Current fuel economy is based on non renewable sources usually
fossil fuel as oil or coal. Furthermore, consumption and price
of these fuels are highly increased in the past decades, for instance,
natural gas consumption has grown more than 4 times in less than
fifty years [1] and its price has been increased from 3.19 USD/
106 Btu in 1991 to 10.61 USD/106 Btu in 2011.