Fuel efficiency comparisons of advanced transit buses using fuel cell and engine hybrid electric drivelines

The attention of air quality regulators has been increasingly on the emissions from transit buses, especially particulate emissions from diesel engines. As a result, there has been considerable R&D effort on the development of diesel hybrid-electric and fuel cell powered transit buses. Fuel cell buses using both hydrogen and methanol with a reformer as the fuel are being developed. In addition, a number of transit agencies have purchased large numbers of compressed natural gas (CNG) fueled buses that are in regular revenue service. The relative emissions and fuel efficiency of transit buses using these various driveline technologies and fuels are of considerable interest and uncertainty. These topics are explored in this paper based on data from dynamometer tests of diesel and CNG fueled conventional and diesel hybrid electric buses and simulations of engine-generator and fuel cell powered buses. The computer simulation results are validated using available data for hybrid electric buses, including the direct hydrogen fuel cell bus that was in revenue service in Chicago