MoTeC Global Forum

Hi Guys,

Im using a motec M150 and am trying to understand how the engine charge cooling gain is applied to engine charge temp model, and how ethanol affects it.

there is no way to set the latent heat of vapourisation of the fuel being used so I'm assuming it is an approximated model and you adjust this cooling value for the % of ethanol in the fuel.

is the resulting charge cooling gain a fixed offset from the sensor reading, so a gain of 13 degrees would mean inlet temp-13 would be the value used as final inlet charge temp or is the charge cooling value scaled by differences in lambda and IAT?

if anyone knows how this is calculated I'd like to learn more about it.

Alex

Your best bet is to watch the webinar that Motec offers. It's best to use a dyno to adjust correctly.

I have watched it,

but I want to understand how it works. most other functions in the help documentation outline exactly how a value is derived, the intake gain value has a unit of temperature only (degrees C), which for a gain value insufficient.

say I set to 20 degrees C. 20 degrees per what?

i understand what it is doing, but i want to understand the correlation to other input parameters such as IAT, AFR, molar mass etc.

there is nowhere to enter the specific heat capacity of the fuel, nor the latent heat of vaporization energy so there is a fudge in the model somewhere.

If you look at the code in M1 build, you can see the calculation for Charge Cooling is:

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Value = Gain.Primary / Fuel.Mixture Aim^2;

(note I've removed the code for Secondary injectors for simplicity)
I guess the units for Gain are degrees C because technically lambda is a ratio and ratios don't have units, so degrees C is a technically correct unit in this case (just not a very helpful one).

It is used to calculate Charge Temperature, using the equation (again I've simplified the calculation a bit)

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Charge Temperature = (Inlet Air Temperature + Charge Temperature Correction) - Engine Charge Cooling

The Charge Temperature Correction value is calculated using the estimated Port Temperature Delta and the Charge Temperature Correction Factor (based on Engine Speed and Inlet Mass Flow).

I see that the available axis for the Charge Cooling Gain Primary (and Secondary) tables is Fuel Composition, so you can insert different gain values for different ethanol percentages.

When you look at the calculation for the Engine Charge Cooling Value, I guess you could look at it as:
"this value is the temperature drop for a stoich mixture, and it will increase rapidly (due to squared term) with richer mixtures and decrease rapidly with leaner mixtures", but it is not a precisely modelled cooling model or anything like that.

Anyway I hope that helps.

Malcolm,

that helps MASSIVELY. thank you very much for your reply.

No problem. If you haven't, it might be worth trying to get access to the M1 Build project for the GPA/GPR (or whatever package you're using). If you understand how basic computer programming languages work then you can usually answer a lot of your own questions and learn a lot about what is going on inside the ECU. Unfortunately (and understandably) for some things the algorithms are hidden and you don't know what happens inside them, only what their inputs and outputs are, but for many things like fuel corrections it's all there in surprisingly simple terms.

I am familiar with code/PLC's and did have a look at the M1 build, but the sample project is missing a lot of the code that would be included in GPA/GPR.

I've tried to find a GPA or GPR build project to download but as I don't have a Dev licence I have been unsuccessful in finding it. It would certainly be useful to see what the code in my ecu looks like, but I have no need to actually compile and run modded code on the ecu itself, so it's not worth paying for the Dev Licence.

If anyone has a GPA or GPR build project they can send me my email is address is ad.burnspp@gmail.com

Hi,

To get access to the M1 Projects, you need to have a MoTeCOnline Login, this is a free service that is organised through your dealer. This will also provide you with a M1 Build Licence (the licence for use in M1 Build that allows for Packages to be built) but not the Development licence, so you cannot load the Package onto an M1 ECU.

I appreciate your input Stephen, I'll follow up with my dealer.