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In order to reduce diesel NOx emissions, aftertreatment methods including LNT (Lean NOx Trap) and urea SCR (Selective Catalytic Reduction) have been researched. One of the shortcomings of urea SCR is its NOx reduction performance degradation at low exhaust gas temperatures and possible emission of unregulated byproducts. Here, a new type of a urea-dosing device to overcome these shortcomings is studied. This dosing device actively produces ammonia without depending upon the exhaust gas temperature, and designed for onboard application. The device incorporates an electrically heated bypass with a hydrolysis catalyst. An injector supplies urea solution into the bypass. The bypass is heated only when thermolysis is needed to produce ammonia (NH3). The hydrolysis catalyst further assists in the production of NH3. The ammonia gas obtained is then mixed with the main exhaust gas flow.

Typical DI diesel engines operate with fuel injection taking place within a range of about 30 crank angle degrees before top dead center, at the end of the compression stroke. When injection takes place far earlier, at the beginning of the compression stroke, another form of combustion occurs, which we termed PREmixed lean Diesel Combustion, or PREDIC. With PREDIC operation, self-ignition occurs near top dead center and NOx emissions are drastically lower. When ignition occurs, the fuel-air mixture is thought to be nearly homogeneous, with only slight heterogeneity. Appropriate fuel spray formation is very important for successful PREDIC operation. Using a single-zone NOx formation model, calculations showed that the mean excess air ratio in the PREDIC combustion zone was 1.87, which resulted in very low (20 ppm) NOx emissions. Conventional combustion at the same conditions resulted in a mean combustion zone excess air ratio of 0.88.