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Diesel Tuning Fundamentals: Effect of Injection Timing on Power and Torque

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Effect of Injection Timing on Power and Torque


00:00 - In this demonstration we're going to have a look at how the injection timing affects the engine operation and in particular how it affects the engine's torque production.
00:08 We'll also have a look at how tuning aspects such as our fuel pressure and our injection pulse width also affect our injection timing or our injector timing events.
00:19 Before we do that though let's have a quick look through the Motec software, so that you've got a better understanding of the tables that we'll be manipulating.
00:26 Here we've got our fuel timing table, this is represented graphically on the right hand side as well as numerically on the left.
00:33 We'll just get rid of our graphical representation for the moment, and we've got a three dimensional table here.
00:40 The vertical axis is our fuel mass being delivered and our horizontal axis is our engine RPM.
00:46 We've got the sort of trends in this table that we'd expect, as we move from low RPM to high RPM we can see that down around idle we're injecting the fuel, starting our injection event I should say at zero degrees at top dead centre.
01:02 However as we move to the right, as our RPM increases we can see that we are advancing the injection point, we're starting the injection earlier in the engine cycle.
01:12 In this case out at 4000 RPM we're around about 25 degrees before top dead centre.
01:17 Likewise if we look, we've also got similar trends as we increase the fuel mass being delivered, so as we move from low fuel mass to high fuel mass.
01:26 Down at low fuel mass we can see that at 2500 RPM we're starting our injection around about three to six degrees before top dead centre.
01:34 However as we increase the mass of fuel being delivered, we can see that we advance that further so that at higher fuel mass we're staring our injection event around about 14 degrees before top dead centre.
01:46 Now on the right hand side we're also got some interesting channels that we're logging here.
01:51 First of all we have our fuel pulse width, so this is the main fuel pulse width, the main injection event pulse width, we can see here at idle we're sitting at around about 0.6 to 0.7 milliseconds.
02:03 We're also able to visualise graphically where the injection event is starting and finishing thanks to our next group of channels here.
02:12 In green we have our injection starting event, in this case zero degrees, and in red we have the point in the engine cycle where our injection event is finishing, in this case minus 3.9, essentially 3.9 degrees after top dead centre.
02:28 And we've also got two further channels down here at the bottom, we've got in blue our fuel mass.
02:33 This is the mass of fuel being delivered by the ECU.
02:35 And in red we've got our fuel pressure, so this is our direct injection, high pressure fuel pressure.
02:42 OK so with that our of the way we're going to perform a few demonstrations.
02:46 What we're going to do is start by getting our engine running and we're going to perform a torque optimisation test.
02:52 So let's get that underway now.
02:54 So for our torque optimisation test I'm going to start by getting our engine running here at 2000 RPM and we're delivering approximately 40 milligrams of fuel.
03:04 And we can see that the cell we're operating in right now, our start of injection is 8.9 degrees before TDC.
03:10 And we can see exactly what's happening over here on the right hand side.
03:14 We can see in green our start of injection event is in fact 8.9 degrees.
03:18 And we can see that our injection event is finishing around about one degree before TDC.
03:25 So our injection event is taking approximately eight degrees of crankshaft rotation there.
03:31 Below we can see the fuel mass being delivered, again 40 milligrams.
03:36 And we can also see our injection pulse width which is approximately 0.6 to 0.7 milliseconds.
03:43 Now before we start this test what I'm going to do is highlight all of the cells around the point we're currently running in and we're going to set them all to minus 10.
03:53 So what this means is we're now starting the injection event 10 degrees after TDC.
03:58 Let's head across to the dyno and we will clear our torque optimisation test and I'll just explain what we're looking at here.
04:06 So our torque optimisation test is going to log the relationship between engine torque and our injection timing, our start of injection timing.
04:15 On the vertical axis here we have our torque being registered by the dyno at the rear wheels, and on our horizontal axis we have our injection timing being delivered to the dyno from the Motec ECU.
04:26 So what I'm going to do now is click begin and I'm going to begin advancing the timing at approximately a degree every second.
04:35 And while I'm going this you'll be able to see that the dyno is drawing in a red line that's showing that relationship between our injection timing and our engine torque.
04:46 Particularly as I begin advancing the timing from our very retarded starting point we're seeing that torque line increase quite dramatically.
04:55 So we're coming through zero degrees now and I'm going to continue advancing the injection timing all the way up in this case to 20 degrees.
05:04 What we're looking for here is to find the injection timing that offers us the optimal amount of torque.
05:12 OK so at this point we're just coming up through 10 degrees of injection timing now.
05:18 We'll keep on climbing and we're seeing that our torque is still increasing slightly as well.
05:23 Coming up through 15 degrees, and we'll continue now, we're starting to actually see our torque begin to drop away as I continue to advance the timing.
05:35 OK we're at 20 degrees now so we'll back off the throttle and we'll have a look at our results.
05:41 Now it is important when we are viewing the results from one of these torque optimisation tests to do a little bit of mental smoothing with the resulting graph, the dyno is very sensitive.
05:51 So we can see that we've got a few dips and peaks in this graph that we would want to just mentally smooth out.
05:58 What we are seeing though is that the dyno is showing us that for that particular operating point, 40 milligrams, and 2000 RPM, the optimal torque was delivered with an injection timing of 15.9 degrees before top dead centre.
06:11 So in this respect it is very similar to optimising the ignition timing in a spark ignition gasoline engine.
06:19 We do need to add a note of caution here though.
06:22 In some instances advancing the injection timing in a diesel engine can in fact be dangerous so this does need to be approached with some caution.
06:32 And in some instances we are better off sacrificing a little bit of performance and a little bit of engine torque in order to ensure engine reliability.
06:41 Now that we've looked at the effect of our engine timing on our engine torque, we're going to go through and have a look at how the fuel pressure affects the injection timing.
06:51 Let's get our engine back up and running again at our same point, 40 milligrams and 2000 RPM.
06:57 We've reverted now to our initial injection timing table.
07:00 And again we'll just have a quick look at the parameters we've got at this operating point.
07:07 We'll just allow the engine to stabilise there.
07:09 And again we can see that our primary injection pulse width is sitting around about 0.7 milliseconds.
07:16 We can see that our start of injection event is 8.9 degrees and we're finishing that approximately eight degrees later at 0.9 degrees before top dead centre.
07:27 So the important points to note here are that we're delivering 40 milligrams of fuel and that our fuel pressure is currently sitting around about 135 to 140 megapascals.
07:39 What we're going to do now is jump across to our fuel pressure table.
07:42 And I'm just going to simply remove 50 megapascals from our fuel pressure target.
07:48 We'll head back to our timing, I don't want you to worry too much about the fuel pressure table at the moment, we look at that in a further demonstration.
07:56 OK so let's have a look at what we've got here.
07:58 The first important thing to note is that our fuel mass being delivered has not changed, we're still sitting essentially at 40 milligrams of fuel being delivered.
08:08 What we can see now though is that our fuel pulse width has increased.
08:12 Remember we were sitting at around about 0.7 milliseconds.
08:15 That's increased up to around about 0.8 to 0.9 milliseconds.
08:20 And the effect of this is on our injection end point.
08:24 Let's have a look at our start and end point here.
08:27 We can see that our start of injection point is still essentially identical, we're sitting at 8.7 degrees.
08:33 But now we can see that our injection event is continuing until 1.7, 1.5 degrees after TDC.
08:42 So essentially our injection event is now taking around about 2.5 degrees longer to complete.
08:51 So the point of this demonstration is that for a given mass of fuel to be delivered into the engine, as we reduce the fuel pressure, the injection pulse width increases.
09:01 The effect of increasing the injection pulse width is that the end of injection point is extended out and it takes physically more crankshaft degrees of rotation for that injection event to be completed.
09:14 We're going to have a look at one last demonstration now and we'll see how adjusting the mass of fuel being delivered to the engine affects our injection pulse width.
09:23 Before making any adjustments to the fuel mass being delivered, I've just reverted to our original fuel pressure.
09:29 So we can see that we're back at the same point delivering approximately 39 to 40 milligrams of fuel and we've got our same start and end of injection values and we're also back to delivering around about 0.6 to 0.7 millisecond pulse width.
09:44 What we'll do is we'll head across to our fuel mass table.
09:47 And what I'm going to do is just highlight the areas that we're currently running in, around about 10% to 15% throttle, and I'm just going to increase these values by 20%, we'll head back to our timing table and see how that's affected our engine operation.
10:03 First thing to note is that we can see our fuel mass has increased and we've jumped all the way from 39 milligrams up to 56, 57 milligrams.
10:13 Now that's had an important change there in that we are now operating at a different point in our fuel injection table, remembering that fuel mass is our load axis.
10:23 So we've now advanced our start of injection point up to approximately 12 degrees before top dead centre.
10:29 The other important effect here is that in order to deliver additional mass of fuel, we can see that our injection pulse width has increased.
10:38 Now we've gone from 0.6 to 0.7 milliseconds out to 0.8 milliseconds.
10:44 So we can see the effect of this on our injection timing.
10:48 So as we've noted, our start of injection timing has advanced anyway by virtue of the numbers in our table, we're now starting our injection event around about 11.7 degrees before TDC.
11:00 And we can see that our injection event is now finishing or completing around about 1.7 degrees before TDC.
11:07 So in other words our injection event has now gone from approximately eight degrees, which is what we were previously using to deliver 39 milligrams of fuel, out to approximately 10 degrees which is what's required to deliver 57 milligrams of fuel.
11:24 So hopefully those demonstrations have helped to reinforce how the injection timing affects the engine operation.