Abstract
Urea-SCR system is currently regarded as promising NOx reduction technology for diesel engines. SCR system has to achieve maximal NOx conversion in combination with minimal NH3 slip. In this study, model based open loop control for urea injection was developed and assessed in the European Transient Cycle (ETC) for heavy duty diesel engine. On the basis of the transient modeling, the kinetic parameters of the NH3 adsorption and desorption are calibrated with the experimental results performed over the zeolite based catalyst. NH3 storage or surface coverage of SCR catalyst can not be measured directly and has to be calculated, which is taken into account as a control parameter in this model. In order to reduce NH3 slip while maintaining NOx reduction, NH3 storage control algorithm was applied to correct the basic urea quantity. If the actual NH3 surface coverage is higher than the maximal NH3 surface coverage, the urea injection quantity is significantly reduced in the ETC cycle. By applying this logic, the resulting NH3 slip peak can be avoided effectively. With optimizing the kinetic parameters based on standard SCR reaction, it suggests that a simplified, less accurate model can be effective to evaluate the capability of model based control in the ETC cycle.
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