Navistar International Corp. has submitted test data to the U.S. Environmental Protection Agency for its first on-road truck engine to meet federal clean-diesel mandates without using selective-catalytic-reduction technology (SCR). Regulators' approval of the 13-liter MaxxForce engine, a necessary step to ensure that Navistar's tailpipe controls work, is expected in three to six months, says the Warrenville, Ill.-based manufacturer. Navistar has objected to SCR, which requires a periodic fill-up with urea, claiming truckers don't want the hassle. The manufacturer is the sole supplier that uses only exhaust-gas recirculation to lower its smog output.
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.