Public service fleets offer an attractive option for introducing new renewable fuels and alternative technologies on a large scale, which allow forthe reduction of both greenhouse gas emissions and exhaust air pollutants. This study examines the use of biomethane, or upgraded biogas, for part of the bus fleet in Dublin. The emissions produced from the 2008 fleet based at one of the cities seven depots were compared to use of new diesel and biomethane buses, which were modeled using COPERT 4. The optimum feedstock for biomethane production in Ireland was then investigated, as well as the quantity of feedstock needed to produce the required biomethane to fuel the bus fleet examined. The merits of producing biomethane in Ireland were analyzed in order to determine the best policy. As expected the results showed a substantial decrease in all exhaust emissions from the use of biomethane buses compared the 2008 fleet. Grass silage was chosen as the optimum feedstock for production of biomethane in Ireland, and it was calculated using a sensitivity analysis that 1,349 ha is the land take needed toproduce the grass silage for biomethane required to run the bus fleet examined.
Abstract