| If the premise is accepted that natural gas (and thus methane) will have an increasingly important role as an energy source in the future, then methane must become the chief energy source for the transportation sector. It is also necessary to consider the opportunities for increasingly efficient and low polluting technologies which may arise in the transportation sector. Six candidate pathways are proposed. These involve the energy currencies methanol, methane and hydrogen and the vehicular energy conversion technologies spark ignition engines and solid polymer fuel cells. The energy conversion processes in each pathway are analyzed from two perspectives based on the second law of thermodynamics: efficiency and emission exergy. The theory of exergy analysis is reviewed, and consideration is given to the use of emission exergy as an indicator of potential for environmental impact. All results are normalized based on the energy service transportation, which is defined as one kilometer of city driving. Hydrogen and fuel cell pathways are found to be optimal using these optics. |
