Elektra ITM Testing Log
by Larry Cottrill, Editor, jetZILLA Online Magazine
- All photos this page Copyright 2003 Larry Cottrill -
Table of Contents [Photo Diary: Sections I-V go back to Page 1]:
Table of Contents [Sections VI-VIII below]:
VI. Initial Test with Propane fuel [19 April 2004]
VII. Initial Test with MAPP gas fuel [22 April 2004]
VIII. Test with propane and auxiliary air [26 April 2004]
IX. Tests with propane / MAPP and intake turbulator [01 May 2004]
X. Tests with propane through high flow volume regulator [04 May 2004]
XI. Propane tests with modifications to intake geometry [10 May 2004]
XII. FIRST SELF-SUSTAINING RUN !!! [18 May 2004]
VI. Initial Test with Propane fuel [19 April 2004]:
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The Elektra I prototype engine set up for its first
test run, right after connecting up the fuel line.
Photo Copyright 2004 Larry Cottrill
Conditions:
Atmospheric: basically cool and dry, approx. 60 deg F
Lighting: dusk
Starting air: compressed air through PRV type regulator
[not used, initially]
Fuel: Propane [vapor only] through PRV type regulator
Spark: constant until continuous combustion achieved
Video: Not used
Test Session Plan:
Using propane vapor for fuel, try to find fuel-feed technique
that will produce continuous pulsing combustion, without the
use of starting air if possible. Observe fuel delivery system
in terms of operating characteristics, limitations, etc.
Summary of testing and observations:
Without starting air, all I got were variations on soft pops
[some of which showed flame out the intake] and the 'silent
blowtorch' effect. Pretty impressive visually, since it was
about dusk, but no discernible power except as heat and light.
Little heating of the chamber or tube.
I decided to try some air, by simply using the starting hose
designed for the Dynajet. By letting the gas flow constantly
and pushing the air closer and closer in toward the intake,
I was able to get very definite weak pulsing. Nothing like
strong explosions, however -- just a nice audible buzz that
sounded like the Dynajet running far, far away.
Nothing I did came close to making me want to put on the ear
muffs. When I was getting the pulsing, there was a little
straight blue flame observable, and the chamber and pipe
heated noticeably. There was absolutely no flame visible at
the intake, but of course, I was dumping air into it like
crazy to keep it going. At best, it was moderate sound volume,
something like a radio playing normally in a home setting.
At that point, the sound was good, though -- sharp and
definite, not at all dull or mushy sounding. It really sounded
like it could go, but as soon as the air was removed it died
into blowtorch mode, instantly.
I think this may be the most important observation: I do not
get more propane flow as I advance the regulator setting -- it
plateaus out at a low flow volume, no matter how much I turn
in the screw. That tells me that there is too much restriction
upstream from the reg, even though I drilled out the check
valve [this outfit was made from a torch head]. I thought that
this would be plenty of delivery, but obviously, I was wrong --
I need to go with a full-size cylinder with a large valve and
stem, for plenty of supply. The trickle of propane I'm getting
just isn't adequate, in my opinion.
I do also have a cylinder of MAPP gas with the same connection,
and I could try that before changing everything on the supply
end. MAPP gas is supposed to be much more powerful by volume --
it costs over three times as much as propane for the same
cylinder size. Most propane torch heads can't take it, although
there are some more expensive ones now that are designed for
both fuel types.
The original test setup for Elektra I, as configured for the test
session which follows. The yellow cylinder is MAPP gas, a much
more powerful fuel gas than propane, seen here surrounded by a
small fire extinguisher and some protective gear. The wooden frame
with large red cylinder is a starting rig built years ago for test
running a Dynajet engine. Its only function for these tests is to
supply the high voltage for spark ignition.
Photo Copyright 2004 Larry Cottrill
VII. Initial Test with MAPP gas fuel [22 April 2004]:
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Conditions:
Atmospheric: cool and dry, approx. 55 deg F
Lighting: dusk to dark
Starting air: not available
Fuel: MAPP gas through PRV type regulator
Spark: constant until continuous combustion achieved
Video: Whole engine seen from left rear quarter
Test Session Plan:
Using MAPP gas for fuel, try to find fuel-feed technique
that will produce continuous pulsing combustion, without the
use of starting air. Observe fuel delivery system in terms
of operating characteristics, limitations, etc.
Summary of testing and observations:
Ran a brief test session, starting very late in the day, using
MAPP gas for fuel. The difference in fuel energy between MAPP and
propane is easily observed. I got some really good bangs, along
with some ghostly howls. The odor is the natural smell of
acetylene, rather than the ethane odor of artificially odorized
propane.
The best explosions were when I 'bumped' the gas quickly on and
off again by quickly turning the regulator screw in and back out,
between once and twice per second. Attempts at steadily trickling
gas in always ended up in a weak, fully internalized howling mode
OR the 'giant blowtorch' mode with a huge flame billowing out the
back, i.e. no internal combustion at all.
The really silly thing was I hadn't prepared by charging up the
compressed air tank on my old Dynajet starter, so I had no air
supply to try driving it with - rats! When I happened upon
'howling' type operation, I think that would be a good time to
ease some air in. Because I wasn't ready for that, I didn't get
the good sounding buzzing operation that I had the other night
with propane. I think, realistically, we're probably going to
need air to start this engine, whether I like it or not. Someone
has said recently that relatively little air is needed [for small
engines], suggesting that even a hair drier would be usable, and
I might try that or have the shop vac handy. I'm sure that the
leaf blower would simply be overkill in this case.
I think another interesting time to start phasing air in would be
when you get the engine flooded with fuel gas [the giant blowtorch]
-- introducing mixing air at that point might have quite an impact
on what's happening. However, I think this would be a poor starting
method, though at the moment I wouldn't turn it down if I ended up
with a running engine!
I had to quit when the fuel cylinder was so iced up it didn't have
enough vapor pressure left to get through the regulator. It appears
that these small torch cylinders are completely inadequate for this
work! But, it's obviously worth trying again, with some air
available, while I still have some of both fuels left. It is also
entirely possible that I haven't given the propane a fair chance
yet, and that better technique in tweaking the gas on and off would
get better bangs than what I saw before.
Some of the bangs throw flame out the intake; some do not. My
preliminary observation is that rich, yellow bursts tend to
backfire through the intake, while good blue blasts seem to head
out the tailpipe more or less exclusively. It's hard to really
watch both places at once, though, so this observation may be
influenced a good deal by wishful thinking.
The small propane / MAPP valve and regulator setup, built from
a cookstove regulator and a propane torch valve head. Easy to
set up and inexpensive, it proved completely inadequate for the
fuel demands of this engine prototype.
Photo Copyright 2004 Larry Cottrill
VIII. Test with propane and auxiliary air [26 April 2004]:
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Conditions:
Atmospheric: cool, quite windy, approx. 55 deg F
Lighting: late afternoon daylight
Starting air: blow dryer, leaf blower
Fuel: Propane through PRV type regulator & needle valve
Spark: constant until continuous combustion achieved
Video: Whole engine seen from left rear quarter
Test Session Plan:
Using propane for fuel, try to find fuel-feed technique
that will produce continuous pulsing combustion, with the help
of starting air. Also tested an improved fuel control setup,
with needle valve for flow control.
Summary of testing and observations:
I tried the engine once again with propane, but this time WITH
boosted air. I started out with the blow dryer, which is pretty
feeble. However, it did create some good howls, which I thought
promising enough to warrant dragging out the new Black and
Decker Leaf Hog blower.
I also decided that I was having very poor control over the fuel
delivery by just trying to adjust the pressure regulator. So, I
quickly added a fair-sized brass body needle valve to the circuit.
This allows me to set a fixed pressure to the valve and then use
the valve for flow adjustment. This turned out to be a far better
scheme for accurate adjustment, and I wish I had done it much
sooner.
I set up the test with constant spark, 10 PSI at the needle valve,
my left hand on the valve and the leaf blower in my right hand.
This worked reasonably well, except that it's hard to maintain a
constant relationship between the leaf blower and the engine intake.
The tests pretty well convinced me that I can get all the air I
need! The action was best when I could get just the right trickle
of air from the edge of the blower nozzle into the intake. The
blower is very noisy, but to my astonishment, the sound muffs I was
using practically cancelled the high-pitched whine while letting
the bangs and hoots of the engine through plainly! The muffs are
definitely the way to go any time the blower is in use.
However, all I got was some impressive pulsejet-like growls when I
managed to get the air positioned just right -- not enough to get
anything up to red heat or burn off any galvanizing, but impressive
sounding, anyway. Obviously not strong enough yet to drive self-
sustaining operation. There were occasionally really good bangs,
when I'd let the blower drift around, or when I tried a kind of
sweeping motion of the air stream across the intake face. On some
bangs [very rich], there was visible flame ejected from the intake
stack, especially right after a quick passage of the blower stream.
Next time, I'll go back to using what remains of the MAPP gas and
try the same sort of technique. With plenty of air at my disposal,
I'm more sure than ever that the flow of fuel gas is too restricted
for propane to be delivered effectively. It should take a lot less
MAPP to get the same energy or higher.
There is also the distinct possibility that fuel/air mixing is not
adequate, due to the smoothness and relatively short path length of
this engine's intake path. I should try to experiment some with
turbulating structures in the intake tube and/or in the bottom of
the chamber where the mixture is diverted forward.
An experimental intake turbulator, used for the following tests
[disclosed on Kenneth Moller's Valveless Pulsejet Forum on
30 April 2004].
IX. Tests with propane / MAPP and intake turbulator
[01 May 2004]:
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Conditions:
Atmospheric: cool, slight breeze, approx. 60 deg F
Lighting: late afternoon daylight
Starting air: leaf blower, shop vacuum cleaner
Fuel: Propane and MAPP through PRV type regulator & needle valve
Spark: constant until continuous combustion achieved
Video: Whole engine seen from left rear quarter
Test Session Plan:
After installing the simple intake turbulator, try to find a
starting technique that will produce continuous pulsing
combustion, with the help of starting air, using both propane
and MAPP gas as fuels.
Summary of testing and observations:
Ran two test sessions until I once again iced up what's left of
the propane and MAPP cylinders. This time I inserted my 'hex
sleeve anchor' turbulator [as described on the Valveless Pulsejet
Forum] in the intake and managed to get some pretty good roars,
though still not nearly enough power to take off and sustain.
Here's what I think I learned this time:
For a given level of fuel input, getting the EXACT airflow needed
is quite critical. It is extremely easy to overblow this engine
with excessive starting air. Using the leaf blower proved very
difficult -- it turned out that the shop vac was much easier to
handle, due to much lower air velocity and volume, but even with
that it was difficult to angle the nozzle just right to get the
exact trickle of air needed. My earlier guesses on starting air
requirements were way too high, at least with the turbulator
positioned anywhere in the intake.
The location of the turbulator makes a significant difference in
the kind of combustion achieved. Basically, it seems to work better
the deeper into the intake you slide it. At first, with it high in
the stack [i.e. fairly near the inlet] it had a barely noticeable
effect; when run down in the middle of the path, its action seems
much better [that is actually about the relationship to the fuel
outlet I had shown in my original drawing in my forum thread].
Farther down might even be better, so that the fuel is introduced
in the laminar portion of air flow and then mixed later as it all
gets vortexed together behind the blades of the turbulator.
I found that it was possible to observe the combustion in the
chamber by looking right 'down the chute' through the intake stack
from a safe distance above and behind. In the common situation of
a too-rich mixture, the yellow flame can be seen firing right
beneath the fuel port, inside the stack! When starting air is
quickly removed and brought back into play, unburned fuel gas that
has accumulated for a split second generates a bang that comes out
both the exhaust and intake. This can be blue, or very rich and
bright yellow with a very loud report. The observed difference is
probably just a matter of the timing and flow of air.
In the odd moments when you happen to get it just right, you can
see the blue explosion flame racing past the angled cutoff face at
the bottom of the stack, just as intended! If you can hold this
orientation a little while, you start to get some heating of the
tailpipe; not enough to actually burn the galvanizing, but it
dulling it to the appearance of grey primer. At any rate, it was
fun to see good combustion moving right past that port, without
even a hint of flame diverted up the dark walls of the stack!
Exactly the 'Reynst breathing' condition desired.
Under such cool conditions, it's hard to keep the propane or MAPP
flowing very well for very long. I got lots of good bangs and roars,
even some higher pitched brief squeals at odd moments. I'm sure that
the regulator and tiny gas cylinders used cause serious fuel
restrictions before getting very far into the tests, since the first
moments always seem to be the only time for really good results.
I did finally obtain a 20 lb tank of propane, and I now have my old
Victor high flow volume regulator set up with the proper stem to
connect it, along with the large face gauge and needle valve needed.
Next time, I hope to be able to run a lot longer! I don't know if the
same left-hand threaded stem will work for the valve of a large MAPP
cylinder, however.
X. Tests with propane through high flow volume regulator
[04 May 2004]:
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Conditions:
Atmospheric: warm & dry, windy, approx. 70 deg F
Lighting: early afternoon daylight
Starting air: blow dryer, shop vacuum cleaner, leaf blower
Fuel: Propane through high-volume PRV type regulator & needle valve
Spark: constant until continuous combustion achieved
Video: Whole test area seen from right rear quarter of engine
Test Session Plan:
After changing to the high-volume regulator, try to find a
starting technique that will produce continuous pulsing
combustion, with the help of starting air, using propane as
fuel.
A much better propane regulator and valve setup, built from
a high volume air regulator and needle valve. This proved more
than ample for the fuel demands of the Elektra I prototype.
Photo Copyright 2004 Larry Cottrill
Summary of testing and observations:
This was the first test session using my 20lb propane tank and the
Victor high flow regulator. What a difference! I got lots of good
bangs and reasonably good roars, but still not self-sustaining
operation. The heat of the pipe after running a few minutes might
have been just barely red hot -- not enough to see in daylight,
and I couldn't re-run at dusk due to other commitments. The main
lessons learned this time seem to be:
The observation from my last test that only a trickle of air is
needed now seems erroneous. I believe that conclusion was the result
of self-limited fuel flow due to the restrictions in the regulator
and cooling of the fuel cylinder. In this latest test, I found it
was possible to provide so much fuel flow that the mixture would not
ignite, even with maximum air supplied from the leaf blower. On
several occasions, I actually had to back off the fuel flow in order
to re-establish ignition.
I get the best operation and best power from the highest air volume
I can supply -- the leaf blower at full force and zero spacing from
the intake face. [At this point, there is still no intake flare or
taper, just a slightly rounded edge on a straight pipe. When I get
the fuel set up right for the air volume delivered, I get a nice roar
of maybe a little under 200 hz. As the air supply is pulled back
slowly, this gets weaker and is soon drowned out by the blower noise,
then dies.
At this high air volume, my turbulator doesn't seem to help much,
though it seemed highly effective at low air flows. I think a good
explanation might be that the leaf blower with its short snout [i.e.
extension nozzle not used] contributes significant turbulence of its
own, which carries down through the stack some distance before the
flow smooths out. That might also explain the rapid 'tapering off' of
power as the blower is backed away from the port [of course, the air
velocity is dropping off also].
Something that might help a lot in the 'transition' from blown air to
self-breathing would be an intake flare. Everyone agrees that this
detail is critical to success with all or most valveless designs.
And, of course, Mike Everman's suggestion of tapering the intake
could still be tried [the idea being to raise the input impedance
significantly].
There are occasional VERY loud bangs [much louder than the best
cyclical roar, so far] that deliver enough force to shake the engine
on its mounts AND produce a pressure wave out through the intake. When
this happens, the impact is felt right up through the leaf blower,
like the recoil of a small pistol. The condition under which this
happens seems to be whenever the air stream is briefly interrupted and
then resumed -- apparently from the accumulation of rich mixture
[since fuel flow is constant] and the sudden reintroduction of excess
air.
With plenty of air and fuel, good roaring operation is definitely
achieved -- what I got in the earlier tests were mere howls by
comparison. It is also still true that, regardless of power level
achieved, I can still observe the desired passage of exhaust gas past
the bottom of the intake stack [except when the snout of the leaf
blower is in the way]. This will be the indication of true Reynst
pattern breathing, if the engine ever becomes self-sustaining.
With the new fuel setup, I'm pretty confident that I can deliver all
the fuel needed to make it run. I can get a little more velocity and
less turbulence out of the leaf blower by snapping on the long nozzle.
I could easily set up an intake flare [not necessarily permanent] and/or
the intake taper [permanent unless I want to cut and re-weld].
XI. Propane tests with modifications to intake geometry
[10 May 2004]:
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A temporary intake flare for the next test session was cut from
the neck of a polyethylene bottle identical to the one shown. It is
held tightly in place at the top of the intake tube with a hose
clamp. It is slitted and notched to fit around the fuel pipe.
Photo Copyright 2004 Larry Cottrill
Conditions:
Atmospheric: warm & humid, light breeze, approx. 75 deg F
Lighting: late afternoon overcast
Starting air: leaf blower
Fuel: Propane through high-volume PRV type regulator & needle valve
Spark: constant until continuous combustion achieved
Video: Whole test area seen from right rear quarter of engine
Test Session Plan:
Test the effects of using a flared intake; test using the intake
slightly flattened into a crude venturi, for higher impedence.
Secondarily, try to achieve better pulsating combustion, with the
help of starting air, using propane as fuel.
Summary of testing and observations:
For this session, I tried two basic changes: First, I used an 'intake
flare' which I cut from a funnel-shaped polyethylene bottle neck. This
is held in place snugly around the top of the intake tube with a hose
clamp. Next, I tried squeezing a long diffuser and venturi in the
protruding length of intake pipe. I used this with the flare still in
place. These changes were proposed by Mike Everman in a post on the
Valveless Pulsejet Forum, though I did not go as far with the venturi
as Mike had calculated -- it is just slightly elliptical at this point,
not really 'flattened' yet at the sides. Just enough for me to think
of it as a significant though small area reduction.
These were the best runs obtained so far, even though I still could
not coax the engine into self-sustaining operation. At best, I was able
to get a seemingly full-powered roar, similar to the Dynajet in both
character and loudness, at least as far as I could tell under hearing
protection. In the last run, I got red hot metal within less than a
minute after leaning out the mixture. The red hot zones were the flat
sides of the chamber, the first few inches of exhaust pipe and the very
bottom half inch or so of the intake tube [down inside the chamber
where the exhaust slips around it to get to the tailpipe]. Looking down
in there from a distance above and behind, it is something to see --
the red hot rim with blue fire streaming past the hole! Unfortunately,
I could still only get the best running power with the nozzle of the
blower right down on the intake.
So, I can get a horrendous roar that sounds just like the Dynajet, and
metal parts that start to glow. But try as I might, I cannot find a
fuel setting that will let it keep running when I pull the air away. If
I back the blower off slowly, it either quits [if set for rich running]
or slowly fades into weaker pulsing, rapidly devolving into dull howling,
and then 'blowtorch' mode operation [if set lean]. No matter what 'in
between' setting I try, it won't catch and go on its own.
It is vaguely possible that I just haven't perfected the technique of
properly wielding the blower. I don't feel that this is a likely cause
of the problem, though; I think I've tried about every distance and angle
I can think of, and lots of slow and fast variations of flow into the
pipe. Possibly, the intake still just isn't exactly right. What it
appears to boil down to, though is this: It simply does not seem to
develop a really good suction wave on its own. Or, the timing of the
wave is somehow skewed enough to not provide maximum suction at the
precise moment it's needed to re-charge the chamber with new air and
fuel vapor.
From these runs, it now seems to me that everything about this engine is
doing what it's supposed to as long as I'm forcing it to run. I think
the intake flow must be curling up from the bottom of the intake so the
explosion takes place right up front; the explosion is driving the blast
right past the pipe into the intake; and so on. And, I'm now convinced
that the explosions are finally solid enough that they should be able to
carry the cycle! I really think that the geometry is basically working.
The fatal flaw must be some defect in the wave timing, especially of the
low pressure wave traveling forward from the pressure node at the tail.
Hypothesis:
Perhaps the blast mass is getting completely past the intake way before
the pressure trough [suction wave] can get back under the end of the
pipe; so, when the intake is valved open, there's very little pressure
difference. Then, the air just slowly fills in the pressure drop as the
wave finally moves into the chamber. This could be too soft an action
to create the sharp, forward curling blast of air needed to feed the
intended combustion zone at the front wall.
This could be tested by significantly shortening the tailpipe, to allow
the reflected low-pressure wave to arrive at the chamber more quickly.
XII. FIRST SELF-SUSTAINING RUN !!! [18 May 2004]:
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Conditions:
Atmospheric: warm & dry, light breeze, approx. 75 deg F
Lighting: early afternoon full sunlight
Starting air: leaf blower
Fuel: Propane through high-volume PRV type regulator & needle valve
Spark: constant until continuous combustion achieved
Video: Whole test area seen from right rear quarter of engine
Test Session Plan:
Test different tailpipe lengths to find an engine length that
will carry full self-sustaining operation.
Summary of testing and observations:
With the tailpipe lengthened significantly, the engine started easily
with the leaf blower. It ran without spark or added air for something
less than two minutes. I think it died either due to heat deformation
of the temporary intake flare or my trying to lean out the fuel flow a
little too much.
However, operation was not quite as envisioned and showed that the
design obviously needs some corrective work.
BASIC FINDINGS -
I managed to get sustained operation using a not-quite snug fitting
sleeve set up for a tailpipe length of 35 inches, or a total engine
length of 38.5 inches from front wall to exhaust port. Starting was
very easy at this length, once the propane was set anywhere within a
reasonable range. This was set up without the intake turbulator, and
with an intake pinch of approximately 0.5 inch minor axis width, only
slightly flattened from a true elliptical section. The polyethylene
intake flare was in place, as before. Air supply was the leaf blower,
but it worked fine with its nozzle several inches away from the intake
flare, and it is easy to believe that a small stream of compressed air
would have worked just as well, but I didn't have time or air ready
to try it. Fuel feed is still just the simple 1/8-inch OD copper line
spilling propane at a point about halfway down the intake tube.
TEST METHOD -
I stopped at the nearest Menards store, looking to buy a short piece of
larger conduit to use as an extension sleeve, but this was too heavy and
expensive, and there were only ten foot lengths available. What I did
find, though, was a wonderful piece of material: 1.25-inch OD TV antenna
mast. This is painted mild steel tubing, perhaps 1/20 inch in thickness;
very easy to cut with a hacksaw. I cut two extension sleeves, one 15
inches long and the other 22 inches long [the original tailpipe length].
This slips over the 1-inch ID conduit tailpipe with just enough gap to
prevent binding up when things get hot. In my first tests, it kept
creeping longer as I tried to run the engine, but was easily tightened
by deforming it to a slight ellipse with ordinary pliers. That having
been done, I could position the sleeve with ease and get it to stay put.
Various lengths were tried with not much variation, at increments of a
couple of inches. When I finally got out to 28 inches, it became apparent
that good roaring could be obtained with the leaf blower a lot farther
back from the intake flare. Obviously, a good sign. By the time I got out
to 32 inches, I ran out of video tape, just as I thought things were
starting to get good. Also, I only had a few minutes left to keep trying it.
So, I decided to keep going for a couple more small increments before
folding for the day, even though I couldn't tape any more.
When I increased the tailpipe length to 34 inches, I knew it was going to
run, because suddenly, the exact aim of the leaf blower was no longer
critical! About anything you could do with it about 6 inches out from the
intake would get roaring operation, as long as enough propane was going in.
I increased it just one more inch and tried again, and knew for sure that
I had it -- I could just tell! Once the roar started, I just moved the blast
of air off of the intake and shut it off, and there it was, running on its
own! Next, I stopped the Model T coil that provides ignition voltage and
unhooked the spark plug leads. I was able to gradually lean the mixture out
little by little, getting smoother and quieter running until it finally
quit after a run of probably less than two minutes.
POSITIVES NOTED:
FUEL FEED - There turns out to be nothing obviously wrong with this crude
type of fuel delivery arrangement. Of course, more complex fuel arrangements
should be tested as well; it should be reiterated that the reason I use this
method is so that a standard regulator and needle valve can be used to finely
adjust and maintain the fuel flow.
INTAKE FLARE - Since the flare was distorted and actually ended up with a
hole melted in one side, I removed it for the final test. Now, though the
engine could be made to roar with boosted air, the aim of the blower was very
critical, and it was absolutely impossible to get sustaining operation back
again. Thanks to my friend Mike Everman, for emphasizing this to me on
Kenneth Moller's pulse-jets.com forum -- yes, that flare IS important for
good starting and running!
DEFICIENCIES NOTED:
TOO LONG - How can an engine with such relatively small explosion volume
need this kind of length? It's ridiculous -- there is just no way this
engine should have to be this long. Of course, there is some chance that a
solid tailpipe [vs a slightly leaky sleeve] would behave properly at a
significantly shorter length.
EJECTION FROM INTAKE - There is a LOT of ejection from the intake pipe. It
is not uncomfortably hot a few inches out, and was not hot enough to cause
even the slightest dulling of the plating that is still on the intake tube.
It did, however, start to melt the polyethylene 'flare kit', actually
melting a pea-size hole in one side of it. This does NOT look good in terms
of validating my design theory for the extended intake with carefully
angled cutoff in the chamber.
WEAK EJECTION FROM TAILPIPE - Although the noise from this engine is
unbelievably good [so much like the Dynajet I honestly can't hear the
difference] the output from the extended tailpipe is incredibly weak. When
I put my hand back there about a foot behind the extension, I was totally
disappointed. The leaf blower does better than this! Of course, again, this
may have something to do with the slight leakage of air around the extension
sleeve.
PROBABLE MODE OF OPERATION - I believe that the engine in this configuration
is operating as an abysmally tuned Lockwood; or perhaps, this is the normal
mode of operation of the "Chinese" design. NO WONDER they have that intake
pointing to the rear! At any rate, that seems to be the mode right now --
very energetic alternating exhaust gas and air through the intake pipe, with
the alternating blasts from the tailpipe running a poor second.
HEATING - During the self-sustaining run, absolutely no red hot zones were
observed. This was afternoon daylight, not dusk [as when the last photos were
taken], so maybe that just wasn't a long enough run for it to be visible. It
seems to me that as hard as this mill was running, there should have been some
observable heating, as in the Dynajet. Of course, the Djet is stainless and
the shell is probably one eighth as thick as the parts of Elektra I!
RUNNING SHORT FUTILE - As predicted by various forum participants, running with
a severely shortened tailpipe was futile. What I was able to get, interestingly
enough, was a kind of loud, low growl -- a sort of "sub-roar" that didn't come
close to being able to sustain. That was a tailpipe cut down to 15 inches, with
the total engine length equal to the full length of the Dynajet tailpipe
section. The sleeve used for all of the more successful tests was slipped onto
this very abbreviated tailpipe. I assume the basic problem here is that the hot
air mass in the pipe is now far too small to generate good suction behind it as
it moves out through the pipe.
ODD RESONANCE EFFECT: FREQUENCY NOT A FUNCTION OF ENGINE LENGTH!
The Elektra I engine, as presently configured, does NOT obtain its frequency
of operation in any way from the length of the tailpipe or from the overall
length of the engine! Now, of course, it does care about the length in terms of
how hard it will pulse, how much air you have to push in, and whether it will
self-sustain -- but it doesn't care about the length in terms of operating
frequency, once true pulse combustion is achieved. Though I have seen this
engine pulse only a few times, and only once self-sustaining, I have seen
strong pulsing operation throughout a wide range of engine lengths; easily
enough variation to cover more than half an octave of frequency variation --
but it doesn't happen. It also does not seem to increase in frequency as it
heats up [although this may be deceptive, since I'm used to hearing the
Dynajet, which changes temperature very quickly after startup].
I believe that this engine, as presently configured, is able to control the
frequency entirely from front-end resonance, and I am almost sure that the
basic controlling factor is the "cold air column" of the intake, which is
able to maintain a fairly stable temperature regardless of power being
developed. True, the engine is pumped by the tailpipe "piston mass", but it
is entirely controlled by the front end geometry and gas condition in that
column [I think ...]
Obviously, altering the engine enough to run as my theory predicts it should
might completely change this characteristic. I have no idea whether any builder
of a "Chinese" type engine might bear witness to anything like this from
similar experience.
Hypothesis:
I think that, right now, the acoustics of the chamber-tailpipe combination
don't matter in terms of frequency. The only functions of the tailpipe seem to
be to set up a workable mass to achieve proper compression to support the
cycle, and get it in the best resonance possible with the engine 'front end'!
I have never read of anyone coming to this conclusion concerning any other
pulsejet geometry. It makes me wonder if a VERY long tailpipe could even set
up a condition where the engine would self-start without forced air, say by
just starting the spark and goosing it with a rapid opening of the fuel valve.
Who knows?
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