to keep it 100 percent clean. You’ll eventually have enough soot buildup in your filter to require active regeneration,” he says. In active regeneration, fuel is injected into the filter and ignited to oxidize the soot buildup. This will occur once or twice a day for a period of 10 to 15 minutes and will be transparent to the driver. “The only reason the driver would be aware of it is that there will be an indicator light on the dash saying that diesel particulate filter regeneration is taking place. There is no loss of power during this process,” says McKenna.

Proper care and feeding
One important distinction to note is that engines with diesel particulate filters must use ultra-low-sulfur diesel fuel. ULSF, as it’s often referred to, contains just 15 parts per million sulfur, compared with 500 ppm sulfur in today’s fuel. There is some concern as to whether fuel companies can reliably supply this fuel everywhere by the date the EPA has set: October 15, 2006 – the result of a 45-day extension granted in November. If today’s regular diesel is used in an engine with a catalyzed diesel particulate filter, the catalyst will be poisoned and require replacement at the owner’s expense as misfueling is not a warrantable repair.

Because sulfur is a biocide and lubricant, ultra-low-sulfur diesel will have additives to serve those functions. A new lube oil formulation, currently called PC-10, is designed to work with ULSF, and both must be considered a package. Both can be used in pre-’07 engines as long as they’re used together. McKenna encourages owners to discuss fuel concerns with their suppliers.