Emissions Testing of a Hybrid Fuel Cell Bus

The fuel cell bus program at Georgetown University (GU) has directed the operational development and testing of three hybrid fuel cell powered buses for transit operation. These are the world's first liquid-fueled, fuel cell powered road vehicles. This paper describes the emissions testing of one of these buses on a heavy duty chassis dynamometer at West Virginia University (WVU). The tested bus was driven by a 120 kW DC motor and utilized a 50 kW phosphoric acid fuel cell (PAFC) as an energy source with a 100 kW battery for supplemental power. A methanol/water fuel mixture was converted by a steam reformer to a hydrogen rich gas mixture for use in a fuel cell stack. Emissions from the reformer, fuel cell stack and startup burner were monitored for both transient and steady-state operation. It was concluded that this first-generation fuel cell bus offers an attractive approach to reducing emissions of particulate matter (PM), oxides of nitrogen (NO_x), hydrocarbons (HC) and carbon dioxide (CO₂) relative to conventional drivetrain transit buses operating on both diesel and alternative fuels. Carbon monoxide (CO) emissions were similar to existing alternative fuel buses, and further analysis revealed the cause of this unexpected result was linked to the flow of methanol into the reformer burner. Alternative operating strategies are being incorporated into the next generation fuel cell buses resulting in greatly reduced carbon monoxide emissions.