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Ethanol & Flex Fuel Tuning: What Is Flex Fuel

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What Is Flex Fuel


00:00 - When it comes to tuning an engine to run on ethanol fuels, there are several options available to us.
00:06 The simplest of course is to tune the engine for a dedicated blend of ethanol.
00:11 Beyond this we may also have dual maps where we'd have one map optimised for gasoline, and the other for whatever blend of ethanol we want to run.
00:21 Given the fluctuation in the ethanol content of pump E85 that we've just discussed, this can lead to reliability issues if the actual ethanol content varies from whatever we had when the engine was tuned.
00:35 We can also see variations in the ethanol content, by virtue of the residual fuel remaining in the fuel system when switching from one fuel to the other as it's very difficult to completely drain the fuel tank.
00:49 The last option we have is to employ a full flex fuel system to take care of the fluctuation in ethanol content.
00:57 And automatically adjust the tuning to keep the engine operating correctly.
01:02 Let's take a step back though and look at why the engine operation will vary as the ethanol content changes.
01:10 One of the aspects that's important to understand when tuning for a fuel such as E85, is that the properties of the fuel require a much different volume of fuel to be injected into the engine in order for it to run properly.
01:25 For those who want a thorough understanding of how the fuel properties affect how much fuel we need to supply, we'll go through the workings behind this a little further into the course, however for now it's enough to know that if we take an engine, tune for gasoline, and swap to E85, we're going to need to supply it with around 40% more fuel by volume.
01:48 Considering that E85 isn't available everywhere, as well as the fluctuating ethanol content of pump E85, this represents a problem for OE manufacturers who wanted to offer vehicles compatible with ethanol blended fuels.
02:02 In order to take advantage of ethanol fuel these manufacturers needed a method for allowing the engine to run correctly on any fuel composition from pure gasoline all the way through to pure ethanol.
02:16 This was achieved with a flex fuel system.
02:19 With the current crop of flex fuel systems used in OE applications, the ethanol content is often derived based on the required fuel trims to maintain a stoichiometric air fuel ratio during closed loop operation.
02:34 For the OEs, this keeps their costs down, because they don't require a sensor to directly monitor the ethanol content anymore.
02:42 This technology hasn't been embraced in the aftermarket standalone world as yet and instead the heart of a flex fuel system is a fuel composition sensor or flex fuel sensor that tells the ECU directly what the current ethanol content of the fuel is.
03:00 This sensor coincidentally was also the basis of older generations of factory flex fuel systems.
03:08 Once the ECU knows what the ethanol content is, it can then make the required changes to the tuning to maintain stable and consistent engine operation as the ethanol content fluctuates, as well as taking advantage of the properties of ethanol in order to offer an improvement in performance.
03:27 The same sensors that were used in the older generation of OE flex fuel vehicles, are also available to us in the aftermarket, and allow us the ability to replicate OE flex fuel capability in many aftermarket standalone ECUs.
03:43 This does mean the the tuner's job becomes a little more involved.
03:47 As now we need to not only tune the engine on two fuels, but also check that everything still works correctly as the ethanol content changes.
03:57 While flex fuel isn't an essential way of tuning to take advantage of ethanol fuel, it does mean that the ECU can automatically compensate the tune if you happen to get a tank of fuel with a vastly different ethanol content.
04:11 And this is a great way of ensuring reliability if you were using pump E85.
04:17 This course will cover tuning to suit ethanol fuel with dual switchable maps, and full flex fuel system so that you'll be able to understand both options.
04:27 We'll also look at the tuning options for both standalone and factory applications.
04:33 Wherever possible I'd strongly recommend the addition of a fuel composition sensor, even if you aren't using flex fuel.