Particle Free Exhaust Gas Recirculation by Molecular Diffusion: Proof of Concept

This work included design and fabrication of a particle free exhaust gas recirculation element (PF-EGR-E) that included two concentric tubes, one for a clean air stream and the other for a simulated exhaust stream. The inner tube was a perforated tube to allow molecular diffusion between the two streams. The design and dimension of the PF-EGR-E was guided with the help of theoretical prediction of gas and particle diffusion. The goal was to build a PF-EGR-E that retains particles in a dilute exhaust stream while allowing maximum molecular exchange with the air stream. The performance of the PF-EGR-E was investigated using dilute diesel engine exhaust and clean air flowing in parallel at different flow and temperature levels. Measurements of NO_X, CO₂, and particle concentration at inlet and exit of the perforated tube demonstrated that it was possible to achieve high molecular transfer between a dilute exhaust stream and clean air stream while particle transfer was still at minimum level.

This work proofed the concept of achieving particle free EGR with a single perforated tube using molecular and particle diffusion principles. The next step will be to demonstrate this concept in a prototype system to be used on a diesel engine.