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Diesel Tuning Fundamentals: Effect of Injection Timing on EGT

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Effect of Injection Timing on EGT

07.30

00:00 - Within the course we've already discussed the fact that our exhaust gas temperature is heavily affected by the mass of fuel that we choose to deliver into our diesel engine, or in other words the air fuel ratio that we choose to run the engine at.
00:14 In this practical demonstration we're going to take a deeper look at that relationship and see exactly what happens to our exhaust gas temperature as we add or remove fuel from our tune.
00:25 Now in order to measure exhaust gas temperature our Toyota 1KD engine has been fitted with four individual cylinder K type EGT thermocouples.
00:35 These are being delivered into our Motec ECU, and for the purposes of our demonstration today, what we're actually looking at is the average of those four individual cylinder exhaust gas temperature probes.
00:47 We can see that on our laptop software here, our bottom channel here in purple is our exhaust gas temperature.
00:54 And we can see that at idle we're currently sitting at about 120 degrees.
00:57 Now for our first demonstration we're going to have a look at how the mass of fuel that we deliver affects that exhaust gas temperature.
01:06 We're going to look at a single operating point.
01:08 We're going to be running here in our table at 2000 RPM and wide open throttle.
01:13 We can see at the moment I've got a value of 40% set in our fuel mass nominal table.
01:18 Now remember that that delivers 40% of whatever fuel value we have in our fuel mass limit main table which you can see at 2000 RPM is 115 milligrams.
01:30 So we're gonna be delivering 40% of 115 milligrams.
01:34 Let's get our engine up and running and we'll see what that actually gives us.
01:37 OK so we can see that we are currently delivering around about 47 to 48 milligrams of fuel into the engine.
01:45 And we're also running at a relatively lean air fuel ratio, we're running at around about 1.7 lambda which is quite lean given that fact we are at wide open throttle.
01:56 And we're seeing the exhaust gas temperature's currently sitting at about 420 degrees.
02:01 Now there is a little biti of latency in our exhaust gas temperature reading.
02:05 It also takes a little while for the system to reach equilibrium.
02:08 And at the moment it's sitting relatively stationary.
02:10 So what we're going to do now is increase the value in our fuel mass nominal table, we're gonna increase that from 40% up to 65%.
02:22 And we're gonna see the effect on our tune.
02:25 So straight away we can see that we've gone from 47 to 48 milligrams of fuel delivered up to 75 milligrams.
02:32 And you'll remember that our exhaust gas temperature was previously about 420, we can see that that's jumped quite massively.
02:38 We've gone up about 130 degrees centigrade 140 degrees centigrade, we're sitting at 560 degrees now.
02:45 And we can see that our lambda has dropped from, previously we were at 1.7, we're now at lambda 1.1, 1.2 Let's go a little bit further though.
02:55 Let's take our fuel delivery up to 75% nominal.
02:59 And we can see that our lambda is now sitting at about 1.1, so we're probably right on that smoke limit or may even producing some exhaust smoke.
03:08 We see that our exhaust gas temperature has now climbed further, we're up to 630 degrees and our fuel mass being delivered into the engine is 87 to 88 milligrams.
03:19 So you can see there's quite a dramatic effect there as we vary our fuel delivery.
03:23 Let's have a look at those three points again.
03:26 We started out to the left here, and our lambda was 1.7 We were delivering 47, 48 milligrams of fuel, and our exhaust gas temperature was 425 degrees centigrade.
03:38 Our second test point there where we're delivering 75 milligrams of fuel, we can see our exhaust lambda was about 1.1 to 1.2 and our exhaust gas temperature crept up to 580 degrees centigrade.
03:52 Our final test point there, our lambda was just a little bit richer actually at this point than 1.1, we're about 1.07 We're delivering 87 milligrams of fuel and our exhaust gas temperature has jumped up to almost 650 degrees centigrade.
04:08 So these are parameters that we do need to be aware of and understand as we're varying our fuel delivery.
04:15 For our next demonstration we're going to have a look at the effect of our fuel pressure for a fixed mass of fuel on our exhaust gas temperature.
04:23 And what we're expecting here is that as we drop our fuel pressure, the pulse width of the fuel delivery is increased, and this means that the fuel burn continues, or the combustion process continues further through the engine cycle.
04:36 So the expectation here is that our exhaust gas temperature reading will increase as we drop our fuel pressure.
04:42 Let's get up and running at exactly the same operating point in our table.
04:47 Alright we'll just allow our exhaust gas temperature to reach equilibrium for a moment.
04:52 In the meantime though we can see that we're currently operating around this point in our fuel pressure target table.
04:58 We can see on the right hand side, our fuel pressure target versus our measured fuel pressure.
05:04 You can see that we're sitting at around about 187 megapascals.
05:07 We're seeing that our exhaust gas temperature is still climbing, but we're just about at equilibrium around about 545, 550 degrees centigrade.
05:19 So what I'm going to do is we'll make quite a dramatic change to our fuel pressure.
05:24 What I'm going to do is take 90 megapascals out of our target.
05:28 So we can see that as I've done that, our fuel pressure has dropped to a target of 97 megapascals.
05:35 We're seeing that our exhaust gas temperature is now beginning to climb.
05:39 Remember we were sitting at about 550 before I made that change, we're seeing that we're still climbing through about 580, 590 degrees centigrade.
05:48 So we've seen that relationship there as we've reduced our fuel pressure, our exhaust gas temperature has climbed.
05:56 For our last demonstration we're going to have a look at the relationship between our injection timing and our exhaust gas temperature.
06:03 So again we'll be using our same operating point 2000 RPM and wide open throttle.
06:08 So let's get the engine up and running there now.
06:11 So we can see that at the moment our injection timing is sitting at around about 15 degrees before top dead centre.
06:18 Again we're just allowing our exhaust gas temperature to reach equilibrium, we're seeing that coming up through 530, 540 degrees centigrade right now.
06:27 Now again the expectation here is that as we retard the injection timing, the combustion process occurs later in the engine cycle, so this should result in our exhaust gas temperature increasing.
06:38 So right now our exhaust gas temperature's sitting at about 560, still climbing slightly but it has levelled off.
06:44 What I'm going to do is highlight the operating area there of our injection target table and we'll retard our timing to zero degrees, and we're starting to see our exhaust gas temperature climb.
06:56 So we're sitting up at about 590 degrees at the moment, and our exhaust gas temperature is continuing to climb.
07:04 So the relationship we see there is exactly what we would expect.