Engine mass Flow rates

[Bishop]

Would anyone happpen to have any figures for mass flow rate/pressure throughout the engine rev range with the rescrictor in place? I've worked out the maximum mass flow possible to be about 0.06-0.07kg/s (god bless John Heywood's book) but becasue of problems with the dyno have not got any "real data" and with major project deadlines looming any help would really be appricated.

Thank you

[Bishop]

Would anyone happpen to have any figures for mass flow rate/pressure throughout the engine rev range with the rescrictor in place? I've worked out the maximum mass flow possible to be about 0.06-0.07kg/s (god bless John Heywood's book) but becasue of problems with the dyno have not got any "real data" and with major project deadlines looming any help would really be appricated.

Thank you

[Frank]

im not exactly sure what your after,

and im not exactly sure why you don't head toward a flow bench (Superflow SF600's will choke a restrictor)

perhaps this is useful

The restrictor is dumping into a 10" round pipe (part of the flow bench)

The "pressure" is the difference in static pressure from atmosphere to the "plenum"

You will notice exit diameter is important (with diminishing gains for larger diameters), and that our engine pulls about 5Kpa (in the plenum) at maximum power.

This was a 76Hp (at output shaft) engine.


http://www.uq.edu.au/fsae/restrictors.jpg

[Bishop]

That is useful but what i was really after is some figures that will tell me at a given Rpm how much air is the engine using, I have tried using formula but they seem to tell me mass flow rates below that at which the restrictor cuts in - hence it would appear the restrictor does nothing - which i know is not true!

[Frank]

I do not see how knowing everyones metrics are really going to make your engine more powerful.

A flow bench will, and secondarily a dynamometer will.

Any number you get from anywhere collected by students may be more than a few percent wrong, they may not be collected correctly altogether.

I'm assuming you want data that says "our engine pulls x kg/s at y static pressure (where exactly you haven't specified.. But I assume in the plenum somewhere), at z rpm. Do you want data taken from a mass flow rate meter stuck in the inlet tract whilst the engine is on a dyno? If so, of what type?. And the static pressure? Where measured?, and by what means?

The data I showed you is from a flow bench, and for a specific restrictor design (the throttle was 34 mm, the throat was a 60 mm radius, the inlet 30 included angle, the exit angle 10 deg included angle, the surface finish near the throat less than 1um, and there's two different exit diameters compared.). In addition, I have expressed the static pressure in the plenum at maximum power, which we measured. We had the engine pulling max power on the dyno, and we ran a static port into water, and measured the column height. The engine makes 76 hp at 10100 rpm.

Absolute numbers are not really necessary to make a 20 mm hole flow better, an understanding of the ballpark pressures, the actual losses, the mass flow rate vs pressure graph, and experimenting with shapes does.

You might find that a "good" restrictor is very long and may require a large plenum volume, you might even start to think that the "optimum" design considers space and ease of manufacture.

In my opinion, the 20 mm hole, and the geometry downstream of it, should be where you start your development.

After this development, there is a host of things you can do. Like change runner lengths, change cams, polish heads, change valve seat geometry, change plenum configurations, change exhaust pipes, try different runner inlet radii ("airhorns"�). Etc etc etc

I've just assumed your making a car also.

The conclusion I have come to from doing this stuff a while ago, is that "optimal" conical shapes are NOT usually the the easiest way to get better lap times in this competition.

[flybywire]

This is not my area of expertise but maybe the formula are right. Considering that the restrictor won't see steady state flow with a finite sized pleneum. Meaning the resitrictor will 'kick-in' much sooner than the average flow would suggest.

I know our intake guy last year wrestled with CFM and pleneum volumes trying to get as close to steady state as possible through the restrictor without throwing the throttle response right out the window. http://fsae.com/groupee_common/emoticons/icon_frown.gif

[Charlie]

We've taken quite a bit of mass flow data on our 2003 car. I used a Ford Focus MAF. The problem is the calibration tables are for that MAF in its entire intake system (that we've removed it from). So the numbers we get are questionable (and seem rather high). We use it for comparison purposes only.

Perhaps this will help answer your question though, I did not see the airflow start to level off until around 12,500.