Numerical Simulation Research On The Lean-NO_x-Trap Of Lean Burn Gasoline Engine Based On The Stuttgart Principle

With the growing seriousness of the energy crisis and environmental pollution, a lot attention has been paid on the lean burn gasoline engine for its advantage on fuel economy and low emission level. However, the NO_x emission has been a key factor that’s hindering the development of the lean burn engine. Lean NO_x trap（LNT） provides an effective aftertreatment solution for the NO_x emission control of the lean burn engine. In this paper, a model based on Stuttgart principle was built to accurately simulate the working process of the LNT. The simulation results was achieved from the analysis of NO_x adsorption and desorption process considering particle model、channel model and LNT integral model. The influence of the storage ability、space velocity of the inlet boundary and reducing agent on the performance of LNT was researched, which will provide theoretical basis for the practical application of LNT.The influence of the storage ability of storage material inside the LNT on the performance of LNT was studied. The result shows that, the improvement of storage ability will have a positive impact on the efficiency of LNT. The consequence of different gas space velocity in the inlet boundary of LNT was also researched in this paper. The result shows that the conversion efficiency will decrease when increasing the gas space velocity and the ash core depth would penetrate deeper, the penetrate level will increase along the axial direction of LNT. This research provides a theoretical basis for the matching process of the LNT to a lean burn engine, the storage ability and the gas space velocity in the inlet boundary of LNT should be taken into consideration to achieve the best NO_x control.The reduction effect of three classical reduction agent（H₂,CO,C₃H₆） was also explored and the regeneration capacity during continuous working cycles was further analyzed. The results show that H₂ has the best reducing ability, followed by CO, and C₃H₆ to be the worst. The LNT is able to work continuously with H₂ and CO as reduction agents while C₃H₆ will lead to an incomplete regeneration process and influence the efficiency of LNT. Further research indicates that water vapor has a positive effect on the reduction ability of CO, because the NO_x breakthrough can be decreased during the switch. By increasing the concentration of water vapor in the exhaust gas, the overall conversion efficiency of LNT will be significantly improved.