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Variable Cam Control Tuning: Effect of Cam Timing on Emissions

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Effect of Cam Timing on Emissions


00:00 - In the aftermarket when it comes to tuning, typically what we're trying to do is increase our power and our torque values.
00:07 And as we've gone through this course you've seen that the cam control or particularly continuously variable cam control has a large influence over our power and torque curve.
00:17 And aspect though that's easy to lose track of is that as we're adjusting our cam timing, this will also in turn influence our tail pipe emissions.
00:26 And increasingly emissions has become more and more of a stumbling block for tuners in the aftermarket and particularly if you live in a country where emissions standards need to be adhered to, making sure that your tune does meet the legislation is going to be a big factor.
00:42 Otherwise realistically it doesn't matter how much power and torque you are making if your car's not emissions legal, it's not going to make it onto the road.
00:50 So in this module we're going to have a look at how the cam timing influences our engine torque as well as our emissions.
00:59 To do this we have got a 5 gas analyser hooked up to our Subaru STi.
01:04 For the purposes of this demonstration, we are using the Haltech Elite software and while there will be variations of course between different software packages, essentially the relationship between our cam tuning and our emissions is going to remain the same.
01:19 Now with the 5 gas analyser, as its name implies we are analysing a variety of different components of the tailpipe emissions just to make things really simple for our demonstration today we're going to be focusing on just one of those metrics which is our NOx or oxides of nitrogen output measured in parts per million.
01:38 So just so you've got some insight into how this is going to go, let's just jump quickly into our Haltech ESP tuning software and we'll go through some of the aspects that we will be adjusting.
01:48 Now for a start here we are on our cam tuning tab and this is our cam timing table for our intake cam.
01:56 While the STi that we are tuning has quad variable cam control, so both the intake and the exhaust cams are variable.
02:04 Again for simplicity here we're going to be focusing on just our intake cam.
02:07 Of course the exhaust cam has as much influence, or has also some influence over the emissions but this should be enough to give you a bit of a guide as to how the emissions is affected by our cam tuning anyway.
02:20 So the area I've just highlighted in the table there, we can see that we've got a range of cells that I have set to zero.
02:27 So for our test what we're going to be doing is focusing on this cell here, -20 kPa 3000 RPM.
02:34 The reason that I have also highlighted the cells surrounding that is that this way, setting all of the cells to the same value, just makes sure that we aren't going to have interpolation affecting our results.
02:46 Now of course cam timing is not the only aspect that influences our tailpipe emissions.
02:51 Air/fuel ratio will be another big driver in that.
02:54 So for the purposes of this experiment we really want to make sure that as many of our operating parameters as possible are held steady so that we're really only influencing the emissions with our cam timing.
03:06 To help us with this, we are running the Elite 2500 ECU in closed loop mode and here we can see the left hand side, we've got our wideband air/fuel ratio, our measured air/fuel ratio and beside this we've got our short term fuel trim from our closed loop.
03:21 This is actually not active right now at idle but as we come up to our 3000 RPM, -20 kPa site we're going to see that short term fuel trim start moving around.
03:32 And what it's going to do is just make adjustments as I move the cam timing so that the air/fuel ratio always tracks stoichiometric or 14.7:1 for the pump gas we are running.
03:44 Another consideration here is our ignition timing and we're just going to be leaving this static at a fixed value so that again we're trying to only influence our cam timing as we go through this particular test.
03:57 Up here we will be able to view our cam timing along with our cam target.
04:02 At the moment you can see the top value that's moving around, that's our current cam angle, sitting at about 1°.
04:07 Our cam target at the moment sitting at 0 and that will also be tracked in real time using our time graph here on the left hand side.
04:16 Now in order to track what's going on, let's head over to our dyno and we'll see how our test is set up.
04:23 Alright so what we've got here is a torque optimisation test and I often use this feature on our Mainline dyno to help optimise our ignition timing but it can be used for a variety of other aspects as well.
04:34 On the left hand axis here, we've got our torque being measured by the dyno in pound foot.
04:39 Along the horizontal axis here we can see that we've got our inlet cam angle.
04:43 That's being sent to the dyno from the Haltech Elite ECU via a CAN communication bus.
04:50 On the right hand side, we've got our NOx or oxides of nitrogen output there between 0 and 4000 and over on the right hand side we can see here at idle at the moment we've got a measurement of our oxides of nitrogen of about 500 parts per million.
05:05 So what we'll do now is get the engine up and running, we'll allow our NOx value to stabilise and we can get our test started.
05:12 Just before we start the test I'll just explain how I'm going to do this.
05:15 The 5 gas analyser in particular does have a reasonable amount of latency before the reading will update so it's not instantaneous like we'd see from the likes of our wideband air/fuel ratio meter.
05:28 So what I'm going to do is I'm going to step our cam timing in 2° increments and each time I make a step change I'm going to allow about 5 or 6 seconds for our NOx reading to update.
05:38 So we're going to speed this process up because otherwise it's going to take a little while to do.
05:42 You'll see the 2 graphs being updated as we go through the test, we'll swing the cam timing from 0 through to 50° and once we've got those 2 graphs up, we'll be able to talk about the results.
05:55 You will notice as these graphs develop that they are a little bit erratic, there's a little bit of noise in these graphs so we'd need to do a little bit of mental smoothing but we can talk about that once the test is complete.
06:06 Alright so we'll just make sure that we are stable in the centre of our cell here and we'll allow our NOx value to stabilise and we'll get our test underway.
06:41 Alright so we've got our test complete there and again as I mentioned, the 2 graphs we've drawn, I've got a little bit of noise associated with them but we do see some pretty clear trends so it's not very difficult to do a little bit of mental smoothing around those graphs.
06:54 First of all, looking at our red graph which is our torque, we can see with 0° advance we were sitting at around about 300 pound foot of torque.
07:04 We've seen a small increase there, we've gone from 300 up to around about 330 pound foot.
07:11 We're actually pretty flat there from about 10° of cam timing all the way through to about 35°, the dyno has shown us that if we want to split hairs, the peak value there occurred with a cam advance of 26.2° for that particular cell.
07:27 Looking at our yellow graph for our oxides of nitrogen though we can see at the start of the test we're sitting, uses the right graph I should point out here, we're sitting at around about 3200, maybe 3300 parts per million.
07:43 As we begin advancing the cam we actually see that initially that value does increase, we peak here around about 15° of advance, pretty close to about 3400, 3500 parts per million.
07:58 And we can see that as we continue to advance the cam here, we can see that our oxides of nitrogen values actually drop and by the time we're at 50° maximum advance, we'd dropped down to about 2300 parts per million.
08:13 So what this means is that if we look at our maximum and our minimum values, we are looking at about an 800 part per million decrease by adjusting our cam timing.
08:25 Now obviously this does to a degree come at the expense of some of our torque.
08:28 Looking at the point where we saw minimal NOx emissions is at 50° cam advance and here we can see that our torque has dropped back down to around about 310 pound foot.
08:41 So we've sacrificed 20 pound foot of torque there to improve our oxides of nitrogen emissions at the tailpipe.
08:50 Realistically this is something you need to factor into your tuning if you are going to try and meet emissions standards.
08:56 The decision as to what you're aiming for, whether you're looking at peak power, peak torque or you're looking for minimal tailpipe emissions, or a balance of those aspects, really just comes down to the task you're trying to complete, this module is simply here to show you that relationship, it's certainly not supposed to be an all encompassing lesson on emissions because it is a very complex topic.
09:21 Here we have only looked at the intake cam.
09:24 As I mentioned, we've got the ability to move the exhaust cam as well and of course this will influence the emissions further.
09:32 In particular when we have variable intake and exhaust cam control, we've got the ability to essentially create internal EGR or exhaust gas recirculation.
09:42 That's one of the techniques that OE manufacturers use to reduce oxides of nitrogen emissions at the tailpipe and in fact emissions in general.
09:51 The idea here is that we're purposefully making sure that there is some exhaust gas left over inside the cylinder for the new intake charge.
10:00 What that's going to do is we've got this inert gas, the exhaust gas that's remaining.
10:04 That's not obviously going to combust, it's inert as its name implies there, it's not taking part in the combustion process.
10:11 But the important part here from an emissions standpoint is that it is displacing some of the volume of fresh air and fuel charge that now can't fit into the cylinder.
10:20 So we're essentially purposefully decreasing the cylinder fill.
10:24 This in turn is the same as essentially reducing our volumetric efficiency.
10:28 It also creates a smaller combustion event and oxides of nitrogen in particular are driven by the combustion temperature.
10:36 So if we can lower our combustion temperature, then this in turn will drive our NOx values lower.
10:42 So there you go, just a little bit of insight into the emissions controls that we have at our fingertips with continuously variable cam control.