Ethanol & Flex Fuel Tuning: MBT Timing vs Ethanol Content - Practical Demonstration
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MBT Timing vs Ethanol Content - Practical Demonstration
09.43
| 00:00 | - What we're going to look at in this module is a demonstration of how the ethanol content in the fuel affects the optimal ignition timing. |
| 00:08 | And we're going to perform two tests on gasoline and then two tests on ethanol. |
| 00:12 | We're going to choose first of all a point where the engine is not knock limited on pump gasoline. |
| 00:19 | And then we're going to also choose a point under boost where the engine is knock limited. |
| 00:23 | On this Toyota 86 it is a factory naturally aspirated engine with a 12 point 5:1 compression ratio, which we've added a turbo charger to. |
| 00:32 | Understandably with such a high compression ratio the engine is heavily knock limited once we're on boost. |
| 00:38 | Once we've gone through our test on gasoline and found our optimal timing or alternatively the amount of ignition timing we can use before the onset of detonation, we're going to drain the fuel, we're going to replace it with E85, and then we're going to test again to find out how that ethanol content affects the optimal timing. |
| 00:57 | Let's have a quick look at what we've done here in the laptop software first. |
| 01:00 | At the moment you can see we're on our main ignition table. |
| 01:04 | This ignition table is the ignition table used for gasoline. |
| 01:08 | And what you can see I've done here is I've taken a large block of the ignition table and set it all currently to 10 degrees. |
| 01:15 | The two points that we're going to test here are 2500 RPM, and 60 kPa. |
| 01:22 | So this is in vacuum, and at this point the engine is not knock limited on gasoline. |
| 01:27 | Once we've tested at that point, we're also going to increase the throttle position, bring the engine up onto boost. |
| 01:33 | and we're going to test again at 120 kPa, a point where the engine is knock limited. |
| 01:39 | What we're going to be using just to demonstrate knock is a little warning box down in the bottom left hand corner. |
| 01:44 | This is going to flash red when the built in knock control strategy on the Motec ECU detects that the engine is detonating. |
| 01:53 | Once we've done this test we're going to move forward and we're going to do exactly the same on our ethanol ignition timing map. |
| 02:01 | And we're going to be using an E85 blend. |
| 02:04 | If we jump across to our flex fuel worksheet, you can see at the moment we do have a very small amount of ethanol still in our tank, we've got about 3% there. |
| 02:13 | That's not really going to affect this demonstration. |
| 02:16 | Let's get our engine up and running and we'll perform our first torque optimisation test. |
| 02:21 | OK we've got our engine up and running, you can see we're now sitting right in the centre of our 60 kPa, 2500 RPM cell. |
| 02:30 | What I'm going to do during this torque optimization test is I'm actually going to make changes to the block of cells surrounding that cell that we're interested in. |
| 02:38 | And this is just going to mean that we're not going to be affected by any interpolation from the surrounding cells. |
| 02:45 | Let's jump across to our dyno screen. |
| 02:47 | We've got our torque optimisation test set up. |
| 02:50 | This is going to plot how the torque changes with ignition timing, and this is going to help us to find MBT or the maximum brake torque timing, or also known as minimum timing for best torque. |
| 03:03 | On the vertical axis here we have our engine torque and on the horizontal axis we have the ignition timing coming across from the Motec ECU. |
| 03:12 | So I'm just going to click begin, and now I'm just going to advance our timing at a degree every second and we'll see how the torque is affected by the ignition timing. |
| 03:43 | Ok so that's our first torque optimisation test complete. |
| 03:46 | And what we can see here is that the dyno's drawn in a cross hairs at 32.7 degrees of ignition advance. |
| 03:53 | At this point we've achieved 111 newton metres of torque. |
| 03:57 | So what this means is that for pump gasoline at 60 kPa and 2500 RPM, we can achieve MBT without knock, and MBT timing is 32.7 degrees. |
| 04:10 | We're now going to go ahead and repeat this test only this time we're going to go up to 120 kPa. |
| 04:17 | OK we're up and running now at our second point. |
| 04:19 | You can see that we're in the centre of our 120 kPa 2500 RPM cell. |
| 04:24 | And we're going to go through exactly the same process. |
| 04:27 | This time what we're going to do is advance timing till we either reach MBT or much more likely we're going to have our knock warning indicator in the bottom left hand corner of our screen come on. |
| 04:38 | So let's go through the test now and see what our results are. |
| 04:52 | OK so we've just had to abort that test, we got up to just on 20 degrees of ignition timing, ignition advance, and the knock warning came on. |
| 05:00 | And that's the onset of detonation so we can't advance the timing beyond that point and in fact what we'd actually need to do to provide some safety is retard the timing a little bit from the point where we first encountered knock. |
| 05:14 | So it's likely we'd end up with our ignition timing limited to perhaps only 16 or 17 degrees. |
| 05:21 | We can see on our dyno screen that we reached 378 newton metres of torque at 19.4 degrees of ignition advance, but if we look at the trend of our graph, we can see that the trend shows that the torque is still increasing. |
| 05:37 | Now that we've preformed our test on gasoline we're going to drain the fuel, refill it with E85, and we'll have a look at those two points again and see what the difference in ignition timing is. |
| 05:49 | With our fuel now changed over, let's have a look in our laptop software. |
| 05:53 | And we can see that we're sitting at 84% ethanol content, so just a touch under our 85% target. |
| 06:00 | We're currently looking at our ignition table for ethanol fuel. |
| 06:05 | So this is our second ignition table, and you can see that we've also set the same block of values in this ignition table to 10 degrees. |
| 06:13 | Now at this point the ECU is using a blend table to define how much of the second ignition table is being used. |
| 06:20 | If we have a look at the blend table, we can see at the current point we're sitting at, from 80% ethanol and above in fact, we're 100% referencing our second ignition table. |
| 06:31 | So everything that the ECU supplies is coming from our second ignition table. |
| 06:36 | Let's get our engine up and running and we're going to retest our first point at 2500 RPM and 60 kPa. |
| 06:43 | OK we're up and running at our first test point, you can see that we're sitting at 60 kPa and 2500 RPM. |
| 06:49 | We're going to again just highlight all of the cells surrounding that particular zone so there's no danger of any interpolation. |
| 06:57 | And what we're going to do is just begin our torque optimisation test. |
| 07:20 | So with our test there at 60 kPa on E85 we can see that the optimal ignition timing, as displayed by the dyno is 29.8 degrees. |
| 07:31 | So we're around about three degrees lower or less in our ignition advance than what we needed at the same point on gasoline. |
| 07:40 | We can see however that our engine torque is almost identical, 116 newton metres, so the variation that we're seeing here is really just the variation that we'd expect with this sort of a test. |
| 07:53 | This indicates that really the engine torque hasn't been affected by the change from gasoline to E85, at a point in the ignition table where the engine wasn't previously knock limited. |
| 08:04 | Let's get our engine running again and we'll repeat the test at 120 kPa. |
| 08:09 | Alright we're central in our 120 kPa zone now, so we'll start our torque optimisation test and see what our results are. |
| 08:29 | What we can see from this test is that optimal timing was 24.9 degrees of ignition advance. |
| 08:35 | This was our MBT timing on E85. |
| 08:38 | And this also provided us with 423 newton metres of torque. |
| 08:43 | Now remember in our first test we struck detonation at 20 degrees of ignition advance and that was giving us 378 newton metres of torque. |
| 08:53 | So we've gained approximately 45 newton metres of torque there by being able to optimise the ignition timing all the way through to MBT with no detonation being recorded. |
| 09:03 | So this represents about a 12% increase in torque going from gasoline to E85. |
| 09:10 | So the takeaway from this demonstration really just reiterates what we've already talked about in the body of the course. |
| 09:16 | If our engine is not knock limited on gasoline then we can expect the engine to want less ignition timing to achieve MBT when we move to an ethanol blended fuel. |
| 09:27 | If on the other hand the engine is knock limited on gasoline, we may be able to advance the timing further when we move to an ethanol blended fuel. |
| 09:34 | And in many instances we may still be able to tune the ignition timing to achieve MBT. |
