6 January 2005
Urea-based selective catalytic reduction (SCR) technology may not be the best solution for customers or regulators, according to J. Parker, Vice President, Caterpillar Power Systems Marketing, who issued a statement regarding 2010 emissions technology.
“At Caterpillar, we urge the on-highway market to keep the technology options open regarding 2010 emissions. Several engine manufacturers have indicated that SCR is the only viable path for meeting the 2010 EPA standard—however, our research indicates SCR might not be the best choice for on-highway applications,” said Caterpillar.
Caterpillar indicated it is working on engine combustion technology solutions that have been promising in tests. The company said it has engines running in test labs that are meeting the 2010 emission regulations without the use of SCR. In addition to combustion technologies, Caterpillar also has established an Environmental Technologies Group that is working on aftertreatment technologies in the area of diesel particulate filters (DPF) and NOx aftertreatment, which will be a part of the solution for 2010.
Caterpillar intends to meet the 2010 standards by developing a system solution, as it was the case with the ACERT technology launched in 2003. This approach combines combustion technologies, fuel system technologies, electronics and aftertreatment.
The 2010 aftertreatment system will not include urea-SCR, but may utilize other types of NOx reduction catalysts. Although no details were given in the statement, Caterpillar has been working on NOx adsorber-catalyst systems, as well as on lean NOx catalysts. The latter technology—which works on the principle of selective catalytic reduction by hydrocarbons and requires hydrocarbon injection to reach higher NOx reductions—could be simpler and less costly than NOx adsorbers. It could be also compatible with particulate filters regenerated through diesel fuel injection in the exhaust system—the type of DPF system that was employed in Caterpillar 2007 heavy-duty truck prototype.
In the statement, Caterpillar identified several issues that exist with urea-SCR: (1) regulating the required urea addition to tanks would be a challenge, (2) a urea infrastructure would have to be built in North America, (3) the cost benefit from the use of SCR in mobile applications in Europe has not been as good as originally expected, (4) issues such as the weight of the urea tank and the system’s vulnerability to external damage may further increase owning and operating costs.
It is envisioned that urea-SCR will be used as the major technology for meeting the European Euro V (2008) standards. Several manufacturers are launching SCR trucks already at the Euro IV stage (2005)—a move driven largely by the anticipated savings from increased fuel economy. Even in Europe, however, there is no consensus on the use of urea-SCR. Germany’s MAN Nutzfahrzeuge has launched Euro IV engines utilizing a PM aftertreatment system trade-named PM-KAT (a “partial particulate filter” system) and exhaust gas recirculation (EGR). MAN has also announced plans to offer an analogue solution for the Euro V stage. Some manufacturers (e.g., Scania) provide both alternatives—urea-SCR or EGR—in their Euro IV engines.