With the introduction of Phase 2 of the Environmental Protection Agency’s greenhouse emissions reduction plan, fleets must find ways to reduce emissions-related maintenance costs, specifically, aftertreatment system maintenance.
This is becoming one of the more costly maintenance items on many of today’s heavy-duty trucks. A proper preventive maintenance program and constant tech training can help reduce costs and improve how your fleet runs, as well as the use of renewable fuels, such as renewable diesel.
Aftertreatment Systems 101
In most cases, your aftertreatment system usually consists of two parts for any on-road engines manufactured since 2010. A diesel particulate filter (DPF) traps and converts soot to carbon dioxide gas and, while the selective catalytic reduction (SCR) system reduces nitrogen oxides (NOx) emissions.
The system injects small amounts of diesel exhaust fluid (DEF), a water-based solution containing urea, into an engine’s hot exhaust stream to reduce emissions of NOx. The DEF vaporizes, forming ammonia and carbon dioxide, and when the exhaust gas and ammonia pass over a catalyst, NOx is converted into nitrogen and water.
The DEF is contained in a separate reservoir that must be maintained by the fleet technicians and/or driver, keeping it free of impurities, which could cause the catalyst to fail – at a cost of $8,000 to $15,000 to replace. To avoid DEF contamination, it should be kept away from fuel, oil, grease, water, dust, dirt, and other contaminants. On top of that, make sure to clean the DEF fueling equipment with de-mineralized water only; store and dispense DEF with the recommended equipment only; refrain from using funnels or bottles that have not been used for other fluids; and avoid refilling containers that were previously used to store DEF.
The DPF continuously traps partially burned fuel (soot) in a catalytically treated ceramic filter. As the filter fills with soot the back pressure on the engine builds. Under normal operation, temperature spikes in the exhaust gas temperature can be sufficient to start oxidizing the accumulated soot into carbon dioxide gas – clearing the filter. If the normal drive cycle does not create sufficient temperature, the DPF can begin to fill up and a forced regeneration is needed. Forced regenerations require the vehicle to be parked for 20-40 minutes. During forced regeneration diesel fuel is injected directly into the exhaust stream ahead of the DPF to generate the temperatures required to start regeneration.
Renewable diesel typically creates 30-60% less soot than petroleum diesel in the same engine. Every molecule in renewable diesel is in petroleum diesel. But renewable diesel does not contain the molecules in petroleum diesel that burn poorly and create ash. This means lower engine back pressure and longer intervals between regenerations.
Cleaning the Filter
Metals from the fuel and lubricant will become trapped in the DPF along with the soot. These materials do not oxidize and remain in the DPF as ash. Remember to clean diesel particulate filers (DPFs) as recommended by the manufacturer, usually somewhere around the 200,000-mile mark. This requires removing the DPF and blowing it clear or using alternative means. A clean diesel particulate filter can improve fuel economy by 2% to 3%, according to North American Council for Freight Efficiency (NACFE). Intervals can vary by engine/truck manufacturer and duty cycle.
Added Benefits of Using Renewable Diesel
In terms of the use of renewable diesel, most of the challenges that can be experienced with the use of biodiesel are alleviated. Since the fuel consists of pure hydrocarbons and has a performance that is similar to conventional diesel, it meets the petroleum diesel ATSM D975 standard. This allows it to be used on any vehicle that uses diesel fuel, and ensure it is covered under manufacturer warranties.
Many engine manufacturers have approved the use of renewable diesel in many of their engines. At the end of May, Cummins announced that its B4.5, B6.7, and L9 engine platforms are compatible with certain kinds of renewable diesel fuels. The manufacturer touted that using renewable diesel with these engines could cut GHG emissions by 40% to 90% over the total life of the vehicle.
The results came after an 18-month field test of its engines running 100% paraffinic diesel fuels. Volvo and Mack have also approved its use in all their engines after seeing a 15% to 80% reduction in emissions and reduced maintenance costs compared to other available alt fuel options. Lower emissions means less stress on aftertreatment systems, which results in less maintenance and reduced downtime.