The Future for Ethanol

 
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Non-ideal Combustion

Because it contains oxygen, ethanol can help ensure the complete combustion of other compounds in a fuel mix - the combustion equations given are very much the ideal situation, and a fair amount of hydrocarbon may end up as 'half-burned' products - chief among these are the polyaromatic hydrocarbons, which are implicated in carcinogenesis (causing cancer). As you can see, the compounds shown below have clearly lost a lot of hydrogen to get where they are, but have plenty of carbon that could still combust.

        
Chrysene and buckminster fullerene, two polyaromatic compounds that have been found in the emissions from petrol engines.

Besides these carbon compounds, incomplete burning also generates a lot of carbon monoxide (CO). Though not a greenhouse gas, this is a toxic and nasty compound that is a major cause of air-pollution related malaise in urban centres. Providing oxygen within the fuel in the form of an oxygen-containing compound can greatly reduce the amount of CO produced.

Methyl tertiary butyl ether (MTBE) was introduced to reduce emissions from automobile fuel in the 1980s, but has since achieved notoreity as a groundwater contaminant. Ethanol is a simple, non-toxic, and economical replacement fuel additive.


The fuel additive methyl tertiary butyl ether (MTBE)