Honey, they shrunk the emissions – again. 2007 engines must put out less than half the NOx and less than a tenth of the particulate of 2002 models. How are manufacturers meeting these requirements? How will maintenance practices change?
Diesel engines face tough emissions standards for 2007. In 2002, only nitrogen oxide (NOx) had to drop; in 2007, both NOx and particulate must drop, and to very low levels. Two separate technologies will be needed to do the job.
NOx is generated when combustion overheats the air. The natural nitrogen and oxygen combine, creating nitrogen oxide, a chemical that forms much of the basis for smog.
Particulate comes from three sources. One is carbon, generated because diesels mix fuel and air gradually during each injection cycle. Another source is the sulfur in fuel. That source largely will be dealt with at the refinery, due to a government mandate, with side benefits for the driver. A third source of particulate is ash, which mostly comes from the additives in oil.
Because NOx and particulate are different types of pollutant, they will be decreased in two different ways.
NOx must drop to an average 1.1 grams per horsepower-hour, from its present level of 2.5 grams. All engine manufacturers will do this using familiar technology. As they did in 2002, Cummins, Detroit Diesel, Mack and Volvo will use exhaust gas recirculation to cut NOx. Even on Volvo engines, the EGR system will use a variable geometry turbocharger to do the job the pulse EGR system does today. A stainless steel cooler will still transfer the heat to the engine coolant, and EGR valves and plumbing will look like those on present engines.
To cut NOx so much, a lot more exhaust will have to be recirculated. Precisely how much is hard to say. “The amount of the increase changes as a function of speed and load, so there is no single value or percentage that represents the change,” says Tim Tindall, director of emissions programs at Detroit Diesel.
EGR rates for 2007 might be double those of 2002, based on estimates from oil company experts. That would mean an increase in engine pressure stresses, which Tindall believes may slightly affect horsepower.
On the other hand, by 2006, fuel sulfur will drop to 15 parts per million, or less, from the present 500 ppm, says Jim McGeehan of ChevronTexaco, who serves as chairman of the American Society of Testing & Materials Heavy-Duty Engine Oil Classification Panel. “Fortunately, the use of 10 ppm fuel sulfur minimizes the concerns of extra acid in the cylinder due to EGR,” he says. Engine parts weakened by acid was a top concern in 2002. Enabling the engines to tolerate more EGR is one reason for the reduction in sulfur.
In other words, Tindall says, “Engine heat rejection is expected to increase, and vehicle cooling systems will need to be modified to handle the increased heat rejection.” This means continuing concern about radiator and fan design and cooling system maintenance, and more engines likely will be de-rated during long climbs.
Caterpillar won’t use EGR for 2007 but will continue with its own system, Advanced Combustion Emissions Reduction Technology. ACERT injects the fuel in separate spurts during each cycle rather than all at once, which reduces heat buildup. Volvo and Mack will adopt something similar, while still relying on EGR.
Caterpillar has said little about how its air management system works. It appears that the 2007 ACERT engines will be very similar to current ACERT engines.
Cutting fuel sulfur will help cut particulate, some of which is nothing more than bits of sulfur, known as sulfates. However, the new standard is very clean, dropping from 0.1 to 0.01 grams per brake-horsepower-hour, or a tenth of the present level. This means that after-treatment will be necessary on all engines.
Details are unclear, but all the engines will use some kind of mechanical diesel particulate filter, or DPF in the exhaust. This filter will require both regeneration (injecting a little fuel into the exhaust right before the trap so it will heat up enough to burn the soot off) and maintenance.
The filter will consist of a very fine mesh of heat-resistant material, such as metal and ceramic fibers woven together. The mesh will catch the particulate much as an oil filter traps particles of metal or carbon.
By silencing exhaust, the filter will probably replace the muffler, says Tindall of Detroit Diesel. The filter will be placed closer to the engine, though, to keep it hot enough to burn off the bits of particulate that are pure carbon, Tindall says. Depending on the manufacturer, the filter may be coated with a catalyst, a metal that would speed up the burning without being burned up itself. (One such metal is platinum, which doesn’t come cheap.)
To keep the filter from clogging when the engine is idling or otherwise not working hard, a small amount of fuel will be introduced into the exhaust just before the filter. That will produce enough heat to burn off the carbon.
Besides sulfur and carbon, another type of particulate is ash, which comes from the oil the engine consumes. Virtually all oil additives, even detergents, turn into ash, and ash, as anyone who’s doused a campfire can tell you, does not burn off at high temperatures.
That’s why the new engine oil, known as PC-10 because it is still under development for 2007, will have a limit of 1 percent sulfated ash. Tindall says that might “make the maintenance interval more challenging,” but McGeehan says engine durability will not be compromised.
The new DPF in the 2007 engines mean additional maintenance, in a different form from what drivers are used to. “The cleaning process will likely require heating to burn off any unburned fuel or oil residue and blowing air through the filter in the reverse direction from exhaust flow, while collecting the ash in a filter,” says Tony Greszler of Volvo Powertrain.
The cost of the filters is unknown. Big fleets will likely have their own cleaning equipment, but a one- or two-truck independent will likely take the filter to his truck or engine dealer and pay a cleaning fee.
The Environmental Protection Agency says the filter must go at least 150,000 miles between cleanings. Most engine makers are optimistic that it can go at least that long. Drivers can experiment to find the ideal cleaning interval for their operations, “which could actually be much higher than 150,000 miles,” Greszler says.
The new particulate standard affects one more engine system: the crankcase. The 2007 engines will have a closed ventilation system that will flow anything coming out of the crankcase through the DPF. A line will run from the crankcase vent to the exhaust system, just upstream of the DPF. An oil separator will allow oil to drop out of the airflow and return to the sump. The air from the crankcase will be drawn into the exhaust system through a simple venturi passage, so no pump is needed. Minor cleanings might be required, each 500,000 miles.
Drivers worried about keeping track of this new maintenance should know that for the DPF and all these other systems, federal law will require onboard diagnostics to tell the driver when and where maintenance or repair is needed.
The bottom line is that buyers of any brand of 2007 engine will find no major changes from 2002 models, though all will have advanced methods of reducing NOx and particulates. None of the technologies should produce significant changes in performance or efficiency, though owners should be more careful than ever to run and maintain the equipment wisely.
THE HOT BUTTONS
It’s still early for precise forecasts about the 2007 engines, but based on experts’ comments and other information, expect this:
COST. The 2007 price almost certainly will be more, maybe a lot more, than the 2004 price. Rainer Schmueckle, Freightliner president and chief executive officer, estimates increases will be $4,500 to $6,000.
FUEL. Estimates vary, but the likely change is a slight increase in fuel consumption when hauling light loads because regeneration – extra injection to burn off soot – may be more frequent.
OIL. Maintenance intervals likely won’t change. The new 1 percent standard for oil ash is near enough to present levels that the oil will probably be backward-compatible with earlier engines and will probably protect the engine about as well as present oils. Drivers will need to maintain cooling systems carefully.
PERFORMANCE. Response on Caterpillar’s ACERT engines with twin turbochargers should continue to be very good. All the EGR engines will have variable geometry turbochargers, and because of the way the variable geometry nozzle adjusts when the driver opens the throttle, response should be as fast as it is today.
Brand By Brand
Here’s what each manufacturer has to say about its 2007 engines.
CATERPILLAR. Caterpillar’s Greg Gauger, director of on-highway engine products, and Mike Powers, product development manager, say Caterpillar will meet the NOx standard by fine-tuning ACERT. That means “tweaking the fuel system and computer a little, and making some air system adjustments,” Gauger says. The C15 and C13 will incorporate Caterpillar A4, the next generation of electronics, before 2007.
Caterpillar will include a diesel particulate filter. The design isn’t finalized, but the company is dedicated to simplifying the cleaning process, Gauger and Powers say.
The overall cost of operation should not be significantly affected, they say. Power ratings, fuel economy and oil change intervals should be much the same. Gearing and operating recommendations will not change.
CUMMINS. Cummins will uses cooled EGR because “the technology provides a lot of flexibility, and can adapt well to different operating conditions,” says Tom Kieffer, executive director of marketing. “Its reliability has also been proven.”
Cummins’ aftertreatment will be an active diesel particulate filter, “which means it will be regenerated as necessary,” he says. “But, when operating conditions keep it at a high enough temperature, regeneration will not occur. Pickup and delivery would be typical of conditions when regeneration would be necessary.”
The engines’ internal hardware will remain unchanged.
“We believe there will be little to no change in maintenance intervals or fuel economy,” Kieffer says. “The only new addition to service will be cleaning of the diesel particulate filter at some point. You will basically take it off and empty the ash.” Large fleets will probably use their own cleaning equipment; most owner-operators will go to an engine dealer for the service.
“Our goal is to have the maintenance interval longer than the required 150,000 miles and thus minimize the total cost of ownership,” he says.
Cummins expects to have today’s horsepower ratings, “plus additional ratings we will introduce between now and 2007,” Kieffer says.
DETROIT DIESEL. Engine heat rejection is expected to increase, and cooling systems must be modified to handle it, says Tim Tindall, director of emissions programs at Detroit Diesel. “The experience gained on EGR engines over the last years is the building block to accomplish the higher rate of EGR for 2007,” he says.
In most applications, normal exhaust should be sufficient for Detroit Diesel’s filter to oxidize soot, Tindall says. This passive regeneration won’t suffice, however, when exhaust temperatures are low, for example at lower speeds or during extended idling. In those instances, Tindall says, regeneration has to be a more active process. “Fuel consumption will be a challenge to maintain. The particulate filter alone would consume fuel to regenerate actively.”
Overall, fuel consumption will be more sensitive to the duty cycle, Tindall says.
Horsepower may be somewhat reduced, but Tindall expects no major problems.
The primary new maintenance will be cleaning the particulate filter at 150,000 miles.
VOLVO/MACK. Mack and Volvo will have a new global engine platform by 2007, one that “will share common architecture and technology” but be “customized to meet the performance expectations of each brand’s customers,” says Mack’s John Walsh, manager of trade relations. In other words, Volvo and Mack engines will share some parts.
The engine will have high-pressure fuel injection with multiple injections per stroke, says Tony Greszler, vice president of engineering for Volvo Powertrain, which supplies engines for Mack and Volvo Trucks North America. A single-stage, variable geometry turbo-charger, similar to what Mack has now, will replace the pulse EGR system used on Volvo engines. Stronger base engine components will handle internal loads, and the truck design will incorporate a high-capacity cooling system and a diesel particulate filter. An EGR valve of “proven design” will be used, Greszler says.
The most obvious changes will be rearranged EGR coolers and a diesel particulate filter integrated with a larger muffler.
“The testing indicates that, in general, fuel economy is on track to be as good or better than current engines,” Greszler says. “In addition, we have outstanding engine response for excellent drivability.”