Odd Metal jars

[PyroJoe]

I found this coefficients table for orifices in a very old book. The topic of the section pertained to controlling the flow of water through a pipe or a dam. I think Cv is a coefficient for velocity? Cc maybe current?

I like the sharp edge illustration. The others akin to snorkels.
I apologize for the tilted effect.

Related:
http://en.wikipedia.org/wiki/Vena_contracta

http://en.wikipedia.org/wiki/Rocket_engine_nozzles

Stumbled across this Vena Contracta information. This is cool stuff.

[Al Belli]

Hi,

Cv is the flow coefficient used to calculate the pressure drop across the orifice.

see - http://www.jegasho.net/rotron%20pages/o ... lation.htm


Al Belli

[PyroJoe]

Thanks for the added information.

[Mike Everman]

Hi,

Cv is the flow coefficient used to calculate the pressure drop across the orifice.

Orifice Flow Calculation

To determine air flow through an orifice:

Where:
V = Velocity in feet per minute (fpm)
C = Orifice Coefficient
K = Constant = 14,786 when P is expressed in In. Hg
21,094 when P is expressed in PSIG
4,005 when P is expressed in In. of Water
(Above constants are based on an air density of 0.075 lbs/ft)
P = Pressure differential across the orifice
Q = Flow rate in cubic feet per minute (CFM)
A = Total orifice area expressed in square feet
VP = Velocity pressure (units are those of pressure)


Al Belli

Hi Al! Sounds good, are you going to post the equation that goes with this? ;-)

[Al Belli]

Hi Mike,

Here it is:

http://www.jegasho.net/rotron%20pages/o ... lation.htm

Al Belli

[PyroJoe]

#6 and #7 look typical for jars. Maybe #4 and #5 for snorkelers. #8 looks like trouble. #1 looks nice and slippery, this must be why it is so important to flare the intakes on VPJ.

[PyroJoe]

I found this post that describes what Eric calls "power extinction". It also describes the ability of his jet to throttle above thermal breathing and beyond and back down to very low thermal breathing. This is a very advanced design.

http://www.pulse-jets.com/phpbb2/viewto ... hlight=180

Look at the length of the CC and the length/angle of the neck. The way the intake joins to the chamber.

The CC and neck look a bit like Marks' heavy pipe jar. The one with the reducer on top.

It also echo's of Reynsts' Improved Pot.

Here is a hardy Jar built by Steve:

http://www.pulse-jets.com/phpbb2/viewto ... &start=180

[PyroJoe]

I attempted a intake pipe on several "L" engines using propane, for some reason I always end up with a flame cycling in the intake pipe. It doesn't "feel" like the flame wants to reside in the chamber with a intake pipe. I often will reduce the exhaust length to bring the flame into the chamber, but this has not worked in all the previous attempts.

It will just cycle up until flame out, right there in the intake. This has been a on going struggle.


In reviewing many designs, I decided to build an "L" engine CC with the same dimensions as my best metal jar.
Also in the design a "compression neck" was used. I approached this design as basically a jar with an exhaust attached. Fueling was with HEET methanol, bottom fed. I stepped drilled up to 1/2" which felt about right.

The new design gives a healthy shot gun blast at each fresh start. It then runs stronger than a jar of the same CC volume.

I welded a tab near the intake that can be used to fasten nozzles and such. There is one configuration I keep coming back to. For practical purposes, I call it a "separator". Basically it seperates the exhaust stream from the intake more than would be achieved by "open" breathing. I tested it with this engine and it really revs when I spray alcohol on the surface 1/2" away from the CC opening.

[GRIM]

Hey Joe you are not the only one , I too have spent hours trying to get this thing stable , the sparkplug has become essential, simply wont start with a lighter anymore ,

I have had it resonating for breif periods but it is just so temperamental,

I thought that i had cracked it, drilled a small hole in the side of the cc and poked the injector in there , definitely burns in the cc and not in the inlet tube and makes some amazing noises until it warms up , then quits alltogether ,

The next step is compressed air we shall see, all fun, but the truth is that this is rapidly turning into a mini 90 degree lockwood , (sparkplugs , fuel injectors in the cc, air start) a long way from the original concept

[PyroJoe]

"Hey Joe you are not the only one , I too have spent hours trying to get this thing stable , the sparkplug has become essential, simply wont start with a lighter anymore ,

I have had it resonating for breif periods but it is just so temperamental, "

--No worries, these little guys are trouble with propane. I was very happy to hear it revs on alcohol with the 5/16" opening. I think each fuel demand it's own adaptations.


"The next step is compressed air we shall see, all fun, but the truth is that this is rapidly turning into a mini 90 degree lockwood , (sparkplugs , fuel injectors in the cc, air start) a long way from the original concept"

--I think the more fussy the less fun. I enjoy engines that just need the fuel poured in and lit with a lighter. These little guys aren't worth much struggle, they just don't produce any appreciable thrust yet.

Looking at the heat pattern of the burned yellow paint, I think I may be able to go a little shorter with my CC.

[PyroJoe]

Here is something I sketched up. The Reynst pots are often said to be difficult to start. This may help warm the chamber using a draft pipe, after the chamber is warm and running well, the valve could be pulled shut.

I think a shorter CC could be used with this setup.
Any thoughts, suggestions?


I was working with the yellow draft engine last night using methanol as the fuel. I have become nervous at lighting it the first time, because the shotgun blast thing. I tested a new method of lighting. Just one small squirt of the fuel and bark the CC then two squirts and bark the CC. This pollutes the air stream with combustion products and prevents the BANG. Then I put in about 25 squirts. ha

At relighting a lazy flame was just setting there in the opening, Like a jar does sometimes.

A slight breath, and VROOOOOOOOOOOOOOOOOOOOOOOMMMMMMMMM. I was startled at the speed and initial noise. Zero to full tilt in less than a blink.

In working with propane I have become accustomed to ducking when I here the whoosh of propane ignite. I didn't realize it until I stayed with some family a few weeks ago. As luck would have it The bed I was in was very near the main central heat and air unit. Every time the heat unit would ignite I would here the whoosh in my sleep and automatically duck! This woke me up about 5 times that night. ha

[PyroJoe]

Here are some design tips to remind myself what to strive towards. These where taken partially from rocket type operation and observations of jars and draft engines:


Create & trap highest gas pressure then convert -> to kinetic gas movement efficiently.

Balance this with the speed at which I can clear exhaust from chamber and reload/compress with fresh charge and still create ignition. (freq.)
EDIT: it is good to think of this in terms of flow.

Compression is important, as it will determine the oxygen/fuel DENSITY used to drive the peak pressure.

[PyroJoe]

This one ran weakly. Will cut it apart and swap CC ends soon.

[GRIM]

Here is a still from a night time start up Whoosh! of one of my engines ,(just one frame) thats about 0.06 second, it wasnt there in the previous frame or the subsequent,

Now i understand why a smell of singed hair usually accompanies the lighting ceremony of the draft type engines using a bic lighter ,
Firstly in the day time you cant see it,
Secondly its so damn fast you probably cant feel it either, just the hot air passing by and maybe some of them microscopic metallic particles getting embedded into your forearm , No probs with the eyes because we allways wear safety glasses dont we

[PyroJoe]

I usually light from the bottom of the opening, and avoid crossing the path of the dragons breath.

The current project is a large beast, CC is about 10" diameter. With this one I light with a MAPP torch behind a smallish plywood shield. Also, keep a shovel handy to pat out the occasional fires in the yard, I say green Bermuda grass seems flammable at times.

Working outside, I can clearly see this one shoots 6 to 12" smoke rings from the draft pipe.

lil over 2" dia. draft pipe, approx. 10" dia. CC, 2" dia. opening 4" dia. seperator. (6' 2" Gringo) Runs on gas or propane and is a hungry thing. Not fussy on propane at all, a first for me.