Devices of this type include: PVI, Gasaver, CTech 3000, FuelSaverDevice

All modern petrol cars are fitted with catalytic converters, which contain small amounts of the precious metals platinum, rhodium and palladium. These metals act on the exhaust gases and promote conversion of toxic chemicals such as unburnt hydrocarbons to more benign substances such as water and carbon dioxide.

Various companies have noted this technology and devised systems to deliver small quantities of platinum (and other metals) to the engine along with the intake air, the theory being that the catalysts will also act in the combustion chamber to promote faster and more complete burning. The typical claim is that around 20% of the intake fuel is not burnt in the engine, but escapes and is burnt in the catalytic converter where it just produces useless heat. By adding the platinum to the combustion mix, supposedly this unburnt fuel fraction is greatly reduced.

In principle there is some sense to this. Some respected research institutions have investigated catalytically coated pistons which aim to act in the same way to reduce unburnt hydrocarbons. However in practice this technology is - like all other fuel "saving" devices I have investigated - deeply flawed.

The first and most fundamental point is that the unburnt fuel fraction in a modern engine under typical operating conditions is far less than 20% - around 2% is much more usual. That is to say, only one fiftieth of the injected fuel escapes unburnt from the engine. The remaining 98 - 99% is completely broken down into smaller molecules and burnt to form carbon dioxide and water. So even if the device could significantly reduce this unburnt fuel fraction, the overall fuel saving would be extremely small.

If it really were true that around 20% of the fuel was being burnt in the catalytic converter, you would expect the gas emerging from the cat to be much hotter than that entering. I have worked on dozens of vehicles equipped with "pre-cat" and "post-cat" thermocouples, and have never seen a significant temperature rise except under fault conditions such as a misfire. Indeed, if you turn off ignition to one cylinder of a V8 engine (so that 12% of the fuel is burnt in the catalyst) then the heat release is so great that the catalyst would be quickly destroyed when the engine is at full power. To suggest that 20% is burnt in the catalyst under normal conditions is just not true.

The second point is that any true catalytic influence on the combustion must cause it to speed up. That is the definition of a catalyst, and is also the only plausible means by which the burn could be made more complete. However, the ignition timing on any engine is carefully optimised to suit the burn rate of the fuel/air mix. If the burn rate is altered, then the ignition timing must be altered to suit - yet no makers of platinum combustion enhancers suggest changing ignition settings.

An interesting aside is that all the systems I have seen advertised use engine manifold vacuum to draw the platinum solution into the engine. This means that the larger the vacuum, the more platinum is injected. However, the air flow into the engine is smallest at high vacuum, and largest when there is no vacuum at all (wide open throttle). So the amount of platinum added to the engine is inversely proportional to the amount of fuel and air taken in! At very light loads the platinum fraction is relatively high, at full load there is none at all. One might then wonder how the device can function optimally under all conditions. (A correspondent pointed out to me that using the vacuum between the air filter and the throttle would solve this problem - which it would, but it would also introduce other problems.)

The proof of such devices is, of course, in the test results. As usual, makers of platinum combustion enhancers quote many apparently impressive customer testimonials and on-road fuel economy results, but these do not represent any sort of proof (see general comments here). However, the "original" platinum-based fuel "saving" device - the "PVI" system - has however been scientifically evaluated by the US Environmental Protection Agency - here is their report (pdf format). The conclusion was that the device had no significant effect on either economy or emissions. Following this testing, the company was fined $75,000 in 2002 for making false claims (and subsequently lost their 2004 appeal as well.) The Canadian Broadcasting Corporation also ran an excellent story on the "PVI" system in 2002, which makes for interesting reading.

The apparently very similar "Ctech 3000" in the UK was also heavily criticised by the Advertising Standards Authority in July 2005.

Does this prove that all platinum combustion enhancement fuel "saving" devices are worthless? No, but since they all seem to be broadly similar in operation and claims, it does strongly point in that direction.

NB Since the devices usually also pass air into the inlet manifold, you may see effects similar to air-bleed devices - which may include reductions in HC and CO emissions at idle on older cars. These apparent emissions reductions do not, however, imply that the device is operating in the claimed manner.

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.)