System and method to calculate concentration of diesel exhaust fluid (def)

Abstract

A system to calculate concentration of diesel exhaust fluid (DEF) in an exhaust of an engine is disclosed. The system includes a selective catalytic reduction (SCR) module, a diesel exhaust fluid (DEF) module, a first NOx sensor, a second NOx sensor, and a control module. The SCR module is adapted to receive exhaust gas. The diesel exhaust fluid (DEF) module introduces the diesel exhaust fluid (DEF) into the exhaust and is upstream of the SCR module. The first NOx sensor is in fluid communication with exhaust to detect a first NOx value of the exhaust gas at a location upstream of the SCR module. The second NOx sensor is in fluid communication with exhaust to detect a second NOx value of the exhaust gas at a location downstream of the SCR module. The control module is in communication with the first NOx sensor, the SCR module, and the second NOx sensor to calculate a numeric value of the concentration of the diesel exhaust fluid (DEF) based on a conversion ratio. The conversion ratio is calculated according to a NOx differential between the first NOx sensor and the second NOx sensor relative to a predicted NOx differential for a given amount of DEF injected.

What is claimed is: 
     
         1 . A system to calculate concentration of diesel exhaust fluid (DEF) in an exhaust of an engine, the system comprising:
 a selective catalytic reduction (SCR) module adapted to receive exhaust gas;   a diesel exhaust fluid (DEF) module for introducing the diesel exhaust fluid (DEF) into the exhaust, upstream of the SCR module;   a first NOx sensor in fluid communication with exhaust to detect a first NOx value of the exhaust gas at a location upstream of the SCR module;   a second NOx sensor in fluid communication with exhaust to detect a second NOx value of the exhaust gas at a location downstream of the SCR module; and   a control module in communication with the first NOx sensor, the SCR module, and the second NOx sensor, the control module calculates a numeric value of the concentration of the diesel exhaust fluid (DEF) based on a conversion ratio;   wherein the conversion ratio is calculated according to a NOx differential between the first NOx sensor and the second NOx sensor relative to a predicted NOx differential for a given amount of DEF injected.