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Diesel Tuning Fundamentals: Smoke Limit Practical

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Smoke Limit Practical


00:00 - In this demonstration we're going to take a look at how the various aspects of diesel fuel injection affect the smoke output in the exhaust.
00:07 Now we're going to be measuring that smoke output directly using an opacity meter connected to our Mainline dyno.
00:14 And we'll be able to see the effect of the tuning changes that I make relatively quickly being displayed on the dyno screen.
00:23 Now we'll have a quick look at the aspects that we've got on our dyno screen.
00:28 We've got our engine running at the moment and what we're going to be looking at for our opacity or smoke output is this yellow line here on our moving time graph.
00:36 So right now we can see at the bottom that we're registering 4% opacity.
00:42 So it's a relatively small amount.
00:44 There's no visual smoke output from the exhaust with such a low smoke reading.
00:49 So once we get into the demonstration we'll be able to monitor and see how that yellow line is moving as we make our tuning changes.
00:56 First of all let's have a look at how the Motec ECU deals with smoke limiting.
01:00 In this case there are two tables in the ECU.
01:03 We are going to start here on our fuel mass limit smoke table.
01:07 This is a three dimensional table, where essentially we have our engine load on the vertical axis and we have our engine speed on the horizontal axis.
01:16 Now the point of this table is that at any particular combination of load and RPM, we can define a maximum fuel mass that will be delivered.
01:25 And this overrides any other fuel mass commands from other tables inside the ECU.
01:32 So what we can do is essentially drive the engine on the dyno at each point in this table and we can set a fuel mass limit that is going to provide what we deem to be an acceptable smoke output from the exhaust.
01:45 The other option which we aren't using at this point is our fuel mixture minimum table.
01:52 As it's name implies, this is simply the minimum lambda target that can be commanded by the ECU.
01:59 Again we have our same axis, we've got our engine charge on the vertical axis and engine RPM on the horizontal.
02:06 And inside this table we simply command our minimum lambda that we're happy with.
02:11 Whatever minimum lambda we find gives us an acceptable smoke output from the exhaust.
02:17 Right now you can see that I've got this table filled with a target of 0.2 lambda.
02:22 Essentially this just deems this table completely ineffective.
02:26 And we're going to be making our smoke limiting changes here in the fuel mass limit smoke table instead.
02:34 OK let's have a look and see how that table works.
02:38 What we're going to do is start by jumping back to our fuel mass table, this is our main tuning table where we're going to command the percentage of our fuel mass limit.
02:49 Let's have a look at the interaction of these smoke limit tables now with the fuel delivery and we'll see how it affects the smoke output from the engine.
02:57 Let's start by doing a quick demonstration here.
02:59 We're going to go to 1500 RPM at wide open throttle.
03:03 And at the moment we can see that we are requesting 60% of our fuel mass limit main value.
03:12 This is delivering 65 milligrams of fuel.
03:15 If we head over to our dyno we can see that this is resulting in an opacity of around about 13% to 14%.
03:22 We'll just come back down to idle, and we'll have a look at those results.
03:27 Now with an opacity value of 13% to 14% this is not going to deliver any visible smoke out of the exhaust.
03:35 Let's also have a look in our laptop tuning software and we can see that that was delivering an exhaust lambda of 1.2 so again generally this is lean enough that we're not going to end up with any visible smoke from the exhaust.
03:49 Now remember that we had at this point 65 milligrams of fuel being delivered into the engine, and if we head across to our smoke limit table, we can see at the point that we were operating, we're at around about 1000 milligrams of engine load and 1500 RPM.
04:06 The limit in this case is 80 milligrams.
04:09 Because we're delivering 65 milligrams which is below that limit, all of the fuel that we are commanding will be delivered into the engine.
04:17 OK so what we're going to do now is make some changes to our fuel mass and we'll see how that affects the exhaust smoke.
04:25 What we're going to do is highlight the cell that we were operating, 60% that we had there at 1500 RPM and 100% throttle, and instead we're going to take this now up to 75%.
04:38 So we're going to be commanding more fuel delivery.
04:41 Let's go back to that same point and we'll have a look at the effect on our exhaust opacity.
04:46 OK so straight away we can see a huge increase in our opacity.
04:50 We've come up to around about 58%, 59% exhaust opacity.
04:55 So this would be sufficient to provide us with significant exhaust smoke.
05:01 Let's come back down to idle and we'll have a look at our parameters inside our ECU.
05:06 So on our time graph here, we've paused that, and we can see that where we're at 1500 RPM in wide open throttle, our lambda this time, instead of being 1.2 as we had in our first test, we're now sitting at around about 1.03 so again a rough rule of thumb there, anything richer than approximately 1.1 lambda is likely to result in exhaust smoke.
05:28 Now let's have a look as well at the amount of fuel being delivered, and we can see that in this instance we're sitting almost bang on our limit of 80 milligrams.
05:38 So we've gone from 65 milligrams up to 80 milligrams.
05:42 OK so let's now have a look at how we can use that smoke limit table.
05:46 Remembering we are operating in this region of our smoke limit table here.
05:50 We know that with 65 milligrams of fuel being delivered, we had no visible smoke from our exhaust, so what I'll do is just set those two cells there that we're interpolating across back down to 65 milligrams.
06:04 Let's do one further test here.
06:07 Now you'll note before I start this test, that I haven't changed our value in our main, our fuel mass nominal table, our main fuel delivery table.
06:17 We're still at 75% there.
06:19 So let's get back up and running and we'll see the effect of using that smoke limit table.
06:25 OK so again on our dyno here we can see that our opacity is sitting around about 14%.
06:31 So again we're not going to get any visible smoke with that sort of opacity reading.
06:38 Let's come back down to idle and have a look at our parameters inside our laptop software.
06:43 OK so again we can see that our lambda is now 1.2 so the same as what we had in our first test which isn't particularly surprising.
06:50 What we can see now is if we look at our fuel mass being delivered, our fuel mass being delivered is 65 milligrams.
06:58 Remember that is what we set our smoke limit table to.
07:01 Below this though in red we can see the channel fuel mass unlimited, and we see that that's sitting at 80 milligrams.
07:09 So a fuel mass unlimited channel in the Motec ECU is telling us what the main fuel tables are actually commanding.
07:17 But in this case we are reducing that fuel mass down because of our smoke limit table.
07:23 So this is how we can use the interaction of that smoke limit table to control the particulate matter from our exhaust.
07:30 But it's also important to understand that if we are making changes to our fuel delivery and we're not seeing any effect from those changes, we do need to just check and make sure that there isn't a smoke limit table or some limiting table that's actually reducing the final fuel being delivered into the engine.
07:51 Now we're going to have a look at how two other aspects of our fuel delivery affect the smoke output from our exhaust.
07:57 We're going to be making these tuning changes in the same site that we were previously running, wide open throttle and 1500 RPM.
08:04 Let's start by seeing the effect of reducing our fuel pressure.
08:09 Now you'll remember that when we reduce our fuel pressure, we're going to need our injection pulse width to increase in order to deliver the same mass of fuel into the engine.
08:21 This has the effect of moving our 50% burn point further past top dead centre and our burn or combustion is going to continue further through the engine cycle.
08:32 So let's have a look at that now, and we are expecting that this will increase our particulate matter in the exhaust and that should be shown by a higher opacity reading.
08:42 Let's get started now.
08:44 OK we'll get our engine up and running here and we can see that at the moment our fuel pressure target is sitting at around about 186 megapascals.
08:53 Let's have a look at our smoke output, we can see that's sitting at about 22%.
08:57 Let's bring our fuel pressure target down to 130 megapascals.
09:02 And let's see what that does to our smoke output.
09:05 And we can see that straight away that's jumped up to 50%.
09:08 Now we're still delivering the same mass of fuel but this time we are delivering it with a lower fuel pressure.
09:14 Let's come back down to idle and we'll have a look at the results there.
09:17 Alright again at the bottom of our channels here we have our fuel pressure so we can see the point where we've made that fuel pressure change.
09:24 What we're looking at here though is our injection pulse width.
09:28 So prior to dropping that fuel pressure we can see our main injection pulse width is sitting at 0.8 milliseconds.
09:35 After we've dropped that fuel pressure down though the injection pulse width has increased to 0.9 milliseconds.
09:41 Now we can also see the effect albeit subtle in our injection timing.
09:45 Initially with our higher fuel pressure we see that our injection event starts 8.4 degrees before top dead centre and it finishes 0.9 degrees before top dead centre.
09:58 After we have reduced our fuel pressure though we can see that our start of injection point has stayed the same, 8.4 degrees before top dead centre.
10:06 But our injection event is now finishing half a degree after top dead centre.
10:11 So the effect of dropping our fuel pressure there has increased our pulse width and we see the effect in increasing the exhaust opacity or exhaust smoke output.
10:21 For our last test we're going to see the effect of our injection timing on our exhaust smoke output.
10:27 For this test we're going to go to exactly the same cell that we've been operating in so far, 1500 RPM, and wide open throttle.
10:34 So let's get up and running there.
10:36 Alright so we can see that our initial injection timing is eight degrees before top dead centre.
10:41 And we can see if we look across to the dyno, that currently we're sitting at about 22% to 23% smoke output.
10:48 Let's now highlight all of the cells we're operating in here and we'll retard the timing back to TDC.
10:55 Straight away we can see the smoke output jump up on our dyno screen, we're up to about 54%.
11:01 Let's try advancing the timing now, instead of eight degrees we'll go to 14.
11:06 And we'll see that the smoke output straight away drops away.
11:10 In this case we've dropped down to 10%.
11:14 Remember with eight degrees injection timing we were sitting at about 22% to 23%.
11:20 So we can see that the injection timing actually has a really dramatic effect on the smoke output from our engine.
11:27 So hopefully this demonstration has given you a little bit more understanding on exactly what effect these tuning parameters have on our exhaust smoke output.

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