Acoustic Length Starting Point on Curved Surfaces

[HPSCL]

When using a curved surface to mount your tailpipe and/or intake to, where is the starting point (of the length) of your component?
** Is it at the longest (top) or the shortest (bottom) of where the component enters into the combustion chamber?

Note: Please refer to attached drawing as a reference.

[Viv]

Hi HPSCL (what ever that is)

You can take the mean length of the tube as intersected by the curve of the combustion chamber in your example drawing, treat this as the center frequency of the tube for its acoustic resonance, a slight spread ether side of that gives you a broader bandwidth (or wider range of resonance) this is the same trick Gluhareff used for his fish tail cut in the exhaust pipe of the pressure jet to make them run over a wider range of operating conditions.

See Tip Jets for examples http://www.tipjet.com/ or http://www.tipjet.com/tech_data.htm

Viv

[HPSCL]

Thanks, for the reply, Viv!

To answer your question, "HPSCL" stands for Hydro-Pneumatic Supercharged Combustion Launcher"...
Many years ago, I designed the world's first "supercharged" PVC combustion launcher. They're more commonly referred to as "Hybrids", in the spudgunning community.

At the time, potato cannons had evolved from the hairspray-fueled "spray-and-pray",with BBQ ignitors, to advanced versions fueled by a metered amount of propane gas, which was ignited by modified versions of high-voltage stun guns. The benefits were a higher range of ignition consistency, along with increased power.

Propane has a LEL (Lower Explosive Limit) of approximately 2.1% and an UEL (Upper Explosive Limit) of approximately 9.5% - These combustion launchers are typically dialed in to run somewhere between 4-5% , which is the percentage of fuel (by volume) to the combustion chamber which it is injected into.

By sealing the combustion chamber with a burst-disc (Generally; By using a piece of PET plastic (cut from the side of a 2-Liter soda bottle) and then sandwiching it in between the halves of a PVC Union, the chamber can then have 2,3,4... (and so on) times as much fuel injected into it -- so long as you then inject a corresponding amount of compressed air.

For each 4-5% additional injection of propane, another "atmosphere" of air must then be injected into the chamber. As your mixes get higher, it becomes increasingly difficult to inject the precise amount of compressed air into the chamber. If you're off by a couple of pounds-per-square-inch either way, you're mixture will be too lean or too rich and (obviously) will not ignite.

With the HPSCL, I used water (which cannot be compressed) to act as a "piston" which would compress a single 4-5% injection of propane to whatever pressure you desire. Your only limits with this design, are portability and available pressure, from your buildings hose bib. (Typically up to 75 psi)

When an ideal amount of propane gas/air is ignited inside of an enclosed chamber, it creates a peak combustion pressure of 102psig. (Plus the approximately calculated 0.6psig for the initial injection of propane gas) For each subsequent injection of fuel/air, your peak combustion pressure is raised by the initial pre-ignition pressure plus another 102psig.

They were fun to play with, just as these pulse jets are now fun to play with. Sad though, as once I build something and get it running / take pictures / take videos / post pictures / post videos and everyone on the internet goes; "Oh... that's nice" *yawn* - The thrill is gone and I'm left searching for something new to challenge my limited intellect.

[Viv]

Hi

That's a very creative way of solving a problem, I like the use of a liquid piston as it figures in some of the Stirling engine designs I have been interested in for years, I understand the point of a challenging problem and what happens when you solve it, but there is always another one to take its place I find

A couple of points, keep in mind that you are always using the actual running temperatures to plug in to your acoustic lengths, also keep in mind they are different temperatures for different times during the cycle or part, tailpipes are a lot different to intakes

Viv