[Diy_efi] MAP Sensor

[Kent Martin]

How does one accommodate for air temperature when using a MAP sensor lookup?
Do you add a ratio of the temperature to the map index?
If the temperature was included as an index then you would need a three
dimensional
array for RPM, air temp, and manifold pressure. How do you get around this
so only
2D table is needed?
Kent
----- Original Message -----
From: "Tony Bryant" <brd at paradise.net.nz>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, July 24, 2002 3:27 PM
Subject: Re: [Diy_efi] MAP Sensor


> On Wed, 24 Jul 2002 17:00, you wrote:
> > Hi,
> >
> > Could somebody give me a quick rundown as to how an engine determines
> > "load" ?
> >
>
> "Load" is undefinable, unmeasurable, and irrelevent.
>
> What matters is the engine is consuming a certain amount of air each
cycle,
> and therefore needs a proportional amount of fuel put with it.
>
> The three methods of detemining this amount of air are :
>
> - MAF (Mass air flow) : measure airflow mass or volume rate going into
> engine, divide by cylinders and RPM hence get a air mass per cylinder per
> cycle.
>
> or
>
> - measure MAP (manfold absoulte pressure), and (as a first approximation)
> assume that in each cycle each cylinder will gulp a volume of air equal to
> its displacement volume, which is translatable to a mass via the gas laws
:
> PV=nRT, P is of course the MAP.
>
> In reality the assumption that the cylinder will grab a volume of air
equal
> to its displacement isn't a good assumption, so you end up needing a
software
> table to correct for this lousy assumption.
>
> or
>
> - use throttle plate angle and RPM to index a lookup table, but this
method
> will drive you insane for a variety of reasons I'm not going into today.
> (this method is called N-alpha)
>
>
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>
>



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