Injector Deadtime vs Fuel Charge Cooling vs La Target Table

[RyanG]

Hi guys,

Bit of a long post, sorry. Chasing some info from someone with more experience in regards to tuning both injector dead time and fuel charge cooling coefficient. I've got my car running and tuned on E85 (B18 turbo Honda), but was noticing a couple of issues. 1: A change in target lambda at light cruise was out by quite a bit, 2: Rich on decel even with very low effective min PW, 3: Larger than needed IAT background compensations by the modelled mode formula.

This led me down the rabbit hole of trying to correct the injector data. I want to get this right before going back to pump 98 fuel again. My VE numbers seemed ballpark previously with 55% at idle, but maybe a little high at 121% full boost high rpm. I played with the following settings to try and get more accurate results..

1. Injector Flow. After some research into my specific injectors (040 Bosch 980cc) and seeing tested fuel flow rates, I dropped fuel flow from 980cc to 890cc at 300kpa on E85. This only dropped max VE to around 117%, not quite the large change I was expecting but I think it's closer to the money at 890cc than 980cc. Fuel pump is a Walbro 460. Stock fuel rail and reg (manifold referenced and supposedly 300kpa base).

2. Injector Dead Time -  Given that I was rich on decel with effective PW of <0.3ms I assumed my values were too high. Dropping it down to around 0.95ms gave me the "est mass airflow" of 3.5-4 g/s Evans tuning mentions is ballpark for a 4 cyl at idle, however I then had to raise VE to 65%+ at idle and changed the shape of map considerably. After reading some more, I tried to find a better value by switching between multi-point group 1 and 2 cycles at idle. Bit harder on G4X than G4+ as you can't do it while the engine is running and there is obviously some non-linearity at very low PW. I then tried the method of adjusting deadtime to ensure a change in lambda target at 1-3k rpm in neutral resulted in the correct adjustment. With low deadtimes it overshot by a lot. Going from 1.0 to 0.9La target made it go to more like 0.85La or richer. Increasing dead time made it closer. I then started to look at the effect of fuel charge cooling coefficient.

3. Fuel Charge Cooling Coefficient - I used a value of 10c on pump 98 and it worked perfect under medium load. On E85 it needed to be 7C under the same conditions, which was the opposite direction to what I expected. At idle, I had to turn it all the way to 0C for a change in target lambda to match. This was achieved with a dead time of 1.101ms at 14V. VE is approx 54% and MGP is -67kpa at idle. This dead time is only 1.7% lower than supplied data, but around 10% higher than data people have gathered from bench testing the injectors.

4. Charge Temp Correction - I experimented briefly with charge temp correction. I think it would give me more consistent results as the ecu seems to be over correcting for IAT. When its 10-15C cooler I am ~5% rich and when its 10-15C hotter I am 5-10% lean. If I bias towards ECT to dampen this it would probably help, but it really throws off my VE numbers and table shape so I'm unsure if artificially increasing and dampening IAT is the right move. For example I started getting VE numbers of 65%+ at idle, and then tapering down with RPM due to decreased CTC at higher air flow. I have a fast reacting motorsports IAT sensor mounted in an aluminium charge pipe directly before a silicone joiner onto the TB. It matches ambient with the car off (2C above ECT), doesn't seem to heat-soak while driving, and on a long pull through all the gears it goes from 35C to 48C, so about expected for my small intercooler.

So what's the best way to move forward? At current I've roughed out the new fuel table for the slightly adjusted deadtimes and fuel charge cooling dropped to 0C. I don't want to spend any more time on it until I can get someone else to drive the car so I can test a change in target lambda at higher load where inj dead time plays less of a role. I'm expecting it to under-correct a little, but we'll see. As for the change in fueling vs IAT, first I will double check the IAT calibration, but it is giving seemingly accurate results and certainly not off by a large %. I'm really not too sure why the background calculation is having such a large over-correction for my setup. I'm likely going to setup a simple low-res 4D fuel table with IAT vs X (not sure whether to go MGP, RPM, or Air Flow?) in an attempt to get more consistent results with varying IAT. I'll do some tests by blocking the intercooler to confirm results. I'm also going to order a fuel pressure sensor so that I can reference it in the fuel calc rather than an assumed 300kpa value.

Attached is a copy of my tune and logs. The smaller log is from last night which matches the current tune. The larger log is from a cruise last weekend with cool IATs - https://drive.google.com/drive/folders/1HRLEzSbhF_qzDPXjj4oy1JDqLZ4gA_--?usp=sharin

Would appreciate any insight, I'll update this post with any progress I make.

[essb00]

1. Get an ethanol sensor - so you can use 'modelled-multi-fuel' where you can specify injector characteristics for each fuel blend end range you use (e.g. pure 98octane & E85). Sample below. *Default fuel main & injector setup data for 98, multi-fuel data on E85 section.

2. You normally start with the injector manufacturer-provided dead time data, and tweek +/- from there. This would be very hard to just 'guess' especially on high flow rate injectors where there's a big chunk of non-linear region when you graph volumetric flow vs actual commanded pulse width.

3. Different fuel charge cooling coefficient for different blends can also be set from 'modelled ' multi-fuel' mode.

4. Charge temp correction would be very complicated to figure especially in non-consistent/non-repeatable conditions - that's why expert tuners recommend have this done on the dyno. 

[RyanG]

4 minutes ago, essb00 said:

1. Get an ethanol sensor - so you can use 'modelled-multi-fuel' where you can specify injector characteristics for each fuel blend end range you use (e.g. pure 98octane & E85). Sample below. *Default fuel main & injector setup data for 98, multi-fuel data on E85 section.

2. You normally start with the injector manufacturer provided dead time data, and tweek +/- from there.

3. Different fuel charge cooling coefficient for different blends can also be set from 'modelled ' multi-fuel' mode.

4. Charge temp correction would be very complicated to figure especially in non-consistent/non-repeatable conditions - that's why expert tuners recommend have this done on the dyno. 

Yeah I've purchased an ethanol sensor and will be fitting shortly. I'm aware of the ability to adjust values between each fuels and I've done this, just separately in different maps and only at straight 98 or straight E85. I haven't really gone down the path of flex fuel yet because it just adds another complexity that's not needed until I fully sort it on a single fuel.

Yes manufacturer data is where I've started and tweaked from there as stated. It's the how to go about "tweaking" it I'm really interested in..

[essb00]

 

31 minutes ago, RyanG said:

Yeah I've purchased an ethanol sensor and will be fitting shortly. I'm aware of the ability to adjust values between each fuels and I've done this, just separately in different maps and only at straight 98 or straight E85. I haven't really gone down the path of flex fuel yet because it just adds another complexity that's not needed until I fully sort it on a single fuel.

Yes manufacturer data is where I've started and tweaked from there as stated. It's the how to go about "tweaking" it I'm really interested in..

I suggest leaving the manufacturer-provided injector dead time data as is. You already pointed out the non-linearity of the flow rate, so you should not expect that method with multipoint group 1/2 cycles would get you something good (as you only keep lowering the pw with flow rate into non-linearity).

Focus more on the charge temp approximation table (try engine rpm vs MGP as with the help file).
Disable your IAT fuel corrections.

[Adamw]

Deadtimes and SPWA below for those injectors on petrol at 300Kpa with a G4X driver.  Flowrate for petrol is 892cc @ 300kpa.  They will flow quite a bit less on E85 but I haven't personally tested them with it yet.  Your high VE will most likely be because the flow rate is too high for E85.  Similar injectors that I have tested flow 10-15% less on pure ethanol Vs Petrol.  

IAT trim needs to be disabled, set up the charge temp table similar to the example in the help file, which is usually a reasonable starting point for common single throttle plenum type manifolds.  

 

[RyanG]

On 3/11/2023 at 11:25 PM, Adamw said:

Deadtimes and SPWA below for those injectors on petrol at 300Kpa with a G4X driver.  Flowrate for petrol is 892cc @ 300kpa.  They will flow quite a bit less on E85 but I haven't personally tested them with it yet.  Your high VE will most likely be because the flow rate is too high for E85.  Similar injectors that I have tested flow 10-15% less on pure ethanol Vs Petrol.  

IAT trim needs to be disabled, set up the charge temp table similar to the example in the help file, which is usually a reasonable starting point for common single throttle plenum type manifolds.  

 

Thanks Adam, I'll try those values and recommendations this week. If they do only flow ~800cc on E85, that probably explains why I got to ~90% Inj DC quicker than I expected.