Spray Modeling for Lean NO _x Trap Aftertreatment System Design 2009-28-0016

Diesel engine exhaust has been an area of research since the early 80's because of their harmful nature. The upcoming EPA regulations require substantial reductions in NO_x and Particulate Matter (PM) and an aftertreatment system will likely be needed to meet these regulatory emissions levels. A more advanced technology in Aftertreatment system uses in-line fuel reformer to convert injected diesel fuel to hydrogen-rich reformates. It is used as the rich component for regenerating the Lean NO_x Trap (LNT). The LNT regeneration process produces ammonia (NH3) that enables further NO_x reduction in a downstream Selective Catalytic Reduction (SCR). A Diesel Particulate Filter (DPF) provides PM reduction capability in the system. The high conversion efficiency of regeneration cycle demands complete vaporization and uniform distribution of the injected fuel. Computational Fluid Dynamics simulation is effective in optimizing geometrical parameters to achieve the above requirements.

This paper discusses simulations carried out to guide the experimental setup, compare fuel injection systems and to optimize the location and the orientation of mixing elements. The results obtained were qualitatively validated with test data. An innovative technique has been implemented in FLUENT 6.3 to model the spray formation to overcome the detailed modeling of the injector. This technique takes input from experimental spray distribution data. The system parameters such as mixing elements, dozer location, fluid properties and dozer types were optimized. However, in order to reduce the dependency on the experiment, separate study is also carried out to simulate the injection phenomena that include internal flow of the injector and spray characteristic as well. This simulation manifests the underlying complex spray physics and predicts the spray parameters. The methodology that has been developed during these studies can be leveraged for investigation of droplet distribution, mixing flow and phase transformation