Global warming due to emission of GHGs from transportation vehicles is an issue of great concern globally. To cut down on the emission of greenhouse gases, finding alternative to the traditional transportation fuels like diesel and petrol is a continuing process worldwide. The Government of India recommends a blend that has 5% ethanol in petrol for use in vehicles to reduce environmental pollution. The percentage of ethanol is likely to go up to 10% by 2008. Ethanol is used in alcoholic beverages and easy to manufacture from wide variety of raw materials such as sugarcane, corn, molasses, grains, fruits, etc etc. Ethanol is supposed to be cheaper and much environmentally cleaner fuel than petroleum products. Several countries, including US, Sweden, Brazil and Australia are already produce cars which run on petrol-ethanol blends. For example, 30% of vehicular fuel produced in Brazil is ethanol. Day will not be far off when vehicles will be designed to use 100% ethanol to cut down the environmental pollution. Comparatively, CNG is environmentally cleaner than diesel/petrol.
For example, it is reported that the air pollution level in Mumbai city is decreasing since almost all the taxis (over 55,000) have switched over to CNG since 2000 and more and more auto-rickshaws and BEST buses in Mumbai are now run on CNG. However, uncontrolled growth of vehicular population can deteriorate the air quality again. Indian railways, which is one of the biggest consumers of diesel has taken a lead in switching over to bio-diesel or its mix with diesel to reduce GHG emissions. Good move indeed.
Comparison of GHG emissions from some of the transportation fuels were made considering the total fuel cycle emissions for gasoline, compressed natural gas (CNG), liquefied petroleum gas (LPG) from oil and gas and ethanol from corn (ANL/DOE, USA reports). The major conclusions are:
CNG produces the lowest level of carbon dioxide emissions across the total fuel cycle, followed closely by LPG and ethanol from corn. In addition, over the entire fuel cycle, there is marginal increase in weighted GHG emissions (emissions in moles of carbon dioxide per vehicle mile traveled x global warming potential per mole relative to carbon dioxide) if one switches from gasoline (10.71) to ethanol (13.88). It was also concluded that ethanol from corn produces the largest nitrous oxide emissions across the total fuel cycle.
Thus, it can be concluded that except that it is cheaper, from the consideration of global warming, contribution from ethanol is reported to be higher than gasoline. In fact, use of LPG (8.61) and CNG (9.03) contribute less as compared to ethanol (13.88) to the global warming. Then, why ethanol mix? Any answers?
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