Odds and ends

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Re: Odds and ends

Post by Mark » Sat Feb 03, 2018 3:10 pm

I see there are some funny new aluminum bottles out there.
http://420living.com/wp-content/uploads ... -cream.jpg
http://www.abcchapter.com/bottles/soda/ ... l%20v2.jpg

The forming process is reminiscent of clay in a hydraulic press.

Still fiddling with this beer bottle from time to time and trying some half-baked fueling method where it was hoped higher pressure fuel would travel to a lower pressure area. I can see the fuel gets pushed along when I go to light it angled at about 25 degrees tail up but it's either dampening feedback from too much fuel or it's sensing the aberrations made to it for some reason. The little 10-32 threaded fitting fits flush with the inside of the somewhat thick-walled snorkel tubing. The tubing of course is situated/held at the lowest point so that the puddle of fuel in the bottom of the bottle covers the press fit fuel line - just a hole that I forced the silicone tubing into near the bottom of the bottle.
Pulsating combustion can be very fragile or fussy as you may know. Even on a standard store-bought pulse jet it can take some effort to get it going if conditions aren't right. One time the tiniest tassel/wisp of Teflon tape was getting caught in the airflow of an exhaust on one design, which completely disrupted feedback.
Typically there's about 30 ml of fuel in the bottom of the bottle when starting these but for a 5 second burst to sustain probably/maybe just the fuel in a fuel line would be close to enough. Using the heat from the engine would be another way to pressurize the fuel flow or maybe get it to vaporize before being ingested or even butane - so many variables. I thought about putting the fitting a little bit lower down too in the neck region.

Long ago I used that method to fuel my Logan, fuel was pushed from the terminal end of the jet to the side port and on one design the fuel went in just where the side port exhaust threaded to the combustion chamber. It was later that I took to introducing fuel right where the side port meets the combustion chamber, a little hole drilled in the side port to accept the tiny copper fuel line. In this photo it's running full grease and lasted about 10-15 seconds if I recall.
Just a rev/review to sense how the primitive/non-idealized Logan sounded.
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Re: Odds and ends

Post by Mark » Sun Feb 04, 2018 12:33 am

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Re: Odds and ends

Post by Mark » Wed Feb 07, 2018 2:59 pm

Out of curiosity, these hollow brass candle holders that were going to be throw out were spritzed with methanol and lit at the narrow end via a threaded hole that held the "wax catcher" cup part on. The threaded hole accepted or matched well enough a typical spark plug thread and aside from that the candle holder also unscrews about midway as seen in the photo.
So the notable thing is that if you prime or swirl some methanol in the candle holder to coat the inside and light the small open end with a lighter, a terrific gunshot is heard - the propagation of the flame front quite brisk. It sort of strikes you as odd with such a large opening for the hot gases to escape or seemingly little confinement for the meager volume. It might be fun to try some long gradual cone shapes open at both ends as well like some of those vortex cannon shapes.
While the report of the candlestick holder is very sharp, it's also remarkably base. I was startled by the force of the sound, lighting it sideways and for the first time. Another thing is you'd be hard-pressed to hold it down on some flat surface and lighting from the hole in the top after spritzing it with methanol. It's got quite a kick in that mode.
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Re: Odds and ends

Post by Mark » Fri Feb 09, 2018 12:14 am

So just a quick demonstration of the genie in a brass bottle effect or the sudden propagation of a flame front ...
Candlestick Holder with Methanol
DSC_0001 (1).JPG
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Re: Odds and ends

Post by tufty » Mon Feb 12, 2018 3:47 pm

You might find this interesting, perhaps even related...

http://bora.uib.no/bitstream/handle/195 ... sAllowed=y

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Re: Odds and ends

Post by Mark » Tue Feb 13, 2018 3:54 pm

That Norwegian thesis had some fun facts to ponder over. Funny that substituting one relatively inert gas for the other can make such a difference as when they switched the nitrogen to helium for example and that hydrogen doesn't produce as much pressure piling as a slower fuel.

I noticed on this can and bottle toy if the length of clear plastic tubing connected to the aluminum beer bottle was longer than what was used in this video, the little can that was sleeved in the bottle deformed severely, the concave bottom of the can was completely bent out to a convex shape and the end of the aluminum bottle where the can shot out of was torn and frayed like a rifle fired with an obstruction in the barrel, along with a deafening report. If you use too short piece of "lead up" tubing to the bottle chamber the bang is greatly reduce.

It comes to mind the platinum catalyst powder I sprinkled into a glass gallon jug one day, the specks of powder started to glow spontaneously like fireflies as they slowly floated down into the methanol vapor contained in the jug and then there was a deafening bang. While probably the interior point of ignition created the bang instead of the typical whoosh bottle effect, it seems by having multiple points of ignitions an explosion could be greatly increased akin to pressure piling by injecting a jet of hot gases and free radicals swirled and intimately mixed and shot into a secondary chamber.

Some tidbits from the article ...

In these situations peak pressure and rate of pressure rise can be several factors higher than in
comparable single vessel explosions. The term pressure piling or pre-compression is used to
describes explosions that show such characteristics pressure development

The computed values of the turbulence intensity in both chambers demonstrated that turbulence induced in the secondary vessel is a major factor
affecting explosion violence.

The turbulent burning velocity S has been shown to be a phenomenological meaningful
quantity as various experimental investigations indicate ...

4.7 Sources of error
Resonance effects
In general the fast burning mixtures showed considerable local variation often of periodic
character. Such effects could have been caused by resonance effect in the geometry ...

Condensed water
After a few tests water will typically condense on the inside of the vessel walls and may
represents a significant source of error. Water may evaporate from the warm vessel walls during
gas filling and the subsequent period of turbulence settling, altering the gas composition. Water
in the gas mixture may affect reaction mechanisms and heat capacity, whereas a small portion
of the water at the vessel walls may evaporate during the explosion. It is generally assumed that
the explosions will be to rapid for significant amounts of water to evaporate.

Orifice diameter below 5.6mm gave no ignition in secondary chamber.

Since the laminar burning velocity of hydrogen is
roughly 6 times that of methane, the time needed for the flame to arrive at the orifice is much
shorter. In the current geometry, the short distance, and thereby the small time span between
primary and secondary ignition did not allow for a significant amount of gas to flow into the
secondary chamber. Consequently the level of pressure piling was severely reduced.

The explanation for the strong dependency of volume ratio is twofold: First the larger scale of
the primary chamber result in a longer time gap between primary and secondary ignition, and
during this time gap more chemically bound energy will be transferred to the secondary
chamber. Secondly the higher volume ratio will in it self result in higher compression of the gas
in the secondary chamber

In experiments, radiation
will be much larger for rich mixtures due to the formation of soot, which have high emissivity.

In nearly all conducted experiments, methane gave higher peak pressure in secondary
chamber than hydrogen. The main reason for this is that methane has a slow laminar
burning velocity that causes late ignition in the secondary chamber and high peak
pressure. Due to of hydrogen’s high (laminar) burning velocity, less time is available
for pre compression of the secondary chamber and consequently peak pressures are
lower for this gas. This trend is expected to be valid for all geometries resembling the
ones used in the experiment, but might not be invalid for large-scale situations

Some important geometrical factors are:
• Volume ratio between vessels
• Cross-sectional area of connection
• Scale
• Shape of vessel
• Point of ignition

The presence of “inert species” for example nitrogen or solid surfaces pose further
complications. They are generally not recognized to participate in the reaction, but may have a
catalyzing role in some reactions and may affect the process as heat sinks or alter diffusivity.
The replacement of nitrogen with helium in a methane-air mixture will for instance triples the
burning velocity (Glassman 1987).
http://bora.uib.no/bitstream/handle/195 ... sAllowed=y
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