zpiloto |
01-17-2007 12:23 PM |
Quote:
Originally Posted by MetroMPG
(Post 38096)
There's no doubt that by spoofing the O2 sensor, you can lean the mixture and increase fuel economy.
But leaning the mixture will also increase production of NOX emissions in engines that weren't specifically designed to run lean (e.g. through combustion chamber design, or intake charge concentration, like the Honda lean burn motors).
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From Tony fuel saving page
The three "regulated pollutants" are unburnt hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). All three are serious human health hazards. NOx is nitrogen with added oxygen; HC and CO represent incomplete combustion. What the catalyst does is to remove the oxygen from the NOx and give it to the HC and CO. The result is plain nitrogen, carbon dioxide and water, all of which are essentially harmless. But to work, the lambda value must be just right. If the mixture is too rich then the oxygen in the NOx is not enough to give to the HC and CO, so they pass through unconverted. If the mixture is too lean then the "spare" oxygen is given to the HC and CO, and the NOx passes through unconverted. The overall effect of lambda on post-catalyst emissions is like this:
There is a very narrow "window" between lambda 0.99 and lambda 1.00 where all three pollutants are effectively cleaned up. It is precisely because the engine must operate in this "window" that modern engines are fitted with lambda sensors.
Now, under most circumstances the lambda sensor will correct for any fuelling deviations introduced by the "fuel saving device". But the sensor has limited "authority" - it can only add up to about 10 - 15% additional fuel, since otherwise a faulty sensor could result in an extremely rich mixture, leading to engine problems. If the deviation exceeds this limit, then the lambda sensor can no longer compensate and a lean mixture is the result. So the result of fitting one of these devices may be a lambda around 1.05 - 1.10. This will give a small improvement in fuel consumption (about 2 - 5%) and, as the graph above shows, reductions in HC and CO. This sort of result is often shown by makers of such devices as "proof" of emissions reduction. However, the NOx emissions will increase massively - perhaps 20 times - as the catalyst can no longer clean them up. Since NOx is not usually measured by workshop test equipment, this is not picked up. The overall effect is a very large increase in toxic pollutants, which does not fit the "green" claims of such devices.
(On a vehicle without a catalyst, leaning the mixture will greatly reduce CO and significantly increase NOx. HC may go up or down, depending on the engine and the test conditions.)
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