Alcohol Fuels

Methanol and Ethanol

Methanol and Ethanol both have advantages and disadvantages over fossil fuels, such as petrol and diesel. For instance, both alcohols can run at a much higher compression ratio without octane-boosting additives (ethanol's octane rating is 129 (RON), equal to 102 (MON) or 116 (AKI), with methanol at 123 (RON) as opposed to approximately 91 (RON), 81 (MON), 86 (AKI) for ordinary European petrol; note that American 'regular-grade gasoline' is about 1 point higher on all 3 scales, but still offers very similar performance.) Alcohols burn more completely because their molecules contain oxygen; carbon monoxide emissions are 100% lower than fossil-fueled engines because the only products of an alcohol combustion reaction are carbon dioxide, water, and heat. Despite this reduction in carbon monoxide, alcohol releases as much or more carbon dioxide than its gasoline counterpart (though this carbon dioxide has previously been drawn from the air in biologically-produced ethanol, so there is no net modern release, as there is for fossil fuels). There are also lower NOx emissions, as ethanol needs more energy to vaporise than petrol - so it draws more heat out of the air in a cylinder than petrol, having a greater cooling effect, which reduces the opportunity for nitrogen and oxygen in the cylinder (as air) to fuse into poisonous nitrogen oxides.

However, ethanol is degrading to some plastic or rubber parts of fuel delivery systems designed to use petrol, and has 37% less energy per litre than petrol. Methanol is even more corrosive and its energy per liter is 55% lower than that of petrol. High compression ratios and corrosion-resistant materials can overcome these issues, but require extensive engine modification. The sort of compression- and corrosion-resistant materials needed to run an engine on ethanol or methanol tend to be expensive compounds, such as stainless steel.