When two fossil fuels are better than one.

When two fossil fuels are better than one.

Hybrids are a common sight on America’s roads these days. While some models are likely more green-washing than green policy, the principle of hybridization is easy to understand. Have two fuel options available in the same car to the strengths of one compensates for the weaknesses of another. In the standard petroleum-electric hybrids, like the Prius or Volt, the car gains some part of its propulsive energy from electricity, which is highly efficient and GHG friendly. When the batteries are depleted, the conventional engine takes over, burning gasoline or diesel, which is very energy-dense and can be refueled quickly.

Recently, several car makers are hoping to extend this model to vehicles that use two different fossil fuels, gasoline and natural gas. Natural gas burns much cleaner than gasoline, in terms of both GHGs and air pollutants. Like electricity, however, it is bulky to store and because of the pressures it’s stored at, refueling can often be slow. As the attahced Green Car Congress article explains, a new hybrid concept seeks to incorporate both fuels into one vehicle. The same internal combustion engine can be used for both, with the car sensing which fuel is in use at a given time and adjusting its combustion parameters accordingly. Natural gas refueling would take place either at home, using a small compressor to slowly push gas from municipal pipelines into the tank, or at CNG fueling stations. Most models are predicted to have 50-75 miles of range, which is more than enough to cover the average daily commute for most drivers. For those who find themselves on longer journeys without a CNG station available, the car would carry a few gallons of gasoline to give a total range comparable to today’s gasoline vehicles.

Natural gas is a complicated subject for transportation and energy policy experts. On one hand, it is usually less GHG intensive than gasoline or diesel. On the other hand, it is still a fossil fuel and it may be impossible to meet long-term reduction targets if natural gas is the dominant fuel. 

Is a short term GHG benefit worth committing to an infrastructure that, in the long term, is only slightly less unsustainable than the gasoline one we’re trying to replace right now? I would argue a heavily qualified yes, for two reasons. First, there has been precious little political will to engage in any meaningful GHG reductions, in the U.S. as well as abroad. Natural gas may be able to make its own way into the marketplace based on cost, policy makers should probably save their political capital for other, more important battles. Second: we are increasingly improving our understanding about the mechanisms of climate change. One thing that is quite apparent it that a ton of carbon dioxide emission avoided today makes a  bigger impact than a ton avoided five years from now. Natural gas is poised to make small, but significant reductions in GHG emissions in the immediate future, whereas future GHG reductions have a history of being more smoke than fire. If we can actually attain meaningful reductions in the short term, we should do so.


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