Selective catalytic reduction
It’s coming…are you ready?
Tips for operating under new EPA emissions standards
• Make sure DEF (diesel exhaust fluid) is high quality and meets federal standards.
• Top off tanks during routine maintenance and inspections.
• Carry back-up 2.5-gallon bottle in truck to avoid engine derating if fluid runs out.
By David Fenderson, Windward Petroleum
Since the early 1990s, the Environmental Protection Agency (EPA) has been pushing the requirements for reductions in particulate and NOx emissions for modern diesel engines. These reductions are targeted to reduce the environmental impact and the health hazards associated with diesel emissions.
The 2010 requirements are .20 (g/hp-hr), an 83 percent reduction, and .01 PM (g/hp-hr), a 90 percent reduction since 1994. One 2010 on-highway engine will emit the same amount of pollutants as 65 of the equivalent engines that were built in 1994.
Many changes have occurred in both engine technology and fuels in the last 15 years to meet these stringent EPA requirements.
Most notably, the sulfur content of diesel fuels has dropped from 500 PPM in 1993 to 15 PPM in 2006. Additionally engine manufacturers have employed changes in engine timing, exhaust gas recirculation (EGR) and diesel exhaust particulate filtration. Most recently, selective catalytic reduction (SCR) has changed to meet these mandated emission levels.
SCR will be the most noticeable change in truck engine design and performance and may be the final chapter in reducing NOx emissions. SCR is an exhaust after treatment that manages NOx emissions downstream of the diesel particulate filter and uses DEF (diesel exhaust fluid) to neutralize toxic NOx gasses. DEF is injected into the emissions to create a reaction between the NOx and the catalyst to create harmless nitrogen gas and water vapor. SCR allows the engine to function at higher combustion temperatures, providing increased fuel efficiency and power. It has been reported that fuel consumption can be improved as much as 6.5 percent with trucks using SCR as their chosen method for NOx reduction.
The application of DEF in the engine will be simple. Each truck is outfitted with an outboard storage tank between three and 24 gallons depending on class of vehicle. The level of NOx in the emissions system will transmit a need for DEF to be injected into the system as a fine mist. This DEF mist will hydrolyze into ammonia gas (NH3) and react with the NOx in the SCR catalyst to form nitrogen and water.
DEF is a high purity mixture of 32.5 percent urea and deionized water meeting the stringent ISO 22241-1 quality standards. The amount of DEF required will vary by engine manufacturer, horsepower and load. However, on average, one can expect to use 3-5 percent of DEF in relation to the fuel consumed. The average truck going 100,000 miles per year at six-miles-per-gallon will consume between 500 and 850 gallons of DEF. Although the 2010 engines are more costly to purchase than later model engines, this cost, as well as the cost to purchase DEF, will be offset by significant improvements in fuel consumption and by a much cleaner and safer environment for generations to come.
The critical issues surrounding DEF will be handling and storage, as any contamination to the fluid will result in significant threats to the catalysts and engine performance. It will be very important to use only a certified DEF, as both the urea and the water used to blend DEF are required to meet very close tolerances. It also will be advisable to top off DEF tanks during routine maintenance and inspections and to carry a 2.5-gallon bottle on board the truck as an emergency dose. The average truck will go 400 miles on 2.5 gallons of DEF.
Of potential concern to DEF users in Maine as well as other cold weather states, DEF will freeze when the temperature drops below 11° F. Fortunately, the SCR systems are designed for this and will not crack the DEF dispensing equipment. They quickly thaw as hot engine coolant circulates through heating coils in the system. Additionally, during typical engine start up, the need for DEF is limited, as the equipment has very low NOx emissions. The recommendation is to follow the OEM instructions for cold-weather operation, Ultimately, that means increased idling to ensure the DEF is thawed.
Fortunately the European Union has been using SCR for more than 10 years in many of the world’s coldest environments with excellent results.
Each SCR truck will be equipped with onboard hardware to detect levels of DEF in the storage tank. If the truck runs out of DEF – or if the wrong or contaminated fluid is used – the engine will derate (run at a reduced level). It is possible for the engine to derate to a maximum speed of five miles per hour due to these conditions. Again, it cannot be emphasized enough to keep appropriate levels and quality of DEF in your truck’s reservoir to avoid these costly conditions.
David W.H. Fenderson STLE, CLS, is senior vice president of marketing for Windward Petroleum. For more information, firstname.lastname@example.org