Simultaneous Control of Unburned NH3 and NOx Emissions From High Load Dual-Fuel Ammonia Operation on a High-Speed Diesel Engine Using a Cu-SCR System

Abstract Dual-fuel ammonia strategies are being investigated as a promising way to utilize NH3 as an alternative fuel for internal combustion engines in the maritime sector. One of the remaining barriers to implementing dual-fuel NH3 combustion strategies is understanding ways to minimize unburned NH3 and nitrogen oxide (NOx) emissions from these engines, both of which are elevated relative to a conventional diesel baseline. Selective catalytic reduction (SCR) systems are widely used for lean NOx emission controls for engines across transportation and stationary energy applications. SCR systems use a reducing agent, such as NH3, to react with NOx in the exhaust, converting it into nitrogen and water. Typically, NH3 is injected into the exhaust as a urea solution. In dual-fuel NH3 engines, where unburned NH3 is present in the exhaust, an SCR system could be used to mitigate both NH3 and NOx emissions. The presented work evaluates a commercial copper-zeolite SCR and ammonia slip catalyst system, designed for on-road diesel engine applications, for controlling unburned NH3 and NOx emissions from a dual-fuel NH3 combustion engine. The aftertreatment system was installed downstream of a single-cylinder four-stroke diesel engine that has been modified for dual-fuel ammonia use. The emissions were characterized by using a Fourier transform infrared spectrometer for both late- and early-injection diesel pilot strategies over three air–fuel equivalence ratios spanning from 1.6 to 1.0 at 1200 rpm and 12.6 bar IMEPg condition (with greater than 95% ammonia energy fraction). Initial findings indicate that the SCR achieves more than 99% NOx conversion with less than 50 ppm NH3 slip at air–fuel equivalence ratios greater than 1.4 at the operating conditions investigated. However, these benefits are accompanied by additional N2O emissions that are formed over the Cu-SCR.