Fuel Additives

by TSOC Webmaster - 14:46 on 17 November 2009

Reproduced in full from the FBHVC Website of which the TSOC is a member in compliance with their Copyright rules

ETHANOL IN PETROL
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 car owners to blends containing ethanol is increasingly likely as time goes on.

At concentrations of less than 5% there is no obligation for the petrol pumps to be labelled at point of sale, so petrol on sale can be 0% - 5% ethanol.

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 cars, i.e. zinc, brass, copper, lead-coated steel. On this basis, the type of car 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. 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. Any tank sealant manufactured in USA should not be affected by ethanol (e.g. the Frost brand) as ethanol has been in USA petrol for some time. To be sure of avoiding problems customers should check that any such product does indicate it can be used with fuel containing ethanol.

A solvent is available to remove existing tank sealant, Epoxy Remover made by Tank Cure. However the active ingredient in this product is methylene chloride, aka paint stripper, which unfortunately is the subject of a proposed EU ban.

Many seals have a ‘memory’ and may leak when introduced to ethanol when they are old. The same type of seal may not leak when new.

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.

The Effect on Specific Gravity of Blending Ethanol into Petrol
Petrol metering systems in general are affected by the specific gravity of the fuel, and we have been asked this question in connection with autovacs. Devices which employ a float as part of the mechanism to control either the pumping or metering of fuel are likely to be affected by changes in its specific gravity, or density.
Ethanol added to petrol is usually about 96% pure ethanol and 4% water. The density of pure ethanol is 0.789kg/litre. Allowing for the presence of 4% water (SG 1.0; density 1kg/litre) will increase the density of the fuel ethanol to 0.797kg/litre.

Petrol in the UK is sold under the BS EN 228 specification which permits the density of the fuel to lie anywhere between 0.720 and 0.775kg/litre. This flexibility is necessary because petrol is not a single substance but is made up of many different hydrocarbons, depending on crude oil source and the configuration of the refinery producing the fuel. Density may also alter during the year as a result of blending changes needed to produce fuels of different volatility for winter and summer for example. There is thus a considerable range of fuel density, but in practice most petrol will have a density lying in the range 0.735 to 0.76kg/litre. For the purposes of this simple analysis, a value of 0.745kg/litre will be assumed.

Adding 5% of ethanol by volume (5.35% by mass) to petrol will raise the density of the blend by a small amount, i.e. about 0.4% from 0.745kg/litre to 0.748kg/litre. This change is clearly well within the normal range of variation in density which is permitted by the EN 228 specification, and in truth is unlikely to make any significant difference to the operation of fuel metering or pumping systems.

Where more ethanol is added to the blend, for example 10% or 20%, changes in the density of the fuel will be more noticeable, increasing linearly in proportion to the added ethanol, although such changes are still relatively small. However, at these higher blends, other aspects, for example fuel volatility, or effects on the materials of construction of the fuel system, are likely to have a more noticeable effect on operation than fuel density changes.

Additives

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