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Ethanol & Flex Fuel Tuning: VE Based Flex Fuel System Tour

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VE Based Flex Fuel System Tour

08.37

00:00 - In this module we're going to have a walkthrough of a volumetric efficiency based flex fuel system and see what the typical layout of that system looks like, and what settings are available.
00:11 Now for this example we are going to be using our custom coded flex fuel system for the Motec M150 ECU.
00:19 But it doesn't really matter what particular ECU platform you're tuning on, we're going to be looking at the fundamentals here of a volumetric efficiency based flex fuel system.
00:29 So let's jump into the software.
00:31 And at the moment I'm on our fuel worksheet.
00:34 And this is where we set up the base volumetric efficiency table.
00:38 So the volumetric efficiency table that we can see over here on the right hand side is what we tune for gasoline.
00:45 So this would be for a non flex fuel system.
00:49 Likewise if we move across to our ignition worksheet we can see our gasoline based ignition table here.
00:56 So again this is what we'd be looking at if we were just tuning for gasoline with no flex fuel at all.
01:03 If we move across to our flex fuel worksheet which we can see over here, this gives us all of the settings for our flex fuel system.
01:11 And I just wanna walk through those one by one.
01:14 For a start we can see here that we have an ethanol mode.
01:18 So this is where we can enable or disable the flex fuel system.
01:22 Of course if we're just tuning for one fuel this would normally be disabled.
01:28 Moving down we can see that we have some settings for the flex fuel sensor or ethanol content sensor, and in particular we can see at the moment, we're looking at the calibration for ethanol content.
01:40 We can see the axes there are in frequency and at 50 hertz of course we have our 0% ethanol setting, and at 150 hertz we have our setting for 100% ethanol.
01:53 These are just standard settings for the Continental fuel composition sensor.
01:58 We can move down and we can see that we have the relevant settings for our fuel temperature as well.
02:04 So this sets up the ECU so that it can see or read ethanol content as well as fuel temperature.
02:13 We'll just move down and we'll have a look at how the Motec M1 ECU deals with the fuel and the ignition trims.
02:22 So in this case with the M1 ECU it bases everything off the volumetric efficiency table that we looked at earlier for gasoline.
02:31 And in this case we have a trim table available.
02:36 We can see that is here.
02:38 And this is a trim that will be applied to the base fuel delivery based off the volumetric efficiency table for gasoline.
02:46 So if we look at that table here we can see that we have a three dimensional table, engine load versus our engine speed.
02:55 And this table for the most part, it's using numbers in the range of about six to 13 at the most.
03:03 So this is reasonably normal, what we would expect to see for most flex fuel installations like this.
03:10 So this is the amount of fuel that the ECU is adding over and above its calculation for gasoline.
03:16 Now of course this needs to work in conjunction with a blend table.
03:21 We can see the blend table right here.
03:23 So in this case the blend is set to 100% from ethanol content of 70% and above.
03:31 And we've simply got a linear interpolation below that.
03:34 So if we look at our graph we can see that it just linearly interpolates from 70% ethanol and below.
03:42 So in this case everything's actually worked out during the tuning of this particular car in line with what we would expect to see.
03:50 Moving down we'll have a look at our ignition table.
03:52 And in this case the Motec ECU actually contains two completely separate ignition tables.
03:58 It's got one ignition table for gasoline and a second ignition table for our maximum blend of ethanol.
04:07 And again there is a blend table that defines how the ECU is going to move from one of these tables to another.
04:15 And we can see in this case we are using all of the second ignition table once we reach an ethanol content of 80% and above.
04:25 Let's just have a look at that graphically so we can see.
04:27 This time we don't have quite such a liner interpolation.
04:32 And we can see as well that we're back to our gasoline ignition table completely once the ethanol content reaches 20% or below.
04:41 So this is a relatively conservative setting.
04:44 If we move down as well we can see that we have some changes to our boost aim.
04:49 So this is a turbo charged car.
04:51 We're adjusting our boost aim based on our ethanol content.
04:54 We can click on that and we can see our boost target.
04:58 We'll just look at this numerically.
05:00 Pretty straightforward here, we're just targeting 70 kPa gauge all of the time, not a particularly high boost setting but this is still a stock engine.
05:09 Conversely when we're running on a gasoline, we're targeting 60 kPa.
05:13 So it's only a relatively small difference.
05:15 It would be typical to be targeting more boost on an ethanol blend but we're keeping this very conservative due to the fact the engine is still stock.
05:24 And again with our boost aim we have a blend table, and again we can see that this is set up quite conservatively.
05:32 We're targeting 100% from our second boost target, so 70 kPa gauge any time we are 70% ethanol or above.
05:42 And you can see that we are back to our gasoline boost target any time we're at 10% ethanol or below.
05:49 We can look at this table graphically as well, and what you can see I'm just using basically a mainly linear interpolation between those two points.
06:00 Moving up as well, in this particular installation you can see we do have an ethanol hold mode, which we've talked about in the body of the course.
06:09 You can see here we have set points for an engine speed threshold as well as an inlet manifold pressure threshold.
06:16 So in this case any time the engine speed is above 4000 RPM and the manifold pressure is above 120 kPa, the ECU will apply a hold to the ethanol content and fix that there, even though in this instance we're not actually seeing our ethanol content change or become erratic as the load and RPM increase.
06:40 On the right hand side we have some parameters so we can actually monitor exactly what's going on here.
06:45 At the top of course we have our ethanol content.
06:48 You can see that's currently sitting at 83%.
06:50 We can also see how much of those second tables are being applied.
06:55 First of all we have our ethanol fuel trim.
06:58 So this is the current fuel trim which is based on our fuel trim table as well as our blend.
07:03 So we can see exactly what that's doing.
07:04 Below that we have our ethanol ignition timing.
07:08 So again this comes from our ethanol ignition timing table and our blend and finally below that we have our boost aim so we can see how that is varying based on our second boost target table and our blend table.
07:24 When it comes to entering the fuel's characteristics or properties we can move through to our engine details worksheet.
07:30 And we can see here for a start we've got the fuel's stoichiometric air fuel ratio, this is a two dimensional table, so we can define how the stoichiometric air fuel ratio moves or changes as our ethanol content changes.
07:43 The ECU can then track and adjust the current stoichiometric air fuel ratio based on the changing ethanol content.
07:51 Moving down we have our fuel density reference.
07:54 So this defines the fuel density for the different blends of fuel.
07:59 Again we have a two dimensional table with our density at E0 and our density at E100 and the ECU can interpolate between.
08:07 Moving down we also have our fuel density temperature coefficient.
08:12 So this is how the fuel density changes with temperature, and again a two dimensional table so that the fuel density temperature coefficient can be tracked as our ethanol content changes.