do fuel additives work?

Most aftermarket fuel additives are not cost-effective. There are various other pills, tablets, magnets, filters, etc. that all claim to improve either fuel economy or performance. Some of these have perfectly sound scientific mechanisms, unfortunately they are not cost-effective. Some do not even have sound scientific mechanisms. Because the same model production vehicles can vary significantly, it's expensive to unambiguously demonstrate these additives are not cost-effective. If you wish to try them, remember the biggest gain is likely to be caused by the lower mass of your wallet/purse.There is one aftermarket additive that may be cost-effective, the lubricity additive used with unleaded gasolines to combat exhaust valve seat recessionon engines that do not have seat inserts. This additive may be routinely added during the first few years of unleaded by the gasoline producers, but in the US this could not occur because they did not have EPA waivers. The amount of recession is very dependent on the engine design and driving style. The long-term solution is to install inserts, or have the seats hardened, at the next top overhaul. Some other fuel additives work, especially those that are carefully formulated into the gasoline by the manufacturer at the refinery, and have often been subjected to decades-long evaluation and use. A typical gasoline may contain:

* Oil-soluble Dye, initially added to leaded gasoline at about 10 ppm to prevent its misuse as an industrial solvent, and now also used to identify grades of product.

* Antioxidants, typically phenylene diamines or hindered phenols, are added to prevent oxidation of unsaturated hydrocarbons.

* Metal Deactivators, typically about 10ppm of chelating agent such as N,N'-disalicylidene-1,2-propanediamine is added to inhibit copper,which can rapidly catalyze oxidation of unsaturated hydrocarbons.

* Corrosion Inhibitors, about 5ppm of oil-soluble surfactants are added to prevent corrosion caused either by water condensing from cooling,water-saturated gasoline, or from condensation from air onto the walls of almost-empty gasoline tanks that drop below the dew point.

* Anti-icing Additives, used mainly with carburetted cars, and usually either a surfactant, alcohol or glycol.

* Anti-wear Additives, these are used to control wear in the upper cylinder and piston ring area that the gasoline contacts, and are usuallyvery light hydrocarbon oils. Phosphorus additives can also be used on engines without exhaust catalyst systems.

* Deposit-modifying Additives, usually surfactants.

1. Carburettor Deposits, additives to prevent these were required when crankcase blow-by (PCV) and exhaust gas recirculation (EGR) controls were introduced. Some fuel components reacted with these gas streams to form deposits on the throat and throttle plate of carburettors.

2. Fuel Injector tips operate about 100C, and deposits form in the annulus during hot soak, mainly from the oxidation and polymerisation of the larger unsaturated hydrocarbons. The additives that preventand unclog these tips are usually polybutene succinimides or polyether amines.

3. Intake Valve Deposits caused major problems in the mid-1980s when some engines had reduced driveability when fully warmed, even though the amount of deposit was below previously acceptable limits. It isbelieved that the new fuels and engine designs were producing a more absorbent deposit that grabbed some passing fuel vapour, causing lean hesitation. Intake valves operate about 300C, and if the valve is kept wet, deposits tend not to form, thus intermittent injectors tend to promote deposits. Oil leaking through the valve guides can be either harmful or beneficial, depending on the type and quantity.Gasoline factors implicated in these deposits include unsaturates andalcohols. Additives to prevent these deposits contain a detergent and/or dispersant in a higher molecular weight solvent or light oil whose low volatility keeps the valve surface wetted.

4. Combustion Chamber Deposits have been targeted in the 1990s, as they are responsible for significant increases in emissions. Recent detergent-dispersant additives have the ability to function in both the liquid and vapour phases to remove existing deposits that have resulted from the use of other additives, and prevent deposit formation.

* Octane Enhancers, these are usually formulated blends of alkyl lead or MMT compounds in a solvent such as toluene, and added at the 100-1000 ppm levels. They have been replaced by hydrocarbons with higher octanes such as aromatics and olefins. These hydrocarbons are now being replaced by a mixture of saturated hydrocarbons and oxygenates.
Fuel Addatives