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Hi folks,
Below is a snopysis of the program thus far, also at bottom of the synopysis
is the e mail address and a web page URL where you can see example of the
programs screens. The synopsis in just my personal observations after
playing with the program for one day/night. I own no stock nor have any
other fiscal interest in the program {:>)
For those of you who contacted me off the list, my apologizes for not
responding back to you individually, just decided this would answer most of
your questions.
The program works for 4 stroke, 2 stroke and rotary engines (treating them
as a two stroke). You can select boost pressure, rpm, inlet (ambient) air
temperature, you can specify intercooler or not and if intercooler what its
efficiency is and the amount of pressure drop (or you can stick with the
program's defaults). You can input your efficiency values in terms of % for
volumetic (Ve), compressor(Ce) and intercooler(Ie) efficiency (there are
reasonable default values set in the program which are fairly conservative -
like 65% for Volumetric efficiency).
When you run the program it basically calculates the pressure ratio p2/p1
and searches its compressor maps to make a match. Whether a match is found
or not, all pressure points are plotted on all the turbo compressor maps and
you can look at each and every one.
You can specify 1 turbo, 2 turbo or 4 turbos.
The program output, in addition to the p2/p1 ratio, are Temp after
turbocharger, temperature drop by intercooler, and temperature at the
manifold (after turbo and intercooler (if one is used)).
You get the NA (Naturally aspired - no turbo) airflow (based on your CID and
HP input) in both CFM and Mass flow in lbs/min. You get the turbocharged
airflow also in terms of CFM and mass flow in lbs/min and also turbocharged
HP. The critical input is your CID and NA HP figure as all else is based on
those inputs. So if you give a nonrepresentative value for your engine
(incorrect CID or HP) then garbage in - garbage out.
For the 2 rotor the CID should be 80 and for the 3 rotor it should be 120
CID, the HP value is up to you. But, whatever NA HP figure you select for
input should correspond to the max rpm you place in the 5th (last) rpm box.
The numeric values it displays (that I mentioned above) are for the last
(5th) rpm value entered. It does calculate the values for the other 4 rpm
values you input, but only displays the resulting P2/P1 point for those rpms
on the compressor maps. Now that is the P2/P1 ratio were P2 = Boost gauge
pressure + P1( ambient pressure). So if you decrease the ambient pressure
the P2/P1 ratio increases and this moves the point up the compressor maps
and possibly into the surge zone.
Of course, you can find the those numerical values for any rpm by placing
that rpm value in the 5th box, however, as I found out - then you must then
adjust your NA HP input to correspond to that RPM. If 180 HP at 6000 rpm NA
and then if interested in numerical data at 5000 rpm you would need to go
back and reduce your HP input to correspond to the 5000 rpm point (like
150HP?) and then input 5000 in the 5th rpm box. You should also adjust your
other 4 rpm points correspondingly if you want the plot of those points on
the compressor map to have any meaning. But, if only interested in the
numerical data generated for a specific rpm thats the way you can do it.
One current limitation of the program is the number and selection of turbo
compressor maps. There are a goodly number of the Garrett more popular (and
smaller turbos) as well as some of the others I mentioned, but to be frank
it could stand a few more maps and I have suggested as much to the program's
author. I believe he is going to see if there is any market for his product
before investing too much more time in installing more maps. Some of the
maps suffer from readibilty but that appears to be due to the poor quality
of the original map scanned in.There are 46 Garrett compressor maps, 9
Holset maps, 6 KKK maps and oneMitsubishi map, just to give you a feel.
As mentioned, there are 5 rpm/boost values you can input along with each
rpms boost psi, Ve, Ce and Ie and whether with and intercooler of not.. The
program appears to attempt to find a map (maps) that contains all 5
resulting pressure points on a compressor map. IF it does not find all five
on the effective area of a compressor map (in other words some of the
pressure points are below the plotted efficiency lines of a compressor map),
then it does not automatically show any matching turbos, however, the
operating pressure points are plotted on all the compressor maps and you can
look at each one to find a possible eyeball match (with perhaps one p2/p1
not on the map) that the program did not.
The reason I found this, is I intend to run low boost pressures, like less
that 5 psi and many compressor maps do not start showing their efficiency
lines until around 7 psi boost at sea level.. Now that is the P2/P1 ratio
were P2 = Boost gauge pressure + ambient. So if you decrease the ambient
pressure the P2/P1 ration increases and this moves the point up onto the
compressor maps. I found no matches for my 2 rotor at sea level with 5 psi
of boost at the rpms I selected. However, when I decreased the ambient
presssure value to simulate 4000 ft and above, there were about 10
compressor map and turbos that gave a match as the p2/p1 ratio and increased
(as P1 decreased). So this is not so much a limitation of the program as it
was an artifact of my operation conditions and the compressor maps.
I was pleased to see that the program did show the effects on increasing
altitude (decreasing ambient pressure) on the operating point p2/p1 on the
compressor maps. It shows how quickly a compressor wheel that works at sea
level could be in the surge zone at altitude. So worthy the price for that
feature along in my book.
If interested the program can be acquired by contacting Jon at addresses
below and see examples of the screens for the program at his URL:
turbocalculator@hotmail.com
www.wfu.edu/~pipejw02/TurboCalculator.html
Rest is up to you.
Ed Anderson
Matthews, NC
RV-6A N494BW
eanderson@carolina.rr.com
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