Detection of Injected Urea Quantity and Correction for SCR Urea Dosing Control

Using urea-based Selected Catalytic Reduction (SCR) systems is an effective way in diesel engine after-treatment systems to meet increasingly stringent emission regulations. The amount of urea injection is critical to achieve high NOx reduction efficiency and low ammonia slip and overdosing or under-dosing of urea injection need to be avoided. One of the difficulties in urea injection amount control lies in the accurate measurement/estimation of the urea injection mass. To effectively address this issue, this paper defined a correction factor for under-dosing or overdosing detection and correction and proposed two methods to identify the correction factor. The first method is based on urea pump model and line pressure. Through frequency analysis, the relation between the urea pump speed and power spectrum characteristics of the line pressure by using FFT method was revealed. The urea pump frequency is extracted from the frequency analysis of the line pressure and used for detecting the urea injection and identifying the correction factor. Second method is based on the effective voltage of the Motor. The relation between urea injection and effective voltage of the Motor was revealed based on the motor dynamic model. The effective voltage of the Motor is used to detect the urea injection and identify the correction factor. The effectiveness of both proposed detection and correction methods are experimentally validated through the urea dosing system.