Fuel Reforming and Catalyst Deactivation Investigated in Real Exhaust Environment 2019-01-0315
Increased in-cylinder hydrogen levels have been shown to improve burn durations, combustion stability, HC emissions and knock resistance which can directly translate into enhanced engine efficiency. Along with in-cylinder enrichment strategies, hardware modification, or fuel chemistry changes, external fuel reformation can also be used to increase the hydrogen yield. During the High-Efficiency, Dilute Gasoline Engine (HEDGE) consortium at Southwest Research Institute (SwRI), the potential of increased hydrogen production in a dedicated-exhaust gas recirculation (D-EGR) engine was evaluated exploiting the water gas shift (WGS) and steam reformation (SR) reactions. It was found that neither approach could produce sustained hydrogen enrichment in a real exhaust environment.
Platinum group metal (PGM) and Ni WGS catalysts were tested with a focus on hydrogen production and catalyst durability. A periodic lean-rich switching strategy was utilized to decrease coking. Although 4% additional hydrogen was initially produced in the EGR stream, leading to improvements in the coefficient of variation (CoV) and brake specific fuel consumption (BSFC), catalyst activity decreased within a few hours regardless of the regeneration strategy employed, even with temperatures above 500 °C. The lean-rich switching proved effective but not sufficient to remove coke under the tested conditions.
SR is an endothermic process that utilizes heat and water in the exhaust stream, along with additionally injected hydrocarbons, to produce carbon monoxide and hydrogen. It consumes waste thermal energy that would otherwise be rejected through the EGR cooler. A small amount of hydrogen was produced in the EGR stream via the WGS reaction but not the SR reaction. Similar to the WGS catalyst testing, the SR catalyst deactivated quickly due to coking. While neither of these approaches displayed acceptable long-term performance, the exhaust environment still poses a significant opportunity for the production of hydrogen rich reformate to deliver improvement in engine efficiency.
Gordon Bartley, Raphael Gukelberger, Robert Henderson, Cary Henry
Bartley Consulting LLC, Southwest Research Institute