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Meeting the 2007 emissions limits has been trouble enough for the engine builders, but putting all necessary exhaust-cleansing equipment aboard a truck chassis — a process called "packaging" — is among the many tasks now being handled by engineers at the truck manufacturers.
They are close to being done with this aspect, and a few took time to describe what 2007 trucks will look like. The engineers confirmed what we guessed, that the dump truck with a close-coupled body and multiple pusher axles, which many CE readers operate, is the most difficult configuration on which to package the new equipment. But they emphasized that they're dealing effectively with this and other types of trucks and tractors.
Engineers have assembled prototypes using '07 engines and exhaust aftertreatment devices, and say that preproduction vehicles will be ready for road testing way before the January '07 deadline. They say the new models with the new engines will work fine, but will certainly cost more than now. How much more is the big question, and nobody yet knows or is willing to talk about it.
Design and installation of engines and aftertreatment equipment have taken two distinct routes: Caterpillar and non-Caterpillar. The non-Cat approach is simpler, many truck makers say. Cummins, Detroit and International engines will use essentially what they now do to meet limits — cooled exhaust-gas recirculation, variable-geometry turbochargers, oxidation catalysts, and other equipment to reduce NOx and other pollutants. They will use higher rates of EGR and more capable combustion design to further cut NOx. And they'll add an exhaust filter to remove tiny particulate matter from the exhaust stream.
Volvo will take a similar approach with "heavier" EGR and the particulate filter, or PF. It will drop its unique V-pulse system that pushes exhaust and air into the manifold and instead use a VG turbo. Volvo and Mack will share common engine "platforms" for '07 and will each tune their models to suit their customers.
Many PFs used by these builders will be in an assembly that will also contain the oxidation catalyst. This assembly looks like a muffler that's slightly larger than the catalyst-muffler now employed. Some applications will require mounting the PF and catalyst separately. The PF and catalyst functions also quiet the exhaust, so no muffling baffles or chambers are needed. Some engineers call the combined assembly a "can," because it's not much larger than now, and mounting it on a truck presents no special problems.
Caterpillar's approach to '07 is somewhat more complex and more difficult to package on a chassis. Cat says it will use cooled exhaust-gas recirculation, something that it has avoided with its ACERT products (though competitors claim that ACERT's variable valve timing is used to achieve internal EGR). Caterpillar calls its version of EGR "clean gas induction" (CGI) because it introduces cleansed exhaust gas, not "dirty" gas, into the engine.
CGI takes filtered gas from the end of the Cat PF and sends it back to the engine. Gas travels through a pipe about 2.5 inches in diameter that generally follows the exhaust piping back to the engine compartment. Total travel varies with the truck model, but 8 feet might be typical. The gas is injected into inlet air downstream of the turbocharger and ahead of the charge-air cooler. Thus the gas is cooled along with compressed inlet air.
Although the exhaust gas heading back to the engine is stripped of particulates, it still contains trace amounts of other impurities, including acids, that can damage the aluminum charge-air cooler (also called the aftercooler). Cat people say that stainless steel would shrug off those impurities, so its '07 aftercoolers would probably have to be made of that material. This will add weight and cost, but such an aftercooler will also be more durable and long-lasting.
The can housing Cat's PF will no longer need an oxidation catalyst, which now generates heat to remove particulates, because the '07 PF will periodically burn off accumulated soot particules. This "regeneration" uses a bit of diesel fuel that's electrically ignited. Other builders' PFs will also use fuel-fired regeneration, and engines with less steady operation, such as those in construction trucks, will need more than those in highway tractors. But while most will still use an oxidation catalyst, Caterpillar's can contains only the PF and a chamber to gather filtered exhaust gas for the CGI pipe.
Still, a Cat can is larger than those needed by non-Cat diesels, engineers say. An '07 Cat can is 14.2 inches in diameter, compared to 13 inches for a current Cat catalyst-muffler. An '07 Cummins can is 13.7 inches in diameter compared to 11 inches now. The larger diameters of the '07 assemblies include a ¾-inch wrap of insulation, totaling 1.5 inches, to retain heat and protect an errant hand or arm.
Although internal temperatures of 900 to 1,000 degrees Fahrenheit during regeneration will be common with the cans, the insulation will hold down external temperatures to about the same as now — too hot to comfortably touch, but not enough to seriously burn someone unless he hung onto it.
Most heavy-duty diesels including Cats will need one can, which can be mounted horizontally on the frame or vertically, in a stack. Customers wanting dual exhausts might not be able to get them unless the can is hung under the cab, and tail pipes then run up each corner of the cab. This will be easy with some truck models but difficult with others. Where this arrangement is possible, it should also be easy to mount any desired body.
Yet Cat C15 diesels rated higher than 550 hp, or 520 hp at International, will need two particulate filters. Each of these is 11.1 inches in diameter; in prototypes, two of these cans are mounted next to each other and joined by a dispersal chamber at their inlet end and a collection chamber at their outlet end. Such a unit is bulky, and has to be hung under the cab if there's room, or if not, behind the cab or from a frame rail.
If the double can is on the side of a rail, it might displace a fuel tank, which would have to go to the other side of a truck. This might displace the battery box, so batteries would go behind the cab or be dispersed elsewhere on the chassis. This is likely with any short-wheelbase truck or tractor, or with a multi-axle dump truck, which has little extra frame room. Buyers of heavy-haul tractors often order over-550-hp engines, and such vehicles usually have enough frame space to accommodate a double can.
Although a big multi-axle dump truck would present problems for mounting the double can, few buyers actually order Big Power C15s. The most popular Cat engine for a heavy dumper is now the C13, which will need only a single exhaust can. If the can must go in a vertical stack, its large diameter might require a cove in one corner of the body, something already done on a few dump bodies for existing catalyst-muffler assemblies. Modifying a cab corner with a cove is possible but pricey, and impossibly expensive as a production option. Dual exhaust stacks would be difficult with a single vertical can, but some insistent buyers might ask for dual cans, with one 11.1-inch-diameter can on each stack. That wouldn't be cheap, either.
Most '07 engines will reject more heat because greater amounts of exhaust gas will pass through special coolers. These are gas-to-water devices where heat is transferred to coolant in the engines' water jackets, then carried to radiators. Truck radiators will be slightly bigger to push this extra heat into the atmosphere, but their larger size might not be noticeable.
Some builders will avoid enlarging the noses of their trucks by using deeper radiators. These will extend farther downward, and engineers will have to be careful not to go too far down so vehicles which travel off road, like our dump-truck example, will still have sufficient ground clearance. You can bet that the builders will watch this, but it wouldn't hurt for you to check it, too.
