Dynamic Characteristics of a Urea SCR Systemfor NOx Reduction in Diesel Engine

Abstract

This paper discusses dynamic characteristics of a ureaSCR (Selective Catalytic Reduction) system. The urea flow rate to improve NOx conversion efficiency is generally determined by parameters such as catalyst temperature and space velocity. The ureaSCR system was tested in the various engine operating conditions governing the raw NOx emission levels, space velocity, and SCR catalyst temperature. These experiments include coldtransients to determine catalyst lightoff temperature and urea flow rate transients. Likewise, ammonia storage dynamics was also investigated.The coldtransient results indicate the lightoff temperature of the catalysts used in these experiments was 200220°C. The ammonia storage and urea flow rate transients all indicate very slow dynamics (on the order of seconds), which presents control challenges for mobile applications. The results presented in this paper should provide an excellent starting point in developing a functional invehicle ureaSCR system.