Greenhouse Gas Emissions with Alternative Fuels

Fossil fuels currently supply about 80% of all primary energy and are expected to remain fundamental to global energy supply for at least the next 20 to 30 years. . Presently, it is estimated that power generation accounts for about 40% and surface transport contributes nearly 20% of global CO₂ emissions.
The Kyoto Protocol signed in December 1997 commits the industrialized countries to legally binding reductions in emissions of greenhouse gases by 2008-2012. Strategy to achieve reduction in CO₂ emissions from transport sector involves essentially the following:

• Reduction in fuel consumption of vehicles.
• Increased use of low carbon alternative fuels and bio fuels.

European Union countries   have introduced CO₂ emission regulations for the automobiles. A voluntary target of 140 g/km average CO₂ emissions for new car sales to be met in 2008 was set that had to be relaxed.  By the year 2012, a goal of 130 g/km of CO₂ to be achieved by engine and vehicle technology, and further reduction to 120g/km by use of renewable fuels has been set by European Union.

 When comparing different fuel and power plant alternatives, life cycle CO₂ equivalent GHG emissions are to be considered. It should account for CO₂ and other GHG emissions generated during production, transportation and use in the vehicles. Lifecycle CO₂ emissions for liquid petroleum fuels, LPG, natural gas and biodiesel for heavy vehicle application are compared in Fig 8.8. The CO₂ emissions yielded during fuel production and during fuel utilization stage in engines are shown separately. Among the alternative fuels, natural gas having lower carbon content in the fuel molecule has advantage over gasoline and diesel fuels as far as CO₂ emissions are concerned. From natural gas vehicles, the greenhouse effect of the fugitive methane emissions as a result of leakage from the transportation and distribution systems is also to be accounted for as methane is nearly 20 times more potent than CO₂ in causing global warming. LPG lies in between the natural gas and liquid petroleum fuels. The bio fuels such as ethanol and biodiesel have much lower lifecycle CO₂ emissions as the carbon dioxide produced on their combustion would be the same that has been fixed from atmosphere during growth of the agriculture crops. These fuels do contribute to net CO₂ emissions resulting from manufacture of fertilizers and other ingredients used for crops and, during processing of these fuels and making them suitable for use in the engines.