By Bob Graham and Shannon Pieper
Published Tuesday, November 29, 2011
Emissions and the environment. These words became a hard reality to Americans back in the early 1960s. Nowhere was that more prevalent than the automotive industry. It took decades for the dictates of the Environmental Protection Agency (EPA) to be worked into a practical manufacturing solution that automotive manufacturers and consumers could accept, eventually becoming what today is a hardly noticed component of daily driving.
The changes eventually hit the apparatus industry, too. In the early 2000s, the EPA set its sights on heavy trucks—including fire apparatus—calling for a reduction in diesel particulates. The major engine manufacturers—Cummins, Caterpillar, Navistar (International) and Detroit Diesel—came up with different ways to meet this mandate. Most involved an emissions-reduction technique called exhaust gas recirculation (EGR) combined with diesel particulate filters (DPF).
Mounted in the exhaust system, the DPF captures diesel particulates (or soot). As the vehicle is driven, the engine gets hot, and so does the exhaust system. This exhaust system heat causes the DPF catalyst to burn the soot away into non-polluting gases in a process called “passive regeneration.” If the vehicle operates only on short runs, or is idled for long periods of time, the exhaust never gets hot enough to trigger the catalytic reaction. When this occurs, the engine will initiate a process called “active regeneration” that artificially increases the exhaust temperature to burn the particulates. Engine-controlled active regeneration can only occur if the vehicle is being driven. If the vehicle is never driven long enough for the engine to initiate active regeneration, it must be initiated manually by the operator. During manual regeneration, the vehicle is parked in a secure area, and the engine increases its rpm and artificially adds heat until the soot is burned away.
Although most of the particulate matter consists of soot that can be burned up in the DPF catalyst, a small fraction is termed ash, and it comes from the sulfur content of the fuel as well as engine oil additives and detergents. This ash is never burned off, but rather accumulates in the DPF over time. Eventually the DPF must be removed from the vehicle and physically cleaned of ash by a pneumatic process. This process can only be performed at a service facility, but it should be hundreds of thousands of miles before it is required.
Although the new engines added a significant cost to the apparatus—estimates range from $8,000 to $15,000—this was the new standard required to clean emissions nationwide, and everyone was expected to get on board.
Apples to Oranges
In the eyes of the EPA, fire apparatus fall under the same category as long-haul trucks. Military vehicles were exempted from the new emissions standard, but not fire apparatus. (Note: Many people in the fire service also cite an “exemption” given to construction vehicles. But the Technical Committee of the Fire Apparatus Manufacturing Association [FAMA] notes that these vehicles weren’t given an exemption, but are instead expected to meet a second set of standards. In comments prepared for this article, the Technical Committee notes, “These non-road standards are currently less stringent than the on-road regulations, but they are on a path that will eventually bring them up to the on-road requirements.”) The problem: Fire apparatus do not operate in the same manner as long-haul trucks.
“Over-the-road trucks drive for 8 or 10 hours straight; the driver may not turn the engine off that whole time,” says Capt. Homer Robertson, who manages the fleet for the Fort Worth (Texas) Fire Department and is a FireRescue/FirefighterNation.com editorial board member. “We’re only making 10 to 20 runs a day, and those could be really short. We might get a call, go out, it’s cancelled so we turn around and back right into the station and shut down.” And the problem with that: The engine doesn’t heat up to the proper operating temperatures to burn off the particulates.
“The magic number is temperature,” says Bill Foster, vice president and co-founder of Spartan Motors. “Temperature plays a huge part in the keeping the DPF clean. It has to be close to 1,200 degrees. You have to make the engine work to drive the temperature of the exhaust to burn off the soot that has congregated on the filter.” Fail to reach those high temperatures on a regular basis, and the DPF will fill up to the point where you have to take the DPF off and send the filter to be professionally cleaned. “That’s several hundred dollars to have it cleaned,” Foster says, “and you can only do it a couple times before it’s rendered unusable.”
Although the ideal regen process occurs through the normal operation of the vehicle, most 2007-compliant engines were designed to be able to regen through operator intervention as well. This involves parking the vehicle and letting it move through a process that revs the engine high enough to generate the needed heat.
How does the operator know when regen needs to be performed? The engine won’t shut down totally if a warning light comes on,” says Tim Johnson, Southern Regional Sales Manager for Rosenbauer and vice chair of the FAMA chassis committee. “There are stages that occur in the process.” A DPF light on the dashboard first lights up to indicate regen is needed. If the normal operation of the truck doesn’t send the engine into regen, the light flashes; if no action is taken, the check engine light and then the stop engine light come on. Once the stop engine light comes on, the truck is inoperable.
Although the process sounds fairly simple, some departments almost immediately reported problems. “On our first apparatus [delivered with a 2007 engine], the problems started almost immediately,” says Tommy Moak, shop supervisor for the Fort Worth Fire Department. “We hadn’t had the truck in service a month and we started having regen issues. The truck just would not do a regen cycle.” (To read more about the regen problems specific departments are having, read Part 2 of this special report.)
Regen is not something that can be scheduled like other regular maintenance. The process is related to the operation of the vehicle,” Johnson says. “Since each department is different, there is no standard interval. Some departments regenerate weekly; some wait until the alarm comes on.”
Engine manufacturers have been working with fire departments to resolve regen issues since the 2007 models first hit the market, and software reprogramming has been able to resolve the problems in some cases. But problems persist for many departments.
One positive note is that issues affecting response or pump operations during a call don’t appear to be widespread. “The system loves the heat generated by responses and pumping operations,” Johnson says. “The longer the engine runs under load, it allows the catalyst to activate and remove the trapped carbon. The only response issues are when the DPF warnings are ignored, requiring a trip to your engine manufacturer’s facility.”
Customizing for the Fire Service
Engine manufacturers recognized early on that engines built for the fire service would require customization due to the unique ways the vehicles are used. Not only do the vehicles not reach temperatures required for regen, but if the regen process were to interfere with vehicle operation on the fireground, the results could be disastrous.
For this reason, fire apparatus engines were customized. “The DPF warning lamp comes on earlier in a fire apparatus to allow the operator a bigger window between the DPF lamp and the check engine lamp,” says Brian Chaput, senior application engineer for Detroit Diesel. “The parked regeneration process can also be interrupted at any time so that fire apparatus are not required to be taken out of service in order to perform a regeneration.”
Specifically, engines for the fire service were built with a regeneration inhibit switch. Information provided by Cummins indicates that “if this switch is enabled by the operator, all after-treatment DPF regenerations will be prevented.” That sounds good—firefighters responding on a call would want the option to delay regen—but Foster says that this switch has actually contributed to problems.
“In 2007, they required a switch to defeat the ability to regen," Foster says. "Well, regen inhibit failed miserably because people would turn off the regen, which would in turn plug up the DPF. The engine would derate and require a forced regen.”
Foster believes other problems also developed in response to fire service concerns about the temperature of the exhaust. "They were slow to use a mitigation device on the exhaust that lowers the exhaust temperature,” he says. “It’s probably the lowest that it’s been in the last 8 to 10 years, regardless of whether the engine is in regen or not, because it’s drawing air into the exhaust.”
Further complicating the issue, engine manufacturers took different approaches in meeting the emissions standards. In 2007, most manufacturers used a diesel oxidation catalyst (DOC) ahead of the DPF to generate the heat. A DOC will burn away any hydrocarbons that remain in the exhaust during normal operation. When active regeneration is required, the engine will inject a small amount of diesel fuel into the exhaust stream. This fuel will react in the DOC and provide the heat required for regeneration to occur. Because the DOC and DPF are packaged tightly together, the heat is all retained in one insulated canister.
Caterpillar, however, opted to go with a blow-torch-like mechanism that ignites a stream of diesel fuel directly behind the turbocharger outlet. Combustion takes place in the exhaust pipes and the super-heated exhaust travels through the pipe to the DPF, where it can burn the soot. Exhaust pipe insulation on the Caterpillar system is therefore critical, and must be maintained intact for the life of the vehicle
In 2010, things got even more complicated. Stricter EPA rules caused engine manufacturers to once again make changes. The only technically viable solution that engine manufacturers found that will meet the regulations without averaging or banking carbon credits was to add an after-treatment device call selective catalytic reduction (SCR). The system adds a catalyst chamber downstream of the DPF filter, into which urea-based diesel exhaust fluid (DEF) is injected. It is designed to cut down on oxides of nitrogen, known as NOx. If the system works correctly, nitrogen and water are the only things coming out the exhaust pipe.
The main emissions advantage to SCR is that it is very efficient at eliminating NOx. This allowed the engine manufacturers using SCR to increase combustion chamber temperatures back to pre-EGR levels. Hotter combustion temperatures improved fuel economy and reduced the amount of soot in the exhaust. With up to 10 times less soot, the DPF does not fill up as quickly, which manufacturers say should greatly reduce manual regeneration frequency.
The SCR system has additional warning lights for apparatus operators and DEF fluid must be replenished when low. Much like the DPF system, should warning lights not be heeded, a series of torque and power-loss scenarios will occur, according to material furnished by Cummins. “All of the 2010-emission engines require additional maintenance,” Johnson says. “The DEF tank is another component that must be checked daily, along with the other fluid checks done.”
But again, approaches differed. Navistar took the tact of not using urea and instead further increased EGR to get closer to compliance on NOx; to meet the EPA regulations, it makes up any deficit by spending emissions credits and by averaging credits gained from production of its cleaner small diesel engines. Caterpillar exited the over-the-road market all together. Some manufacturers and departments bought additional 2007 engines ahead of the 2010 implementation, out of fear that the new regulations would cause even more problems. As a result, many apparatus being delivered today still have 2007-compliant engines.
Put simply: There are now a lot of 2007 engines in use, and a much smaller number of 2010 engines. Some 2007 engines have been reprogrammed; some haven’t. In addition to the different models of 2007 and 2010 engines, there are significant differences among departments and even among stations within the same department. One station with a high call volume that logs highway miles to respond to calls may not have much of an issue; an inner-city department that goes on very short runs and idles at lots of EMS calls could have significant issues. All of this variation has made it very difficult to estimate the extent of the problem and the effect it’s having on fire departments.
One thing is for certain: When the vehicle doesn’t regen automatically, or when it won’t regen manually, serious problems result. “The engine performance is affected when the filter unit starts to become saturated with carbon,” Johnson says. “This will lead to a trip to your engine service facility, since only they can change out a DPF unit due to the EPA regulations.” And changing out that unit not only takes the apparatus out of service, but can cost upward of $5,000.
There are numerous service issues still lingering from the 2007, and possibly new issues emerging with the 2010 engines, but it’s not all the same issue, and that means that no one approach can solve all the problems.
There’s no doubt, however, that although there may not be something wrong with the new EPA-compliant engines, their implementation has caused significant adjustment in the fire service. In Part 2 of this special report, we take a look at the impact these engines are having at three departments.
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