A study of improving NOx conversion efficiency in SCR System

Abstract

The diesel engine is utilized in most of Korea's transportation vehicles to convey goods from various companies; nevertheless, diesel engines emit large amounts of nitrogen oxide (NOx), which is harmful to human health. A common approach for reducing NOx emissions from diesel engines is the selective catalytic reduction (SCR) system; however, many factor create difficulties to reduce NOx emission. The urea particles often get stuck in the injector and cannot spread through the system; the injector often struggles to spray urea in small droplets; the large urea particles from the injector easily attach to the system; the exhaust temperature and wall temperature (Tw) make it difficult to evaporate the urea droplet, which produces solid deposit formations in the system. This study dealing with optical chamber and commercial SCR system from 3L diesel engine and 12L diesel engine. The optical chamber can observe the gas distribution and spray pattern as can’t show in the commercial SCR system; this study was investigate the effects of urea injection timing on prediction NOx conversion in SCR system; the effects of urea injection strategy on solid deposit formation; the analysis of ammonia uniformity to forecast NOx conversion efficiency; and the analysis of different types of urea injectors in an SCR system. 19 gas sensors on the catalyst surface were used to validate the presence of ammonia gas in this study; NOx conversion values from a gas analyzer were used to evaluate the effectiveness of the mixing process between ammonia gas and NOx emission. These evidence shows to improve NOx conversion efficiency in an SCR system, it is necessary to optimize important factors such as temperature, gas flow, wall material, urea injection distribution, urea evaporation, ammonia gas distribution and mixing process as shown in this study.