2.7 Liter Valveless Thermojet... w/video
Posted: Mon Mar 02, 2009 2:04 am
I posted this in another forum, at the site pulsejets.com, hoping that someone would help me with figuring out how to accurately calculate what size nozzle diameter to make for a given-sized chamber...
Oh well, as no one cared to offer any mouse-fart of a hint as where to look for information. - Everyone seems to be caught up in a recent post about this new "Thunderchine", which does, btw, look awesome!
I drifted out of building "spudguns", venturing into playing with blackpowder cannons. They were fun, but no rocket-science calculations to make one, so I quickly got bored with it.
This new-found hobby is my current obsession! I (as anticipated ) just HAD to build somethin' a little bigger, seeing as how I scored a FREE piece of 2-1/2 thinwalled chrome steel pipe (probably off of a Fast and the Furious wannabe's ricer) and also a scrap piece of 5" diameter mild steel exhaust tubing.
Here's the recent post:
Based on the dimensions of something that works (Eric Beck's 3 pound thrust Thermojet plans), I thought that I could combine my extensive knowledge of "potato cannon" design & fabrication with my extremely limited knowledge of pulse jet design.
Eric's "Combustion Chamber" volume of the 3 lb. Thermojet is estimated at 28.27 Cubic Inches. This, of course, is not to include the estimated 5.62 Cubic Inch volume of the truncated cone. - I decided this truncated cone volume was negligible, simply for ease of calculating the new design. The "Barrel" volume of the 3lb. Thermojet is estimated to be 17.79 Cubic Inches ... C:B (Chamber : Barrel) Ratio is: 1.58:1
The estimated volume of the FREE piece of 5" diameter x 8-7/8" Length Exhaust Tubing is 165.65 Cubic Inches. This volume is 5.859 times the volume of the Combustion Chamber on 3 lb. Thermojet. The Barrel volume is estimated at 117.80 Cubic Inches. This gives me a C:B (Chamber : Barrel) Ratio of 1:40:1 --- Smaller than the 3 lb.'s , but it would appear that C:B ratios are hardly a concern, because I've seen plans on the internet with C:B Ratios as little as 0.35:1 .
My #2 main concern, in "upscaling" Eric's design, was the combined volume of Intake Tube(s), which are : 1/2" I.D. x 3" Length (x2) and equates to : 1.17809625 Cubic Inches. So, seeing as how my new one was 5.859 times larger (volume-wise), I made sure that the intake tube length was upscaled as well, to match or slightly exceed this volume.
1.178 x 5.859 = 6.903 Cubic Inches
The estimated volume of the 1" Diameter conduit is 0.7853975 / Inch (length). Dividing the required 6.903 cubic inch volume of the intake tubes by 0.7853975, gave me a length of 8.789 Inches. Divided by 2, gave me a required length of 4.394", for each intake tube... Eh, I rounded it off to 5" each.
The 10" combined length, an "odd multiple" of the 24" length of the Exhaust (Tailpipe) seemed to be OK with what I learned by reading Bruno Ogorelec's Valveless Pulsejets 1.5 - Quoted from the section:
KADENACY OSCILLATION, THERMAL BREATHING AND ACOUSTIC RESONANCE / Elements of Resonance: "... So, the tailpipe length must be an odd multiple of intake pipe lengths for the engine to work properly".
My #1 concern in getting this thing to work, was the size of the injector orifice. As much research as I've done, I'll be damned if I can find even a hint towards how to accurately calculate the required nozzle opening! Although I wanted (so badly) to purchase Eric Beck's "4lb Thrust Thermojet Valveless", my wife (as a surprise) bought me a $120 Thermojet, off of ebay... It came with a lot of information (regardless of how vague, at some points), the biggest of which was the fact that the nozzle diameter was revealed in the included instructions... The diameter of the nozzles were a #71 drill size, which I found to be .025" - .026" in diameter. (Conflicting dimensions on different websites)
Well, the area of a .025" diameter hole is 0.0004908734375". Since my new thermojet's chamber volume is 5.859 times the volume of this little 3 lb.'er, I multiplied 0.0004908734375 by 5.859. - This gave me 0.0028760274703125" . (Mind you, I was doing all this math on my cell phone's calculator) Messin' around with different numbers, first .040, then .050, led me to find that a 0.060" hole is (well, I'll be damned!) ; 0.002827431"
Knowing that a 1/16" drill bit is .0625" , I made the injector(s) out of 3/16" Steel Brake Line, which I picked up at Checker Auto Parts. Cutting the flared tip off of one end, I used a tiny ball-peen hammer to shape the end of the brake line to a rounded point. This rounded point was tapped on end, until it completely closed the hole. Using a small automotive steel pick, I worked the pick until it poked a hole in the end of the line. The hole was worked until (by eyeball- Ha!) was slightly smaller than the 1/16" Drill Bit.
The chamber ignited on the very first try, idling at less than 5psig line pressure. As it warmed up over about a one-minute period, I slowly increased the line pressure to 20psig. - Any higher than that, it started to sputter slightly. Between 20-25psig, a short/slight blast of compressed air allows it to immediately run at a high oscillation. <-- Correct term?
2.7 Liter Valveless Thermojet Video
I absolutely love this new-found hobby! The recent posting of the "Thunderchine", pushed me slightly farther over the edge, to build something a little bigger than my spot-welded party-popper. I've been lucky thus far, after making an altered-version of Beck's 3lb. Thermojet, and another out of an oil filter casing, which I got from work.
Someone... please - Steer me in the right direction towards the proper way to calculate nozzle diameters? It would make this SO much easier.
... I just thought that you guys would get "just as much a kick" out of something that is so easy to build and so obnoxiously loud.
Oh well, as no one cared to offer any mouse-fart of a hint as where to look for information. - Everyone seems to be caught up in a recent post about this new "Thunderchine", which does, btw, look awesome!
I drifted out of building "spudguns", venturing into playing with blackpowder cannons. They were fun, but no rocket-science calculations to make one, so I quickly got bored with it.
This new-found hobby is my current obsession! I (as anticipated ) just HAD to build somethin' a little bigger, seeing as how I scored a FREE piece of 2-1/2 thinwalled chrome steel pipe (probably off of a Fast and the Furious wannabe's ricer) and also a scrap piece of 5" diameter mild steel exhaust tubing.
Here's the recent post:
Based on the dimensions of something that works (Eric Beck's 3 pound thrust Thermojet plans), I thought that I could combine my extensive knowledge of "potato cannon" design & fabrication with my extremely limited knowledge of pulse jet design.
Eric's "Combustion Chamber" volume of the 3 lb. Thermojet is estimated at 28.27 Cubic Inches. This, of course, is not to include the estimated 5.62 Cubic Inch volume of the truncated cone. - I decided this truncated cone volume was negligible, simply for ease of calculating the new design. The "Barrel" volume of the 3lb. Thermojet is estimated to be 17.79 Cubic Inches ... C:B (Chamber : Barrel) Ratio is: 1.58:1
The estimated volume of the FREE piece of 5" diameter x 8-7/8" Length Exhaust Tubing is 165.65 Cubic Inches. This volume is 5.859 times the volume of the Combustion Chamber on 3 lb. Thermojet. The Barrel volume is estimated at 117.80 Cubic Inches. This gives me a C:B (Chamber : Barrel) Ratio of 1:40:1 --- Smaller than the 3 lb.'s , but it would appear that C:B ratios are hardly a concern, because I've seen plans on the internet with C:B Ratios as little as 0.35:1 .
My #2 main concern, in "upscaling" Eric's design, was the combined volume of Intake Tube(s), which are : 1/2" I.D. x 3" Length (x2) and equates to : 1.17809625 Cubic Inches. So, seeing as how my new one was 5.859 times larger (volume-wise), I made sure that the intake tube length was upscaled as well, to match or slightly exceed this volume.
1.178 x 5.859 = 6.903 Cubic Inches
The estimated volume of the 1" Diameter conduit is 0.7853975 / Inch (length). Dividing the required 6.903 cubic inch volume of the intake tubes by 0.7853975, gave me a length of 8.789 Inches. Divided by 2, gave me a required length of 4.394", for each intake tube... Eh, I rounded it off to 5" each.
The 10" combined length, an "odd multiple" of the 24" length of the Exhaust (Tailpipe) seemed to be OK with what I learned by reading Bruno Ogorelec's Valveless Pulsejets 1.5 - Quoted from the section:
KADENACY OSCILLATION, THERMAL BREATHING AND ACOUSTIC RESONANCE / Elements of Resonance: "... So, the tailpipe length must be an odd multiple of intake pipe lengths for the engine to work properly".
My #1 concern in getting this thing to work, was the size of the injector orifice. As much research as I've done, I'll be damned if I can find even a hint towards how to accurately calculate the required nozzle opening! Although I wanted (so badly) to purchase Eric Beck's "4lb Thrust Thermojet Valveless", my wife (as a surprise) bought me a $120 Thermojet, off of ebay... It came with a lot of information (regardless of how vague, at some points), the biggest of which was the fact that the nozzle diameter was revealed in the included instructions... The diameter of the nozzles were a #71 drill size, which I found to be .025" - .026" in diameter. (Conflicting dimensions on different websites)
Well, the area of a .025" diameter hole is 0.0004908734375". Since my new thermojet's chamber volume is 5.859 times the volume of this little 3 lb.'er, I multiplied 0.0004908734375 by 5.859. - This gave me 0.0028760274703125" . (Mind you, I was doing all this math on my cell phone's calculator) Messin' around with different numbers, first .040, then .050, led me to find that a 0.060" hole is (well, I'll be damned!) ; 0.002827431"
Knowing that a 1/16" drill bit is .0625" , I made the injector(s) out of 3/16" Steel Brake Line, which I picked up at Checker Auto Parts. Cutting the flared tip off of one end, I used a tiny ball-peen hammer to shape the end of the brake line to a rounded point. This rounded point was tapped on end, until it completely closed the hole. Using a small automotive steel pick, I worked the pick until it poked a hole in the end of the line. The hole was worked until (by eyeball- Ha!) was slightly smaller than the 1/16" Drill Bit.
The chamber ignited on the very first try, idling at less than 5psig line pressure. As it warmed up over about a one-minute period, I slowly increased the line pressure to 20psig. - Any higher than that, it started to sputter slightly. Between 20-25psig, a short/slight blast of compressed air allows it to immediately run at a high oscillation. <-- Correct term?
2.7 Liter Valveless Thermojet Video
I absolutely love this new-found hobby! The recent posting of the "Thunderchine", pushed me slightly farther over the edge, to build something a little bigger than my spot-welded party-popper. I've been lucky thus far, after making an altered-version of Beck's 3lb. Thermojet, and another out of an oil filter casing, which I got from work.
Someone... please - Steer me in the right direction towards the proper way to calculate nozzle diameters? It would make this SO much easier.
... I just thought that you guys would get "just as much a kick" out of something that is so easy to build and so obnoxiously loud.