Design and testing of an independently controlled urea-SCR system for marine diesel applications

Diesel engine emissions for on-road, stationary and marine applications are regulated through new EPA standards. The most difficult species of exhaust gas constituents to reduce are oxides of nitrogen, NOx. The use of urea selective catalytic reduction (SCR) is promising for NO x abatement as a retrofit application. This work focused on the reduction of NOx by use of a stand alone urea injection system, applicable to marine diesel engines. Most current systems communicate with engine controls to predict NOx emissions based on signals such as torque and engine speed. Many marine engines employ mechanical injection technology and lack communication abilities. This system estimated NOx and measured exhaust flow independent of engine parameters. The system used independent exhaust sensor inputs to estimate NOx levels and exhaust gas flow rate. These sensor inputs were used in an independent controller and an open loop model to estimate the necessary amount of urea needed. The controller then used pulse width modulation (PWM) to power an automotive style injector for urea delivery. The goal of this work was to reduce the engine out NO x levels by 50 percent. Emissions tests were conducted at the West Virginia University\u27s Engine Research Center. The data were analyzed to determine the NOx reduction ability of the system. NOx reduction capabilities of 41-67% were shown on the Non Road Transient Cycle (NRTC) and ICOMIA E5 Steady State cycles. The system was optimized during testing to minimize the dilute ammonia slip to cycle averages of 5-7 ppm. The goal of 50% reduction of NOx can be achieved dependent upon cycle. Further research with control optimization and possible use of oxidation catalysts is recommended to further improve the systems NOx reduction capabilities while minimizing ammonia slip