Vaporate is a recently introduced Australian product claiming to give up to 20% fuel economy benefits through improved fuel vaporisation. Since I have received many requests for comment on this product, I have produced this page specifically relating to Vaporate.

The theory behind Vaporate is that it heats the petrol just before it is injected into the engine, so making it evaporate more quickly. According to Vaporate it is common for 15 - 20% of the injected fuel to remain in liquid form and be ejected as unburnt hydrocarbons in the exhaust.

My general comments on vaporisation-improving devices consider most of these claims, and should be read in detail. However, here is a summary of the aspects relevant to Vaporate:

1) For most reasonably modern engines in good condition, the unburnt hydrocarbons in the exhaust are typically less than 2% of the input fuel. I therefore find it therefore difficult to understand how even completely eliminating this could improve economy by more than 2%.

2) Engines running on fuel that is fully vaporised before injection (for example LPG) do not generally give significantly improved thermal efficiency compared to petrol. To me this does not seem compatible with the idea that the petrol engine typically loses 20% efficiency due to poor vaporisation.

3) Experiments I have performed on engines to get improved fuel preparation through heating - raising the temperature of the fuel and/or air, as well as spraying the fuel onto an electrically heated surface - have never given more than a tiny improvement in economy, even when measured using highly sophisticated engine test beds.

4) It is in fact normal practice to inject the fuel at the point in the engine cycle when the inlet valve is closed ("closed-valve injection"). Rather than the fuel spray directly entering the cylinder, it is directed onto the intake port and the back of the intake valve. It evaporates from here and enters the cylinder predominantly as vapour once the intake valve opens. Since the intake port walls are at 80 celcius or thereabouts in normal running (and the intake valve significantly hotter, due to the effect of combustion gasses), it is hard for me to understand why heating the fuel in the injector to 80 celcius can be of great benefit. (The animation on Vaporate's explanation page shows the alternative "open valve injection" strategy, which is rarely used on modern engines.)

There is one condition where additional heating may be of benefit, and that is in the first few seconds immediately after a cold start. The intake port and valve are cold, and as a result the evaporation is poor and much fuel is indeed wasted. Ironically, this is exactly the condition where Vaporate can not help matters, since the intake manifold is equally cold and there can be no heat transfer to the injector...

So based on my experiences, and knowledge of other work in this field, I find it hard to believe that the benefits of Vaporate can really be as large as claimed. Of course, given sufficiently robust test data, even the most established theory must be revised, so it is useful to examine Vaporate's test results.

Vaporate typically claim fuel savings of around 15 - 20%, based on various on-road measurements. I would not for a moment suggest that these measurements are "fake" or otherwise untrue, but it is unfortunately the case that on-road measurement of fuel consumption has so many confounding factors (traffic, weather, driving style, etc) that these results prove very little. See this page for a general discussion of the the problems of on-road economy measurement.

As a result, regulatory bodies (such as the Advertising Standards Authority in the UK and the Federal Trade Commission in the USA) insist that economy improvement claims are based on rolling-road drive-cycle tests rather than on-road measurements and anecdotal / testimonial evidence. Vaporate do have some drive-cycle test results, but these only show an improvement in economy of around 6.5%. Therefore to me it seems that Vaporate should really only claim this figure as the benefit from their product. With a fitting cost of around 400 AUS$, a 6.5% saving results in a payback time of anything up to three years - which naturally makes the product seem considerably less worthwhile.

It is also worth pointing out that these results fall well short of the standards demanded by, for example, the US Environmental Protection Agency for proving the effectiveness of a fuel saving product. In particular:

• there are far too few tests to evaluate the statistical significance of the results
• there is no A-B-A test (remove the product and check economy gets worse again)
• apparently only one vehicle was tested
• no information is given as to the age and condition of the test vehicle

It is also worth mentioning that there is also a potential risk from the Vaporate system. Controlling the temperature of components in the engine bay is a major headache for car manufacturers, especially in climates as hot as Australia. As a matter of routine, all new car and engine variants are filled with thermocouples early in the development process and driven aggressively in very hot countries to make sure nothing overheats. Since the Vaporate system alters the heat transfer between the manifold and the injectors, there is obviously the potential for trouble unless each and every vehicle application is re-tested for temperature effects with the Vaporate collars fitted. Of course, the vast majority of vehicles will probably work fine, and most others may just suffer slightly worse hot starting (for example), but there is at least a chance that some vehicles may find injectors or other components degrading with time more quickly than expected due to overheating. Without comprehensive measurements, there is no way to be certain this will not happen.

NB A representative of Vaporate e-mailed me on November 6th 2005 to complain (among other matters) that the information here is "false and misleading". I immediately asked for Vaporate to identify the specific areas of concern, and offered to correct any mistakes or errors. At the time of writing, I am still waiting for Vaporate to return my email.

* Vaporate is a registered trade mark of Vaporate Pty Ltd

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).