Examining alternative fuel options and potential emission reductions from changes in public transport bus fleet in Ireland

Abstract

Shifting to alternative fuel options, such as bio-CNG, electricity powered buses in public transit play an important role in reducing the environmental impacts of fossil fuels. Ireland’s target is to reduce its greenhouse gas (GHG) levels by 30% in 2030,relative to its2005 levels (European commission, 2017),which are expected to increase by 14%(EPA, 2017). Public transport offers a wider scope to reduce emission levels on a large scale. While alternative fuel options are successfully being used by other countries, public transport bus fleet in Ireland is almost entirely dependent of fossil fuels. Thus, this paper aims to study the current emission levels resulting from the major public transport bus services (Dublin Bus and Bus Éireann) operating in Ireland and the potential of emission reductions from use of alternative fuel and technologies that are available for buses. Three popular alternative fuel options, CNG (compressed natural gas), bio-CNG and electric buses were evaluated in terms of their potential to reduce emission levels. Additionally, possible emissions reductions from bus fleet renewed with euro 6 buses and enhanced environmental vehicles (EEV) were calculated. It has been found that only by renewing the fleet with diesel fueled euro 6 compliant buses, the CO2(carbon dioxide)emissions can be reduced by 5%.Also, if urban bus trips are replaced by electric buses,CO2emission levels can be reduced by more than 90%. Total energy consumptions in these scenarios were calculated and land area required for grass silage to fulfil the feed stock demand for bio-CNG were calculated based on diesel energy density. Additionally, cost savings due to reduction in emission levels with the use of these fuel options were also presented. The land area required for grass silage to meet the annual biogas demand for public transport bus operation was estimated to be 21091 hectares (ha).