286 Vindication

[Bruce Bowling]

~ >
~ >BTW, my environmental correction WWW page shows the effects
~ >of altitude and barometer on engine HP/torque, and they can be dramatic.
~ 
~ Yes, they sure can.
~ 
~ My final point, if the pressure does not change then you don't have to
~ correct for it.
~ ie. there is nothing to correct.
~ 
~ 
~ 
This sounds good.  However, what value would you choose for the absolute
reference pressure, since this would have to be a hard-wired value.
And what happens if you drive up to the mountains?

Here is the equations which convert the barometric pressure read on a mountaintop
to sea-level (the eqns are from 1978 CRC handbook):

xk = 1.6e06*(1.+.0022222*(temp-32.));
bpc = -((30.48*elev-xk)/(30.48*elev+xk))*bpress;

with:
  bpc = the corrected barometer reading to sea level.
and inputs of
  temp in degrees F,
  elev in feet,
  bpress = actual barometer reading in in. Hg.

I made a simple code which runs through the equation above for various
elevations (the uncorrected barometer and temp is hardwire inputs):

--------------------------------------------------------------------------------------------
main()
{
	float xk, bpc,temp, elev, bpress;

	temp = 70.;
	bpress = 30.00;

	elev = 0;
	printf("For temp of %2.1f degrees F and barometer of %2.2f inches Hg\n\n",temp,bpress);
	printf("Elevation(Feet)  CorrectedBarometer\n---------------------\n");
	while(elev <= 2000.)
	{
		xk = 1.6e06*(1.+.0022222*(temp-32.));
		bpc = -((30.48*elev-xk)/(30.48*elev+xk))*bpress;

		printf("    %4.0f     %f\n",elev,bpc);

		elev = elev + 100.;
       }
}
---------------------------------------------------------------------------------------------

and here is a run of the above code:


For temp of 70.0 degrees F and barometer of 30.00 inches Hg

Elevation(Feet)  CorrectedBarometer
---------------------
     0     30.000000
   100     29.894785
   200     29.789938
   300     29.685459
   400     29.581343
   500     29.477591
   600     29.374197
   700     29.271164
   800     29.168488
   900     29.066166
  1000     28.964199
  1100     28.862583
  1200     28.761314
  1300     28.660397
  1400     28.559824
  1500     28.459595
  1600     28.359709
  1700     28.260162
  1800     28.160955
  1900     28.062088
  2000     27.963554


Does this have an effect on a tuned engine?

- Bruce


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               Bruce A. Bowling
  Staff Scientist - Instrumentation and Controls
 The Continuous Electron Beam Accelerator Facility
    12000 Jefferson Ave - Newport News, VA 23602
                 (804) 249-7240
                bowling at cebaf.gov  
        http://devserve.cebaf.gov/~bowling
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