Fuel calcs

[gearhead]

I think it is best to start with a basic model. You can always extend it. The basic model would neglect humidity. Once you get the basic model controlling an engine then you can improve upon it.

amen, brother!

Lets leave Humidity out for now. I know of no engine controller using it. It looks to be a small part of the eqns. and Bob is right, EGO can be a cure for minor trim issues like this. Let's get the equations laid out, first then figure out the best way to formulate them for calculation sake and determine appropriate DP shifting to make the variables approximate their engineering scale.

Gearhead

[Fred]

At the end of the day, we are stuck with humidity and therefore should be aware of it, but not try to do anything specifically for that.

Lets leave Humidity out for now. I know of no engine controller using it.

As Bob said, it can't be dealt with directly anyway.

Let's get the equations laid out, first then figure out the best way to formulate them for calculation sake and determine appropriate DP shifting to make the variables approximate their engineering scale.

Yes, except I don't think the first/then approach will work as we probably need to know what we are doing with each to get the equations (actual ones used, not theoretical ones) correct for our purposes.

Fred.

[MotoFab]

Also since 10% of the volume is now taken up by non-combustible water vapor the volumetric efficiency changes a bit too (i think).

10% of the mass is water. Which has a nill effect on the mass of O2 per volume of intake charge.

- Jim

[shameem]

The way i understood it-


21% of "air" is oxygen

For dry air - intake charge has 100% air - so for a intake charge of unit 100 - oxygen is 21% of 100 = 21 units of O2
For 10% humiditiy - intake charge has 90% air - so for a intake charge of unit 100 - oxygen is 21% of 90 = 18.9 units of O2

[MotoFab]

Are you speaking in the past tense, Shameem? Understood is past tense, is that what you still understand?

(EDIT)So I got this Board Warning for this post. I sure don't mean to be so misinterpreted. The post above is a straight up question. I want to know if whether you are speaking in the past tense, or if it's only a 'manner of speaking' describing a current understanding. When I get some new information, I speak about what I knew before in the past tense.

[MotoFab]

It's sort of easy to mix up mass and volume.

At 25°C the fully saturated vapor density of air is about 23grams of water (mass) per 1 cubic meter (volume) of air.

23gr of water (mass) is 23milliliters of water (volume), or 0.000023 of a cubic meter.

At 35°C the fully saturated water mass is 40gr or 0.000040m³(40cc)
At 45°C the fully saturated water mass is 65gr or 0.000065m³(65cc)

At 50°C the volume of the water in the fully saturated air occupies only 81cc of the 1,000,000cc in the cubic meter of air. 81 millionths by volume.

The curves posted up earlier in this thread are a graph of grams of water per kilogram of air.

[Fred]

It's sort of easy to mix up mass and volume.

At 25°C the fully saturated vapor density of air is about 23grams of water (mass) per 1 cubic meter (volume) of air.

23gr of water (mass) is 23milliliters of water (volume), or 0.000023 of a cubic meter.

At 35°C the fully saturated water mass is 40gr or 0.000040m³(40cc)
At 45°C the fully saturated water mass is 65gr or 0.000065m³(65cc)

At 50°C the volume of the water in the fully saturated air occupies only 81cc of the 1,000,000cc in the cubic meter of air. 81 millionths by volume.

The curves posted up earlier in this thread are a graph of grams of water per kilogram of air.

Thanks for the explanation :-)

10% of the mass is water. Which has a nill effect on the mass of O2 per volume of intake charge.

So, not nil, but rather negligible.

Fred.

[MotoFab]

So, not nil, but rather negligible.

Heh heh. Exactly, not nil, the water displaces 81 millionths of the O2 volume. Good thing it isn't any higher eh?

- Jim

(Fred I mean this like we are sharing a chuckle.)

[Fred]

Heh heh. Exactly, not nil, the water displaces 81 millionths of the O2 volume. Good thing it isn't any higher eh?

Indeed, because short of trusting an O2 sensor to run our engines or installing humidity sensors there would be little we could do about it :-)

(Fred I mean this like we are sharing a chuckle.)

I'm quick to forgive, but slow to forget ;-) No need to say.

Fred.

[Fred]

I just found austinbobs posts in one of my backups (he edited the interesting stuff out in a tizzy...) so tomorrow I'll restore it all to where it was and maybe have a go at cross referencing it and putting some meat in this sandwich :

http://www.diyefi.org/forum/viewtopic.php?f=8&t=258

Fred.