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Practical Standalone Tuning: Step 7: Steady State Fuel Tuning

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Step 7: Steady State Fuel Tuning

24.15

00:00 - Now that we've got our basics of our idle dialled in, we can move on and begin some of our steady state tuning.
00:06 We're going to start here with our steady state fuel tuning.
00:10 I've already talked about the fact that rotaries, I'm not a big fan of knock control.
00:16 However I do still advocate using audio knock detection when we are tuning a rotary engine, any engine for that matter and while at this point we're going to be focusing solely on the fuel table, we've got an ignition table dialled in there that we know should be conservative, we shouldn't need to worry about knock but it's always a good idea even when we are tuning the fuel to also be listening with our audio headset so that we know if knock is occurring.
00:43 This way, we can stop straight away if something isn't right, we can reduce load or RPM or both on the engine, go to our ignition table and reduce the timing there to safeguard it.
00:55 As I've said with a rotary engine you don't generally get too much opportunity to live through a knock event however if you audibly are hearing it, gives you at least an opportunity to get our of the throttle and give yourself the best chance possible of the engine being saved.
01:11 Now what we're going to do here in our fuel table is we're going to start at as low a load and RPM as we can get and I'm going to probably start here around the 1500 RPM column and you can see we've got some broad numbers in here that's just come from our tuning to date.
01:27 Nothing's really dialled in at the moment, it's definitely not accurate but we have looked at that idle area as you saw in the last step so for a start what we'll do is we'll just get our engine back up and running.
01:45 It is important when we are doing our steady state tuning to make sure that the engine is in fact up to temperature so we don't want to be starting from a cold temperature where we may have some warmup enrichment active.
01:59 Likewise we don't really want a heat soaked engine where the manifold air temperature or inlet air temperature are unrealistically high so it's a good idea to make sure that we're as close to what we'd expect to be normal operating conditions as possible.
02:11 And if we look over here on our Eugene software we can see we've got our engine coolant temperature sitting just below 80, we've got our manifold air temperature sitting at around about 16° so we're know we're in a pretty good situation there.
02:25 Now when we first start running the engine it is likely that as we move from 1000 RPM at idle out to our 1500 RPM here that we may find that our fuelling is a little bit lean.
02:37 And in fact, just given the changes that we've made down here around idle to our fuelling, we can see we've got numbers of 62 and 66% at 40 and 50 kPa respectively, come out to 2000 RPM, you can see we've got the block change that I made there to 60%.
02:56 It's a pretty good chance that that's going to be too lean.
02:59 I'm going to enter values for our 1500 RPM column there of 70% and we've also translated those numbers from 1000 RPM up to 1250 RPM so now what we're going to do is get the engine up and running, we're going to go to 1500 RPM and as low in the load as we can manage on the dyno so let's do that now.
03:24 Alright with our engine now running at 1500 RPM we can see that we can't quite get down into the 40 kPa cell, we're sort of interpolating between the two so what I'll do is I'll get as close as I can into the middle of the 50 kPa cell and it always goes without saying here, when we are making tuning changes to any individual cell, we always want to be as close to the centre of that cell as we can get to avoid the effect of any interpolation.
03:51 So looking at that cell here we can see that our fuelling is actually pretty well on point so not a lot of need to change, that guess of 70% was actually pretty good.
04:01 However if we reduce the throttle down here and we come down as close as we can get to our 40 kPa cell, we can see that we start to move quite rich.
04:12 Now while we can't get into the middle of that 40 kPa cell, what we can do is at least reduce the numbers in that cell to get us a little bit closer to our target.
04:23 So we can see there, just by bringing that down from 70% down to in this case 62%, we're down to about 0.89, we can't get into the middle of the cell so we can't be perfectly accurate.
04:34 I'm going to leave it at 61% there and this is an area that we will need to address and look at when we're on the road because on the road, with the inertia of the car on the road, it is possible to end up a little bit lower in the load than what we can get on the dyno.
04:48 For not, let's come back up to our next cell that we can get to, we're going to come up to 60 kPa and we can see that as we move up to 60 kPa we're now a little bit lean, we're around about 0.95, 0.96 with a target of about 0.92.
05:04 So there's a couple of ways we can make those changes.
05:06 Just going to use the page up key here because we are quite close to our target.
05:10 And we'll get onto our target lambda.
05:13 We can see that we're there now.
05:14 Remembering always our air/fuel ratio's always going to move around a little bit so as long as we're within about 1% I'm going to be pretty happy with that.
05:21 So we know that at this point we have adjusted the number at 60 kPa from 70% up to 76.
05:29 Now if we look at our next cell as we open the throttle further we're going to obviously come up to 80 kPa.
05:35 We've still got a number of 70% in there.
05:38 Chances are we're going to at least be 76% if not a little bit more.
05:43 So we can take a bit of a guess ahead at what that might likely to be.
05:47 Just looking at the trend there, we've gone from 70 to 76% so what I'm actually going to do is enter a value of 80% given that we are moving up 10 kPa, that's likely to get us at least in the ballpark.
06:02 So we'll open our throttle, move up to 80 kPa and we'll see how that guess worked out.
06:07 So as I move the throttle open, we can see we are still a little bit lean.
06:10 I'm not too worried about the leanness at this point, we're still in vacuum there and we're pretty close so you can see that that guess that I made though had us really close so just another couple of percent there and we're right onto our target.
06:22 So again looking at the change we're seeing at the moment, we've gone from 50 kPa to 60 kPa, 60 kPa to 80 kPa and we've seen a change of 6% per 10 kPa initially and then we've seen a change of 6% for 20 kPa so I'm just going to extrapolate that out again as well.
06:42 I'm going from 80 to 100, another 20 kPa step so let's take the number there at 100 kPa up to 88%.
06:50 Might not be quite right but we're probably likely to be pretty close.
06:53 So let's again open our throttle, come up to 100 kPa and we'll see where we're at.
06:58 We can see this time we're actually a little bit rich which isn't a bad place to be.
07:02 I'll just use our page down there to get us onto our target and a few percent out of there and we're right on our target.
07:10 So as you can see here, the process is just guessing ahead, it's always good to be a little bit rich when we move into an untuned zone.
07:17 It's also good to keep in mind as we move up in the RPM and we start getting to a situation where we can produce more boost, you can always back off the throttle, come back into vacuum where there's less stress being applied to the engine, make the change to the cell that you were just addressing and then apply throttle, come back to that cell and see if the effect of your change was correct.
07:36 And this just again reduces the amount of stress and strain we're applying to the engine.
07:40 Should also mention here that at the moment we are tuning on the wastegate spring pressure so we're not using any electronic boost control to add to that boost pressure so this is always a good place to start with a turbocharged engine, we always want to start with our minimum possible boost.
07:55 Alright let's continue our process here, so we've actually gone with two cells now at 82% so what I'm going to do is just highlight the cells below this, let's just start with a slight increase in our VE, not too sure how far we're going to be able to get here given that we've got a reasonable sized turbo, 1500 RPM, we're probably not going to be able to produce much boost but let's go through and see if we can get to 125 kPa.
08:19 Now I'm actually sitting at full throttle and we can't quite get there but you can see that our lambda is right on our target there so that guess of another 2% proved to be pretty accurate.
08:32 Let's just come back to idle and we'll have a quick look at what we've achieved so far.
08:35 So we know that we were only able to tune really quite a small slice of the table there from around about 50 kPa through to just around about 110 kPa.
08:48 So at lower RPM it does limit what we can do.
08:50 So what we want to do as well is just take a bit of an educated guess at what's going to happen there.
08:56 We know we couldn't get up to 150 kPa, what I'm going to do though is just guess ahead that if we were able to get up to 150 kPa, chances our our VE may have increased a little bit more.
09:07 Likewise we weren't really able to do anything much with these lower load areas but again I'm just going to take a bit of a guess here at the likely state of the situation.
09:17 We know that we went from 50 kPa down to 40 kPa, we reduced our VE by 9%.
09:24 Now granted we couldn't quite get down to that cell but that's going to get us close so I'm just going to essentially extrapolate those changes down, again being a little conservative, always nice to be rich rather than too lean so we might take out, let's say we'll take this one down to 54% and we might take this one down to let's say 48%.
09:45 Again they're not going to be right, we're just following the trend, we'll see this trend develop as we go through and again this is an area that we will address when we get the chance to confirm the tune out on the road or the racetrack.
09:57 Bearing in mind though this isn't an area that is going to be very easy to access anyway because it will be only under very light load.
10:04 At this point what I'm going to do is use the shift key and the down arrow key to highlight that entire 1500 RPM column, control C will copy that to the clipboard.
10:14 We can move across to our 2000 RPM column, control V will paste that.
10:20 Now when we move from 1500 to 2000 RPM, rightly I'm going to expect that our fuelling or our VE should increase.
10:28 Our volumetric efficiency should increase when we move from such low RPM up in the RPM.
10:33 So what I'm going to do is just take a rough guess at what this might be and we're going to make a percentage change, remember we do this using the P key.
10:41 And in this case let's add 4% fuel, might not be right but we'll see how easy it is to make adjustments if it proves that our guess is wrong.
10:51 I should have also mentioned here, as per the body of the course, we are going to do this steady state tuning out to around about 2/3 of the engine rev limit.
10:59 I'm going to take this out to 4500 RPM.
11:02 Obviously with a turbocharged engine, as our RPM increases as I've mentioned, we need to be a little bit more mindful of the heat that's being generated and that's why I mentioned earlier about going into positive boost, looking at our air/fuel ratio, coming back into idle, making adjustments or coming back into vacuum I should say, making adjustments to the cell we were in and then going back into the throttle to check, rather than sitting there really pounding away at the engine with high boost, it's going to create a lot of heat and temperature in the entire engine bay, all of the components.
11:33 Alright let's get back up and running, we'll use our dyno to control our set point now to 2000 RPM.
11:41 Alright we're back up and running at 2000 RPM.
11:43 Now before we start making individual changes to a specific cell, what we want to do is just come up to a reasonable amount of load.
11:50 Here we're sitting at around about 70 kPa and we just want to see overall was our guess of the percentage increase correct? And right now you can see that probably we're a little bit optimistic.
12:01 We're sitting at 0.92 lambda and our target there is 0.96 so we're actually a bit rich.
12:07 Again, not a bad place to be but however before we start making individual changes, while I've got that entire 2000 RPM column highlighted, just going to use the down, page down button here and just get us onto our target so 3% out of there and we can see that we're basically where we should be.
12:26 Actually I'll just add a little bit back into that.
12:28 Now you can see that actually on face value, it looks like the numbers between 1500 RPM and 2000 RPM actually very very similar.
12:37 So that's OK, that will happen sometimes.
12:39 Now that we've done the overall column, what we're going to do is reduce our throttle again back down as far as we can, see if we can get down to our 50 kPa cell.
12:49 And in fact we'll see if we can get down into our 40 kPa cell, possibly a little bit optimistic there.
12:59 And we can see we are just crossing over there, we're about 43, 44 kPa so not too bad, we can see that we are actually a little bit lean at that point.
13:09 So just going to highlight 40 kPa, actually I'll highlight all the way up to 50 kPa here.
13:14 And we're just going to add a few percent there until we get onto our target.
13:18 So at this point, the way you make your changes is really up to you.
13:22 Because we're quite close I'm just using the page up and page down.
13:25 Again we can't get into the middle of the 40 kPA cell but we're close enough.
13:29 Let's come up to our 50 kPa cell, looking at our fuelling, we're actually pretty close there, maybe a touch rich but we're within 1%, I'm actually going to leave that as it is.
13:38 We'll continue up here, 60 kPa, look at our change there, pretty much right on our target.
13:45 I'll just add 1% there.
13:47 We'll come up to 80 kPa, again this is the benefit of tuning ahead like this, we can see that we are already very close to our target so just a little bit rich in that particular cell but pretty close.
14:02 We'll come up to 100 kPa.
14:06 We need to be a little bit more mindful of course as we move into positive boost, if we are in a situation where we're a little bit lean, we don't want to hold that situation for extended periods of time.
14:15 We should be able to get to 125 kPa now so we're getting pretty close to full throttle.
14:20 And just a touch lean there, couple of percent more fuel and we are on our target so we'll come back to idle now.
14:30 So at that point we were able to go up to 125 kPa, couldn't get to 150 kPa, again I'm just going to guess ahead that we probably want at least another percent in our VE above that point.
14:42 So again we're going to copy and paste, control C and control V, paste that out to 2500 RPM.
14:49 At this point we really didn't see initially any need for a dramatic change in our VE numbers but that's not always going to be the case and again it's always safest to begin from a situation where we're a touch rich and be able to pull some fuel out rather than move into a higher load, higher RPM region and find that we're already actually a little bit lean so again what I'm going to do is just add a few percent to this.
15:11 We can start to build up a bit of an idea, if our last change was 5% and really we only needed 3% well of course we can manipulate our next addition for the subsequent column.
15:22 So in this case let's add another 3% to 2500 RPM.
15:26 I'm now going to go through the process here up to 4500 RPM and this will just be a rinse and repeat of what you've already seen.
15:35 We'll speed this up a little bit.
15:36 If there are any peculiarities that we do note as I'm going through this, we'll stop and we'll discuss those so you can watch the process being completed from here.
16:22 One of the considerations when we are tuning turbocharged engines which is unique compared to naturally aspirated engines is of course they do produce more heat so one of the things we will find as we move higher in the RPM range is that we do need to be mindful of our engine coolant temperature which we can see we're monitoring here.
16:39 Also our manifold air temperature which is going to be less of a concern today.
16:44 It's quite cool here in Queenstown so we're not likely to see excessive manifold air temperature but if we are tuning at higher RPM under boost we may find that our engine coolant temperature starts to climb and it's a good idea to just keep an eye on this and if you need to, just come back to idle, allow the coolant temperature to come back to normal conditions and then you can go again.
17:06 Patience here is important and we don't want to put any undue stress and load on our engine.
17:13 We're up to 3500 RPM now, so let's continue the process.
17:31 Alright so at this point we've got our engine tuned in steady state up to 3500 RPM and one of the things I'm actually going to do is go back and make a change to our target lambda table.
17:40 This is a consideration with rotary engines, obviously they are susceptible to running quite a lot hotter and this is one of the reasons why we generally tend to run a richer air/fuel ratio than a comparable petrol engine.
17:52 Now this is a bit of a tightrope that we're walking with something that will be used as a street car.
17:58 Obviously under cruise conditions we do want to run the air/fuel ratio as lean as we can, closest to stoich for good fuel economy.
18:05 Tailpipe emissions obviously another consideration but generally not a strong point for a rotary engine in the first place.
18:11 If it was a race only application then I would tend to run the engine a lot richer in these overrun conditions because if you have been watching, we actually have a 0-5 volt external input here.
18:24 This is our exhaust gas temperature so right now sitting here at 1000 RPM idle, and actually about 0.85 lambda, we can see that that's already sitting at around 690°C.
18:34 In the vacuum areas of the map that we've been accessing there we're actually seeing that this is pushing in excess of 900°C.
18:43 Interestingly though as we move higher into load, into boost, because our air/fuel ratio targets are richer, we start to see that EGT drop down to something that's a little bit safer so this is a consideration that is peculiar to rotary engines, the exhaust gas temperature does tend to be a little bit hotter.
18:59 Now of course not everyone's going to have access to exhaust gas temperature sensors which is helpful but certainly not essential.
19:06 What I'm going to do here is go across to our target lambda table and to start with, notice that I had set up these areas here, or actually this entire block out here to 8000 RPM, to a target of lambda one.
19:19 Not strictly necessary that we are running lambda one, particularly in these higher RPM areas.
19:25 Essentially once we are at maybe 3500, 4000 RPM and above, at that point we're not really cruising under those conditions so really the area that we're most interested in fuel economy is sort of the 2500 through to 3000 RPM area so what I'm going to do is actually make a change here to this table and we'll set our overrun areas, our vacuum areas above 3500 RPM to 0.95 lambda so just using a little bit more fuel to help cool and control those combustion temperatures and again if this was a race engine I wouldn't bother trying to set my 2500, 3000 RPM zones to lambda one either, we want the benefit of the additional fuel there for some additional cooling.
20:07 Alright let's carry on now and we'll move out now to our 4000 RPM column and continue our tuning.
20:48 Alright so at this point we've got our fuel tuned out to 4500 RPM and what we can see straight away if we look at our map visually is we've got a reasonably consistent pattern showing up in that table which is pretty typical.
21:01 Regardless whether the engine is piston or rotary, this is the sort of pattern or trend that we're likely to see in a fuel map.
21:09 What we're going to do now is extend the numbers that we've got out there into the untuned areas and basically just take some educated guesses in those areas which are going to stand us in pretty good steed once we move through into our wide open throttle ramp run tuning and we move past our current 4500 RPM range.
21:27 So what I'm going to do is just copy our 4500 RPM column out here and we'll just copy this across and once I've done this we're also just going to take again a bit of an educated guess at what we might see eventuate in terms of a bit of a pattern here.
21:42 So I'm expecting that we might see a bit of an increase in our VE numbers around about 5500 RPM so what I'm going to do is just add another couple of percent here, likewise we will probably start to see our VE start to taper off once we get up above about 6500 RPM so we can just guess these values, we don't have to be pinpoint accurate, we're just trying to add a little bit of shape into this table so that when we get into those untuned areas we're already going to be reasonably close.
22:17 We're going to obviously be able to address them though when we get through to our ramp run tuning.
22:22 Now this also leaves a pretty ugly area of our table down at the low RPM region where we couldn't really get to under wide open throttle ramp run tuning, sorry we couldn't get to under steady state tuning.
22:34 The engine's not going to be very happy about being loaded at 750 to 1000 RPM.
22:38 What we can do though is take a little bit of note of the numbers we've got here at idle, we are currently actually a touch rich here anyway so what I'm going to do, we know that we've tuned our 1500 RPM column, just going to copy and paste that down to 1000 RPM and what we're going to do then is highlight the entire column and we'll just lean that out until we get onto our target there.
23:01 Once we've done that, what we can do is then highlight across there and we can use the horizontal interpolation which is the X key, that will just interpolate between 1000 RPM and 1250 RPM.
23:16 We're then going to copy our 1000 RPM column and we'll paste that down to our lower regions.
23:23 Now it's likely that we are probably going to end up with our VE a little bit lower at those lower RPM ranges as well so again we can just take a bit of an educated guess at what the shape of that table is likely to be.
23:38 So with a relatively minimal amount of effort, we've now got a table that looks a bit more like what we'd expect from a VE table.
23:47 We know that at least in those cruise areas which are so crucial for a street driven car, we know that our air/fuel ratio is on point, we're going to get good control of our air/fuel ratio, we've richened those vacuum area target lambda numbers for control over our exhaust gas temperature at higher RPM where we're not going to be so worried about our fuel economy.