Because my readers know I'm completely fed up with fuel-saving gadgets and potions, and want me to suffer, several of them have e-mailed me today to alert me to this Gizmodo piece about "Blade Exhaust Filters".
The Sabertec Blade is a doodad that you bolt onto the end of your car's exhaust pipe to "reduce emissions of CO2 and toxic particulate material, and it improves fuel economy to save you hundreds of dollars per year on gas"!
It is alleged to achieve this feat by doing something to the series of pressure pulses coming out through the exhaust system, thereby:
1: Increasing the efficiency of the catalytic converter. For the few minutes after you start the car, by restricting exhaust flow and thus letting the catalyst heat up faster. Whoopee.
2: "Increasing the Volumetric Efficiency (VE) of the engine"; allegedly allowing the engine to more easily get fresh air into its cylinders. The explanation given for this once again has to do with the pressure pulses of the exhaust; apparently the Blade is meant to act sort of like a tuned pipe for a two-stroke engine. It strikes me as rather implausible that a device attached to the end of the exhaust pipe shared by all of the cylinders can significantly (positively...) affect the breathing of each cylinder in turn.
The Blade is also claimed to be a filter that "physically captures gasoline and hydrocarbon particulates, as well as other solid inorganic emissions".
Pretty much zero "gasoline" should be making it past the catalyst anyway, which is just as well, because I can't imagine that a filter for volatile hydrocarbons would do anything other than stop a pulse of unburned fuel (when, for instance, you've just started a beat-up old engine) from all escaping at once. It'd just absorb it like a sponge and then let it slowly escape over time. Net gain, zero.
As far as filtering for particulate matter goes, "soot filters" for large diesel engines are quite common, but - as you'd expect - get clogged pretty quickly if they're not able to burn the soot off somehow (giving slightly higher CO2 emissions, but lower particulate emissions). The Blade has a replaceable filter cartridge - a new and a used one are shown in the pictures on this page. Apparently you're meant to replace the filter every seven to ten thousand miles; replacement filters cost $US19.99, while the Blade device itself costs $US199.
The Blade filter is, however, somehow supposed to decrease CO2 emissions as well, by "up to 12%". This strikes me as a very peculiar claim. What's it doing with the CO2? Cracking it to carbon that stays in the filter and oxygen that's released?
Let's assume, for the sake of argument, that this near-magical feat is in fact what it's doing. Doing this with nothing but exhaust heat to work with would, I think, be a Nobel-prize-winning achievement, but never mind. How much carbon would the thing actually have to catch, even if you replaced it every 7000 miles on the dot?
Well, the carbon dioxide molecule contains two oxygen atoms (atomic weight 16) and one carbon (atomic weight 12). So by weight, it's about 27.3% carbon.
7000 miles of driving is 11265 kilometres. If you're driving a car which emits a mere 100 grams of CO2 per kilometre, it'll emit a total mass of 1126.5 kilograms of CO2 over that period. The total mass of the carbon atoms in that much CO2 is 307.2 kilograms. Let's say that in this case the Blade's "up to 12%" CO2 catching turns out to mean "6%". 6% of 307.2 kilograms is 18.4 kilograms.
So if there isn't eighteen kilograms of soot in the filter when you replace it, you haven't caught six per cent of the carbon.
Note that carbon also isn't very dense. Even diamond only weighs about 3.5 grams per cubic centimetre. So even if the magic filter turned the magically extracted carbon into diamonds, you'd still end up with 5267 cubic centimetres, 312 cubic inches, of them clogging up the filter in the above situation. Graphite is only about 2.2 grams per cubic centimetre; that'd be 8379cc, 511 cubic inches, 2.2 US gallons, all somehow having to fit in the filter.
You could deal with the gallons of carbon clog by just burning off the carbon, but that would of course defeat the purpose of collecting it in the first place. Or you could just blow the soot out the exhaust pipe, but this would increase particulate matter emissions, which the Blade, you'll recall, is meant to reduce.
As far as improved fuel economy goes, it's uncontroversial that you can reduce the fuel consumption of internal combustion engines by restricting the air intake or, less elegantly, the exhaust. Restricting air intake is exactly what you're doing whenever you don't have the throttle wide open.
If you add more restriction one way or another, the airflow to and from the engine will fall for a given throttle setting, and at that throttle setting you will now use less fuel. But you'll also get less power. All you're really doing is saying "from now on, pushing the throttle all the way will do what pushing it four-fifths of the way used to do". You can achieve the same result by simply driving with less gusto, and never using full throttle.
This could be related to the fact that the Blade installation manual quietly says "The BLADE is not recommended for performance cars".
Oh, and what do you get if you search for the address of the one lab that allegedly found the Blade to work wonderfully well, in the single test of the device that's apparently ever been published?
Well, as I write this, you get the Web sites of people selling a crankcase ventilation doodad, the Fitch Fuel Catalyst, some concoction that's meant to give you a "more efficient and complete fuel burn" (when fuel is already almost 100% burned in modern engines...), and one of those electrolytic-hydrogen "combustion enhancers". I hope this lab will soon tell us all what it is that they do to get all of these devices to work so well, since they seem much less impressive when most people test them.
(Oh, and the Gizmodo piece says "Blade does have support from both the California Air Resources Board and the EPA". This is not true. What Blade actually say is that the laboratory that did the tests is "accepted by" the EPA and licensed by the CARB. This may indeed be the case, but it doesn't mean the government's checking their work, or has ever even seen the Blade test results. Treehugger made the same mistake when they wrote about the Blade and interviewed the CEO. Commenters there, and a couple of months earlier at AutoblogGreen, were unimpressed.)
As usual, if the Blade works as advertised it'd be worth hundreds of millions of dollars a year. But instead of getting it properly tested by a variety of labs and then licensing it for gigabucks to car manufacturers, major fleet operators, huge industrial concerns and so on, Sabertec instead sell it directly to motorists. Just like the Fitch Fuel Catalyst, fuel-combustion-improvers, hydrogen generators, and the Firepower pill.
If you believe those things work, then the Blade will be another fine belief to add to your portfolio. Use all of this stuff on your car at once and I bet it'll start creating petrol while you drive.
