Study On Response Characteristics Of Diesel Urea SCR System

Stricter emission legislation for diesel vehicles will make exhaust after-treatment mandatory in the near future. Since its perfect effectiveness in reducing NOX and fuel efficiency, Urea-SCR has been chosen for NOX reduction on trucks and busses. In a diesel Urea-SCR system, with additional injection of urea solution and catalyzing from catalyst coated on carriers, it can reduce NOX to harmless N2.The objective of this research is how to elevate the NOX conversion efficiency, with study on response characteristics of SCR and analyze the key response steps, this work reveals the factors which affect the conversion efficiency of the system. The main contents of this paper are expressed as follows.（1） The principle and time scales on working processes of the SCR system are studied. The relevant theory and mathematical models are studied. Primary study are focused on Multiple response reaction kinetics and adsorption response on surface of catalyst.（2） A one-dimensional model is set up to describe the performance of an ideal SCR monolithic reactor. With addition of reaction rate equation, dependence of NO conversion efficiency on temperature, space velocity and different NH₃/NO rate are studied. Meanwhile, dependence of NOx conversion efficiency on temperature, space velocity, reducing agent, diesel quality, particulate matter are studied by experiments.（3） The effect of reactive temperature and space velocity on storage-release characteristics of NH₃ is investigated on dynamic reaction model of SCR catalytic reaction.（4） Non-uniform catalyst models are set up, considering of reaction kinetics model and surface reaction mechanism, conversion efficiency of axial and radial non-uniform catalyst is studied. This type of catalyst could improve the conversion efficiency of the catalytic converter and the flow field distribution in monolith.