The DISI-MZR fuel system (Warning: Science Heavy)

EDIT: This post is no longer relevant.

 

MAJOR UPDATE!

OK, some of you might be aware I was working on "something special" for the past couple of days, and I'm happy to report that I've got it mostly figured out, barring a couple things. Special thanks to @Poon_Flavored_Tang for the logs he provided that helped me figure at least this section out, and to the others that tried, but ultimately could not provide what I was looking for.

First Revelation:
Everyone (myself included, originally) thinks that logged IDC is a bullshit number because the math never quite adds up. How can you add timing and have the IDC not change? That doesn't make sense.
For now, I'm going to say that this is false, but more research is needed (and could be answered by one log). Let me further state that it's probably false until certain conditions are met, and then it becomes true; more on that later.

Second Revelation:
Injector Duty Cycle is unaffected by VVT.
This is data based on the logs I've looked at, at any rate, but that may change if someone somehow exceeds 100% IDC while VVT is in full on pork flow mode. I doubt anyone wants to test this for me though, so I'll just leave it at that.

Third Revelation:
Injector duty cycle is always based on 360 degree injection window. This is, of course, barring the results from the logged information that I still need to examine. But wait, how is this possible? You can't spray fuel anywhere outside of intake and compression strokes!
Incorrect.

Fourth Revelation:
Stock camshaft timing plays a big role here (specifically the exhaust), and makes me fearful regarding upgraded cams possibly hurting the engine due to how the fueling window is actually calculated.


How it all fits together:
First thing's first; let's look at the cam profiles:

Most of you, if you're reading this, should know what valve overlap is. If not, it's where both intake and exhaust valves are open at the same time. It's likely the Mazda engineers chose a profile with 16 degrees of separation (that's -16 degrees overlap) for a couple reasons; one of those being emissions, as camshaft profiles with even a little overlap tend to allow raw fuel into the exhaust on port injected cars. Port injected cars, however, don't have a fueling window limit like DI cars do; this is why we may have 1700 CC per minute injectors, but can only use about 850ccs (~400 WHP @ 100% IDC) worth of fueling through them. The second reason Mazda might do this is to either simplify injection timing logic or to preserve potential power production up to a point. I don't think they anticipated this platform running any sort of alcohol fuel when it was designed, so I'm going to go for the former rather than the latter.

Moving on, let's look at the math:


The spreadsheet diarrhea above is about 3 solid days worth of banging my head against the keyboard. On the far left side, the yellow cells represent actual logged values, and are entered into the formula which calculates everything out in stages. With a listed RPM of 6388, each degree of crankshaft rotation is exactly 0.0261 milliseconds; not a lot of time to be sure. Just below it is the base DI window as calculated for one complete rotation of the crank at that RPM in milliseconds. Still not much time. Below that is ignition timing, which is in degrees of crankshaft rotation before top dead center.

Now, you would normally think that ignition timing would detract from the fueling window, because spraying fuel after the spark event could be seriously bad juju as far as cylinder temps and power production goes, so you'd want to remove the timing from the IDC calculation. Makes sense, right? Well, if you do that, your numbers will never, ever line up. In the middle of the screenshot above, the IDC column at the bottom shows 102.98%; this is the row we will be working with (the one separate from the ones above it).

Keeping that number in mind, manually calculating the IDC works out as follows (logged IPW is listed in a yellow field above):
Injector Duty Cycle = Injector Pulse Width / (crankshaft degrees * Milliseconds Per Degree) * 100%

Now with numbers:
IDC = 9.67 / (343 * 0.0261) * 100 -=== note that 343 degrees comes from 17 degrees timing minus 360 degrees rotation) ===-
IDC = 9.67 / (8.9523) * 100
IDC = 1.08016.... * 100
IDC = 108.016%

As you can see, it doesn't add up to the logged value.
However, if you use the same exact formula above, but leave the crankshaft rotation at 360 degrees, it comes out to 102.91%. I know it's not exact, but that can be explained by the response time of the logging system pulling down an accurate RPM number. With the rounding I'm using, the RPM window for accurate math comes out to 23 RPM or in this case between 6374 6397 RPM; a super loose variance of 14 RPM below actual logged values.

So how did I figure this all out? Good question. I'll repost the above screenshot to minimize scrolling for the explanation:


Now on the right hand side, there's some obvious columns like IDC (Injector Duty Cycle), IPW (Injector Pulse Width) and IgnTim (Ignition Timing), which are all values pulled right out of the log. On the left hand side, are some random values floating to the side of the big block of code we were talking about earlier; this is how I found out what was going on. In that third column, next to the "MS Per Degree" column, is a formula I was randomly throwing numbers into multiplied by the MS Per Degree value; I was doing this to get the value next to "Eff. DI Window" value up high enough to make the value next to "Logged IPW," which is actually the spreadsheet calculated IDC, to match the logged IDC values. This is the value I placed in the "Adjust" column. It took a while to realize that the adjustment was actually really close to the logged timing values, so that's when I added the timing column for comparison.

The "Closed" column has the timing information from each dataset I manually entered, which turned out to be the exact same value (in some cases, dead on balls accurate in some) as the "Timing MS" value on the left (light purple color). This represents how far before the intake valve opens (time wise) that the injector starts firing.

The "DegA" column represents a conversion from milliseconds back into degrees of crankshaft rotation, and uses both the "Adjust" and "Eff. DI Window" (dark green on the left) values combined and mathed based on the "MS Per Degree" value. This is when I noticed the trend that sent me down this rabbit hole.

Finally, the "DegU" column is the IPW expressed in degrees of crankshaft rotation, and matches the IDC perfectly (when divided by 360).


The Great Epiphany & TLDR:
What does this all mean?

1. Our stock cam timings are part of the fueling equation, and changing them can have unexpected results on fueling window; I suspect that this hasn't been much of an issue because people running aftermarket cams are also running aux fuel to make use of them in most cases.

2. Cars running high timing are likely to encounter a lower IDC threshold before running lean and/or misfiring. This is especially true since the piston is likely to still be encroaching on top dead center when the spark event goes off.

3. Cars running high timing are probably more likely to spray fuel into a cylinder with an open exhaust valve.

4. The picture is not yet complete; I need a car with specific configuration (including tune) to log data for me so that I can figure out which one of the following possibilities is true:
a. The fueling logic is static and as listed above; this would mean ultra high timing is worse than high IDCs on most non aux fuel vehicles
b. The fueling logic adjusts the fueling window (and thus IDC calculation) based on timing up to 16 degrees of camshaft deadspace; this would mean that high timing and high IDCs are equivalent in their "badness" as far as most cars are concerned.

Edit 2:
5. It is still unclear if an increase in IDC will go only forwards (after the spark event), before (eat up more cam "dead" space) or both.
End Edit

6. This affords us a unique opportunity; the opportunity to change fueling logic for the tuning devices that will support doing so, and if upgraded injectors come out, this will ultimately be a requirement for cars that are trying to push the envelope without aux fueling, as the bigger the injector the more loss there is when spraying during an open exhaust valve and/or after the spark event


Theories:
1. The cause of the lean event on most cars is not a result of high IDCs, but rather, the injector being open when cylinder pressures are high for a higher fraction of the injection cycle. This is less running out of fuel than it is running out of window.

2. A car running high timing is more likely to experience an IDC overrun misfire (spark blowout; aggressive leaning) than it is to run lean gradually. This would be because cylinder pressures will be significantly higher with the higher timing as the spark event happens while the compression stroke is still taking place, and an open injector is likely to have a higher backpressure into the rail in those conditions which would drastically decrease flow into the cylinder vs cars running lower timing.

3. Aftermarket cams are likely to cause the engine to run leaner than reported, as some raw fuel will find it's way into the exhaust, thus skewing AFRs. Thus, they are more likely to blow up or hurt otherwise stock engines that are not running a aux fuel; better yet, run aux fuel for cooling only and don't tune for it; let the engine run rich if you're going to run cams for safety.


Footnote:
If anyone is willing to fill in the last bit of info I need to understand this whole thing completely, here is what I need specifically:
1. Any gen vehicle
2. Must be big turbo
3. Must be running a corn mix
4. Must NOT have aux fuel installed or enabled (stock injectors should be the only thing supplying fuel)
5. Ignition timing must be at/over 18 degrees
6. Injector duty cycle must be at/over 105% (if not misfiring/leaning out; if it is, this information is still helpful)
7. The following information *MUST* be present in the log (at a minimum; more information is OK) to be of any use:
a. RPM
b. IDC
c. AFR
d. Ignition Timing
e. IPW
f. Though not required in the log itself, it would be helpful to know what your fueling target is.

EDIT:
Next on the agenda:
Trying to figure out maximum safe IDC before having issues like leaning out or misfires
"Fueling Cheat Sheets" where applicable based on the above result

Questions? Comments? Concerns?

 

theory number 3 has my brain a churning

 

Review of a couple new logs suggests that fueling logic follows the static method originally proposed in Epiphany 4; thus, going over 16 degrees timing probably isn't the best idea if your exhaust is free flowing at higher RPMs, and it would be better to add boost instead to an unidentified degree.

 

Something else to think about:
Note that white text = more than 360 degrees = more than 100% IDCs.

 

So @rfinkle2 challenged my thought processes behind the prior big update post (in a constructive way) and this is the result of further discussion and looking over some logs he provided for analysis:

1. VVT does not affect IDCs even a little; logged vs calculated output was between .01% and .001% accuracy, and this was done with a car running 10 degrees of VVT @ 6063 RPM with 99.19% IDC, 15 degrees timing and 9.82 IPW.

2. HPFP pressure variance is unlikely to have much effect on fuel targeting; as stated previously by Steve over at VersaTune, fuel flow increases with the square of pressure. I'm sure this isn't quite right, but the way I picture this statement is as follows:

Flow = 1 Pressure = 1
Flow = 2 Pressure = 2
Flow = 3 Pressure = 4
Flow = 4 Pressure = 8
Flow = 5 Pressure = 16
Flow = 6 Pressure = 256

Another analogy is that the difference between 1800 and 2000 PSI on our cars is probably equivalent to the difference in flow between 40 and 44.5 psi on a PI car; not that much.

Maybe someone can chime in with a better example; further questions, comments, and concerns are always welcome.

 

Need to post a correction; valve overlap is actually -38 degrees, not -16.

Don't really think it changes the math any, though.

 

RISE FROM YOUR GRAVE!

HOKAY so quite a bit of my prior math was wrong; I wasn't thinking about shit properly and it didn't dawn on me until last night when I tried to figure out load vs AFR vs injection amount. I wound up throwing my notebook (covered in math) down on the table in disgust after realizing that the numbers I was looking for was one of the ones I was starting out with (more on that in a bit), and that spilled over into the realization that I was doing my flow calculations for the HPFP and injectors incorrectly.

Let's take a look, shall we?


We will skip the top section for now as I covered all of that (except BSFC, which doesn't need to be explained here really) in a prior post; starting at the first line after the black bar:

RPM:
This is engine RPM. Duh.

HPFP Flow CC:
This is how much fuel the high pressure fuel pump is capable of moving at a given RPM.

Est. Flow WHP / WTQ:
This is the mathed out (inaccurate, not real world) estimate of how much power and torque to the wheels the HPFP is capable of feeding.

Injector Overrun CC:
This is where things get interesting. A negative number here is how much more the injectors can flow than the HPFP (in CC/Min) and a positive number is how much more the HPFP can flow than the injectors (in CC/Min). With Autotechs (referenced in parent image), we run out of injector pretty quick.

Offset WHP:
This is how much WHP is lost by not having a large enough HPFP (negative number) or by upgrading to larger injectors (positive number; these don't really exist BTW) that matches either the injector or HPFP flow rate.

HPFP + Inj. WHP / WTQ:
This is the mathed out (inaccurate, not real world) estimate of how much power and torque to the wheels the HPFP and injectors are capable of feeding, limited by the lower flowing of the two per RPM. This is why torque drops off right as horsepower plateus; you go from the HPFP being the limiting factor to the injectors being the limiting factor. Simple.


So, why does this matter to anyone? Well, let's take a look at some stock HPFP data:



Looks like it's possible to max out the injectors with the stock HPFP. All you'd need is a bigger turbo and a tune to do it (probably shouldn't try this, unless you're actually interested in the result in which case, PM me for science).

What about if we fill the tank with corn?



Ouch. Limited to 221 WTQ (ish, this doesn't factor timing only fuel) and 252 WHP @ 6k (which should look familliar to most stock turbo owners).

What about corn and Autotechs you ask?



Looks a lot like a stock turbo tune, doesn't it?

"Well, that's all well and good, but why should I give a shit about this, you fucking spreadsheet nerd?"
This stuff, I don't expect anyone to care about. What I do next, however, will probably turn a head or two.

How would those of you that tune, self or otherwise, like to input a torque/power curve and get back a per-AFR and RPM target table that has all the calculated load values in it?

Not blowin your skirt up much? Ok, well what about automatically calculating the MAF curve for aux fuel and stock injector cutoffs and shit like that for a given power target, with the injector, nozzle, and duty cycles laid out for you for 5th/6th port, pi and meth?

Still not enough? Have another idea that fits in with this theme? Make a request; I'm not going anywhere.

In the mean time I'm going to bounce this output table I have set up (that already matches a log file or two) against some more pro tuners (thumbs up already acquired from VegaTuned and PDTuning) before I move forward on the other goodies.

 

This is tittylicious. We had to do quite a few AUX fuel (maf cal subtraction) revisions to get the AFR's and IDC's in the spot we wanted them on le port.

Let me know what you need...I haz logs.

 

I've got the thumbs up from enough pro-tuners to move forward, so I'll start working on the real shit here soon. Thanks for the support man.

 

Anytime brother.

When I get home tonight, I'll crack a beer and put some data out there for you. Just need the Split Second Controller maf voltage vs rpm, WOT log, and MAF cal?

Edit: I think we will also have to take into account the lb/hr these injectors flow as well. This could complicate things a bit as all injectors do not behave exactly to their specs.

 

Let me get to the point where I'm ready to start calculating the aux fuel stuff and I'll hit you up about the split second controller configuration stuff. Don't want to get ahead of myself just yet.
[doublepost=1477374398][/doublepost]Discussion here:

http://mazdaspeeds.org/index.php?threads/enkiworks-pre-tune.3397/

Edit:
@HawkeyeGeoff I'm ready for that info now.

 

UPDATE

Back in March I posted about how exhaust cam timing was likely a major factor in fueling for our cars (along with ignition timing; scroll up to post #22), and how people with aftermarket cams would likely need to take this into consideration. Well, after much hemming and hawwing, and because I'm officially on vacation again, I finally sat down and did the chart to figure this out.

I'm glad I did, because I wasn't too thrilled with the results.

Before I get into that, I have to make a statement to I explain what these charts represent: I'm not trying to be a doomsayer alarmist, and it's likely that overrunning IDCs is relatively safe and won't seriously impact engine longevity provided it's not already tuned to the edge.

That said, on with the show.

I made these charts in two parts so we can see the ranges for most applications separately; first up is for cars without alcohol: (Edit: -16 degree cam timing / top row represents stock cams, as measured by another member)



And for cars likely to be running some kind of alcohol, either in tank or sprayed pre intake valve: (Edit: -16 degree cam timing / top row represents stock cams, as measured by another member)


So, what are we looking at, and why is there so much fucking red?

Well, that's the thing. If the injection window is a dumb, static 360 degrees of crank rotation, and is simply shoved back towards the exhaust close event like I believe it is, then either going over 16 degrees timing, installing cams that close the exhaust valve after 16 degrees BTDC, or going over the charted % IDCs listed above will likely result in fuel spraying into the exhaust stream, after the spark or (insert deities of your choice here) forbid: both.

So, the above represents the maximum (calculated) safe IDC for a given cam and timing configuration.

"Nuh-uh Enki! I hit 1xx% IDC all the time with no issues!"
That's cool (insert name here), so did I for a long ass time (although it usually wasn't over 105%). Doesn't mean I was right in thinking that was safe. In fact, here's a preemptive shame on me for doing that to my car, if that was indeed a bad thing to do (if we ever even find out if that's the case).


OK, so, we already know that some cars get further on the IDC window than others before issues arise. That evidence is almost literally raining from the skies; the questions we need answered to understand why this is, however, are as follows:

1. Stock cams? If not, when does the exhaust valve close? Cams that close later might have power drop off after the charted threshold is breached, even if the AFRs look good and there's no knock likely due to raw fuel is going into the exhaust instead of exploding in the cylinder like it should. PI cars don't have this issue, because fuel and air stop entering the cylinder after the intake valve closes.

2. What fuel is in the tank? Depending on the content of the fuel, the susceptibility to issues might be more or less prevalent (ideally, this should be tested IDC vs IDC)

3. How much timing is being commanded when issues happen, and at what RPM? A very low timing/stock map is less likely to have issues than a full corn tune running damn near triple the stock timing.

4. How much backpressure is there in the exhaust manifold if spraying > 100% IDC? I would wager that freer flowing exhausts (huge turbos with dump pipes and headwork) will encounter issues more readily than, say, a BNR S3 on stock manifold would.

5. How much aux fuel is being run? I figure this is important, due to a larger fraction of fuel being delivered pre-valve as *reducing* the negative effects of IDC overrun. An example of this would be running 110% IDC with issues, then adding aux fuel, upping boost and running the same IDC of 110% without issues could be caused by the reduction in overall fuel flow that's being burned late or dumped out the shitter pipes. WIth 1500 CC of fueling, that's basically 50% more fuel being tossed at each cylinder, and (correct me if I'm wrong) would reduce the 10% overrun to an effective 5%.

If anyone wants to confirm/deny/test any of this, please do so; if you're going to test, let me know before you do so I can help make doubly sure that nothing dangerous (to the engine or owner) is done.

Questions? Comments? Concerns?