Total Life Cycle Analysis of CNG and Hydrogen Enriched CNG Powered Vehicles : A Comparative Evaluation

Vehicles consume energy and release harmful emissions throughout their life period from the manufacturing stage of raw materials to the vehicle scrapyard. Current Green-House Gas (GHG) emissions with gasoline and diesel vehicles are reported to be 164 gCO2/km and 156 gCO2/km respectively. Thus, enormous researches are carried out for low-carbon alternatives replacing conventional gasoline and diesel vehicles to reduce GHG emissions. The continuous research on hydrogen as a transportation fuel has demonstrated the potential of reduced vehicular emissions compared to conventional fuels. Life cycle assessment (LCA) is a comprehensive technique used to estimate the overall environmental impact of vehicles. In this present work, a comparative LCA is conducted between Compressed Natural gas (CNG) powered vehicles and H-CNG powered vehicles. Also sustainable indicators such as Net Energy Ratio, Fossil Energy Ratio are evaluated for the test cases. The impact of the two alternative vehicles is assessed from various points in their lifetime using the GREET model software. The analysis is done in two stages namely, well to pump and pump to the wheel. The obtained results of the preliminary analysis reveal that the H-CNG fuel exhibits a favorable reduction in CO emissions by 64%, CO2 emissions by 43%, and SOX emissions by 28%. It is also found that there is no significant reduction in NOX emissions. Further, economic indicators such as Benefit-to-cost ratio, cost per liter of the fuel are evaluated and the same is compared between the two alternatives. The H-CNG refueling sites are equipped with on-site small scale reformers for producing hydrogen, which is blended with CNG and then pressurized on-site for vehicle fueling. The proposed H-CNG production process is cheaper than the conventional physical blending process and thus paving way for the potential usage of H-CNG fuel. Keywords: Life Cycle Assessment, Compressed Natural gas, Hydrogen enriched CNG, sustainable parameters, economic analysis.