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

Recent research has focused on engine combustion technology as well as application of after-treatment in order to comply with emission regulation. However, it is much more efficient way to control emissions from engine itself and furthermore research on engine control will provide the direction of after-treatment technology in future. Furthermore, emission standard regulation for passenger diesel vehicles has been stringent compared to others and nano-particles will be included in EURO6 regulation in Europe and similar emission standard will be introduced in Korea. A 3.0-liter high-speed diesel engine equipped with by CRDI system of 160 MPa injection pressure, and an intake/exhaust system of V type 6-cylinder turbo-intercooler was applied. The conditions of fuel spray and combustion were investigated by setting up an ETAS system which is a similar condition to the engine dynamometer test.

The selective catalytic reduction system has been known well so far in the reduction of NOx emission in diesel vehicles. On the other hand ammonia slip from SCR reactors must be avoided in the process of catalytic conversion. This research focused to investigate optimal urea injection conditions for urea-SCR system using visualization techniques and evaluate the performance of urea-SCR system in a heavy-duty diesel engine. The parametric study was made on gas temperatures, SVs (space velocity) and ARs (aspect ratio). The urea injector was located at the opposite direction of exhaust gases emitted to an exhaust duct. An optimal quantity of urea and conversion efficient at each mode of ND-13 mode was estimated. Furthermore, NOx emission and applied amounts of urea was investigated with respect to driving modes under the condition of with/without SCR, This research may provide fundamentals for the practical use of urea-SCR in future.