A Study on the Urea-Water Solution Dosing Strategy by NO/NO _X Ratio of DeNO _X SCR System

In this study, SCR system is employed to selectively reduce NO_X that is a major cause of environmental pollution from diesel engines. In particular, this paper focuses on urea injection strategies dependent on NO/ NO_X ratio. An injection control algorithm is developed based on the chemical ratio between the amount of engine out NO_X data obtained from Engine Management System (EMS) and the amount of NH₃. Therefore, in order to decide the amount of injection quantity, the NO/NO_X ratio from the engine out NO_X should be considered in order to minimize NH₃ slip while maximizing NO_X reduction.

Experiments are conducted with a 2.2-liter diesel engine for passenger vehicles with Diesel Oxidation Catalyst (DOC) and Diesel Particle Filter (DPF). Real time control, using Pulse Width Modulation (PWM) duty ratio for dosing module and supply module, is performed by real time computer with its injection control algorithm developed in the Matlab Simulink environment. By analyzing the NO_X emission measurement the performance of the proposed injection strategy algorithm is verified.