Design and testing of an independently controlled urea SCR retrofit system for the reduction of NOx emissions from marine diesels.
Diesel engine emissions for on-road, stationary and marine applications are regulated in the United States via standards set by the Environmental Protection Agency (EPA). A major component of diesel exhaust that is difficult to reduce is nitrogen oxides (NOx). Selective catalytic reduction (SCR) has been in use for many years for stationary applications, including external combustion boilers, and is promising for NOx abatement as a retrofit for mobile applications where diesel compression ignition engines are used. The research presented in this paper is the first phase of a program focused on the reduction of NOx by use of a stand-alone urea injection system, applicable to marine diesel engines typical of work boats (e.g., tugs). Most current urea SCR systems communicate with engine controls to predict NOx emissions based on signals such as torque and engine speed, however many marine engines in use still employ mechanical injection technology and lack electronic communication abilities. The system developed and discussed in this paper controls NOx emissions independentof engine operating parameters and measures NOx and exhaust flow using the following exhaust sensor inputs: absolute pressure, differential pressure, temperature, and NOx concentration. These sensor inputs were integrated into an independent controller and open loop architecture to estimate the necessary amount of urea needed, and the controller uses pulse width modulation (PWM) to power an automotive fuel injector for airless urea delivery. The system was tested in a transient test cell on a 350 hp engine certified at 4 g/bhp-hr of NOx, with a goal of reducing the engine out NOx levels by 50%. NOx reduction capabilities of 41-67% were shown on the non road transient cycle (NRTC) and ICOMIA E5 steady state cycles with system optimization 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, urea distribution and possible use of oxidation catalysts is recommended to improve the NOx reduction capabilities while minimizing ammonia slip.
Johnson
Derek R
DR
West Virginia University, College of Engineering and Mineral Resources, Mechanical and Aerospace Engineering Department, Morgantown, West Virginia 26506, United States of America. djohnso9@mix.wvu.edu
Bedick
Clinton R
CR
Clark
Nigel N
NN
McKain
David L
DL
D002384:Catalysis; D052918:Environmental Restoration and Remediation / Q000379:methods*; D018986:Motor Vehicles; D009589:Nitrogen Oxides / Q000737:chemistry*; D012623:Seawater; D012767:Ships; D014508:Urea / Q000737:chemistry*; D001335:Vehicle Emissions / Q000517:prevention & control*
D009589:Nitrogen Oxides; D001335:Vehicle Emissions; D014508:Urea