New on-road motorcycles pretty much all have catalytic converters now, and fuel injection maps designed to minimize emissions.
For heavy trucks (class 8 ) most of them are using urea injection.
The U.S. Environmental Protection Agency has required all diesel engines manufactured on or after Jan. 1 to reduce nitrogen oxide emissions by 83 percent from the 2007 standard —to 0.2 grams per brake horsepower hour from 1.2g/bhp-hr.
To meet the new standard, most engine original equipment manufacturers, including Cummins, Detroit Diesel, General Motors and ICTA, among others — have employed selective catalytic reduction technology, or SCR.
This technology reduces NOx levels by injecting small amounts of urea-based solution called diesel exhaust fluid, or DEF, into a catalyst, which reacts with the NOx captured in the catalyst to convert the pollutant into harmless nitrogen and water before it’s emitted into the environment.