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Start Of Injection vs Duration Of Injection vs End Of Injection

Practical Diesel Tuning

Discussion and questions related to the course Practical Diesel Tuning


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Hi there ,

First of all , i want to thank all who maed these courses possible , it helps a lot having some key concepts explained in practics , and by who really knows what is doing by the way .. lol

With this post i would like to know if there are some general formulas that we can apply to calculate SOI , DOI and EOI ? I know that maybe for OE calibrators they must have constant values on these formulas to take more account about emissions and fuel consumption than performance (im guessing here , correct me if im wrong )

But ive used files in the past from reputable tuners , that dont just use percentage increments on DOI table for example , but instead they have the whole DOI table calculated , and im guessing that they do this job applying formulas on an excel sheet or something ? :)

Just trying to improve my knowledge a bit futher here .

Thank you

scummy,

I like that you're trying to get to the point of visualizing exactly what's going on physically vs. what's being commanded electronically. The best way to know the delay between injector energizing and SOI is to have a common rail shop shoot high speed footage. One of the better videos I've seen on the topic can be found here [url=https://www.youtube.com/watch?v=tcadEVB_h4k&feature=emb_logo]https://www.youtube.com/watch?v=tcadEVB_h4k&feature=emb_logo

There's quite a bit of difference between the different injector architectures. One things I found particularly interesting is how far the EOI can be skewed past the end of energize point.

One particularly useful method I've found for calculating the window of injection is to look at the Injector characterization table and follow one fuel pressure column. In the factory table you can calculate how much extra duration is needed to go from 60mm3 to 80mm3. This will give you a much better idea of how much duration to add to achieve 20mm3 instead of looking at the 20mm3 cell (which is characterized by 20mm3 + injector latency) and simply adding that duration to your overall.

Hope this is helpful,

Nick

Thanks for the answer Nick ,

Actually the video is quite good and explains a few key thoretical concepts but doesnt say much about the math behind that .

Lets say that i want to extend my DOI table , to reach more IQ (mm3) and more rail , you are saying this 'is calculated just by direct proportionality ?

Can I post here a few excell sheets just to try to reverse engeneer them , to find out the way it was done ?

This is a process that i would really like to understand the math behind it , because with an already existing table , its easy to do increments . But let's say I had to create one from scratch ... That is the real challenge .

Thank you .

scummy,

Go ahead and post some docs and I'll take a look to make sure we're on the same page. Certainly flow bench testing is the most precise way to deveolope and injector characterization map but working in proportions will get you pretty close.

-Nick

Hi there ,

I made an excel sheet with the subject i was talking about , please note that some rows and columns on the axis were rescaled ( i put them in red ) , and on X axis I applied the factor 0,008350 , to convert mm3 to Mg.

Hopefully we can go somewhere with this , this is just a curiosity i have to perfect my tuning capabilities :)

If you need some more data , let me know .

Thank you very much

Attached Files

Scummy,

I went through your sheet. I think for the most part you have the right idea. By changing 7/6 rows and columns I think you may have caused more work for yourself. I've made some slight adjustments to the original just changing one row and one column. Highlighted for reference, I'd replace the red row and red column with the green. I realize there's a large gap in fuel rate between 83.5 and 135 but you've go no reason to believe the injector doesn't act in a predictable way over those fuel rates. Remember the ECU will interpolate as needed between fueling numbers.

I left some of my math in the columns and row so you can follow along. Column AF shows me breaking fuel flow down by the 75.1mm3->83.5mm3. That gives us 8.4mm3 and the corresponding pulsewidths below it. Column AH I've grown those number by multiplying them by the multiple 6.13 (51.5/8.4).

On the pressure side I've taken your desired pressure of 2000 bar and realized that as a 1.111 growth from 1800 bar (row 59). Flow grows as a sqrt to pressure so the row below that is the sqrt (row 60) and then in row 61 is the new pulsewidth reduced by the product of the square root.

Clear as mud, right :)

Nick

Attached Files

Hi Nick , once again , thanks for the time and all , the patience of checking my excell sheet .

Understood clearly as mud what you did there .. ahah

And i know ecu interpolates values , but isnt there a big gap between 1600bar Rail , and 2000 ? And the same story between 75 mg IQ and 135 mg ..

ALL of this is at WOT operation , so i know it wont make a big difference , and i know im over complicating this stuff .. But i know the guy that made these files works all about math , he calculates everything like OEM ecu calibrators .

Doesnt mean i will do this , i would need a month just to finish a file for a customer :D

Thanks

It is always best, in my opinion to RE-calibrate stock ECU maps. IF you need little bit more fuel from your system ( stage 1 per say) you can extrapolate the last column ( using delta micro-seconds per mg or mm3).

If you need A LOT more fuel from your system you can even alter the entire maps- with keeping smooth running control in check, like the videos say, no spikes and so on.

The picture i attached has fuel duration map REcalibrated for 140 mm3, from stock 80 mm3.

Bigger nozzles and HPFP. Blue cells are lower value than stock, and red- higher values.

Car runs perfect, makes aprox 320-330 BHP from stock 145-150. Turbo-diesel 1.9 L engine.

Y -axis is BAR- Rail Pressure

X- axis is mm3 :)

With DEcalibrated DOI ( + 25% and so on ) the ECU will not make correct LAMBDA calculations anymore. Also on torque based systems you can get pretty close to the real power if you make the right calculations ( taking into consideration approximate pumping losses and VE )

Best regards,

Bogdan.

Attached Files

Hi doc93 , thanks for your reply.

This kind of calibration you showed is the kind of thing i was talking about .

How do you calculate an entire fuel table ? Or fuel cell , same thing .

Thank you