Diesel Particulate Filters Present Packaging Problem

OEMs tell NTEA members how they're trying to make life easier for body builders - and they're strongly advising extra training for drivers.

Tom Berg • Senior Equipment Editor

Original equipment manufacturers continue to design special exhaust systems for their EPA-'07 diesels so upfitters can more easily install bodies and equipment on truck chassis. These same OEMs have sounded a new alert regarding the engines themselves: Routine regeneration of particulate filters in the exhausts might occasionally require drivers to stop during their runs to let the high-heat event run its course.

This was the message at the National Truck Equipment Association's recent Product Meeting in Dearborn, Mich, where OEMs also showed off a variety of exhaust diffusers that will dissipate heat at the end of tail pipes during the "regens," lowering gas temperatures to safe levels to avoid burning anything nearby. Truck builders also reminded upfitters that '07 diesel exhausts must not be modified except with parts supplied by OEMs, and that changing a system could cost as much as $10,000.

Bulky diesel particulate filters required on `07 engines have posed a packaging challenge to OEMs who want to keep behind-cab areas "clean" so bodies can easily be installed. Builders have designed as many as a dozen exhaust configurations for each of their medium- and heavy-duty truck models to keep frames clear and to accommodate varying locations for battery boxes and fuel and air tanks. Designs include horizontal and vertical mountings for DPFs, which double as mufflers, and for tailpipes. Vertical pipes run up either the right or left side of cabs, depending on what upfitters and users need for various applications.

The shorter the wheelbase, the harder it's been to design the new exhaust systems, engineers said. They had to lengthen a few of their shortest wheelbases by 2 or so inches to provide room for the exhaust equipment and sometimes convoluted routing of piping. In general, conventional-cab trucks have relatively unobstructed behind-cab areas, but sometimes had to go to smaller fuel tanks to make room to mount the DPF under their cabs. Some low-cab-forward trucks need a few more inches behind the cab to fit everything. Long-wheelbase conventional and LCF trucks could usually carry everything alongside or below their frame rails, if van, flat and other high-sill bodies are to be used. Deep-sided beverage and sweeper bodies, however, need compact systems confined under or directly behind their cabs.

Smaller trucks sometimes have DPFs under their cabs and alongside transmissions. This impedes and sometimes prevents the mounting of power take-off gearboxes on a transmission's right side. Dodge outlined instructions on how to remove an exhaust pipe to mount the PTO, but of course the pipe must be put back on. Other builders advised using a left-side or rear PTO mount.

Correctly spec'ing a truck for the application has always been wise, but it's now even more important because of the prohibition against changing the exhaust. This is necessary because systems with DPFs are part of the new engines' emissions controls, and OEMs must certify them with the U.S. Environmental Protection Agency. It's possible to follow the old practice of taking a truck out of dealer stock and changing its exhaust to make way for a body not planned for in its original specifications, but a legal OEM kit must be used, and the cost of its parts, plus installation after removing the original parts, will run $6,000 to $10,000, one builder estimated.

The regeneration situation involving medium-duty diesels was brought up by representatives of some of the 10 OEMs making presentations at the meeting, and others acknowledged it. They explained that most "active" DPF regens, in which extra heat burns away motor oil ash accumulated in the filters, occur automatically. Drivers need not worry about those and might not even know they're happening, except for an indicator light in the instrument panel.

However, in some stop-and-start operations, not enough heat will be generated to burn up the ash. Then the engine controls might call for a manual regen by illuminating warning lights - usually an amber followed by a red. Drivers will have as many as 90 miles before they actually have to push a special button to initiate the regen.

Before pushing the button, a driver must park, set the parking brake and prepare to wait about 30 minutes until the regen is completed. He must stop because, unlike an automatic active regeneration, a manual regen includes idling the engine faster and closing a valve upstream of the DPF to concentrate heat in there. Under those conditions the engine cannot propel the truck or run a PTO, engineers explained, and the regen shouldn't be interrupted.

They emphasized that a manual regen will be rare, and that drivers will have enough warning of one that they can usually finish their days' work. A manual regen could then be initiated when the truck returns home for the night, or before it leaves the next day, eliminating any possible operating interruptions. Retail rental fleets might want to occasionally run a manual regen before releasing a truck to a customer.

Instructions about what do if a manual regen is required are included in owners' manuals. Because few drivers read those books, they should be told about the possibility of a manual regeneration, OEM reps said. In trucks without manual-regen switches, a Check Engine light might come on and the vehicle should go to a dealer for DPF service.

Most OEMs will include warning lights and manual regen switches in their medium-duty trucks because they want operators to have the option of handling the DPF regeneration themselves. But not all will. Ford, for instance, will not put the switches in any of its diesel-powered trucks, partly because engineers feel the need for manual regens will be extremely rare and also because they don't want to put customers in the position of causing damage to people or property.

If a driver parks in tall grass and pushes the button and exhaust heat ignites a grass fire, the truck could be destroyed and he and his company could be sued, Ford's reasoning goes. General Motors will include the switch in its midrange diesel-powered trucks, which are usually operated by professionals, but not in its light-duty pickups, which are often owned by consumers or drivers whose main concerns are other than driving.

During any active regeneration, exhaust gas at the end of the tailpipe will be as high as 1,200 degrees - hot enough to set grass or leaves afire and burn flesh. That's why many of them designed diffusers that mix the gas with outside air, cutting temperatures about in half. The devices range from a simple pan-shaped pipe extender (Freightliner) to an extra cylinder with forward-facing vents that bring in outside air (GM and others). None has any moving parts and most are made of rust-resistant stainless steel, but some could conceivably snag on high obstructions if trucks go off-road.

Those who use diffusers put them on horizontal exhausts because tailpipes could touch grass or, if they exit near a truck's side, flesh. Usually diffusers will not be put on vertical pipes unless the trucks will regularly go under tree limbs; this might be true of municipally operated vehicles, for example.

At least two builders saw no need for diffusers. Dodge feels the long tailpipe on its pickups and conventional mediums will dissipate heat, while Hino says its diesels' exhaust is cool enough in the first place.

Isuzu noted that its diesels burn cleanly enough to be exempt from anti-idling rules going into effect Jan. 1 in California. The rules, decreed by the state's Air Resources Board, require oxides of nitrogen levels lower than allowed by federal EPA limits, and diesels emitting higher amounts of NOx may not idle for longer than 5 minutes. 2008-model Isuzus destined for California will have special "Certified Clean Idle" stickers that will allow drivers to idle engines longer than the 5-minute limit. (In an announcement a week later, Cummins said its engines also qualify for the California exemption.)

OEM reps spent most of their presentation times outlining various other changes to their chassis that could affect upfitters' efforts to build and install truck bodies and equipment. Most involve measurements between frames and major components, and builders either gave out CDs with Body Builder manuals or directed attendees to web sites from which the manuals can be read and downloaded. During vehicle display sessions, some upfitters used tape measures to check certain areas. Upfitters generally aren't pleased at complications presented by the new exhaust systems, but said dealing with chassis-to-body challenges are simply part of what they do.