A number of technical challenges are faced when applying wall flow Diesel Particulate Filter (DPF) systems to large high horsepower off-highway applications, locomotives, and marine diesel engine applications due to the size of the DPF system required and the space constraints associated with these applications. Experimental results show that a new approach of adding an exhaust bypass valve, creating a partial-flow DPF system, can greatly reduce the DPF package size while continuing to offer significant PM emission reductions. The exhaust bypass valve is configured to open proportionally to maintain a pre-set maximum engine backpressure as the exhaust flow increases.

Proof-of-concept testing of an experimental partial flow DPF system was conducted on a 3MW, 4-stroke locomotive engine, following U.S. EPA locomotive certification test protocols. These tests showed that the experimental DPF system, which was approximately 40 percent smaller than what would be expected for this application, provided an 84 percent PM reduction over the US-EPA Switcher Cycle and 59 percent reduction over the Line-Haul Cycle. It was calculated that the system could provide a 91 percent PM reduction over the Switcher Cycle and 76 percent PM reduction over the Line-Haul Cycle with addition of a DOC in the bypass exhaust flow.

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