Simulation-Based Evaluation of Electronic Energy Storage Devices in Buses for Reducing Emissions

Emerging concerns about emissions and increasing energy costs have led to interest in developing and applying electronic devices for energy storage (popularly known as flywheel batteries or simply flywheels) in transportation applications to recover the energy used in braking rather than dissipating it as heat. Each time a vehicle stops, its kinetic energy is dissipated as heat. Fuel is then used to accelerate the vehicle again. A flywheel energy storage device that stores the braking energy and then reuses it for acceleration has the potential to improve fuel economy and reduce pollution. It is important to evaluate the application of this technology in transit buses to assess better any need for increased development. A three-step computer simulation is used to evaluate the reduced emissions of carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxides (NO_x) in a flywheel-equipped bus. First, drive cycles over which buses operate are specified. Second, because flywheel energy storage reduces the effects of acceleration and deceleration to the engine, the emissions models (which are sensitive to acceleration and deceleration modes) are identified and selected. Finally, emissions are computed and compared with emissions for a bus without a flywheel. Results indicate conceptually that the flywheel application reduces acceleration effects, which in turn significantly reduce emissions. It is therefore strongly recommended that the flywheel energy storage device be further researched for transportation applications.