Study: Well-to-wheels emissions for CNG vehicles lower than diesel hybrids, fuel cell vehicles

In a paper published in the journal Biofuels, Bioproducts and Biorefining, Joshua Gifford, a Master's student in mechanical engineering at Iowa State University (ISU), along with Robert C. Brown, director of ISU's center for sustainable environmental technologies, propose the evaluation of four metrics in well-to-wheels (WTW) analysis of automotive vehicles – primary energy consumption, greenhouse gas (GHG) emissions, water usage and cost of vehicle operation. As Gifford and Brown explain:

Life cycle analysis for automotive transportation, commonly known as well-to-wheels analysis, has traditionally focused on GHG emissions and primary energy consumption. Clearly, economizing on the use of primary energy sources and the amount of GHG emissions associated with automotive transportation are important sustainability metrics. Other important metrics are water usage and cost of vehicle operation.

No scenario is likely to simultaneously minimize all four metrics, suggesting the identification of a single figure of merit that encompasses all four economies of transportation fuels. We employed a normalization scheme that allowed calculation of a single composite score for each scenario called the CWEG (Cost-Water-Energy-GHG) score. Automotive transportation scenarios evaluated in this paper include a variety of fossil and renewable primary energy sources; several energy carriers as transportation fuels; and three distinct vehicle platforms including internal combustion engines, battery electric vehicles, and fuel cell electric vehicles.

Okay, with that complex explanation out of the way, here's what Gifford and Brown discovered: compressed natural gas vehicles dominated the eco-standings, with CWEG scores ranging from 71 to 74 out of a possible 100. Diesel-electric vehicles (aka hybrids) scored 45 out of 100. Meanwhile, fuel cell vehicles, running on hydrogen generated by using power from the U.S.' electric grid, had the lowest CWEG scores, ranging from 13 to 15. The article costs money to access, and the abstract doesn't tell us what the score for BEVs was. Kudos to Gifford and Brown for including water – a vital substance if there ever was one – in their analysis.

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[Source: Green Car Congress]