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Use of Ethanol in petrol

Petrol pump filling nozzleSome concerns have been raised recently about the use of ethyl alcohol, or ethanol, in petrol.  The product added to petrol may also be called bio-ethanol to link its use with non-fossil derived or renewable buo-fuels.  Bio-ethanol has been used at times over the decades, but its recent use is linked to EU directives to increase the proportion of automotive fuel derived from renewable sources, in order to reduce carbon dioxide (CO2) emissions.

Ethanol has been blended into petrol in recent years by, among others, Tesco, who use it in their premium 99 octane unleaded petrol blend.  Ethanol has a very high octane quality, and so is a valuable blending component for use in the production of high octane unleaded petrol.  Its use in this application is limited to 5% volume and is acknowledged by a label on the pump according to the Tesco help line, although this may not always be the case.  Although the EU is believed to be considering the mandatory use of bio-ethanol in petrol in the future, at present it is to be hoped that classic vehicle owners would not encounter the blended product without some form of pump marking.  If any owners have concerns over using petrol containing 5% ethanol, it would be useful to check fuel before purchase by inspecting pump labels.

Concerns expressed have centred on possible water contamination, degradation of plastic and rubber seals and possible negative effects on foams used in racing tanks to prevent fuel fires and explosions.  The position on these issues is not straightforward and is still being investigated in order to establish an accurate understanding.  Also, as the proportion of ethanol in the blend is increased, so any difficulties are more likely to become apparent.

Although the 5% ethanol blend can give higher octane quality, volatility is also likely to be higher for this blend of fuel.  Some owners are already troubled by driving problems associated with high volatility (vapour lock, fuel starvation, bad hot starting etc. in hot weather), so using a 5% ethanol blend could make such problems worse.

The following report gives a more detailed picture of the likely effects of the use of ethanol-petrol blend fuel.

Aspects of the use of petrol containing ethanol - Based on a recently published public domain document, CONCAWE Report number 3/08

Fuel volatility

Blending small amounts of ethanol (up to 5%) into petrol does produce a measurable increase in volatility. Oil companies must ensure that fuel volatility meets specified limits (EN 228) so petrol containing ethanol will be adjusted to this specification. However, if fuel containing ethanol is mixed in the vehicle tank with purely hydrocarbon fuel an increase in the volatility of the blend in the tank can result. This may produce unwelcome symptoms of poor hot starting, erratic running including running too rich, or too lean, associated with excessive fuel volatility. The FBHVC caters for a wide range of vehicle ages, and it is highly probable that some will be less able to cope with an unintended increase in fuel volatility, and also some time-related deterioration in performance of cooling systems.  Unfortunately, it seems that not all fuel containing up to 5% ethanol is labelled as such, so the scenario of mixing two types of fuel in the vehicle tank is a realistic one, with a significant probability that driving difficulties may result. Volatility related problems have been discussed before, and there are a number of often fairly simple remedies.

Octane quality

The addition of 5% ethanol increases petrol octane quality by about one octane number.  For this reason high octane unleaded petrol (nominally 98 Research Octane Number or RON) is more likely to contain ethanol than the normal 95 RON standard or ‘Premium’ product.  Refiners do not like giving quality away, so if ethanol is added to the standard product, the blend may be adjusted so that octane quality remains at 95 RON.  Those owners of high performance cars originally requiring high octane five star petrol are more likely to buy 98 RON unleaded, so they are more likely to encounter blends containing ethanol.  However, given the high octane quality of ethanol, and the EU-driven enthusiasm for bio-fuel inclusion, use of ethanol in the normal 95 RON unleaded petrol cannot be ruled out.  Exposure of the majority of historic vehicle owners to blends containing ethanol is increasingly likely as time goes on.

Effects on fuel system metals

Briefly, the presence of ethanol in petrol increases the risk of corrosion of metallic fuel system materials.  This difficulty is recognised from long experience, and effective corrosion inhibitors have been developed.  Responsible fuel retailers should employ a suitable additive to protect their customers’ treasured possessions, but this may not always be the case.  CONCAWE Report 3/08 gives a list of metals not recommended for use with petrol containing ethanol which reads like a metal who’s who for vintage and classic vehicles, i.e.  zinc, brass, copper, lead-coated steel.  On this basis, the type of vehicle favoured by those represented by the FBHVC could have problems in the petrol tank, fuel pipe, carburettor and most fittings.  Modern vehicles have tended to maximise the use of engineering plastics, so will have less of a problem.  However, to avoid sounding too gloomy, it should be remembered that corrosion inhibitor additives are usually very effective in providing protection, and if the products used by the fuel retailers do not perform, a low cost after-market product may well become available for owners of vulnerable vehicles to use.  


Effects on seals, plastics and other materials

Other no-no materials mentioned by Report 3/08 are shellac, cork, nylon and GRP materials, plus various elastomer and seal materials.  Recommended materials include Viton, Fluorosilicone, neoprene and Buna-N for hoses and gaskets (but neither of these for seals).  Teflon tape is recommended in preference to alcohol based pipe and thread sealing materials.  Tank lining materials used to prevent small leaks in tanks are also in the not-recommended category for ethanol fuels.  This is consistent with a report received by the FBHVC this summer from one owner who had treated his tank with a proprietary sealing product, after which fuel containing ethanol had been used, resulting in a proverbial gooey mess.  The scale of the problem in this case led to the need to strip the fuel system.  It is not currently known whether tank sealant manufacturers are able to supply products compatible with fuels containing ethanol, but their availability would certainly be an advantage.  If such products are not available, their use is likely to decline and rather more traditional methods of tank repair, or even re-manufacture, may become a growth industry.

Effect on gums, sediments etc.

Over time all fuel handling systems tend to accumulate deposits of one kind or another in crevices and corners.  Sediments, gums, rust, lacquer and other materials fall into this category, and generally the older the fuel system the more of such material there will be.  Unfortunately fuels containing ethanol tend to loosen these deposits which then move on to plague the driver with mysterious fuel starvation problems.  There have been a number of references to such problems recently, including in cars used for racing, which arguably may be more likely to be using fuel containing ethanol through the high octane route.  Irritating though this problem must be, there is arguably a finite amount of such material in fuel systems, and thus after a certain time, which will be shortened by thorough cleaning, further use of ethanol fuels will not dislodge more sediment to block filters or jets, so hopefully this problem will fade with time.

Fire safety

Fuels containing ethanol at low levels (5-10%) behave very similarly to those not containing ethanol when burning, so safety considerations and fire-fighting techniques will be similar.  However, high ethanol content fuels have been shown to be capable of de-stabilising or collapsing foams used to fight fuel fires.  Also, pure ethanol burns with no visible flame so making fire fighting more difficult.  Alcohol resistant fire fighting foams should be used with fires in fuel containing more than 10% ethanol, but given the difficulty of knowing what sort of fuel blend is in use in certain older racing vehicles, this type of foam would be a wise choice for all racing applications.

In conclusion, there are a number of unfortunate or negative aspects to the use in older vehicles, of fuel containing even 5% ethanol.  These can be summarised as: an increased tendency to vapour lock, fuel system corrosion and random fuel starvation events from dislodged deposits.  These potential problems in general would support the view ‘if in doubt avoid’.  Unfortunately it seems increasingly clear that it will become harder and harder to do this, so that perhaps inevitably such fuels will become just another part of the picture of using a historic vehicle in today’s world.  Experience is being gained all the time, so maybe a clearer picture will emerge with use.  Historic vehicle owners should be aware of potential pitfalls, as they may be able to take precautions, or may more easily find a suitable remedy for problems which do occur.

From the Federation of British Historic Vehicle Clubs newsletters numbers. 3 & 5 - 2008.

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