Assessing Cleaner Energy Alternatives for Bus Transit in Rio de Janeiro: A Life Cycle Inventory Analysis

Abstract

From 2003 to 2009 in Brazilian municipalities of over 60,000 inhabitants, buses accounted for more than 25% of urban trips. This trend is not expected to change in the medium term. Worldwide, buses rely on petroleum diesel as fuel. In Brazil, alternative fuels such as biodiesel, natural gas and ethanol are available and the choice among them should depend on the assessment of the entire life cycle of such fuels. This paper uses a Life Cycle Inventory, which is essential to the implementation of a Life Cycle Assessment, to assess six energy alternatives: petroleum diesel, biodiesel, petroleum diesel with 5% of biodiesel, compressed natural gas, additivated hydrous ethanol and dual-fuel system composed by petroleum diesel with 5% of biodiesel and compressed natural gas. In saving total energy consumption, pure petroleum diesel or mixed with 5% biodiesel and dual-fuel systems stand out, in that order. If renewable energy use and net carbon dioxide emissions reduction are the goals, ethanol and biodiesel should be given preference. The addition of 5% of biodiesel in petroleum diesel increases the share of renewable energy in the supply chain of petroleum diesel by 47.5% with an increase of 0.58% in total energy consumption and a reduction of 3.8% in net CO2 emissions during the life cycle. In the case of biodiesel, the addition of 5% of biodiesel in petroleum diesel increases the share of renewable energy in the supply chain by 51.15% with an increase of 0.03% in the total energy consumption and a decrease of 7% in net CO2 emissions in the life cycle. The use of 5% of biodiesel in petroleum diesel does not significantly affect the use of renewable energy (+0.69%) or total energy consumption (+0.04%) in ethanol supply chain, which already shows a great use of renewable energy input. However, a decrease of 9.29% in the net CO2 emissions in the supply chain occurs, which reaches 5.28% in the life cycle.