Experimental Study Of Conversion Efficiency And Ammonia Storage In Selective Catalytic Reduction System For Diesel Engines

As the diesel engine emission regulation has become more and more strict recently, the emission after-treatment has been the necessary method for diesel engine to meet the emission regulation. Most pollutants in diesel engine emission are nitrogen oxides(NOX) and particulate matter(PM). Urea SCR is considered to be one of the emission after-treatments for the medium and heavy duty diesel vehicles to reduce NOX emission because of its advantages in many aspects. Urea SCR gains high NOX conversion efficiency and can improve fuel economy indirectly. The reductant of urea SCR is safe and cheap, and the demand of sulfur in the fuel is not high for the catalyst. It has become the focus of research for the universities and enterprises at home and abroad.It is always the target for SCR urea injection control strategies to improve NOX conversion rate and reduce ammonia slip in the process of diesel engine operation. In this paper a method to monitor the ammonia slip downstream of the catalytic converter using the ammonia cross-sensitivity of the NOX sensor is proposed. The urea SCR reaction characteristics and ammonia storage characteristics of catalytic converter are investigated on engine test bench by the SCR system that the injection quantity can be controlled independently and the preliminary SCR urea injection control strategies on steady working condition have been designed. The research contents conclude that:(1) A ammonia slip monitoring system is designed and arranged downstream of SCR catalytic converter based on the ammonia cross-sensitivity of the NOX sensor. The influences of NH3/NOX on NOX conversion efficiency and ammonia slip are analyzed. The ammonia slip monitoring system is proved to be feasible.(2) The influences of catalytic converter temperature and space velocity on the NOX conversion efficiency and the reaction rate, as well as the influences of the distance between the nozzle and catalytic converter on the NOX conversion efficiency are investigated on engine test bench by the SCR system.(3) The influences of catalytic converter temperature and space velocity on ammonia slip and ammonia storage along with the influences of ammonia accumulated storage on NOX real-time conversion efficiency are investigated using the ammonia slip monitoring system.(4) The preliminary SCR urea injection control strategies on steady working condition are designed and the NOX emission tests are done on both original engine and engine with SCR system. The NOX emission is reduced on each working condition, especially on the catalyst activity temperature range, the average of NOX conversion efficiency can reach 75%.