The well-to-wheel analysis of hydrogen enriched compressed natural gas for heavy-duty vehicles: An LCA approach for HCNG fuel cycle

Increasing urban air pollution, greenhouse gases, and declining fossil energy sources are the three major problems of transportation sector which drive the use of alternative vehicular fuels to prevent energy shortage, reduce oil dependency, and decrease tailpipe emissions including air pollutants and greenhouse gas emissions. This research work is contextual life cycle analysis of HCNG® in which 20% gaseous hydrogen blended compressed natural gas has been investigated in terms of net energy ratio, GHG value, and cost-effectiveness. A mix of various hydrogen pathways has been considered here based on data adapted from literature reviews and surveys of relevant previous work. The functional unit considered in this study is “per MJ of energy output” from the engine fueled with 0%HCNG and 20%HCNG. The pump-to-wheel has been extracted from Ma, Wang, Ding, and Jiang (2009) which is the paper published from our research team. The well-to-pump data for various hydrogen pathways with a variety of feedstocks has been gathered from literature surveys. Additionally, an engineering economic approach has been used to evaluate cost-effectiveness ratio of CNG and 20%HCNG pathways derived from fuel economy improvement. It has been shown that at pump-to-wheel stage, 7% reduction in fuel consumption can be achieved together with 11% reduction in GHGs, 7% reduction in energy consumption at operation and 7% reduction in total costs (RMB/MJ) for 20%HCNG compared with CNG. In this work, rank has been assigned for every 20%HCNG pathway based on well-to-wheel energy ratio and GHG emissions (1 means ‘best and 10 means ‘worst’) which shows that renewable based hydrogen pathways such as solar, wind and biomass showed dual benefits of lower energy consumption and lower GHG emissions whereas grid electricity-to-hydrogen displayed the worst case in both scenarios. It is also very important to visualize energy consumption by a hydrogen pathway in two perspectives: qualitative and quantitative. Usually, biomass based HCNG pathways may have higher net energy ratio, but the sources are cleaner, and renewable in nature. Net energy ratio is also affected by energy efficiency. The energy efficiency of fossil based pathways such as natural gas, coal, etc. is higher than biomass gasification pathway.