Development and analysis of new pneumatic based powering options for transit buses: A comparative assessment

Abstract

Carbon dioxide reduction has been the central focus of current climate change public policy and largely determines procurement of next generation ‘clean’ transit buses. Development of alternative nature-friendly systems for clean transportation is critical in the transition of the sector from conventional fossil fuel-based powertrains. The current study undertakes the design and analysis of a newly-developed hybrid pneumatic powertrain concept for fourty-foot public transit buses using liquid nitrogen and compressed natural gas as a secondary fuel. Various fuel types for system hybridization are investigated comparatively in terms of fuel economy and well-to-wheel carbon dioxide emission ratios. A pure pneumatic configuration is also considered as a base case and discussed accordingly. The performance of the proposed system is evaluated through parametric studies by considering primary design and operational parameters. In similar operational conditions, the performance of a conventional diesel bus, a plug-in hybrid electric bus, a battery-electric bus and a hydrogen fuel cell electric bus is considered in the further comparative assessment of the proposed system. From a well-to-wheel point of view, the emission ratio of the developed hybrid pneumatic system is evaluated at 0.1452 kg carbon dioxide equivalent per kilometer of city driving, which corresponds to a 95% emission reduction compared to conventional diesel buses. The present study results indicate that a hybrid pneumatic configuration carries significant potential for a green transition in the public transit sector. Furthermore, eliminating the need for charging infrastructure, grid upgrading and additional infrastructure capacity, the system can be assembled with readily available off-the-shelf components.