Comparison of solid ammonium SCR system and urea SCR system in a 2.5L diesel engine
Sangho Lee, Korea Institute of Machinery & Materials
Solid ammonium SCR system has been investigated to reduce NOx emission from diesel engine. Solid ammoniums such as ammonium carbamate and ammonium carbonate have 2~3 times higher ammonia storage density than 32.5% urea solution. The solid ammoniums are decomposed into ammonia gas before injection. The ammonia gas injection is helpful to mixing and NOx reduction at low temperature. The solid ammonium SCR system is developed to control generation and dosing rates of ammonia gas. The solid SCR system consists of reactor, heater, dosing module and controller. Compact dosing module is developed including sensors, a regulator and an injector. Heating time and energy are reduced by the compact dosing module. Ammonium carbamate is used as an ammonia carrier. 6 bar of reactor pressure and over 100°C of dosing module temperature are required to inject ammonia and prevent solidification. At cold start, the reactor pressure and the dosing module temperature are reached within 180s. Decomposition rate of ammonium carbamate is measured depending on electrical power input. The solid SCR system is tested using a 2.5L engine at European stationary cycle (ESC). NOx conversions of the solid ammonium SCR system and urea SCR system are compared. The solid ammonium SCR system is also tested when SCR catalyst temperature is under 200°C. Urea injection is unavailable under 200°C because of solid deposit formation. The low temperature operation of SCR system could reduce NOx emission during urban driving.