Numerical And Theoretical Studies On The Improved Performance Of SCR System For Marine Diesel Engine

Marine diesel engines are extensively used for transportation and as well as for power generation purpose because of its high durability,thermal and fuel efficiency than the gasoline engines.But the marine diesel engine produced severe NOx emissions that are currently well discussed issue needed to be solved due to its serious health and environmental problems.At the same time,because of increasing stringent regulations of NOx emissions it is necessary for ships to meet the international maritime organization(IMO)Tier Ⅲ regulations in NOx emission control areas(ECA).It is enforced for the vessels that are constructed on and after the 1st January 2016.Therefore,a demand for well-functioning NOx reduction technology is required.Currently Selective catalyst reduction(SCR)is the most prominent and mature technology used to reduce NOx emissions.However,to obtain maximum NOx removal with minimum ammonia slip remains a challenge.This study is divided into two parts.First part is related to the theoretical studies about the SCR technology.Actually SCR catalyst is the core part of SCR technology;hence at the first a comprehensive review about SCR catalysts by focusing impacts of sulfur on SCR performance has also been discussed.In other part numerical studies have been performed in order to get the maximum SCR efficiency.Therefore,in this regard,new mixers are designed in order to obtain the flow and reaction optimization of SCR system.This paper reports performance parameters such as uniformity of velocity,ammonia uniformity distribution,temperature distribution and wall film.Also,a numerical model is developed to investigate the interaction of urea droplet with exhaust gas and its effects by using line(LM)and swirl(SM)type mixers alone and in combination(LSM).The urea droplet residence time and its interaction in straight pipe are also investigated.Model calculations proved the improvement in velocity uniformity,distribution of ammonia uniformity,and temperature distribution for LSM.Prominent enhancement in the evaporation rate was also achieved by using LSM,which may be due to the breaking of urea droplets into droplets of smaller diameter.Therefore,the SCR system accomplished higher urea conversion efficiency by using LSM.It has also been observed that,concentration deviation of NH3 and velocity standard deviation at the upstream of catalyst section was less than 10%and 15%,which strongly meets with the designing conditions of the SCR system.Lastly,the ISO 8178 standard engine test cycle E3 was used to verify the simulation results.It has been observed that the average weighted value of NOx emission obtained at SCR outlet using LSM was 2.44 g/kWh,which strongly meets International Maritime Organization(IMO)Tier Ⅲ NO,emission regulations.