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Ethanol & Flex Fuel Tuning: 6. Confirm Tune at Varying Ethanol Percentages

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6. Confirm Tune at Varying Ethanol Percentages

15.24

00:00 - With our pump fuel and our E85 tunes now complete, the last step of our flex fuel tuning process is to check and optimise our blend tables at a few points in between E0 and E85.
00:13 Now the process we're going to go through here with this VW Corrado is slightly simplified just simply because we are only expecting this car to run on either E85 or pump fuel.
00:25 The reason that we are incorporating a full flex fuel system here is simply so that if there is some residual fuel left in the tank when the fuels are changed from pump to E85 or vice versa, that the G4+ modelled multi fuel system will be able to account for those small fluctuations in ethanol content.
00:43 So on this basis, we're really expecting the car to be either running on E0 to perhaps E15 when it's on pump gas and when it's on E85 we're expecting the ethanol content to be somewhere between perhaps E75 and maybe as high as E90.
00:58 So we're not as concerned at the in between ethanol contents as we would be for a full flex fuel system.
01:05 The tuning process we're going to look at however is exactly the same.
01:09 For a full flex fuel system you may simply want to add some additional test points in between E0 and E85.
01:17 Likewise with this car, because we're only running 2 boost set points, and we're being quite conservative at where we drop both the boost down to our pump gas target as well as removing timing back to our pump gas ignition table as the ethanol content reduces, we're not really trying with this application to optimise the engine performance at every ethanol blend between E0 and E85.
01:42 For your own purposes, if you want to get optimum performance at each of the ethanol contents between E0 and E85, you'd simply need to also optimise your ignition table blend and you'd also want to optimise your boost to whatever the octane of the fuel will allow at your specific ethanol contents.
02:03 Now for our example here, what we've decided to do is test at 3 ethanol contents.
02:09 We've selected E70 which would sort of indicate the lower range of the ethanol content we'd expect to ever see when the car's truly running on E85.
02:19 We're going to also test at E20, again this is the higher range of where we'd likely see the car when it's running on pump fuel.
02:26 Then we'll choose an arbitrary in between at E50.
02:29 So right now what I've done is I've topped up the remaining E85 in our fuel tank and I've got us to around about E70.
02:37 As you can see on our G4+ software at the moment, it's actually showing 69% ethanol.
02:42 Now when we are adjusting our blend, we do want to try our very best to be as accurate as we can.
02:48 What we're trying to do here is make sure that we're in the centre of one of the break points in our blend tables.
02:55 The closer we can get to the centre of one of these break points, the more accurate our changes are going to be and the better our results will be.
03:03 It is however incredibly difficult to be pinpoint accurate when we are adjusting our ethanol content, particularly if we've got a fuel system that incorporates a surge tank.
03:13 So as long as you're within +/- about 1%, I'd be happy with that.
03:19 Before we get into the tuning, we'll just recap what we're going to be focusing on here.
03:23 Remember we've already optimised our fuel and ignition tables on both pump gas and E85 so when we're checking the blends in between, what we're really wanting to do is make our adjustments to the blend tables.
03:35 As we've discussed here, we're going to be really focusing on just making sure our air/fuel ratio continues to match our target.
03:42 And we can do that by going to our fuel menu, we want to go down to fuel corrections, dual fuel table and fuel table ratio table.
03:52 This is the table where we're going to be adjusting our blend if our air/fuell ratio doesn't match our target.
03:58 So what I mean by this is what we're trying to achieve is a fixed or consistent air/fuel ratio as we move between E85 and E0.
04:05 Now this table you'll remember works on the basis of how the ECU is interpolating between fuel table one and fuel table two.
04:14 When we have a value of 0 in this table, it's working solely off our fuel table one or our pump gas fuel table.
04:20 When we have a value of 100% in here, it's operating solely on our fuel table 2 value which was our ethanol fuel table.
04:29 Obviously in between, the ECU is interpolating between those two tables.
04:33 So what we want to do here is make adjustments if our air/fuel ratio is not tracking our target.
04:38 And for instance, we already found that our fuel table two values, the table we tuned for E85, tended to be a little bit higher than the values we had in fuel table one.
04:49 What this means is that if we perform a run on the dyno and we find that our air/fuel ratio tends to be leaner than what we had on E85 or pump gas, what we need to do is interpolate more towards that fuel table two, the fuel table with the higher values so we would simply increase the values in this table, we can see at the moment we're sitting at that 70% ethanol break point so we'd simply increase that value from 87.5% and you'll also remember for the purposes of our demonstration, we had simply performed a linear interpolation between 80% ethanol and 0% ethanol.
05:25 While we can broadly expect this table to be relatively consistent, it's likely that once it's completely tuned, it's not going to be fully linear.
05:34 An important consideration just to note here is that we do have two boost set points.
05:40 You'll remember we've got our low boost pump gas tune and we've got our high boost 24 psi setting that we use for E85.
05:47 Now a consideration with this is that as we move from E85 to E0 to pump fuel at our low boost setting, we should retain a consistent air/fuel ratio, that shouldn't vary if our blend table is set correctly.
06:01 However, remember that we couldn't tune to 24 psi on pump fuel.
06:06 Just simply wasn't safe to tune that high in the boost pressure so what this means is that at higher boost levels, our fuel table one values may not be entirely accurate.
06:16 All we've done at this point is extrapolated the values that we found around 100 to 120 kPa upwards towards those higher boost levels.
06:25 So the effect of this is what we want to do is begin our tuning as we drop our ethanol content at our low boost pump fuel boost setting.
06:35 This is where we're going to be adjusting our blend table.
06:38 What we're doing is adjusting our blend table here so that our air/fuel ratio tracks the same as what we saw on E85 and on pump fuel.
06:47 Once we've got our blend table set at our low boost setting, we're going to raise our boost pressure at this E70 point, up to our 24 psi high boost level and we're going to test again.
06:59 Now at this point, at high boost, if we do have a discrepancy in our air/fuel ratio, instead of adjusting the blend table, what we're actually going to do is make adjustments just in that high boost area of our fuel table one because this indicates that our extrapolation was incorrect, it suggests that the numbers that we extrapolated up to those high boost regions on our fuel table one were possibly a little bit incorrect.
07:25 So that's where we need to make that adjustment.
07:26 If we tried to do this through the blend table it would mean that when we drop the boost back down to 15 psi, our air/fuel ratio wouldn't be correct there, likewise it wouldn't be correct in vacuum, idle and cruise.
07:39 Right so we've got our ethanol content currently set to 69%. Let's get our engine running and we'll perform our first run at our low boost setting.
08:10 That's our first run complete there on our low boost setting with our ethanol content sitting at 69% and the important points to note here are that our air/fuel ratio is essentially identical to the grey line that we've overlaid ontop of.
08:25 We're tracking really nicely right on our target of 0.80 lambda so at this point the blend is working correctly, our ethanol or multi fuel, modelled multi fuel mode in the G4+ is actually tracking really nicely, simply with our linear interpolation between E80 and E0.
08:44 So at our low boost setting here, we know that our blend is correct, so there's no work for us to do.
08:51 What we're going to do now is raise the boost pressure, get our engine running and we're just going to confirm that our air/fuel ratio is also still accurate at our high boost pressure of 24 psi.
09:01 Let's have a look at that now.
09:21 Alright we've completed our second run there at E70 and our high boost setting, 24 psi and again we can see that our air/fuel ratio is pretty much exactly where we were targeting, sitting right at 0.80 right through that run.
09:37 So this is a great start, it means that we've got no work at that E70 point to do to our blend table.
09:44 What we're going to do now is drop our ethanol content down further, down to E50 and we'll test again.
10:09 OK so on that run, while everything looks pretty good, if we look at our air/fuel ratio once we're up on boost, we can see that for the most part we're actually just marginally below our target of 0.8.
10:22 We're probably in the region of about 2% richer than our target through that run.
10:27 Now while for this example that doesn't specifically bother me, let's have a look at how we can go about correcting that.
10:35 So what we'll do is bring up our fuel table ratio table and remember we're sitting at 50% ethanol here.
10:42 Now in order to lean out the air/fuel ratio at our 50% blend, what we need to do is reduce the number in this table.
10:51 Now we can't specifically calculate the exact value we need to go to here, this is really a case of making a small adjustment and seeing what the results are.
11:01 What I'm going to do for this demonstration is just remove 4% from my blend table at 50% ethanol.
11:10 We'll store that change, let's get up and running and see what the result of that small change has been.
11:35 So with that small change that we've made to our blend table, you can see our air/fuel ratio is now much closer to our target.
11:43 Now certainly I'm happy with the results I've got there at 50% ethanol considering that we're not really expecting the car to run there.
11:51 Of course you can now make further changes to the blend table as you see fit to get yourself completely onto your desired target.
11:59 Now I've got one more job to do here before I add some more pump fuel and reduce our ethanol content further.
12:06 Remember we have tested at E70 and we've also tested at E50.
12:11 What I want to do is just interpolate those results that we've found across the E60 site.
12:18 Now it's only a very small change but this will just help keep the blend consistent at the areas of the blend table that we aren't testing.
12:28 Let's now add some more fuel and we'll check our third point at E20.
12:34 As you can see, we've now got our ethanol content down to right on 20% so this is our third and final test point.
12:41 Remembering obviously we're only testing here at our low boost setting as we did with our 50% test point.
12:47 Let's get our engine up and running, we'll perform a dyno run and see what our air/fuel ratio looks like.
13:12 So with our test complete there at E20, what we can see straight away is that our air/fuel ratio is essentially identical to our target, identical to what we achieved on pump fuel and this means that there's no work for us to do here in our blend table.
13:29 Also we can notice that our power is almost identical to our pump gas tune as well, as is our boost and that's really to be expected.
13:38 Remember we were tapering our ignition timing back quite aggressively so that at E20 we're essentially running almost solely on the pump gas ignition table.
13:48 So there's no real reason for us to be seeing power gains at this ethanol content and that's exactly what we're targeting here, for our worked example we wanted a nice safe and conservative tune.
14:00 Now we have made some changes to our blend table though, remember that we made an adjustment here at 50%.
14:08 Now we've just tested at E20 and we know we don't need to adjust our blend table there.
14:15 What I'm going to do just for the sake of completeness is just interpolate between those two points between 20 and 50% just like we did previously between 50 and 80.
14:26 We can do that just by using the control and i key to perform a linear interpolation.
14:31 Now at this point we've got our blend table complete and we can see that we've made some small adjustments but essentially it hasn't varied too much from a completely linear interpolation which would be theoretically ideal.
14:48 Now that's not to say that this is going to be the case for every tuning example that we perform.
14:55 It is normal to expect some variation in this blend table.
15:00 In the case of our VW Corrado, we've probably been quite fortunate that this has worked out so close to linear.
15:07 So this completes our worked example on the VW Corrado using our G4+ modelled multi fuel mode.