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Re: I know you know... Posted by JimBlake [Email] (#141) [Profile/Gallery] (more from JimBlake) on Thu, 9 Jul 2009 13:35:37 In Reply to: I know you know..., PGAero [Profile/Gallery] , Thu, 9 Jul 2009 11:16:30 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Anti-knock additives generally have SOME fuel value, it's just lower than gasoline. But they're added in small quantities so the overall heat-value (LHV) of the fuel isn't degraded by much. An exception is ethanol, which is added in single-digit percentages. Old-school stuff (tetra-ethyl lead) was added in tiny amounts that barely show up in the overall LHV of the fuel.
But the misleading thing about the "energy density" business, is that the fuel-management system will add as much fuel as it needs to keep stoichiometry happy (per O2 sensor).
Sure, ethanol has a high octane. And yes, the engine will adjust spark timing & boost to some extent to take advantage of that octane. But at the same time, it will add enough extra fuel to "use up" the available oxygen.
This is especially true for an engine that's capable of using E85 (85% ethanol). The fuel system will happily inject 25% more fuel without screaming & setting off warning lights.
So the real answer is "ITS NOT THAT SIMPLE".
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