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Diesel Tuning Fundamentals: Effect of AFR on Power and Torque

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Effect of AFR on Power and Torque

08.58

00:00 - In this demonstration we're going to be looking at how the air fuel ratio or the amount of fuel that we deliver to the engine affects the engine's operation, specifically in terms of engine power and engine torque.
00:11 Before we jump into the demonstration though we'll just take a few moments to go over the tables that we're going to be adjusting in the Motec ECU.
00:18 Just so you understand what these tables actually mean.
00:21 And how they're going to affect the fuel being delivered to the engine.
00:25 We're going to start here on our fuel mass limit main table.
00:30 As you can see, this is a simple two dimensional table.
00:33 It simply defines the maximum amount of fuel in terms of milligrams, we're looking at fuel mass here, that will be delivered to the engine at each RPM point in this table.
00:44 So for example here we can see that at 2500 RPM the maximum amount of fuel that can be delivered is 117 milligrams of diesel.
00:53 Now this table works in conjunction with the next table that we'll look at, which is our fuel mass nominal table.
01:00 Now this time we've got a three dimensional table.
01:02 On our vertical axis here we have our throttle position, and on our horizontal axis we have our engine speed.
01:09 Now the numbers in this table are a percentage of our fuel mass limit table that we just looked at.
01:17 So for example if we have a fuel mass limit of 117 milligrams, and then we had a number in our fuel mass nominal table of 100%, this would mean that the entire 117 milligrams from our fuel mass limit table will be delivered to the engine.
01:35 So it's important to understand that the table we're looking at here is a percentage of our fuel mass limit.
01:41 This is a percentage of the fuel maximum that we're going to be delivering into the engine.
01:47 Let's just close that down now.
01:49 And the other aspect that we're going to be looking at here is on the right hand side in our time graphs we can see that we have our exhaust lambda so this is coming from a wideband air fuel ratio sensor fitted into the exhaust of the engine.
02:00 OK with that out of the way, what we're going to do is perform two tests, we're going to start by running the engine at part throttle at 2000 RPM and we'll have a look at how adjusting the air fuel ratio or in other words the mass of fuel that we're delivering to the engine affects the engine torque.
02:17 So let's get up and running now on our Mainline dyno.
02:20 Alright we're up and running now in fourth gear at 2000 RPM.
02:23 And you can see at the moment that I'm just sitting at part throttle, we're sitting at 20% throttle.
02:28 And this is a common area that we might be sitting at, at part throttle during cruise.
02:32 Now the important point to note here is we can see that our exhaust lambda is sitting at around about 1.9 lambda.
02:40 So again much leaner than stoichiometric which is exactly what we'd expect, particularly at light throttle cruise, where we are now.
02:47 If we head across to our dyno we can also see our current engine torque or our torque being registered at the rear rollers.
02:56 We can see that we're sitting at around about 96 to 97 foot pound, and this also equates to about 33 to 34 horsepower being measured at the rear wheels.
03:08 Now if we jump back into our laptop software for a moment we can see that at the moment the fuel mass being delivered into the engine is sitting at around about 41 milligrams.
03:18 That's to be expected given our current fuel mass limit as well as our fuel mass nominal value.
03:26 So what I'm going to do here is take our fuel mass nominal value from 44% up to 54%, so we're simply adding 10% here.
03:34 So remember before I make this change, we'll just check our lambda, we can see that's sitting at around about 1.9, we'll make that change, and we can see that our lambda goes from 1.9 down to 1.65 To confirm that change we can see that our fuel mass being delivered to the engine has jumped from 41 milligrams up to about 50 milligrams, 49.9 milligrams.
03:57 And if we have a look at our dyno we can see that we've now jumped up to around about 120 foot pound of torque and we've gone from 33 to 34 horsepower at the rear wheels up to 43 horsepower.
04:10 So quite a significant jump considering we've just made an adjustmtent there of around about eight milligrams of fuel being delivered to the engine.
04:19 Now that we've had a look at that test there at part throttle, we're going to repeat the test at exactly the same point, 2000 RPM, but this time we're going to go to wide open throttle.
04:29 OK so we're sitting now at wide open throttle at 2000 RPM and we can see that the value we've got in our fuel mass nominal table is currently 69%.
04:39 Remember that's 69% of our fuel mass limit.
04:42 We can see over here on the left that our fuel mass limit at this point is 95.6 milligrams.
04:48 So that gives us a final fuel value being delivered into the engine of 66 milligrams.
04:54 We can see that equates here to an exhaust lambda of about 1.2 to 1.3 If we head across to our dyno we can see that that's also giving us around about 165, 166 foot pound of torque at the rear rollers, and around about 58 horsepower at the rear wheels.
05:13 Now again we'll make the same change here back into our laptop software, we're going to add 10% there.
05:20 We'll go from 69% to 79%.
05:22 You can see that takes our fuel mass being delivered up to 76, 75.7 milligrams.
05:30 At the same time we can see that our exhaust lambda has dropped richer as we'd expect, now to 1.15 Again if we head across to our dyno screen we can see that that change there has resulted in our torque increasing up to 190 foot pound, and we've seen that also result in our rear wheel horsepower increasing up to 66 horsepower.
05:52 Now that we've had a look at how the air fuel ratio affects the engine's operation there under steady state conditions, we're going to repeat this test only this time we're going to look at the operation under a ramp run condition.
06:04 For our first ramp run test here we're going to leave our fuel table delivering relatively lean air fuel ratio, and then we'll perform a further test richening the mixture so we'll see how that affects our power and torque.
06:15 Let's get our first run underway.
06:40 So there's our first run complete and we've registered 167.2 horsepower at the rear wheels.
06:45 We can see that our boost peaked at a little over 120 kPa or a little over 18 psi and for the most part we managed to maintain our air fuel ratio, a lambda there around about 1.3 which is relatively conservative.
07:00 What we're going to do now is save that run and we're going to perform a second test.
07:06 Before we do that though let's just jump back into our tuning software.
07:09 And what I'm going to do here is simply highlight the entire wide open throttle operating area and we're just simply going to add 10% into our fuel mass nominal table.
07:21 So remember this is just going to add some additional fuel.
07:24 This is going to richen the air fuel ratio up, so let's now perform a second test.
07:28 We'll overlay that directly on top of our first test and we'll see the effect of that richer air fuel ratio.
07:58 OK so our second run's complete there, we can see that we're now making 179.1 horsepower so a pretty significant increase in our power, given that one simple change by just adding a little bit of additional fuel.
08:10 And that is represented by our top graph here which is our lambda plot.
08:14 We can see the purple line which is still there from our first run.
08:17 Remember we were sitting at around about 1.3 lambda on that first test.
08:21 Our red plot now for our lambda shows that we're hovering around about 1.1 lambda give or take so this is probably about as rich as we would like to run.
08:31 And we can see in our bottom plot here, the power curve versus our first run, and we've essentially picked up power right through the entire rev range.
08:41 Despite this we can see at least our peak boost pressure has remained relatively unchanged.