A hybrid life cycle assessment of public transportation buses with alternative fuel options

Abstract

Purpose Alternative fuel options are gaining popularity in the vehicle market. Adopting alternative fuel options for public transportation compared to passenger vehicles contributes exponentially to reductions in transportation-related environmental impacts. Therefore, this study aims to present total air pollutant emissions and water withdrawal impacts through the lifetime of a transit bus with different fuel options. Methods In consideration of market share and future development trends, diesel, biodiesel, compressed natural gas (CNG), liquefied natural gas (LNG), hybrid (diesel-electric), and battery electric (BE) transit buses are analyzed with an inputoutput (IO)-based hybrid life cycle assessment (LCA) model. In order to accommodate the sensitivity of total impacts to fuel economy, three commonly used driving cycles are considered: Manhattan, Central Business District (CBD), and Orange County Transit Authority (OCTA). Fuel economy for each of these driving cycles varies over the year with other impacts, so a normal distribution of fuel economy is developed with a Monte Carlo simulation model for each driving cycle and corresponding fuel type. Results and discussion Impacts from a solar panel (photovoltaic, PV) charging scenario and different grid mix scenarios are evaluated and compared to the nation's average grid mix impacts from energy generation to accommodate the lifetime electricity needs for the BE transit bus. From these results, it was found that the BE transit bus causes significantly low CO 2 emissions than diesel and other alternative fuel options, while some of the driving cycles of the hybrid-powered transit bus cause comparable emissions to BE transit bus. On the other hand, lifetime water withdrawal impacts of the diesel and hybrid options are more feasible compared to other options, since electricity generation and natural gas manufacturing are both heavily dependent on water withdrawal. In addition, the North American Electricity Reliability Corporation's (NERC) regional electricity grid mix impacts on CO 2 emissions and water withdrawal are presented for the BE transit bus.Conclusions As an addition of current literature, LCA of alternative fuel options was performed in this paper for transit buses with the consideration of a wide variety of environmental indicators. Although the results indicate that BE and hybrid-powered buses have less environmental emissions, the US's dependency on fossil fuel for electricity generation continues to yield significant lifetime impacts on BE transit bus operation. With respect to water withdrawal impacts, we believe that the adoption of BE transit buses will be faster and more environmentally feasible for some NREC regions than for others.

Petroleum substitution, greenhouse gas emissions reduction and environmental benefits from the development of natural gas vehicles in China

“…For the LNG HDT application type, the value of the net GHG reduction rate (NGRR) in this study is 8%, a positive result similar to that obtained in other studies on China and other countries (Arteconi et al 2010;Tu et al 2013b). For the LNG bus application type, the result in this study is 7%, a more pessimistic result than that of other studies specific to China but similar to the findings of studies from other countries (Beer et al 2002;Ercan and Tatari 2015;Lin et al 2015). For the CNG LDT application type, the result of this study is 10.4%, which is a more pessimistic result than that obtained for Canada (Shahraeeni et al 2015).…”

“…For the CNG LDT application type, the result of this study is 10.4%, which is a more pessimistic result than that obtained for Canada (Shahraeeni et al 2015). For the CNG bus application type, all studies (including this study) have similar positive results (Beer et al 2002;Ercan and Tatari 2015;Fang 2009;Wang 2015;Xu et al 2015). For the CNG PV application type, the studies specific to China (including this study) have similar NGRR figures, but they have a more optimistic result than that found for (Curran et al 2014;Fang 2009;Wang 2015).…”

“…Differences between life-cycle energy use and GHG emissions results among studies of NGVs in China and other countries are largely due to (1) the difference in the adopted fuel consumption rate, including the impact of different application types and tonnage types. For example, a study by Tu et al (2013b) evaluated the life-cycle emissions of GHGs and other pollutants from NG-powered concrete-mixer trucks, a typical type of truck (Cai et al 2017;Hao et al 2015;Song et al 2017;Tu et al 2013b); (2) differences in the energy consumption and GHG emissions produced in the process of fuel acquisition, particularly for widely used industry boilers largely fuelled by coal, which have an low efficiency compared with the global level (Cai et al 2017;Ou et al 2010;Wang 2015); and (3) different operating environments (Ercan and Tatari 2015;Lajunen and Lipman 2016;Lin et al 2015). …”

On the Front Lines of a Sustainable Transportation Fleet: Applications of Vehicle-to-Grid Technology for Transit and School Buses

“…In addition to the use phase of buses, some of other LCA phases are excluded from this study such as manufacturing and end-of-life. Since two different fuel options are considered for two different types of buses, use phase impacts are distinct for the comparison of these bus type combinations and even though the fuel types are different, manufacturing impacts can be assumed similar due to identical body (shell) types for buses [23,30]. Moreover, this research emphasizes on V2G application for transit and school buses, which is affecting the use phase related impacts.…”

“…Ercan and Tatari [30] Diesel, hybrid, BE, biodiesel, Compressed Natural Gas (CNG), and Liquefied Natural Gas (LNG) fuel options of transit buses in terms of their lifetime environmental emissions and water withdrawal impacts with the consideration of regional electricity generation mixes.…”