Emissions Tuning Fundamentals: DFCO Off Demo

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DFCO Off Demo

05.22

00:00	For this test, we're going to be disabling the diesel fuel cutoff system.
00:04	So, when that's disabled, we'll continue fueling the engine while decelerating.
00:09	In a typical vehicle, you're not going to want to do this, because it saves fuel if you shut the fuel off during diesel.
00:16	It also reduces emissions, since no combustion is occurring.
00:20	But just to show you what would happen, here we go.
00:23	I'm going to perform a hot 505 test with a stock calibration, except for diesel fuel cutoff disabled.
00:42	All right, we have a big deceleration event coming here.
00:48	Slowing down, declutch.
01:01	And then the modal data, that'll be nice to easily compare against a run where we did have diesel fuel cutting off.
01:08	So in my tuning software here, if I pull that section up, we see a long area cruising, followed by diesel.
01:17	And in this area, where fuel would typically shut off, see that our air-fuel ratio is reading about 0.93 lambda there, 0.98, not going to fresh air reading.
01:30	And closed-loop trimming continues to operate.
01:34	Looks like the target was 0.99 on diesel during that area.
01:37	And if we pull up a prior log during this period of time, we see the air-fuel sensor reading 1.39 lambda, and that's simply as high as it goes.
01:51	There's actually no combustion occurring, and that is just fresh air.
01:54	One thing of note on this particular ECU, because it may be something that you'll find on another as well, is if you look at the injector pulse width or injector duty cycle during this time, it actually calculates that as if the fuel is still being injected, while it's actually not.
02:12	So it's important to view a couple things.
02:14	The air-fuel ratio sensor, to see that you're getting fresh air rather than combustion occurring.
02:19	And there's also a fuel cutoff monitor, which allows you to verify things another way.
02:24	So I'll add that here.
02:27	Fuel cut flag in green, so you can see here, right there as I lift throttle, fuel cut flag kicks in, and then as I get down near idle, it turns back off.
02:42	So we go from 1 here, which would be on, back to 0 here, which is off, as we resume injection.
02:49	In our diesel fuel cutoff test, we started with a baseline using a stock calibration that does have diesel fuel cutoff, and that engages any time the engine was over about 1700 RPM when it was warmed up.
03:02	On our test where we've disabled that, it never comes on.
03:05	So we continue combusting and burning fuel every time we're decelerating the car.
03:10	And let's see what type of changes that made.
03:13	So I have my baseline file up.
03:15	I'm going to compare that to our diesel fuel cutoff disabled run.
03:24	Looks like those are overlaid nicely.
03:26	I did stop that test early because I really just wanted to show this main diesel area right here, where we go from about 32 miles per hour down to Now, of note on that test, you can see a drastic difference in lambda when we look at our data log on our Cobb software.
03:45	We go from a fresh air reading during diesel fuel cutoff to running about lambda 1 when we don't shut it off.
03:51	So with a lambda 1 target, we should still be getting clean combustion.
03:55	And the result of that is similar emissions results.
03:59	As we look here, our NOx results are pretty similar.
04:02	Very low, very close to zero.
04:04	That's what we want to see.
04:05	On hydrocarbons, we were actually slightly lower on the second run with diesel fuel cutoff disabled, which just means that the cat was likely warmed up, working really nicely there, and it just cleaned up slightly better than before.
04:25	But really no significant difference there.
04:29	In terms of CO, also very similar, almost zero.
04:35	And then when it comes to CO2, we had a little bit of a reduction there.
04:43	And again, this is just a good example of where hitting lambda 1, you don't necessarily need to stop fuel altogether just to have decent emissions.
04:52	So as long as you're on that target, you should be in pretty good shape.
04:55	What is going to change is your fuel economy.
04:58	Obviously, the difference between injecting fuel and not injecting fuel will impact that for sure.
05:04	So it's not something that you generally want to disable on a streetcar, but we do want to demonstrate that as long as you're combusting properly, this isn't necessarily an area of massive concern for the emissions results, just for fuel economy.