The "packaging" of bulky components on sometimes-crowded truck frames is becoming more of an issue as new Caterpillar diesels appear. Clean Power engines built since October 2002 avoid the complexity and expense of cooled exhaust-gas recirculation, but require large catalytic converters to strip exhaust of oxides of nitrogen, the main target of the latest EPA regulations.
The converters are combined with mufflers to save some space, as only one item instead of two need be mounted. But to get enough catalyst volume, the converter/muffler combo must be bigger than a muffler alone.
The easiest way is to hang a single converter/muffler on the frame, with a short tail pipe exiting right there. This is not always possible, especially on short-wheelbase tractors or trucks, or those with pusher-type lift axles. Also, road salt and grime beat on the appliance and hasten the day when it must be replaced. This is not a big deal with a $100 or $200 muffler, but is a real issue now because a converter/muffler costs about $1,000.
The next easiest way is a set of dual exhaust stacks. Peterbilt and International are among the builders choosing that route for big-bore (10 liters and up) Cat engines, as converter/mufflers are 10 inches in diameter, as before, and fit at the cab corners.
Customers who want to stay with one exhaust stack are faced with a single appliance that's 14 inches in diameter—too big to fit at a cab corner without extending beyond the body's width. It can go behind the cab, and that works for tractors and trucks whose bodies are not closely mounted to the cab.
If the body snugs up to the cab, as with most dump trucks, space has to be made for the exhaust. One solution we just saw at a recent International Truck event is a notched-out body corner. This "cut out" on a J&J aluminum body sat on an International 7600 chassis with a Cat C-12. J&J says the cut-out body and cab shield costs about $500. We'll see more of these solutions because Cat's C-12 and C-15 are popular among dump truckers, and the upcoming ACERT versions will also use converter/mufflers.
A still-unresolved question is how to get exhaust gas to the floor of heated dump bodies. The exhaust cutout used up to now was upstream of the muffler, which was okay because the floor chamber acted as a muffler. But now the cleansed gas must be taken downstream of the converter/muffler; a frame-mount muffler can be plumbed into the body's floor, but a vertical stack is out of reach. Body and chassis people are still pondering this.