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Diesel Tuning Fundamentals: Pilot Pulse vs Diesel Knock

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Pilot Pulse vs Diesel Knock


00:00 - For this demonstration we're going to have a look at the effect of pilot injection pulses on the audible knocking sound that diesel engines are so well known for, particularly at idle.
00:10 Now for all of the demonstrations in this course we are using a Motec M150 aftermarket standalone ECU running Motec's GPR diesel package.
00:20 Now this is relatively rare in the aftermarket for tuners to be using an aftermarket standalone ECU.
00:27 But the reason that we are using this to demonstrate the aspects that we want to look at in this course is that it allows us to make these changes in real time.
00:36 We can make these changes live and they'll take effect instantly.
00:39 Makes it much more powerful for us to demonstrate exactly what's going on, as opposed to reflashing a factory fitted ECU where we physically need to shut the engine off, reflash the new calibration into the ECU, and then start the engine and perform another test.
00:55 So this just speeds up the process and allows us to really clearly demonstrate the aspect that we're trying the focus on.
01:01 Now of course for those of you who are already familiar with diesel tuning, and are coming from a reflashing background, the tables that we may be looking at in the M150 ECU may look a little bit different, but I'll be explaining it each step of the way what those tables are, and remember what we're really trying to focus on here is the core fundamental principles.
01:21 And these don't change regardless whether we're using an aftermarket standalone ECU or we are reflashing the factory fitted ECU.
01:28 As well as the ECU we will be demonstrating all of these aspects using our Toyota 1KD four cylinder three litre turbo diesel engine.
01:38 OK with that introduction out of the way, let's have a look at pilot injection.
01:42 So what I'll do first of all is give you a quick tour of the relevant tables in the M150 ECU so that we can see exactly what's going on.
01:51 We start here on our first pilot worksheet.
01:55 This is where we can configure the mass of fuel that will be delivered by our first pilot pulse as well as the injection timing.
02:02 So we can see here we've got our table that defines the mass of fuel that will be delivered by that first pilot pulse.
02:10 Right now you can see that I've set that table to zero.
02:13 So at the moment we have no pilot injection operating.
02:16 Below this we have our injection timing for our pilot pulse and this defines exactly where abouts in the engine cycle that pilot pulse will occur.
02:26 So you can see we've got some timing values in there.
02:28 We're not gonna be focusing too much on those timing values right now.
02:31 We'll just see the actual effect of having pilot pulse versus no pilot pulse.
02:35 We'll move across as well we also have our second pilot pulse.
02:40 So the Motec M150 GPR diesel package allows us to run one or two pilot pulses.
02:47 So this looks much the same.
02:49 Again, particularly in the idle area here, we've got our second pilot table set to zero so it's delivering no fuel mass.
02:57 And of course we also have our timing for our second pilot pulse.
03:01 So you can see the numbers in this table are a little bit more retarded than our first pilot, obviously this is happening, our second pilot pulse is happening after our first pilot pulse.
03:11 OK let's get our engine up and running.
03:14 So we're just going to start it, we'll allow it to idle and you'll be able to audibly hear the knocking sound that is so common from a diesel engine with no pilot injection.
03:33 So this is the sort of audible knocking sound that we've come to expect from older diesel engines.
03:39 Now what we're going to do is add in our pilot pulse one and pilot pulse two and we'll see the effect on that audible knocking sound.
03:47 And in this instance all I'm going to do is add one milligram of fuel to each of those tables.
03:52 Let's do that now, we'll start on our second pilot table here.
03:56 So we can also see there is a little grey box that shows us exactly where we're operating at the moment.
04:02 We've got axis here of engine RPM on the horizontal axis, and our vertical axis here is the fuel mass being delivered.
04:10 So right now we're under idle conditions.
04:12 What I'm going to do is just highlight the entire section of that table, covering the area we're idling in, and we'll just set that to one milligram.
04:19 We'll head across to our first pilot table now and again we'll highlight that entire area and we'll set that to one milligram as well.
04:27 So now we've got our two pilot injection pulses occurring and straight away audibly we can hear how much quieter the engine is.
04:41 So straight away you can hear the difference in that audible knocking sound just by the addition of those two pilot injection pulses.
04:48 So that we can see exactly what's going on inside the ECU and how the ECU is controlling the fuel injectors, let's just have a look at the parameters or channels in our time graph, we'll just enlarge these.
05:01 At the top of our time graph we've got our engine RPM.
05:03 We can see we're sitting at an 800 RPM idle.
05:06 Below this we have our fuel mass being delivered by the injector through the three pulses that the injector is delivering, our pilot pulse one, pilot pulse two, and then our main pulse.
05:17 You can see that those are 0.8 milligrams, 1.0 milligrams and then 1.3 milligrams respectively.
05:23 Below this we can see how that corresponds to the actual pulse width required from the injector in order to deliver that mass of fuel.
05:30 Again, 0.4, 0.4, and 0.5 milliseconds.
05:35 And lastly we can see the injection timing events, those three pulses.
05:40 So our initial pilot pulse one is starting 18 degrees before TDC, our second pilot pulse is beginning at 10 degrees before top dead centre, and our main fuel injection event there is beginning zero degrees before top dead centre, so right when the piston is at the top of the stroke.
05:58 So this demonstrates the effect of pilot injection on reducing the audible knocking sound from our diesel engines.
06:05 Now OE manufacturers will be developing their pilot injection strategy with the aid of in cylinder pressure monitoring.
06:12 For us in the aftermarket though, we're unlikely to have access to that sort of data.
06:17 Instead what we're going to need to do is rely on our ears and the effect of changes on the pilot injection to the audible knocking from the engine.
06:26 Fortunately though we're unlikely to need to develop our pilot injection maps from scratch and in most instances, we will be basing our tuning changes on an existing factory developed pilot injection map, and this may not even need any changes from us.

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