Ask the maintenance manager of any fleet operating heavy duty diesel trucks what their most common issue is, and you will likely hear – without any hesitation – “aftertreatment systems.” When U.S. regulations went into effect starting with the 2007 model year requiring diesel engines to emit lower levels of nitrogen oxide (NOx) and particulate matter into the atmosphere, OEMs had to meet those new requirements. As with most new technologies, aftertreatment systems had various bugs and issues from the start.
Compounding the problem was the fact that fleets had no experience with these complex exhaust treatment systems, so the only knowledge they had regarding how to service and maintain them was what the OEMs provided, not real-world trial and error. Fleets that had not yet experienced the new aftertreatment systems delayed replacing their older trucks as long as possible after hearing of troubles from fleets that had, but most eventually had to concede and purchase vehicles equipped with these systems.
OEMs have made drastic improvements to aftertreatment systems over the years, but regulations have also tightened further, requiring additional components and making the systems even more efficient, but also more complex. Phase 1 emissions standards impacted trucks starting with the 2014 model year, and fleets are still seeing repercussions from those regulations today since many operate vehicles up to five years before replacing them.
Aftertreatment system maintenance
Some fleets today estimate that up to 50 percent of their downtime is due to aftertreatment system issues, though they say there is a downward trend in aftertreatment-related downtime as they replace their trucks with model year 2019 and newer vehicles. It seems that OEMs have been able to tweak and improve the systems, resolving common issues as they are discovered.
It also helps that fleets have had time to learn the ins and outs of these systems and the best ways to maintain them in order to prevent unscheduled downtime. One common trend among fleets in keeping aftertreatment systems in good health is diesel particulate filter (DPF) regenerations (regens).
Fleets are training their drivers to always allow trucks to run regens when the vehicle’s systems require it, since ignoring the warning light often leads to more trouble down the road. They are also frequently running forced regens using OEM or aftermarket diagnostic tools. Some fleets will run forced regens on trucks whenever they are parked in the yard. This preventive maintenance can help prevent aftertreatment issues later on.
Another way fleets avoid aftertreatment issues is by monitoring and limiting idle time. Idling a diesel engine can clog the DPF since it is not running hot enough to perform a regen. Using auxiliary power units (APUs) or bunk heaters can help mitigate this issue by reducing the amount of time the truck idles, especially during periods of cold or hot weather when cabin climate control is necessary.
Fleets also cite technician training as imperative in keeping aftertreatment systems operating smoothly. Engine manufacturers are able to train fleet technicians on the latest technologies, ensuring they have the latest knowledge and expertise on aftertreatment systems. This is especially important considering Phase 2 emissions standards will impact 2021 and newer model year trucks.
Alternative fuel considerations
As emissions regulations have become more and more strict, OEMs have made necessary changes to engine aftertreatment systems to meet the requirements. But many have also begun to develop engines powered by alternative fuels that require simpler aftertreatment or no aftertreatment systems at all.
The solution that has received the most attention has been battery electric vehicles (BEVs). BEVs have been making their way into the passenger car segment, and we are just starting to see the very first electric trucks make their way to the market as well. While BEVs have zero tailpipe emissions with no aftertreatment system at all, there are several hurdles to overcome before this solution is ready for the masses. For one, the U.S. power grid and charging infrastructure is nowhere near ready to charge BEVs for every fleet (not to mention consumer vehicle charging). Plus, battery technology has not yet reached the tipping point where batteries can both provide enough range and be lightweight enough to be usable for long haul truck routes.
Other alternatives, including propane autogas and hydrogen fuel cell vehicles, can also produce zero or near-zero tailpipe emissions with little or no aftertreatment systems. Hydrogen fuel cell technology is still in its infancy, but concept trucks from manufacturers such as Kenworth, Nikola, Hyundai, Mercedes-Benz, Daimler, and Hino show it could be a promising solution in the future for fleets looking to move away from traditional diesel trucks and their aftertreatment systems.
Propane autogas vehicles are on the market today and have been slowly gaining popularity. While they are mainly seen in the light and medium duty commercial vehicle segments, propane autogas vehicles require much less complex aftertreatment systems to meet and exceed government regulations, meaning less maintenance and downtime.
“Propane’s low-carbon chemical properties allow it to power an engine while reducing the emissions released into the atmosphere,” says Todd Mouw, president of ROUSH CleanTech. “Engines fueled by propane autogas … do not need additional emission fluids or extra valve adjustments.”
Read more about propane autogas solutions.
There is no one-size-fits-all solution for every fleet when it comes to solving the aftertreatment system problem. Alternative fuel vehicles may be a solution for many fleets in the future, but for now, the updates and improvements OEMs are continually making to diesel engines will help reduce downtime, both scheduled and unscheduled.
