Devices of this type include: Broquet, Fitch Fuel Catalyst, Prozone, Fuelcat, Enviromax Plus, Vitalizer, Firepower, PICC, Euro FuelSaver

A vast array of usually tin-based products, either dropped in the tank or fitted in the fuel line, claim to improve the fuel quality and so improve power and economy. (NB This page is about "fit and forget" devices; for information on products to be added at every tank fill, see the fuel additives page.)

Some of these products claim to allow the use of unleaded petrol in leaded-only engines. That is largely outside the scope of this site, but it is worth noting that this is quite a difficult claim to prove through purely anecdotal evidence, since many "leaded-only" engines would in any case survive running on unleaded fuel providing they were only ever driven gently (which could be the case with a cherished classic).

Turning away from this issue, there are two basic questions to be answered:
a) Can a tin-based catalyst affect fuel properties?
b) Can such a change give a significiant fuel economy improvement?

For the first question, an important point to note is that tin is not generally regarded as an efficient catalyst for hydrocarbons. The "catalytic cracking" systems in oil refineries often cited by makers of these devices in fact use Zeolites, composed mostly of aluminium and silicon. The catalytic converters in vehicle exhausts use platinum, rhodium and palladium. Tin is not a major consituent of either type of product - although some prominent "mainstream" companies have proposed fuel catalysts where tin is present to some extent.

The mechanisms by which tin catalysts are claimed to work are quite varied, and include both claims to alter the basic properties of the fuel before it enters the engine, and claims to alter the combustion process due to the presence of microscopic particles of tin / tin compounds in the fuel. It is true that at least some makers of such devices do have data that appears to show changes in fuel properties, either by conventional analytical techniques such as mass spectroscopy or other tests such as thermal stability, and there is also a plausible mechanism whereby tin catalysts could reduce bacterial growth in fuel (various compounds of tin beinq quite toxic). What is considerably less clear to me is whether these changes are significant, or indeed beneficial, to engine operation.

The basic problem is that modern engines are optimised around the combustion of "normal" fuel and changes to the fuel properties and/or combustion process, even if theoretically beneficial, are unlikely to give significant fuel economy benefits unless the engine design and/or engine management system settings are adjusted to suit. An obvious example would be speeding up the burn - while this may have some benefit under at least some conditions, it is essential to retard the spark (petrol) or injection (diesel) timing to keep the central part of the burn occuring at the optimum time. Without this retard (which is very unlikely to occur automatically, even on the most advanced car / light truck engines) the result is likely to be worse fuel economy or even engine damage. It is also surprising that not one maker of such products, so far as I can tell, has been willing to back up claims of a faster burn with the relatively cheap and simple tests needed to actually measure burn rate and show that it has changed. Likewise, increasing octane rating of petrol (gasoline) can in theory improve performance, but only on the few engines that can take advantage of this.

The mechanism by which catalytic devices often claim to work is by converting long-chain fuel molecules to short-chain ones. It is of course true that petrol and diesel consist of many different molecules, ranging from large ones such as octane (C₈H₁₈) to small ones such as butane (C₄H₁₀). Longer molecules can in theory be broken down into shorter ones, though this process normally requires heat and pressure, as well as the presence of a catalyst. But even if the fuel "saving" device does break the molecules down, this does not automatically imply improved fuel consumption or emissions.

Firstly, the precise blend of components of modern petrol (and indeed diesel) is quite carefully "tuned" to match the requirements of the engine. This even involves selling different petrol in summer and winter to compensate for differing temperatures! The proportion of the fuel that evaporates at different temperatures (the "boiling curve") is determined by the blend of high boiling point (long-chain) components and low boiling point (short-chain) components. If the proportions are altered, then the boiling characteristics of the fuel will change. The likely effects are either poor cold starting or poor hot starting, with increased emissions in each case.

Secondly, short-chain molecules do not generally produce significantly more energy when burnt. The calorific values of most hydrocarbon fuels are around 44 - 46 MJ/kg, with smaller molecules producing only slightly more energy than larger ones. Claims that smaller molecules burn "better", "more completely", or "more energetically" are not supported by experimental data (consider, for example, the fuel economy of LPG vehicles).

General claims of making the burn "more complete" should also be considered with some scepticism, since only about one or two percent of the injected fuel escapes unburnt from the engine (because it was trapped in the head gasket crevice, for example). The other 99% is totally broken down into smaller molecules, and then combined with oxygen to form water, carbon dioxide and carbon monoxide. Essentially all the chemical energy in the fuel is released as heat. How can the burning be any "better" than this?

Where a "more complete" burn might genuinely give benefit is in the reduction of toxic pollutants, especially diesel smoke. Increasing the percentage fuel burnt from 98 to 99% gives an almost immeasurable improvement in economy, but halves the emissions of HC / CO / smoke (all of which are partially or totally unburnt fuel). The production of diesel smoke / soot in particular involves some highly complex reactions, and a mechanism that enhances the conversion of soot particles to CO2 could give a worthwhile reduction in exhaust smoke. The fact that various metallic compounds are used to promote soot-burn off in some diesel particle filters gives some credence to this theory, and some makers of tin-based fuel catalysts have apparently robust data to support smoke reduction in certain applications.

Various products also claim a cleaning effect.

Some commentators claim that the various catalysts work very well in theory, but the evil oil companies specifically add products to their fuel to "disable" them. Even if true (which would be easy enough to prove by carrying out scientific tests on the product using an alternative fuel), you have to ask why these catalytic products are not simply sold in other countries where the fuel blend is different.

In conclusion, it seems that there is reasonable evidence to conclude that at least some tin-based catalysts do affect fuel, and it is not implausible that some beneficial changes - most notably diesel soot reduction - occur as a result. There is even some evidence of very modest (no more than 5%) fuel economy benefit on at least some engines under at least some conditions - while the evidence so far has not been entirely robust, an improvement of this size is just about within the range of what might seem plausible given the changes described above.

There is, however, also plenty of evidence for complete lack of effectiveness. For example, when the Fitch Fuel Catalyst was tested in February 2008 by the Australian motoring organisation, the NRMA, essentially no benefit in either emissions or fuel consumption was found on the two petrol (gasoline) vehicles tested. Supporters of this technology claim that the tests were flawed in some way - either due to incorrect installation, or insufficient "conditioning period" between installing the device and performing the test. While this cannot be disproved, the negative results still represent a significant challenge to the makers of such devices.

Interestingly, certain makers of both catalyst and magnet-based fuel "saving" devices claim that they were used by the RAF during World War 2. Amazing that the British armed forces should have found not one, but two, miraculous fuel-saving devices; even more amazing that they have apparently now "lost" both of them. (Since getting fuel to the front line is a major logistical problem, the armed forces are more interested in fuel consumption than you might think.) A sceptic might wonder how much truth there is in either claim.

Use in other applications: my field of expertise is engines for cars and light trucks, and that is the central subject of this Web site. Many people claim benefits from their "fuel catalysts" in very different applications such as large marine engines and industrial burners; I remain sceptical of these claims, but cannot comment definitively on them as I have little experience with such applications, and there are significant differences to car / light truck engines.

(NB AdBlue is a quite genuine additive that will be used to enhance catalytic reduction of NOx emissions on many future diesel trucks. Negative comments on this site regarding fuel additives and "catalysts" do not in any way refer to AdBlue, which is only of use on engines specifically designed for it.)

Please also read the general comments on fuel "saving" devices, if you have not done so already

If you found this page helpful, you may like to support my work. If you think I have made a mistake, or am talking complete nonsense, please take a moment to read the Response to Critics before saying so in public (on discussion Forums and the like).