Up Up and Away

[Phil Lamovie]

Hi John et al,
 sorry 'bout the html had to reload NT (i moved the mouse)and got all
of the default settings.

Now to buisness.

The abundance of calculations offered is in no way
justified by the starting assumptions.

The tribology of gaseous flows is both relevant and
irrelevant in the same breath.

The approach to fuel injection as a science of calculations
is not a valid one if you accept that the simplest solution is the
best.

The "manifold absolute pressure" is by it's very explanation
a measure of the environment INSIDE the manifold. It has no concern
with the outside weather conditions ONLY the inside.

The original question remains unanswered. How can the engine tell...

Lets take an engine on the dyno at 35% throttle at 3000 rpm.

Air temp 20 deg C pressure in manifold 70 kPa Absolute.
We adjust our fuel and spark table to give target A/F ratio
of 13.5:1 with MBT as the spark setting. 

I will assume that at this time all the relevant perturbations of the
air column are taking place in all of their Bernoullian Wonderment. 

The very simple point to be had here is that next time the same air
temp and pressure are found at the same rpm then the same stored
values for fuel and spark will of course produce the same A/F ratio. 

Note how I completely left out the throttle position. It may be that
at 15,000 feet ASL the WOT pressure will be only 70 kPa. If the engine
is at 3000 rpm and the air temp is the same the Volumetric efficiency
of the engine is the same. 

The real test for flow is NOT across the butterfly !!! It is of course
a variable device where as the inlet port is not. The speed of the air
through the inlet port will of course be the same at the same manifold
ABSOLUTE pressure and temp and rpm.

Carbys care about air velocity EFI couldn't give a rats arse.
 
This is very relevant with plenum type manifolds some what diff with
individual trumpets as the mass of the External fraction causes the
MBT to be found at slightly shorter trumpet lengths.

As all of the mechanical components are bound by their shape in the
repetition of their function so is the ecu bound to give the same
values for fuel and spark.

The point of measuring the pressure is to know what map point to use
and how much interpolation b/w points is required.

There is absolutely no need to calculate the mass of the atmosphere on
Earth and then divide that by the ratio of volume of inlet manifold.
Though it would work.

Please note the total lack of Patents for Altitude correction of
aircraft fuel injection computers. Also total lack of altitude sensors
on all Ford and GM vehicles. I suppose they don't have mountains in
the 
USA.

My company has also supplied ECUs for Aircraft that have flown from
England to Australia, film is available from National Geographic.
I promise they were all fitted with absolute sensors. The engine were
all dynoed on a thirty foot tower (they had very big props about 33
feet
span) 650 hp at sea level)) and then flew half way around the world.

Hope the simplicity of it is not too hard to fathom.

Phil

Injec Racing Developments