mga peeps, full article at this link.
Fuel saving - a professional engineer's view
Fuel "saving" gadgets I have worked in the car industry for over fifteen years, everything from development of novel fuel-efficient engines to mapping of production vehicles. In that time I've seen dozens if not hundreds of supposed "fuel saving devices" advertised. Without exception, I advise you not to buy them!
Over and over again, a company starts selling a "miracle" fuel-saving product, which of course is supposedly revolutionary and different to every other product that's been offered in the past;
over and over again, the product turns out to be bogus and buyers lose thousands (or even millions) of pounds / dollars. To the best of my knowledge,
no "add-on" fuel economy device or product has ever demonstrated worthwhile savings, yet new ones are always being introduced to the market, and uninformed customers are easily taken in by the claims and marketing "hype".
I have no involvement with any of the companies selling these fuel "saving" devices, nor do I get any benefit if people don't buy them. But I'm an honest sort of guy who doesn't like to see people get ripped off, and felt it was time to explain the engineering truth behind the claims. I also object to the fact that some of these devices make emissions worse, which obviously is bad for people's health. Finally, as a car industry engineer, I resent the implication that my colleagues and I are "too stupid" to see the benefits of these fantastic planet-saving gizmos!
I haven't tested every one of them personally, but the physical processes they claim to use are well understood and I have sound practical and theoretical knowledge to go on. Anybody who doubts my views can find a mountain of supporting evidence in the technical literature, based on work by the many thousands of expert reserchers in the field. These are however my own personal views and not those of my employers.
Most "fuel saving devices" fit this pattern:
- About a 10 - 15% claimed fuel saving (gas saving / gas mileage improvement)
- Claimed reduced emissions
- Claimed improved performance
- Cost about £50 (80 US$) (so costs about £5 to make!)
There are many different types, and you can find information on the technical problems with each below. But there are also some general issues with all of them.
Firstly, it's very rare to have any good test data for these devices. Some have been tested scientifically, but often on very old cars, and the data is either suspect, or irrelevant to more modern vehicles.
Measurements showing
emissions reduction are nearly always taken from the UK MoT test or something equivalent. This consists of measures of hydrocarbons (HC), carbon monoxide (CO) and carbon dioxide (CO2), and is taken at idle. This completely ignores oxides of nitrogen (NOx), one of the most dangerous pollutants from car engines. It also ignores the fact that the emissions while driving are very different to the emissions at idle, because of the higher load and speed.
Sometimes with catalysed cars you will see results such as "reduction in hydrocarbons from 10 ppm to 5 ppm - a 50% improvement!". This is an essentially meaningless result, since the accuracy of typical workshop test equipment is only about +/- 5 ppm. In any case, 10 ppm means that only about one part in 5000 of the fuel used in the engine is escaping from the exhaust, so the effect on fuel consumption or overall emissions is pretty marginal.
Performance increases are usually just users reporting "my car feels quicker now" (memorably described by one US commentator as a "butt dyno".) What kind of evidence is that? It's hard for a driver to detect small changes in performance, and measures such as 0 - 60 time are extremely dependant on driving style. There are objective ways to measure car performance, the main ones being in-gear acceleration times and "before and after" rolling road measurements. Companies selling devices that genuinely improve performance (such as "chipping" upgrades) always quote measurements of this sort, and they are not difficult or expensive to do. So when somebody claims a performance increase but doesn't have any data of this sort to back it up, ask yourself why. (Also note that variations of two or three percent on rolling-road tests are not at all unusual, due to such things as changing air temperature, so unless there are several "with" and "without" repeats an apparent improvement of this level is insignificant.)
Fuel consumption is what most people are interested in. Again the claims are almost always based on users reporting fuel consumption improvements, and not any kind of objective measure. The basic problem here is that fuel consumption is extremely sensitive to driving style, type of journey, even the weather. On my own car, I often see variations in excess of +/- 10% from the average fuel consumption. These variations occur both between subsequent refils, and over a longer period of time due to changes in weather and journey type. You can find a lot more information about the dangers of relying on testimonial evidence, including your own personal experiences,
here.
Often some users report big improvements while others find no improvement or even a deterioration in fuel consumption. This is not surprising, given the variability you always see. Funnily enough, the companies selling these devices only report the positive results! There is a long history with fuel "saving" devices of glowing customer testimonials followed by scientific tests proving the device has no significant effect.
It's even worse, though, because it's not a
blind trial. In drug testing, neither the patient or the doctor is allowed to know if they're getting the real drug or a fake, because it affects the results. When the driver knows they have a fuel-saving device fitted, it's bound to affect driving style. (If you inject a hundred sick people with plain
slightly salty water, most of them will report an improvement in their symptoms. That's why we have double-blind trials, control groups and the like - scientific testing, in other words.) With the greatest of respect to people who have tried these things, uncontrolled testing under variable conditions does not constitute proof!
Some people argue that this doesn't matter. If fitting one of these devices apparently improves fuel consumption, does it matter if this is due to a change in driving style rather than an actual technical improvement in how the engine works? (the "
pragmatic fallacy"). Personally, I think it
does matter, as:
- Some devices (eg air bleeds) may greatly increase toxic emissions
- It distracts attention (and money) from genuine ways to save fuel
- The makers are still effectively lying in their advertising
Another issue with these tests is that you almost never see an
A-B-A test. Fit the device, see an improvement in MPG. But to prove the point you must then take it off again and prove the MPG gets worse. Otherwise it could have just been a coincidence, or due to something else changed at the time of fitting.
The "gold standard" for emissions and fuel consumption testing is the
emissions drive cycle. This is a standardised profile of speed against time; all new vehicle models are driven over this cycle on a rolling road to provide legal proof of compliance with emissions limits. The European cycle covers about 5 miles and includes both "town" and "country" driving, so is fairly representative of what happens in the real world. The test is run under absolutely controlled conditions, with even the air temperature fixed, and so gives repeatable results. This test - and
only this test - is accepted by governments all over the world as proof that a particular car has the emissions and fuel consumption that the maker claims.
When a "fuel saving device" presents results from an emissions drive cycle, then there may be something in it. Any other sort of test data should be taken with a large pinch of salt! Many independent test facilities are certified to carry out this testing, and the process is not difficult or time-consuming. As a fraction of the hundreds of thousands of pounds a year profit made by some makers of fuel "saving" devices, the tests are not even particularly expensive. When someone makes claims that are completely at odds with current scientific and engineering knowledge, surely it is up to them to prove that their claims are true, with proper scientific testing.
The definitive guide to testing fuel "saving" devices is that of the US
Environmental Protection Agency The EPA has been testing such devices since the early 1970s - both because of a desire to save fuel, and equally because many such devices actually make emissions
worse. The EPA guidelines clearly explain what must be done to properly evaluate a fuel "saving" device, and in particular make it absolutely clear that emissions measurements on the Inspection & Maintenance test (the equivalent to the UK MoT) are of no value in this evaluation. The essential requirements to prove a fuel "saving" device works are:
- rolling-road tests, over standard cold-start cycles such as the FTP75 (US) or ECE+EUDC (Europe)
- a test car (preferably two) that is reasonably modern, and in good condition (emissions and economy in line with when it was new)
- at least two tests in "standard" condition, followed by at least two with the device fitted (to assess statistical variability)
- ideally, a final pair of tests with the device removed again (to prove it was the device that made the difference, and not some underlying factor such as components bedding-in)
A device that has test data conforming to these requirements, and where the gain is several times larger than the test-to-test variability, is almost certainly of genuine benefit. Anything less rigorous (old car, no repeat tests, etc) should be treated with some suspicion. Many American devices claim "We have a CARB number and so it is legal to fit this device". While true, this does not in any way indicate that CARB (California Air Resources Board) certify that the device actually offers the benefits claimed. The CARB number merely indicates that CARB
do not believe the device makes emissions worse, and does not indicate
anything else. For example, the CARB Executive Order for the
Tornado Fuel Saver specifically states:
This executive order does not constitute a certification, accreditation, approval, or any other type of endorsement by the Air Resources Board of any claims...concerning anti-pollution benefits or any alleged benefits. Since the vast majority of fuel "saving" devices have no effect at all, either positive or negative, it is unsurprising that they can obtain CARB numbers (and in many cases this is based on "engineering judgement" rather than actual tests). To check if a particular device has a CARB number, visit their
database.
People frequently ask why I criticise such devices without having personally tested them. The reason is that I could fit one to my car but it would prove
absolutely nothing. Any fuel economy effect would be lost in the variation of normal driving (as discussed
here). The emissions tests I could do (basically CO and HC at idle, as measured on the MoT test) would say nothing at all about the effect on overall emissions while driving, and hence environmental impact. Proper performance testing would require multiple rolling-road tests with and without the device, which would be expensive and time-consuming. For these reasons, I also believe the customer testimonials often quoted by makers of such devices to be of little value.
Often these devices claim to alter the combustion process in some way. Even assuming that this were possible, remember that the engine has been optimised for the "normal" combustion. To get any benefit from this "altered" combustion you would need to change fuel delivery, ignition timing or even the design of the cylinder head to suit! Diesel combustion is a lot more efficient than petrol combustion, but you can't just fill up your petrol car with diesel and expect a 20% economy improvement (no, don't even
think about trying it - it will be very expensive to repair!)
A typical claim is that the combustion with the device fitted is somehow "better" or "more complete". There is never however any detail as to what is meant by this. And it is a firmly established engineering fact that, on any reasonably modern engine under normal operating conditions, the burn is
already at least 98% complete. The unburnt fuel in the exhaust (even before the cat) represents
1 or 2% at most of the input fuel. If you factor in the energy in the CO emissions, the figure still only rises to 3% maximum. So even if the fuel "saving" device could
totally eliminate unburnt fuel and CO in the exhaust, and give an absolutely 100% complete burn, you would only save 3% of fuel. Claims that 10%, 20% or even more of the fuel is not burnt and escapes into the exhaust are
entirely false - the unburnt fuel figure is higher when the engine is stone-cold, and at high load and speed conditions, but since the engine only spends a small fraction of its time under these conditions their contribution to overall fuel consumption is small.
(NB That is not to say that the overall efficiency of a modern engine is close to 100%. There are losses due to the fundamental nature of the engine cycle (the "Otto cycle" or "Diesel cycle"), which limit even theoretical efficiency to about 40%, and there are also losses due to friction, heat loss to the walls of the cylinder and the piston, "pumping loss" due to sucking air past the partially-open throttle blade, etc. These losses are however well understood and the gains to be had from various technological changes are accurately known.)
The other reason why these devices can't work is simple business. Fuel consumption is a very hot topic in the European car industry at the moment, because it is directly related to carbon dioxide, which is a "greenhouse gas". Consumers and legislators are demanding ever-better fuel consumption from new cars. The industry is investing literally billions of pounds on more efficient engines, for example diesels (and we wouldn't do that if we were
in the pay of oil companies, would we?) But these more efficient engines are also much more expensive to make - for example a diesel will produce about 15 - 20% less carbon dioxide, but adds about £500 - £1000 to the cost of a car. These "fuel saving devices" claim nearly as much benefit for a tenth of the cost - the car industry would not only sell its grandmother for this kind of saving, but sacrifice its first-born son too!
Given that, you have to ask why any such device isn't fitted to new cars as standard. The answer is simple - industry believes they are of
no significant benefit. Otherwise, they would be on new cars. No question. The car industry has seen hundreds of these things go by, and can't afford to waste thousands of pounds on testing each and every one of them. But if you'd invented a miracle gismo like this and
knew it worked, wouldn't you pay your own money on tests to prove it, given that you could then sell millions?
Some people argue that car makers are so keen to reduce costs that even the few pounds that one of these devices costs would be too expensive. And of course on some entry-level cars, and in cheap-gasoline America, there is some truth in that. But in Europe (especially in the UK with CO2-based company car tax) many consumers have proved willing to spend several hundred pounds more on a car if it is more economical. You need only look at the booming sales of diesels, which cost anything up to £1000 more than the petrol equivalent, for proof of this. There is a clear profit incentive for car makers to equip at least part of their range with more economical engines and so the potential market for a genuine fuel saving device runs into tens of millions of pounds a year. Sufficient incentive for any manufacturer of such a device to spend a few thousand on tests, you would think.
Exactly the same argument applies to the claims of increased performance made by many makers of such devices. For some car makers, even just one or two percent more horsepower is worth thousands of pounds. If a cheap and simple device like a magnet, air bleed, fuel "catalyst" or turbulence increaser could really give 5 - 10% more power, would they not be fitted as standard on most BMWs, Porsches, Ferraris, etc?
I have worked for or with some of the world's biggest car makers and component suppliers, and nobody I have spoken to in the industry has ever regarded these fuel "saving" devices as anything other than a con. They are never advertised in the journals aimed at engineers within the new car industry, the makers almost never present results at trade conferences, and no serious books on the subject (of which I have read dozens) even give them a mention. Certainly you don't find car engine designers saying to each other, "If only we could fit (device x) to our engine, but (company y) has got the patent on it". Even at normal market price these devices are allegedly massively more cost-effective than any known fuel-saving technology. Arguments about the difficulty of fitting them to new cars do not wash either, since current cars contain extremely complex devices that only a few years ago would have been considered impossibly difficult; the car industry has a good record of solving such problems.
You may well wonder, if these things don't do what they claim, why are the makers not prosecuted by (in the UK) Trading Standards or the Advertising Standards Authority? The answer is that many are, but it is difficult and expensive to
prove the device doesn't work. The device usually then simply pops up again under a slightly different name claiming some slightly different technical features. For devices sold in the UK, it is however well worth while searching the
ASA website, just in case. Remember that the ASA is effectively funded by the advertising industry, so does not make judgements against advertisers without good reason.
Several such devices proudly state that they are "award-winning!", to which I have just one comment: so were
Milli Vanilli...
One more thing to remember is that thousands of scientists and engineers all over the world have been working on car engines for decades. The physics of engines is pretty well known now and you have to ask yourself if some amazing new breakthrough, only involving bolting something to the outside of your engine, would really have escaped the car industry's notice all that time.
any comments?
Fuel-saving Gizmos: Fact or Fuelishness?
Originally Posted by jonz
my take, i'll just stick to what "stock" setup has on a particular car...
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