Well that's interesting, watching methanol running, it looks nearly twice as fast burning the length of a CC compared to propane. That stuff is quick!
Definitely try the premixing approach, propane has a thick feel to it anyhow, tough to describe. Tested many different nozzles at that time, but no premixing.
Did you notice the flame speed of butane?
Also Methanol will usually cool the air creating a higher oxygen density. If there was anything that could increase flame speed, increased oxygen would do it. Maybe that is why it appears faster, propane displaces oxygen and methanol concentrates it.
Simple Conduit Engine
Moderator: Mike Everman
Re: Simple Conduit Engine
Sorry I couldn't find it in the original source I looked at:PyroJoe wrote: Did you notice the flame speed of butane?
http://www.faqs.org/faqs/autos/gasoline ... amble.html
I did find it here (attached), but it is an old study and the figures are different in value than the source quoted above. As far as I could tell it looks like propane and butane are similar, though there are not figures for methanol. I'm not sure how the cooling effect of methanol evaporation might work in an enclosed space during combustion -- would it increase the charge's air density in a (possibly) fixed volume? And doesn't the expansion of propane in a nozzle/injector also decrease the temperature?
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Simple Conduit Engine
My vote in what you observed would be for better mixing and or better mixture ratio with the methanol trial than with the propane trial. This would certainly affect flame speed.
I'm certain they couldn't have been mixed using the same injection means, since they have such different physical properties. So it would be hard to compare the two on an equal basis in a casual test.
All of this theorizing is guesswork without careful measurement of exhaust gas products, and input fuel and air metering. As well as burning a stabilized mixture, rather than something undergoing mixture motion and compressions in a pulsejet. Exhaust product testing would show if the propane burned completely in a small engine -- also methanol in a similar size. That would tell us a lot about mixing effectiveness and ratios.
From a practical (not theoretical) standpoint, I do believe you that it's hard or impossible, so far, to make propane work in as small a CC as methanol. I probably should have started with a bigger CC.
I'm certain they couldn't have been mixed using the same injection means, since they have such different physical properties. So it would be hard to compare the two on an equal basis in a casual test.
All of this theorizing is guesswork without careful measurement of exhaust gas products, and input fuel and air metering. As well as burning a stabilized mixture, rather than something undergoing mixture motion and compressions in a pulsejet. Exhaust product testing would show if the propane burned completely in a small engine -- also methanol in a similar size. That would tell us a lot about mixing effectiveness and ratios.
From a practical (not theoretical) standpoint, I do believe you that it's hard or impossible, so far, to make propane work in as small a CC as methanol. I probably should have started with a bigger CC.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Simple Conduit Engine
It would be good to see some smaller engines run via the small camp stove propane cylinders(with brass torch head). This would put the fueling system for beginners in the $20 USD range.
Many builder often want to start out with small engines, maybe for safety reasons or by the old adage "to start small and work your way up". Many struggle with the small creations. If a beginner would start with something in the 3" CC range things would be much easier.
This is by no means directed toward you but just seems to be a typical approach.
Not sure what the smallest CC that has run on propane. Anyone know?
When I warned of smallish engines, it is basically a heads up, road may be bumpy ahead. Some folks run tall knobby tires and have few problems with the rough patches.
Many builder often want to start out with small engines, maybe for safety reasons or by the old adage "to start small and work your way up". Many struggle with the small creations. If a beginner would start with something in the 3" CC range things would be much easier.
This is by no means directed toward you but just seems to be a typical approach.
Not sure what the smallest CC that has run on propane. Anyone know?
When I warned of smallish engines, it is basically a heads up, road may be bumpy ahead. Some folks run tall knobby tires and have few problems with the rough patches.
Re: Simple Conduit Engine
Well, for sure 1.93" diameter has been successfully fueled with propane. Mike's pocky locky maybe might even be considered borderline less because the 1.93" dia section was very short and the cone (representing probably a lot of the combustion chamber space) was long. This one was propane fueled with an annular collar, by the way.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Simple Conduit Engine
I also think that there would be nothing wrong with a liquid fueled version, rather than propane, since you mentioned methanol, as long as it was a feed instead of just a batch pool system. In fact I think a lot of people would prefer that to a small propane bottle, me included. As a matter of fact, I wanted to try this on a small scale if I had got the original conduit engine working.
I often wonder about the objections to pressurized liquid if it was done well. Coleman lanterns and stoves have used air pressurized fuel systems for decades. Primus boat stoves as well. So have alcohol boat stoves, and kerosene blowtorches (paraffin blowlamps).
I had a free hour today so I cut out new pieces for the second version of the conduit engine. I also got a small spark plug and fitting half nut yesterday at the hardware store.
I often wonder about the objections to pressurized liquid if it was done well. Coleman lanterns and stoves have used air pressurized fuel systems for decades. Primus boat stoves as well. So have alcohol boat stoves, and kerosene blowtorches (paraffin blowlamps).
I had a free hour today so I cut out new pieces for the second version of the conduit engine. I also got a small spark plug and fitting half nut yesterday at the hardware store.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Simple Conduit Engine
I think with the right configuration, a valveless may be able to use a similar fueling system as a valved version. Using the venturi effect to pull its own liquid without a pressurized fuel system. Even maybe make some thrust, wouldn't that be a trick.
One reason I use 88% intake dia. is the ease of starting. Also if I remember correctly, several valved engines are running around 70% or less.
If a smaller intake is used, shouldn't this increase the intake flow velocity and increase the intake time? I would think this would help the venturi action. The air flowing faster for a longer time span.
Have a modified fueling system derived from the Atom Jet sketched for a future trial. It has been slightly tweaked to apply to a valveless. Strange how a 31 degree angle matches the Atom Jets intake angle reasonably well. Not sure when will have the time to machine it up.
GRIM has a good fueling design he used on his valved engine, its an olive on the end of a tube. Keeping things simple, it would be good to have a design that could be fabricated from a few basic tools or techniques.
Mike also tested a nice setup on his pocket jet.
Would dislike seeing a pressurized system design in the wrong hands, if things go bad, they often go very bad.
One reason I use 88% intake dia. is the ease of starting. Also if I remember correctly, several valved engines are running around 70% or less.
If a smaller intake is used, shouldn't this increase the intake flow velocity and increase the intake time? I would think this would help the venturi action. The air flowing faster for a longer time span.
Have a modified fueling system derived from the Atom Jet sketched for a future trial. It has been slightly tweaked to apply to a valveless. Strange how a 31 degree angle matches the Atom Jets intake angle reasonably well. Not sure when will have the time to machine it up.
GRIM has a good fueling design he used on his valved engine, its an olive on the end of a tube. Keeping things simple, it would be good to have a design that could be fabricated from a few basic tools or techniques.
Mike also tested a nice setup on his pocket jet.
Would dislike seeing a pressurized system design in the wrong hands, if things go bad, they often go very bad.
- Attachments
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- Atom1.JPG (9.75 KiB) Viewed 9701 times
Re: Simple Conduit Engine
I've got no objection to a non-pressurized system if it can be made to work valveless.
And with regard to pressurizarion, I did emphasize if it were done right.
I can't think of an occasion where I've ever read or heard of a typical small commercial pressurized system like a Coleman stove or lantern blowing up. Incidentally, many two cycle outboard gasoline tanks were also squeeze pump pressurized.
I do know of many situations where non-pressurized fuel spills have ignited or exploded, however. I personally knew a boat engine mechanic who died from burns after servicing an engine. We worked restoring the same boat. And most boat explosions occur in the bilge of a very big open uncapped unpressurized container -- the boat.
The fuel to air ratio in a capped fuel tank is usually considered too rich to ignite. Gas tank caps and proper expansion venting are mandatory Coast Guard construction requirements. I really don't understand the Youtube videos I've seen of people operating valveless pulsejets with open mouth containers of fuel nearby siphoning through a handheld small rubber hose. How this can be considered safer than a closed container with an outlet pipe, a shutoff valve, and a pinhole cap vent, I'm not sure. All small gasoline engines cap their fuel tanks.
Don't get me wrong, I'm really not a fan of pressurization if siphoning or gravity feed (light pressurization, actually) will work. I never favor complexity over simplicity or natural process. But I also think that some of the theories I've read about the safety of pressurization are not supported by the relative frequency of actual fueling accidents. Basically you can't eliminate air from any tank, unless it's a bladder, and to me, leaving a tank wide open near a source of extreme heat is not "safer" just because it isn't pressurized or fully contained.
With regard to a poorly constructed pressurized system, no argument there. Bad idea. Also important to avoid siphoning gasoline into a 2000 degree glowing object 2 feet away from an open container while using thumb and forefinger as a shutoff clamp on the dripping hose.
And with regard to pressurizarion, I did emphasize if it were done right.
I can't think of an occasion where I've ever read or heard of a typical small commercial pressurized system like a Coleman stove or lantern blowing up. Incidentally, many two cycle outboard gasoline tanks were also squeeze pump pressurized.
I do know of many situations where non-pressurized fuel spills have ignited or exploded, however. I personally knew a boat engine mechanic who died from burns after servicing an engine. We worked restoring the same boat. And most boat explosions occur in the bilge of a very big open uncapped unpressurized container -- the boat.
The fuel to air ratio in a capped fuel tank is usually considered too rich to ignite. Gas tank caps and proper expansion venting are mandatory Coast Guard construction requirements. I really don't understand the Youtube videos I've seen of people operating valveless pulsejets with open mouth containers of fuel nearby siphoning through a handheld small rubber hose. How this can be considered safer than a closed container with an outlet pipe, a shutoff valve, and a pinhole cap vent, I'm not sure. All small gasoline engines cap their fuel tanks.
Don't get me wrong, I'm really not a fan of pressurization if siphoning or gravity feed (light pressurization, actually) will work. I never favor complexity over simplicity or natural process. But I also think that some of the theories I've read about the safety of pressurization are not supported by the relative frequency of actual fueling accidents. Basically you can't eliminate air from any tank, unless it's a bladder, and to me, leaving a tank wide open near a source of extreme heat is not "safer" just because it isn't pressurized or fully contained.
With regard to a poorly constructed pressurized system, no argument there. Bad idea. Also important to avoid siphoning gasoline into a 2000 degree glowing object 2 feet away from an open container while using thumb and forefinger as a shutoff clamp on the dripping hose.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Simple Conduit Engine
I think it has been done, but not in linear styles:
viewtopic.php?f=3&t=1980
The 88% intake dim. was taken from the dimensions of a chinese design posted in the forum. I found most engines would start easier with a smaller intake diameter, just didn't know how small to go, finally stumbled across those dimensions and adopted it. Maybe a better dimensions could be found, but this one has been working well so far.
Milking the highest thrust from a engine probably does require a 100% intake to tailpipe dia. dimension as seen in many performance engines.
I like the idea of a small marine tank for the biggish engine, have two behind the shop waiting for enlistment. A small lawn mower tank may make a good smaller tank. Both, correctly vented.
viewtopic.php?f=3&t=1980
The 88% intake dim. was taken from the dimensions of a chinese design posted in the forum. I found most engines would start easier with a smaller intake diameter, just didn't know how small to go, finally stumbled across those dimensions and adopted it. Maybe a better dimensions could be found, but this one has been working well so far.
Milking the highest thrust from a engine probably does require a 100% intake to tailpipe dia. dimension as seen in many performance engines.
I like the idea of a small marine tank for the biggish engine, have two behind the shop waiting for enlistment. A small lawn mower tank may make a good smaller tank. Both, correctly vented.
Re: Simple Conduit Engine
Joe, I'd watch out for today's plastic outboard fuel tanks with a big pulsejet engine. They aren't designed to be used near heat. An outboard motor cover is at air temp,and the tank usually remote from it. Sorry I just remember your comment about the big draft engine being too hot to stand near, and I worry about today's plastic tanks and lines with their 140-180 degree F melting point.
To me even a lawnmower tank seems big for a pulsejet that generally runs only a few minutes. But I don't know how big an engine is being contemplated, and how long the run time.
I was thinking recently about all the small metal fuel tanks that used to be available when I was a kid for model airplanes -- all vented -- and the larger ones with suitable outlet tubing IDs for a small engine. I do remember when "clank tanks" came in for R/C -- a weighted swiveling intake line, soon to be replaced by "clunk tanks" which were the polypropylene bottle versions for these. Cheaper to manufacture, and promoted for fuel level visibility, they unfortunately took over. It would be nice to use a real metal model fuel tank for a small pulsejet, if these were still available and reasonable in price.
Of course, back then, in the magazines, there were sometimes plans and instructions for making your own metal fuel tanks -- usually of soldered brass. For a fixed test installation, I might try to make a (non-pressure) fuel tank myself out of a cleaned out pipe cement can. These have a convenient sized cap. I'd need to replace the cap liner with proper fuel proof gasket material, and add a pinhole to the cap for expansion, as is done in a lawnmower tank, a soldered tube outlet with inline valve, etc. I prefer silver solder, even though soft solder's melting point is probably above fuel ignition temperature, and certainly more than the melting point of today's plethora of polypropylene fuel tanks on practically every piece of power equipment.
By the way, though I mentioned Coleman stoves above, I was personally imagining pressurization in a pulsejet for a less volatile fuel like kerosene. And the tank would have to be specially fabricated and pressure tested when filled with water to at least double the designed max operational pressure. This is really not something I'm planning to do any time soon. Just something I was thinking about.
To me even a lawnmower tank seems big for a pulsejet that generally runs only a few minutes. But I don't know how big an engine is being contemplated, and how long the run time.
I was thinking recently about all the small metal fuel tanks that used to be available when I was a kid for model airplanes -- all vented -- and the larger ones with suitable outlet tubing IDs for a small engine. I do remember when "clank tanks" came in for R/C -- a weighted swiveling intake line, soon to be replaced by "clunk tanks" which were the polypropylene bottle versions for these. Cheaper to manufacture, and promoted for fuel level visibility, they unfortunately took over. It would be nice to use a real metal model fuel tank for a small pulsejet, if these were still available and reasonable in price.
Of course, back then, in the magazines, there were sometimes plans and instructions for making your own metal fuel tanks -- usually of soldered brass. For a fixed test installation, I might try to make a (non-pressure) fuel tank myself out of a cleaned out pipe cement can. These have a convenient sized cap. I'd need to replace the cap liner with proper fuel proof gasket material, and add a pinhole to the cap for expansion, as is done in a lawnmower tank, a soldered tube outlet with inline valve, etc. I prefer silver solder, even though soft solder's melting point is probably above fuel ignition temperature, and certainly more than the melting point of today's plethora of polypropylene fuel tanks on practically every piece of power equipment.
By the way, though I mentioned Coleman stoves above, I was personally imagining pressurization in a pulsejet for a less volatile fuel like kerosene. And the tank would have to be specially fabricated and pressure tested when filled with water to at least double the designed max operational pressure. This is really not something I'm planning to do any time soon. Just something I was thinking about.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Simple Conduit Engine
To return to the conduit engine, I had another hour today to weld the pieces together. I gave the dimensions before, but I'll repeat them here with some of the other calculated proportions:
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Simple Conduit Engine
I should have posted that not a significant amount of linears had been liquid fueled. Instead of none. I think there have been a few mentioned in the past. many apologies for the mistake.
Re: Simple Conduit Engine
I had a chance to try to start the two engines today. Both showed a lot of different modes and resonant points for the injector -- a Rossco type made of 3/32" copper tube. I didn't use compressed air or spark, but just lit the injector and inserted it into the intakes. Both engines were clamped to vertical.
I tried a lot of different injector "squeezes" and orientations. It was fairly easy to get both engines to "motorboat" through a throttle range, though it really depended on the injector opening. At one point I seemed to have the "perfect" squeeze on the injector. What looked like a tiny teardrop shape. This would immediately start resonating in strong motorboat mode if the injector tip was about 3/4" down from the CC opening. I was also able to increase throttle up on the version 2 engine to transition to a high pitched run and roar -- I think it was truly running as a pulsejet -- though not a lot of strength out of the exhaust and I didn't need ear protection. Also no combustion chamber glow.
I could also get a MUCH louder run with the injector 1/2" inside the mouth of the inlet -- but it was really rough and filled with backfires. Usually it blew out the injector if I tried to advance throttle too far -- It sounded like a Harley rough idling. It also gradually increased in intensity until it blew out the injector. Much more pressure was coming out of the exhaust .... and the inlet than the other mode.
Unfortunately, I thought I could maybe do better with the injector, and gave it another squeeze. Naturally this didn't work, and I could never re-open it or re-squeeze it to get the engines running as well and surely after that. I tried re-cutting the end as well, but no go.
Anyway, I'm not sure if I achieved stable running in the version 2 engine -- maybe........ not sure. Or that could have been some odd resonant mode, not true running.
I would say from what I tried today it's my belief that BOTH of these engines would run, if injection could be sorted out. Fuel induction in a small engine, using large engine methods, like a pinched injector is very crude, compared to the requirements.
But I don't think it is the size of the CC that is the problem, rather it is injection. Too bad we don't have flame-holders in pulsejets. Flame extinguishing was one of the main problems of starting it this way. Likewise, the speed of the injector stream, volume, and orientation are all very hard to control in this small size pinched injector -- the pinch has to be just right for the throttle volume, and pressure to create just the right length flame. I think larger pulsejets must actually be very tolerant since we can run them with the usual injection methods. We're just put more on our toes with a smaller CC.
I do like the airless sparkless method for allowing me to hear what is going on. It may well be that these engines would start easier with air and spark, but I'd have a lot harder time finding the right squeeze and orientation. With a lit injector, the sound of what is happening is a constant feedback.
I tried a lot of different injector "squeezes" and orientations. It was fairly easy to get both engines to "motorboat" through a throttle range, though it really depended on the injector opening. At one point I seemed to have the "perfect" squeeze on the injector. What looked like a tiny teardrop shape. This would immediately start resonating in strong motorboat mode if the injector tip was about 3/4" down from the CC opening. I was also able to increase throttle up on the version 2 engine to transition to a high pitched run and roar -- I think it was truly running as a pulsejet -- though not a lot of strength out of the exhaust and I didn't need ear protection. Also no combustion chamber glow.
I could also get a MUCH louder run with the injector 1/2" inside the mouth of the inlet -- but it was really rough and filled with backfires. Usually it blew out the injector if I tried to advance throttle too far -- It sounded like a Harley rough idling. It also gradually increased in intensity until it blew out the injector. Much more pressure was coming out of the exhaust .... and the inlet than the other mode.
Unfortunately, I thought I could maybe do better with the injector, and gave it another squeeze. Naturally this didn't work, and I could never re-open it or re-squeeze it to get the engines running as well and surely after that. I tried re-cutting the end as well, but no go.
Anyway, I'm not sure if I achieved stable running in the version 2 engine -- maybe........ not sure. Or that could have been some odd resonant mode, not true running.
I would say from what I tried today it's my belief that BOTH of these engines would run, if injection could be sorted out. Fuel induction in a small engine, using large engine methods, like a pinched injector is very crude, compared to the requirements.
But I don't think it is the size of the CC that is the problem, rather it is injection. Too bad we don't have flame-holders in pulsejets. Flame extinguishing was one of the main problems of starting it this way. Likewise, the speed of the injector stream, volume, and orientation are all very hard to control in this small size pinched injector -- the pinch has to be just right for the throttle volume, and pressure to create just the right length flame. I think larger pulsejets must actually be very tolerant since we can run them with the usual injection methods. We're just put more on our toes with a smaller CC.
I do like the airless sparkless method for allowing me to hear what is going on. It may well be that these engines would start easier with air and spark, but I'd have a lot harder time finding the right squeeze and orientation. With a lit injector, the sound of what is happening is a constant feedback.
- First and second versions, and the injector
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Simple Conduit Engine
I've been playing with these when I get the spare time. I've got the knack now of turning up the gas and lighting the tailpipe end, then throttling down and dropping the flame down the tube to the injector.
I'd like to get some video, since the variety of sounds and modes is interesting and thought you might like to hear/see it. At one point I drilled the lower corner of the CC rim w/a 7/64" drill and tried radial injecting there on the Version 2 jet. It didn't help much. So i tried fueling again from the intake. I found a very high pitched mode fairly far up the the intake. I think that one is from the hole left in the CC. It's made me wonder about secondary air injection.
I'd like to get some video, since the variety of sounds and modes is interesting and thought you might like to hear/see it. At one point I drilled the lower corner of the CC rim w/a 7/64" drill and tried radial injecting there on the Version 2 jet. It didn't help much. So i tried fueling again from the intake. I found a very high pitched mode fairly far up the the intake. I think that one is from the hole left in the CC. It's made me wonder about secondary air injection.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Simple Conduit Engine
I'm wondering about scaling pulsejets again. The method outlined in the Ugly Stick thread (toward the end) was used to create a slightly smaller version of the pipe jet. (Important to note also that no cones were used to replace the pipe reducers of the original, so this may be an important factor in the sustaining difficulties so far).
But I found another thread which described a "Russian" scaling method, where all axial (linear) dimensions are preserved (of a good running engine) while the cross sectional areas are increased or decreased to suit the scaling needs. It was suggested that this was good for scale factors of .7 to 2.0.
That feels like it might work, can't say why... perhaps just that maybe the resonant frequencies would stay similar, while the volumes would increase in the engine sections proportionately.
At first I simplistically translated this in my mind to a scaled increase across the board of section diameters. But of course, areas increase as the square of the diameters, so that's wrong. The scale factor, I believe the Russian translation is saying, applies consistently to the areas, so is more complex to calculate. It's hard to tell since this is translation, and maybe the word "area" isn't meant strictly.
Anyway, I'm curious to calculate out the proportions, reduced to a 1.6" CC ID, of yet another version of this Ugly Stick based conduit jet, using this scaling method.
But I found another thread which described a "Russian" scaling method, where all axial (linear) dimensions are preserved (of a good running engine) while the cross sectional areas are increased or decreased to suit the scaling needs. It was suggested that this was good for scale factors of .7 to 2.0.
That feels like it might work, can't say why... perhaps just that maybe the resonant frequencies would stay similar, while the volumes would increase in the engine sections proportionately.
At first I simplistically translated this in my mind to a scaled increase across the board of section diameters. But of course, areas increase as the square of the diameters, so that's wrong. The scale factor, I believe the Russian translation is saying, applies consistently to the areas, so is more complex to calculate. It's hard to tell since this is translation, and maybe the word "area" isn't meant strictly.
Anyway, I'm curious to calculate out the proportions, reduced to a 1.6" CC ID, of yet another version of this Ugly Stick based conduit jet, using this scaling method.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman