By now, youve heard about the U.S. Environmental Protection Agencys impending 2010 emissions regulations for heavy-duty diesel engines. To comply with these regulations, most major diesel engine builders plan to use selective catalytic reduction (SCR) technology. This will further reduce exhaust emissions that cause environmental pollution – and will add another layer of complexity in the design and operation of 2010 model-year diesel engines.
Modern, heavy-duty diesel engines are required to meet a very stringent exhaust emissions standard in order to reduce environmental pollutants, such as nitrogen oxides (NOx) and diesel particulates. The 2007 EPA emissions regulations for on-highway trucks mandated major reductions in NOx and diesel particulates emissions. For compliance with this standard, diesel-engine builders adopted enhanced Exhaust Gas Recirculation (EGR) to reduce NOx, and utilized after-treatment devices such as Diesel Particulate Filters (DPF) and Diesel Oxidation Catalysts (DOC) to reduce particulates.
Now the 2010 emissions standard for on-highway trucks further ratchets down the NOx limit by more than 80 percent. To attain this rigid NOx emissions limit, most engine builders have announced the use of SCR technology for exhaust aftertreatment. SCR will be an additional exhaust system bolt-on device, on top of the DPF and DOC. Consequently, the 2010 emissions-compliant engines will have the lowest emissions ever implemented in the heavy trucking industry.
In the SCR process, urea – the same chemical used in common fertilizer – reacts with NOx to generate nitrogen and water. For practical application in the vehicles, urea is used as an aqueous solution known as Diesel Exhaust Fluid (DEF). This fluid, a solution comprising roughly 32.5 percent urea in water, is injected upstream of the SCR catalyst. At high temperatures and in the presence of a catalyst, urea converts the NOx in exhaust gas into harmless nitrogen and water. The reaction removes more than 95 percent of the NOx in the exhaust, to fully clean the emissions of pollutants. This helps protect the environment and reduce human and animal health hazards caused by diesel engine emissions.
Most major original equipment manufacturers (OEMs) will install SCR systems in their new diesel-powered vehicles such as heavy trucks, light trucks, buses and utility vehicles to meet 2010 NOx emissions requirements.
The exact amount of DEF used per driven mile or operational hour depends on the type of engine, its service condition and/or application. Engines with higher levels of NOx in the exhaust will need more DEF or use it at a higher rate than engines tuned to produce lower levels of Nox. Most trucks will be equipped with a refillable tank that holds from 5 gallons to 30 gallons of DEF. Some engine builders have stated that in their equipment, one gram per horse-power-hour of NOx reduction will consume DEF at about 2 percent of the amount of fuel consumed. Thus, if the vehicle consumes 100 gallons of diesel fuel in 600 miles, 2 gallons of DEF will be used over that distance.
Based on published DEF consumption rates from some engine builders, it is likely that the typical tank capacity will hold ample DEF to last from six to 10 fueling cycles in most vehicles. Keep in mind that these are only estimates because the OEMs will try to use a combination of EGR and SCR to consume a minimal, yet effective, amount of DEF. This is also impacted by the emissions credits available to the OEMs based on their historic emissions compliance.
Under EPAs 2007 exhaust emissions regulations, engine builders implemented enhanced EGR to reduce NOx. In addition to increased soot production, enhanced EGR reduced power density, increased heat rejection to the coolant, and reduced fuel economy.
Now, with the introduction of SCR in their 2010 models, engine builders may be able to dial back on the EGR – which is advantageous for increasing power density, lowering engine heat and helping to recapture some of the lost fuel economy.
There is a light at the end of the tunnel! As the OEMs tune their emissions with the combination of EGR and SCR, the job of the lubricant may become easier. The API CJ-4 service category remains current and no upgrades in the engine oil will be needed to meet lubrication requirements of 2010 emissions-compliant on-road engines.
Depending on how much the OEMs will retune their EGR, the result will be a cleaner and cooler running engine. Note that EGR will not be completely eliminated because in its absence, the rate of DEF usage would be too high to be practical. The SCR systems are expected to be very reliable and long-lasting, even compared to a diesel particulate filter.
The new engines will be equipped with onboard diagnostic devices to keep tabs on the entire exhaust after-treatment system and to prevent engine operation without DEF. When the DEF level falls below the critical minimum for optimum operation of the exhaust system, fail-proof controls will derate the engine, causing the vehicle to operate at substantially reduced power. (According to the EPA rules, there is a provision for the equipment to operate in limp-home mode, or travel at reduced power so as not to be stranded by an emergency.)
Another wrinkle: Since DEF freezes in cold weather, trucks will keep the solution flowing during operation through the use of a heater. If, however, the unit has to be parked several days in freezing temperatures, the on-board diagnostics will allow the engine to operate for a short period until the DEF thaws and begins to flow again.
Exhaust after-treatment that utilizes DEF and SCR has been used in Europe for several years. In fact, AdBlue is a leading trademark name for the DEF marketed in Europe. Domestically, the major OEMs have announced plans to supply DEF under their own brands for aftermarket service. Additionally, several commercial marketers and suppliers have announced plans to offer DEF through distributor networks and at truck stops.
The DEF will have to meet applicable standards so it will work in all systems. Currently, ISO-22241-1, AUS-32 and DIN70070 are specifications that are on many of the branded fluids. The American Petroleum Institute (API) also has a testing program to certify diesel exhaust fluids, and a logo to identify qualified DEF at the pump.
For more information on the subject of SCR technology, visit www.factsaboutscr. com, a useful website hosted by the North American SCR Stakeholders Group.