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Diesel Tuning Fundamentals: EGR vs EGT and NOx

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EGR vs EGT and NOx

09.33

00:00 - In this demonstration we're going to have a look at some of the aspects that will affect our exhaust emissions from a diesel engine.
00:06 In particular here we're going to be using a five gas analyser connected to our Mainline dyno.
00:12 And this is going to be showing us the oxides of nitrogen or NOx levels in parts per million.
00:18 And we're going to look at three aspects here.
00:21 We're going to look at the exhaust gas recirculation.
00:24 We'll see the effect of EGR on the NOx output.
00:28 We'll also investigate the effect of our injection timing on NOx output, and lastly we'll have a look at our injection pilot pulse, and we'll see what effect that has on our NOx.
00:39 So let's get our engine up and running and we'll have a look at our exhaust gas recirculation first.
00:45 Before we actually make any changes to our exhaust gas recirculation tuning, let's just have a quick look through the Motec M150 worksheet for EGR, and we'll look at the main parameters that we need to understand, and the ones we're going to be adjusting.
00:58 First of all here we have our main EGR engine charge aim table.
01:04 So this is where we're defining essentially the percentage of EGR operation that we want.
01:10 At the moment you can see I've got a value of 2000 milligrams set in this table and essentially that's disabling the system.
01:16 We'll have a quick look at our time graph on the right and we'll see the parameters that are useful or important for us to understand here.
01:23 At the bottom we have our current engine charge versus our engine charge estimate.
01:29 The engine charge estimate is coming from our table that we've just looked at, and the engine charge essentially is a calculated parameter that is based on the air flow into the engine.
01:39 Above this we have our actuator solenoid for our exhaust gas recirculation valve.
01:44 So this is the solenoid that actually opens and closes the EGR valve.
01:48 This is all done using vacuum.
01:51 So at the moment we can see that this is sitting at 85% which is the upper limit of the solenoid's duty cycle.
01:57 Above this we have our feedback from our exhaust gas recirculation position sensor.
02:03 So this tells us, this sensor tells us whether our EGR valve is open or closed.
02:08 At the moment you can see that essentially we're sitting at 0%, the EGR valve is completely closed.
02:12 Now with that out of the way we're going to perform this test at a fixed point.
02:16 We're going to maintain about 40 milligrams of fuel delivery and 1500 RPM, and we're running the car right now in fourth gear on our dyno.
02:23 So we can see the cell that we're currently operating in highlighted here in our exhaust gas recirculation engine charge aim main table.
02:33 Let's head across to the dyno and we'll have a look at what our current NOx output is.
02:38 So we can see this is being demonstrated here on our time graph in green.
02:42 At the bottom here we have our current NOx output which we can see is sitting at the moment at 535 parts per million.
02:50 So now we're going to make some changes to our exhaust gas recirculation.
02:54 We're going to request the ECU opens that EGR valve, so we can have a look at the effect on our emissions.
03:00 So we can do that by going into our exhaust gas recirculation engine charge aim main table.
03:06 Now I'm just going to highlight both the 40 milligram and 30 milligram cells there, as we are slightly interpolating.
03:12 And what I'm going to do is just drop the target there down to 620 milligrams.
03:18 Instantly in our time graph on the right we're seeing the effect of that change.
03:22 In particular we can see our exhaust gas recirculation feedback.
03:26 So this is showing us the position of the exhaust gas recirculation.
03:30 We can see that we're sitting now at about 80% to 85% opening.
03:33 Let's head across to our dyno and we'll see the effect on our NOx emissions.
03:38 Remember we were sitting at about 534, there is a latency in our NOx output changing but we can see that that's dropped dramatically.
03:46 We've gone from about 534 parts per million down to about 226 parts per million.
03:52 It's important to mention at this point as well, we aren't actually closing the throttle body, which would help improve the effect of our EGR system, and that would help further reduce our NOx output.
04:05 Let's head back into our laptop software and we'll just pause our time graph and we'll have a quick look at what actually happened when I made that change.
04:13 So we can see, this is the point right here where I've made that change to our engine charge estimate main table.
04:19 We can see that that's dropped down to 680 milligrams.
04:24 And what we can see is prior to that, our actual engine charge value was sitting at about 890 milligrams.
04:31 Due to the close loop nature of the EGR control.
04:34 We can see our blue line there drops down onto our target.
04:38 Now that's achieved by the solenoid duty cycle changing.
04:42 We can see that in our next group of values here.
04:45 We've got our exhaust gas recirculation actuator solenoid.
04:49 We can see that we started with 85%, as soon as I've made that change, the ECU drives that solenoid, initially down to 30%.
04:57 And then once we actually reached our target, it stabilises at around about 47%.
05:02 Finally we can see the effect of the solenoid on our actual EGR valve position.
05:09 Prior to making the change we can see our EGR valve essentially completely closed sitting at about 3% there.
05:15 We can see initially it opens completely, it goes up to 99.3%.
05:19 And then as we get onto our target, and the closed loop control takes place, we can see that the actuator, or sorry the EGR position stabilises at around about 80%.
05:30 So of course by adjusting our EGR position, we can effect the amount of exhaust gas recirculation going through the engine and in turn the will affect our NOx output.
05:43 Let's move on now and we'll have a look at the effect of our injection timing on the NOx output from the engine.
05:48 Now for this test we have disabled the EGR again.
05:52 So we've essentially got maximum NOx output.
05:55 We aren't using any EGR to artificially reduce our NOx output.
05:59 Let's have a look at our injection timing table.
06:02 And again we're running at approximately 40 milligrams of fuel delivery at 1500 RPM Essentially the same cell that we were previously operating in.
06:11 And you can see that our main injection event is beginning 5.3 degrees before top dead centre.
06:17 Let's head back across to our dyno and just confirm that our NOx output is essentially what we had before.
06:23 We're sitting at about 533 parts per million, of course that is moving around slightly while I'm talking.
06:31 OK so what we're going to do is make two changes here.
06:33 The first change, back into our laptop software, we're going to advance the injection timing.
06:38 We're going to go from 5.3 degrees up to 10 degrees.
06:40 So we're now starting our injection event earlier.
06:43 Let's head across to the dyno and we'll see the effect of advancing our injection timing, and we're seeing our NOx output increase now.
06:51 We've gone from about 530 up to around about 800, 795 parts per million.
06:58 So it's quite a large increase for that five degrees that we've advanced the timing.
07:03 Now we'll head back into our laptop software.
07:05 This time I'm going to retard the timing, so remember we started at 5.3 degrees, we've now gone to zero degrees.
07:12 So we're now starting our injection event right at top dead centre.
07:16 Let's jump back into our dyno screen, and we'll have a look at the effect of our NOx.
07:22 So we were at around about 800 parts per million with our injection timing at 10 degrees before top dead centre.
07:28 Now with our injection timing at TDC, you can see that our NOx output has dropped to around about 430 parts per million.
07:37 So quite a dramatic effect on our NOx output from advancing or retarding our injection timing.
07:44 Of course with our injection timing we do also need to balance the engine torque output with our emissions as the injection timing will effect both our NOx output and our engine torque.
07:55 We're going to perform one more test now and we're going to have a look at the effect of our pilot injection pulse on the NOx output.
08:01 Now to begin this test I've actually disabled our pilot injection event.
08:05 So let's just jump back into the laptop software and we'll have a look at our pilot injection table.
08:11 So this is the area that we're currently operating in here.
08:14 We're only going to use one pilot injection event for this particular demonstration.
08:20 So we can see that currently in the area that we're operating in, I've got our injection pulse set to deliver zero fuel.
08:28 So no injection event is occurring, no pilot injection event is occurring.
08:32 Let's jump across to our dyno screen and we can see that in the current cell that we're operating in, our NOx output is sitting at around about 620 parts per million.
08:42 Let's jump back into our laptop software, and what I'm going to do is set the entire area that we're operating in at the moment to one milligram.
08:50 So we've now introduce our pilot injection event.
08:54 Let's jump back across to the dyno screen and we'll see the effect of that pilot injection.
09:00 Again remembering that there is some latency with the five gas analyser actually catching up.
09:05 So we can see that we've dropped our NOx output from 620 initially down to about 550 parts per million.