Reverse-Flow Oxidation Catalyst with Supplemental Fuel Injection for Lean-Burn Natural Gas Engines

The purpose of this research is to demonstrate that the use of a reverse-flow oxidation catalyst reactor (RFOCR), both with and without supplemental fuel injection (SFI), will result in significant reductions of methane (CH4) in a simulated lean-burn natural gas exhaust mixture. Methane reduction is investigated as a function of the directional duration of the exhaust gases through the oxidation catalyst, gas hourly space velocity (GHSV), and exhaust gas temperature. The CH4 catalytic chemical reaction, at an elevated exhaust gas temperature, is an exothermic reaction and elevating the temperature across the catalyst reactor corresponds to an increase in CH4 conversion. Periodically reversing the inlet and outlet exhaust direction through the catalyst traps the heat released from the chemical reaction, raising the overall temperature of the exhaust gas through the RFOCR. This study demonstrates the ability of the RFOCR to trap heat, thereby increasing CH4 oxidation. This ability to trap heat provides a significant advantage over standard unidirectional flow catalytic converters. Additionally, to increase CH4 conversion at relatively low feed temperatures, the injection of a supplemental fuel mixture consisting of carbon monoxide (CO) and hydrogen (H2) was evaluated.

The experimental results confirm that, when compared with unidirectional flow, periodically reversing the flow of exhaust mixture through a catalyst reactor can significantly improve CH4 conversion. Results also indicate that the effect of switching time (ST) on CH4 conversion vary significantly with gas hourly space velocity (GHSV) and temperature. Furthermore, results indicate that by introducing supplemental fuel into the feed mixture at low engine operating conditions CH4 conversion is notably improved by elevating the temperature across the catalyst reactor through the combustion of carbon monoxide and hydrogen. However, extended durations of increased CH4 conversion during reverse-flow operations is not possible after supplemental fuel injection is terminated.