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Classic Engines, Modern Fuel

Comments on Topic: Petrol treatments/ additives

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Submitted by Anonymous

In the publication Classic Engines, Modern Fuel page 28 Chapter 3 ."Additives reduce the severity of oxidation , where oxygen combines with the molecules on the surface of the metals to create a metal oxide. This is most common when an acid comes into contact with a metal..."

On page 31 Chapter 3 entitled 'Ethanol blended petrol'...quote..." Unfortunately the additives sold to protect fuel systems against Ethanol give no benefit. While they will mix with the petrol, they will not mix with the ethanol/ water mixture..."

From what I have read and understand it is this ethanol/ water mixture that causes the formation of an acid which then attacks the metal surfaces.

My previous understanding was that the treatments / additives researched by the FBHVC addressed the issues of corrosion, is this not right..?

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Submitted by The Author

Unfortunately, the answer to your question is not simple. Are the treatments / additives effective? The answer is yes and no.

When dissolved in petrol, ethanol can "attack" metals in two ways. By oxidation and by galvanic corrosion. In both these cases the additives recommended by the FBHVC are effective. Simplistically, the additives consist of molecules that are like tadpoles with a head that attaches to the metal and a tail that repels the ethanol. This is how they stop the ethanol reaching the metal. These molecules are only active when dissolved in petrol.

When water gets into ethanol blended petrol, the ethanol is drawn out of the petrol into the water which becomes acidic. Unfortunately, the additive molecules are NOT soluble in water and remain in the petrol. As the acidic water drops to the bottom of the petrol tank or float chamber, it displaces the petrol, and the additive molecules. You then have an acid which is in direct contact with the metal - hence the corrosion. In this case the additives do not protect the metal.

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Submitted by JohnT


I appreciate the work you have done and published in your book. I have studied it and researched many of the questions raised. One question that I have is your statement (paraphrased) that addition of water to petrol containing ethanol will cause the ethanol to separate into a petrol phase and an ethanol/water phase, with the ethanol causing the water to be acidic. I'm unclear how the ethanol can make the water acidic. The pH of pure ethanol is 7.33 (1) and water is 7.0. Unlike inorganic compounds, ethanol is doesn't really disassociate in water, Attempts to measure the pH of ethanol/water mixtures and difficult to perform, but seem to indicate little change from neutral. (2)

Could the acidification of the water be from other additives to the petrol, which are trade secrets? Would adding water to E0 petrol also create corrosion?



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Submitted by The Author


Thanks for the comment. Firstly, the process that occurs when ethanol dissolves in water is complex. I have found a number of papers on the subject but the simplest I can find is a

It is clear from the tests that the water resulting from mixing with E10 is highly corrosive (acidic). It is possible it could be caused by other additives in the water and unfortunately, this is not something I tested - I apologies. Perhaps something for me to try when E10 is released in the UK in September. However, I do not think any additives from the petrol dissolved in the water. The test for ethanol in petrol shows that. Mixing water and petrol with ethanol, increases the volume of the water as the ethanol leaves the petrol and enters the water. With non-ethanol blended petrol, the volume of the water did not change.

Its a relatively simple test. I just put 50% water and 50% petrol in a bottle and shook it up. After it had settled (with the water in the bottom), I carefully drained off the petrol then put the metal in the remaining water, sealed the bottle and left them. Even something like nails will be OK for the metal. The only important thing is to degrease them first.


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