Comparison between Bio-ethanol and gasoline

In November 2010 I visited Brazil and was interested to see their use of Bio-ethanol as a fuel for transport. I was amazed to see ethanol fuel pumps at all the petrol stations and to see so many flexi-fuel vehicles driving around (Flexi-fuel vehicles are able to run on both gasoline and fuel ethanol at varying mixtures depending on the particular flex engine in the motor car). For me this was very interesting as here at home in South Africa we have only the option of running our cars on Diesel and gasoline/petrol.

So how does fuel ethanol (bio-ethanol) compare to gasoline? Well Bio-ethanol has a higher octane number, broader flammability limits, higher flame speeds and higher heats of vaporisation than gasoline. These properties allow for a higher compression ratio, shorter burn time, and an engine which burns much leaner. These all suggest that ethanol should be better than gasoline in an internal combustion engine (Balat M. et al, 2007)

Disadvantages of bioethanol include its lower energy density than gasoline (Bioethanol has 66% the energy of gasoline), its corrosiveness, low flame luminosity, low vapor pressure (which makes cold starts difficult), miscibility with water, and toxicity to ecosystems (Balat M., et al, 2007)

So what did the locals have to say about ethanol as a fuel? Well I met many people in Brazil who use ethanol in their cars and for them the major drawcard is that it is much cheaper to purchase than gasoline. Although on the down side many of them said that their cars did not perform as well on ethanol as on gasoline. They found that there cars consumed slightly more fuel per 100km and that there was sligthly less power available for acceleration when they used ethanol instead of gasoline.

So the question for me as to whether I would use ethanol over gasoline based on the above thoughts above is one that requires some more thought. I think I would most definately use ethanol based on the fact that it is much cheaper and it is theoretically better for my cars engine. I think most people would be prepared to sacrifice a lower petrol consumption and less power because of this but my main concern with the use of Bio-ethanol would be whether it is a more sustainable fuel than gasoline. But since sustainability is another entire question I will leave that for another post.


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