Quote:
Originally Posted by ducati
The hijacker is correct. The problem with ethanol is some engine's injectors will max out, then you have too little fuel, too much air, and BOOM.
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Yep. If you were running say, E60 or E70 you would really have to worry about maxing out the injectors. Running straight E85 is just begging for a slow drive home in limp mode.
But the point is that on an engine that is already designed to run E10, there really should be enough leeway in the design specifications of the fuel system's fuel volume ceiling to pump enough gas to make up for the additional 10% of ethanol. A well designed fuel system should never run at full max volume capacity under even the most aggressive driving. There should be a buffer between the designed max fuel delivery volume and the maximum amount of fuel requested by the ECU according to the manufacture's fuel maps. Running E20 just pushes flows up towards that ceiling. We're talking low ethanol blends, not high ethanol blends.
Every US car currently has to adjust for any mix between straight gas to E10 ethanol. (Different states mandate different versions of E10 -- E10 can actually be as low as just E5.7 and it is still labeled E10). There is already an inherent ability for ECU's in modern cars to adjust for variable amounts of ethanol in fuel. Going up towards E20 just takes advantage of the ECU's existing ability to adjust for variable amounts of ethanol.
Knock with low ethanol blends just isn't an issue. In fact, ethanol has some properties in low ethanol blends that reduces the chance of knock.
"The higher ethanol latent heat vaporization increases the engine overall efficiency due to the reduction of heat loss, and reduces the engine tendency to knock;"
http://www.nrel.gov/docs/fy03osti/32206.pdf
(this study is quite a bit out of date - but it is still a fairly good source of information.)
We're talking about a ~3.5% change in stoichiometric between E10 and E20, which is less than the ~7% difference between stoichiometric rich and stoichiometric lean in straight gas. Modern vehicles just shouldn't have a problem with E20 unless they have a lousy design in the first place that can't correct properly for normal every day variances --- like changes in temperature and humidity, or oxygenating fuel additives like MTBE or 10% ethanol, or octane variances, or altitude.
Sorry, no BOOM.