Premium – Regular & the Octane Story Part 3

Following on from part 2 of “Premium – Regular and the Octane Story, this section will discuss ethanol in fuel.

Gasoline blended with ethanol is now available in many countries, most notably Brazil where the minimum ethanol content in all fuel is 25%.  In most other parts of the world using ethanol blends is still a choice although it’s not always made clear whether some fuels are blended or not.

In the majority of cases, modern fuel injected European bikes and scooters are able to run on ethanol blended fuel but at a volume of no more than 10% (E10).  In some cases ratios higher than this (more ethanol) are approved by some manufacturers however this should be confirmed for your particular bike or scooter before using fuel above 10% ethanol.

Whatever the environmental and/or strategic advantages or disadvantages there are in the use of ethanol blended fuel, from a technical point of view there are no advantages at all unless an engine has been specifically designed to use it.

While blending with ethanol effectively increases the octane rating of standard gasoline, it also decreases the over-all energy content.  Performance and fuel economy are therefore also decreased.  An ethanol blended fuel with an octane rating of 98 will return lower performance and fuel economy than an unblended premium gasoline with an octane rating of 98.

The following points should be considered with regard to ethanol blended fuel:

1.     The energy content of pure ethanol is around 20 MJ/l (Megajoules per Litre) compared to straight gasoline which has about 34 MJ/l .  This means that ethanol produces over 30% less energy per unit than gasoline and therefore will give lower performance than gasoline when compared in the same engine.

2.     Total fuel consumption is higher when using ethanol blended fuel compared to gasoline in the same engine due to the reason given in point 1 above.

3.     Ethanol has a higher octane rating than regular or standard gasoline however engines can only take advantage of this if they are designed or modified to suit.

4.     Ethanol is hygroscopic which means that it will absorb moisture from air which contaminates the fuel and can then cause phase separation meaning that the ethanol can split off from the gasoline, evaporate at a different rate thereby seriously compromising the remaining fuel.

5.     Over time ethanol can attack and corrode fuel system components including plastics and aluminium and can also cause fuel system blockage.  For this reason and the one in point 4 above, use of ethanol blends is particularly unsuited to bikes and scooters as they often sit for long periods between use.