The Pressurizing Burner has been running!
And running better than I had ever imagined. I measured a FULL INCH of pressure. :-)
The report for the test is below.
I have a sketch of the test setup.
All the tests after #1 took place with a pretty badly charred diffuser. The pressure might have been even higher if it had remained smooth.
Sunday, August 18, 2002
PRESSURIZING BURNER TEST
Test #1: Diffuser and nozzle were set up per attached sketch, but with diffuser inserted into a length of 3" metal duct. Attempts to ignite gas/air mixture were unsuccessful. (The sketch shows a divergent nozzle with a .035" throat diameter discharging into a diffuser with a 1.07" throat diameter. The nozzle is 5" away from the diffuser. The diffuser diverges at 12 degrees, to almost 3" ID.)
The 3" metal duct was inserted tangentially into the side of a 5 gallon pail near the bottom.
Result: The gas/air mixture ignited in the pail, but then immediately burned through the duct and diffuser and ignited the jet. It scorched the (wooden) diffuser pretty well before I could get it turned off.
Test #2: Same as #1, but 3" duct was replaced with 1.6" ID EMT (electrical conduit) fitted into the diffuser and inserted tangentially in the same 3" hole in the 5 gallon pail.
Result: Mixture ignited well and burned in pail only, but with long soft flame only near perimeter of pail.
Covered top of pail, reducing opening to approx 6 sq in.
Result: Mixture burned much better, filling pail. Observed evidence of pressure from flames coming out 3" hole around EMT.
Test#3: Made combustion chamber from #10 tin can (6" dia x 7" high).
Result: Mixture burned well, filling can.
Open top of can was partially covered with bricks.
Result: Mixture burned even better, with evidence of pressure from sound of flame squirting out between bricks.
Test #4: This is the setup shown in the sketch. (Same nozzle, same diffuser, same 5" spacing, same 1.6" EMT, same can and same bricks, but with a manometer inserted in can right beside EMT entrance.)
1) With bricks pressed tight together (no fire) pressure in can is 1 7/8" of water column. ( ! )
2) Burns well as long as brick are at least 5/16" apart. So the opening is 5/16 x 6 = 1 7/8 sq in. Pressure in can under these conditions is 1" water column.
3) Increasing the opening moderately made little difference in sound or appearance of flame. The pressure dropped to near zero when the spacing between the bricks was 1" or greater.
4) Changing the standoff between the nozzle and diffuser by +-1" made no noticeable difference in the appearance of the flame, sound or pressure.
5) The burner is only moderately noisy. I have no way of measuring the sound, but guess that it would be unnoticeable at 150 feet in a typical urban environment. This is with the burner completely unshielded and un-insulated and discharging directly into the air.
1) The nozzle/diffuser combination will produce a useable pressure output.
2) The max static pressure produced is a little over twice the .92" of water column that I calculated. This implies that the velocity of the gas/air mixture is about 1.4 times the value I previously calculated (64 fps). That calculation was based on a sonic velocity of 672 fps and a discharge rate of 6# /hr for the propane.
3) Interestingly enough, the (previously) measured
discharge rate of the nozzle was considerably larger than the calculated
rate--10.3 #/hr instead of 6 lb/hr. This is 1.7 times as much.
This is somewhat near
the 1.4 times on the velocity, so perhaps my sonic velocity calculation is in error.