Test Report 1, Feb 14, 99
Tri-Mode Launch System
Test Report
February 14, 1999
Summary
Today I tested the a combustion chamber I built with four
fuels and a gutter-type flame holder with one fuel.
Sustained combustion was achieved with each but with
differing strengths.
The testing was captured on 8 mm video tape with stills
shown below.
A decision was reached on a single fuel to pursue.
Construction


- This shows the can-type combustion chamber
used for the testing.
It is 2 inches in diameter (1 D) and 7 inches long,
made from a butane cylinder.
- Six cuts were made around the perimeter then
pried open in order to swirl the air.
These holes ran from 2 inches (1 D) to 2.5 inches.
Six 1/4 inch holes were drilled at 3.75 inches and
6 more at 4.4 inches.
Later, 6 more were added at 4.9 inches and 6 more
at 5.5 inches for a total of 24.
- Three spring tabs were welded to each end to
center the combustion chamber (CC) in the 3 inch
pipe being used for the wind tunnel.


- The wind was being supplied by direct connect
to a Ryobi 31cc leaf blower.
This blower advertises up to 150 mph and up to 340 cfm.

- The fuel was provided via small tubes.
The fuel manifold was a donut made from 1/4 in copper
tubing cut and shaped to fit just within the 2 in
diameter CC.
This was secured in place by three wires.
On the combustion side are six 1/32 brass tubes extending
to just short of the swirl cuts.
On the upwind side one 1/8 inch brass tube was connected
to provide for fuel input.
Can-Type CC


- Prior to testing, propane from a small cylinder
was ignited to provide a baseline and verify earlier testing.
Everything appeared to be functioning as expected.
With the leaf blower at idle a swirling yellow flame
could be seen.
At high speed the flame was mostly blue, had a strong
swirl, and stayed mostly above the swirl cuts.
- The first test fuel was 70% isopropyl alcohol.
This required some propane to get it started but it was
self sustaining afterward.
The flame was a very faint blue which was not detectable
in the video.
There was considerable excess liquid flow, some of which
was water.
While encouraging, this did not have the strong combustion
properties desired.


- The second test fuel was gasoline.
This was started with propane but ignited so easily a
simple spark would probably have sufficed.
The flame was strong and robust.
At low fuel flow the flame maintained well.
At high flow and moderate air flow some of the fuel was
exiting the CC and combusting in the air (first image).
This test was repeated after the additional holes
(totaling 24) were added.
These holes helped combust more of the fuel inside the
CC (second and third images).
Gasoline appears to be a very workable fuel.
- The third test fuel was a mixture containing 1/4
gasoline and 3/4 kerosene.
While ignition and sustained combustion were better than
kerosene they were slightly less than straight gasoline.
Some of the kerosene exited the CC as liquid drops leaving
a spray on the concrete.
A 50/50 mixture would probably be workable.


- The fourth fuel was propane from a large container.
This allowed a higher fuel flow than before.
This test was performed with the 24 holes only.
The flame was well contained (first image), especially
with the higher air flows.
The second image shows the bypass blocked off forcing all
of the leaf blower air through the CC.
Under these conditions the swirl was also highly visible
(second image).
Exhaust temperatures were measured at about 1,000 F a few
inches outside the CC in the center and about 600 F inside
the CC near the wall.
Gutter-Type Flame Holder


- This flame holder was made from the same sheet metal
as the 3 inch wind tunnel.
It was welded then brazed to fill in the holes burned by
the MIG welder.
It measured 3 inches across and 5/8 inch across each bar
(first image).
Only the high pressure propane was used.
- This flame holder was difficult to ignite at first.
The fuel hose was several inches upstream of the flame
holder and ignition would not occur.
The flame holder was moved upwind (closer to the fuel
hose) several times.
Ignition finally occurred when the fuel hose was even
with the downstream edge of the flame holder.
- Once a good placement was found the fuel ignited
easily and the flame held well (second image).
With the air flow on high the flame shrank to cover
only part of the flame holder (third image) but appeared
to combust all of the fuel
Additional Observations
- This design CC is quite workable.
- Simple materials, tools, and techniques will suffice.
- Propane appears to be the best fuel in this size class.
- Higher air flows cause the fuel to be combusted in a shorter distance.
- Higher air flows require higher fuel flows for ignition.
- Ignition and combustion tend to be robust even well off of stoichiometric, though some effort must be made to match the
fuel flow to the application.
Extrapolations
These extrapolations are nothing more than Wild-Assed
Guesses (WAGs).
The are offered only because, for the amateur community,
not better information exists.
Take these with a ton of salt (don't count on them).
Hopefully in the not too distant future better
information will be available to the amateur rocket community.
- For combustion chambers smaller than this the best
fuel may be either butane or propane.
- For this size combustion chamber propane is the
preferable fuel.
- For combustion chambers slightly larger than this
the best fuel may be gasoline or gasoline/kerosene.
- For combustion chambers much larger than this
kerosene will probably be the best fuel.
Future Tests
- This needs to be scaled up to high flow liquid propane
such that the majority of the exhaust gasses are at least
2,000 F in order to get good Isp and thrust.
Page First Created: Feb 14, 1999
Page Last Updated: Feb 14, 1999