IAT fuel multiplier

Tuning, troubleshooting and the nitty gritty of using rusEFI to make your engine run nicely!
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tmbryhn
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Joined: Wed Feb 12, 2020 2:40 am
Location: Norway

IAT fuel multiplier

Post by tmbryhn »

Here's a comparison of the default IAT correction table for Megasquirt and RusEFi:
IAT_MS3_vs_RusEFi.png
IAT_MS3_vs_RusEFi.png (107.85 KiB) Viewed 8270 times
Question: In the current fuel equations for eg. Speed-Density and Alpha-N, is (1) the raw IAT value taken into account to establish a baseline air density based on eg. the ideal gas law, or (2) does the equations use the IAT correction lookup table for that purpose?

If (2) is the case; would it be a good idea to implement an approximation to the ideal gass law values in the IAT correction table by default similar to the MS method?
mck1117
running engine in first post
running engine in first post
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Re: IAT fuel multiplier

Post by mck1117 »

rusEFI uses ideal gas law, but not directly on the intake air temperature. We estimate the temperature at the valve based on a function of IAT, CLT, and airflow. As the airflow slows down, it picks up more heat from the intake/cylinder head on its way by, so it ends up hotter.

This dialog configures that heat transfer:

The table here is derived from the factory GM tune for my V8, and works pretty well.
image.png
image.png (99.56 KiB) Viewed 8261 times
tl;dr: you shouldn't need anything other than flat 1.0 in that IAT fuel mult table. It's there if you need it, but you probably don't.
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AndreyB
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Re: IAT fuel multiplier

Post by AndreyB »

Very limited telepathic abilities - please post logs & tunes where appropriate - http://rusefi.com/s/questions

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tmbryhn
Posts: 169
Joined: Wed Feb 12, 2020 2:40 am
Location: Norway

Re: IAT fuel multiplier

Post by tmbryhn »

Thanks Andrey :)
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AndreyB
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Re: IAT fuel multiplier

Post by AndreyB »

It's hard to notice that help menu but at least some progress I guess :(
image.png
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Very limited telepathic abilities - please post logs & tunes where appropriate - http://rusefi.com/s/questions

Always looking for C/C++/Java/PHP developers! Please help us see https://rusefi.com/s/howtocontribute
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