Last post edited to remove raggy stuff. Apologies.
Towards a wood fueled pulsejet
Moderator: Mike Everman
Re: Towards a wood fueled pulsejet
heh, yeah well..
Last post edited to remove raggy stuff. Apologies.
Last post edited to remove raggy stuff. Apologies.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Towards a wood fueled pulsejet
Had the pulsejet ready to go and I started to pour down rain. It has rained every day here, it seems like for the last 2 months. I think we've had maybe 5 days of clear weather in all that time. It is a torrent right now.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Towards a wood fueled pulsejet
Ace, the problem with using the heat of the pulsejet to promote gassifying is that the time that the heat is needed is really before the pulsejet is started -- we need gas before running. Once gasification begins, it's an exothermic reaction, so we don't actually need heat from the pulsejet to do the conversion.
There is an interesting distinction to be made also between pyrolysis gas and the usual generator gas. Pyrolysis can occur in the absence of air -- in a retort. As a result, it doesn't have the nitrogen mixed in with it that generator gas does. However, when created in a retort, only a portion of the available carbon is converted to gas. A large portion of it is left behind as charcoal. In fact this is how charcoal is produced. Also, there isn't much hydrogen produced. In gas generator gas, the hydrogen production can be encouraged by the action of moisture on the incandescent charcoal -- also known as the water gas reaction.
Anyway, the basic problem with using "excess heat" from a pulsejet to convert wood to gas is that, well, we don't need it. In fact most gas generators use a cooling method to concentrate the gas. When I mentioned maybe using the pulsejet heat in that way, I was simply wrong. Not thinking.
EDIT:
Here are some things that would be useful, if the heat could drive it (and if we're being purists about it without bearings or valves): fresh air flow, amplification of the acoustics. Maybe even a reduction of thrust. Thrust isn't really going to help the alternator we want to drive. And the heat is very destructive. Yes the system uses heat to create and drive oscillation, but much of it goes into radiation from the CC and net thrust which in this application we aren't using.
If we stop being purists, there will be more and more logical reasons to either reinvent the IC piston engine, or the gas turbine,as we gradually attempt to harness the output and heat with mechanical complexity.
There is an interesting distinction to be made also between pyrolysis gas and the usual generator gas. Pyrolysis can occur in the absence of air -- in a retort. As a result, it doesn't have the nitrogen mixed in with it that generator gas does. However, when created in a retort, only a portion of the available carbon is converted to gas. A large portion of it is left behind as charcoal. In fact this is how charcoal is produced. Also, there isn't much hydrogen produced. In gas generator gas, the hydrogen production can be encouraged by the action of moisture on the incandescent charcoal -- also known as the water gas reaction.
Anyway, the basic problem with using "excess heat" from a pulsejet to convert wood to gas is that, well, we don't need it. In fact most gas generators use a cooling method to concentrate the gas. When I mentioned maybe using the pulsejet heat in that way, I was simply wrong. Not thinking.
EDIT:
Here are some things that would be useful, if the heat could drive it (and if we're being purists about it without bearings or valves): fresh air flow, amplification of the acoustics. Maybe even a reduction of thrust. Thrust isn't really going to help the alternator we want to drive. And the heat is very destructive. Yes the system uses heat to create and drive oscillation, but much of it goes into radiation from the CC and net thrust which in this application we aren't using.
If we stop being purists, there will be more and more logical reasons to either reinvent the IC piston engine, or the gas turbine,as we gradually attempt to harness the output and heat with mechanical complexity.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Towards a wood fueled pulsejet
still raining
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
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ace_fedde
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Re: Towards a wood fueled pulsejet
vturbine,
I learned something again. I knew that gassifying is an exothermal process but I didn't know that it is "so exothermal" that it is self sustaining. (This might sound strange to some people but not all exothermal processes can sustain solely at their own heat production, they need added heat to overcome heat losses)
Sidetrack: Would adding steam to an airless (wood fed) pyrolysis process reduce the carbon left overs? (with added heat of course)
Fedde
I learned something again. I knew that gassifying is an exothermal process but I didn't know that it is "so exothermal" that it is self sustaining. (This might sound strange to some people but not all exothermal processes can sustain solely at their own heat production, they need added heat to overcome heat losses)
Sidetrack: Would adding steam to an airless (wood fed) pyrolysis process reduce the carbon left overs? (with added heat of course)
That's my revengevturbine wrote:still raining
Fedde
Your scepticism is fuel for my brain.
Re: Towards a wood fueled pulsejet
I don't know ace. Seems to me the same effect could be had by using high moisture content wood. Generally people using retorts are trying to make charcoal, not gas, so they don't want to reduce their yield. As far as I know charcoal producers prefer dry wood -- possibly for that reason. Don't know.
One thing to keep in mind, once that reaction starts and sustains in a retort, it will go to completion. So you better have something to do with that gas if you turn off your pulsejet. Also throttling will mean that you must get rid of gas. Production in a sealed retort goes at its own rate, not the demand of an engine.
(If you can make rain Ace, there are some arid countries who would love to hear from you!)
And I'm sorry to say, or happy to say, or whatever, it stopped raining here, with the rivers at flood stage -- I can hear Broad Brook roaring outside my window now. And it turned into a clear day without a cloud.
Anyway, I ran down and propped up the new engine with a cage of firebrick, dumped a small amount of methanol in it and lit it off. It jam jarred quietly and slowly, almost imperceptibly until the meth was all gone.
Then I made a quick Rossco snip tip on the 1/4" copper propane line, and tried to start it by lighting the tip and putting it down the intake. That didn't work. Then I squeezed a triple way tip in a Jacobs chuck. I couldn't get the pins to stay in to get a set of orifices, so I tried it as is, filed back to a three-way slit. Got some interesting sounds, a little oscillation, but nothing like a pulsejet roar.
I should explain that my pulsejet isn't a good copy of Grim's design -- a few mistakes were made along the way, so all this is no reflection on that design. The biggest mistakes were, I thought my tube was 1-5/8" rather than 1-3/4" as called out in Grim's design. Unfortunately, my tube was really 1-3/4" OD -- as called for in the design -- my mistake was the classic OD-ID memory of plans vs actually checking plan.
Assuming that 1-5/8" tube would need a slightly narrower CC, I reduced the size of that a little in cross section. I left all lengths alone. CC depth and pipe lengths are as called out.
Maybe that would have worked if the tubes truly were 1-5/8" but since they were full size, all I effectively did was reduce the size of the CC without changing anything else.
Anyway to return to our story, realizing this was probably the cause of the problem in starting, I found some 1-1/2" tube and made inserts for the other tubes by cutting them off to the same length and flaring the ends. I slid them down into the other tubes and the flares held them in place.
I tried again, first with a Rossco snip tip, then with a pinched end and three 1mm holes drilled radially. This last combination of thinner pipe and 3 way tip did start some stronger oscillation. But as soon as it seemed like it would get going, as I turned up the propane the flame would go out. I tried lots of different tip locations from half way up the inlet tube to the bottom of the CC.
The strongest oscillation seemed to be about half way between the lower end of the inlet and the bottom of the CC. As I moved the flame down the oscillation would slow down. But as I increased the gas the rate of oscillation would increase. I would say that these sounded about jam jar speed. So each time I added gas, I'd lower the tip a little and the sound would get louder without slowing down and generally speeding up. It did seem to pulse a little with louder oscillations and an occasional little kick out the intlet. But usually I'd reach a point in throttling up when the flame would blow out.
I didn't use any compressed air. Just the flaming injector, as in the video of Grim's.
So, I don't know what to do from here. I don't know if I've basically ruined the design or whether this one could be made to run. Without the experience of starting these things, I don't know if this is typical of a new engine learning process, or whether this one will never run. I could, if need be, cut off the old pipes and weld in the 1-1/2" pipe permanently. And maybe the inlet length is too long for a slightly smaller version of this engine -- should it be shortened? I don't know.
One thing to keep in mind, once that reaction starts and sustains in a retort, it will go to completion. So you better have something to do with that gas if you turn off your pulsejet. Also throttling will mean that you must get rid of gas. Production in a sealed retort goes at its own rate, not the demand of an engine.
(If you can make rain Ace, there are some arid countries who would love to hear from you!)
And I'm sorry to say, or happy to say, or whatever, it stopped raining here, with the rivers at flood stage -- I can hear Broad Brook roaring outside my window now. And it turned into a clear day without a cloud.
Anyway, I ran down and propped up the new engine with a cage of firebrick, dumped a small amount of methanol in it and lit it off. It jam jarred quietly and slowly, almost imperceptibly until the meth was all gone.
Then I made a quick Rossco snip tip on the 1/4" copper propane line, and tried to start it by lighting the tip and putting it down the intake. That didn't work. Then I squeezed a triple way tip in a Jacobs chuck. I couldn't get the pins to stay in to get a set of orifices, so I tried it as is, filed back to a three-way slit. Got some interesting sounds, a little oscillation, but nothing like a pulsejet roar.
I should explain that my pulsejet isn't a good copy of Grim's design -- a few mistakes were made along the way, so all this is no reflection on that design. The biggest mistakes were, I thought my tube was 1-5/8" rather than 1-3/4" as called out in Grim's design. Unfortunately, my tube was really 1-3/4" OD -- as called for in the design -- my mistake was the classic OD-ID memory of plans vs actually checking plan.
Assuming that 1-5/8" tube would need a slightly narrower CC, I reduced the size of that a little in cross section. I left all lengths alone. CC depth and pipe lengths are as called out.
Maybe that would have worked if the tubes truly were 1-5/8" but since they were full size, all I effectively did was reduce the size of the CC without changing anything else.
Anyway to return to our story, realizing this was probably the cause of the problem in starting, I found some 1-1/2" tube and made inserts for the other tubes by cutting them off to the same length and flaring the ends. I slid them down into the other tubes and the flares held them in place.
I tried again, first with a Rossco snip tip, then with a pinched end and three 1mm holes drilled radially. This last combination of thinner pipe and 3 way tip did start some stronger oscillation. But as soon as it seemed like it would get going, as I turned up the propane the flame would go out. I tried lots of different tip locations from half way up the inlet tube to the bottom of the CC.
The strongest oscillation seemed to be about half way between the lower end of the inlet and the bottom of the CC. As I moved the flame down the oscillation would slow down. But as I increased the gas the rate of oscillation would increase. I would say that these sounded about jam jar speed. So each time I added gas, I'd lower the tip a little and the sound would get louder without slowing down and generally speeding up. It did seem to pulse a little with louder oscillations and an occasional little kick out the intlet. But usually I'd reach a point in throttling up when the flame would blow out.
I didn't use any compressed air. Just the flaming injector, as in the video of Grim's.
So, I don't know what to do from here. I don't know if I've basically ruined the design or whether this one could be made to run. Without the experience of starting these things, I don't know if this is typical of a new engine learning process, or whether this one will never run. I could, if need be, cut off the old pipes and weld in the 1-1/2" pipe permanently. And maybe the inlet length is too long for a slightly smaller version of this engine -- should it be shortened? I don't know.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
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GRIM
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Re: Towards a wood fueled pulsejet
Hi VR
I wouldnt worry about the slightly smaller cc , it should work just fine ,
I also wouldnt worry much about the inlet and exhaust lengths either , this sounds just like a fuel /injector problem ,
If you drill a 1/4" hole in the top corner of the cc and push your injector in there it will start easier , I found though that it was essential to light the injector outside the engine and with just a small flame push it in the hole , then throttle up ,
With the injector down the inlet it does tend to blow the flame out and will take a little experimenting to find the best position,
In either case it does take a little practice ,
One thing I remember whilst experimenting with these is to tack or clamp another 1meter or so of pipe to the exhaust , this seemed to make them "air out" easier and would allow very easy starts ,
Another thing I remember was that it is easier to start with the exhaust /cc cold , but this is subtle, and with a little practice you will get it to start hot or cold ,
One quick and dirty way is with a sparkler and a tiny amount of compressed air , but not everybody has them at hand(sparklers) another thing I have used is "wire wool" the stuff without soap , this burns for a a short while , but beware once it starts both will rocket out of the exhaust
I would say the best option is with the injector in the hole , or if you dont want to drill the hole , a tightly pinched rosscoe down the inlet , just keep tying IT WILL GO ,
I wouldnt worry about the slightly smaller cc , it should work just fine ,
I also wouldnt worry much about the inlet and exhaust lengths either , this sounds just like a fuel /injector problem ,
If you drill a 1/4" hole in the top corner of the cc and push your injector in there it will start easier , I found though that it was essential to light the injector outside the engine and with just a small flame push it in the hole , then throttle up ,
With the injector down the inlet it does tend to blow the flame out and will take a little experimenting to find the best position,
In either case it does take a little practice ,
One thing I remember whilst experimenting with these is to tack or clamp another 1meter or so of pipe to the exhaust , this seemed to make them "air out" easier and would allow very easy starts ,
Another thing I remember was that it is easier to start with the exhaust /cc cold , but this is subtle, and with a little practice you will get it to start hot or cold ,
One quick and dirty way is with a sparkler and a tiny amount of compressed air , but not everybody has them at hand(sparklers) another thing I have used is "wire wool" the stuff without soap , this burns for a a short while , but beware once it starts both will rocket out of the exhaust
I would say the best option is with the injector in the hole , or if you dont want to drill the hole , a tightly pinched rosscoe down the inlet , just keep tying IT WILL GO ,
Re: Towards a wood fueled pulsejet
Ah, Grim yes, I am happy for the encouragement, AND I just found your earlier postings in "Odd Metal Jam Jars" where you fully explain how to make the 3 point injector, and all the details and movies of the similar smaller draft engines. I had missed all that. I only started reading at the later plan stage. Now I know probably why it wouldn't easily start the way I was doing it.
I do have a feeling that besides the right injector in the right place, I may have to change out the pipes for a smaller diameter. That wouldn't be hard, I'd cut off the old ones leaving say a 4mm lip, then use that to weld to the 1-1/2" pipes. I could probably do it in 20 minutes. But I will try your injector, in the right place and at the right angle first.
I also just noticed that my inlet pipe is not centered in the radius of the big end of the oval. It is closer to the front edge -- away from the tailpipe. This gives less room for the injector. I think if I can't get it running as is, I should also move that pipe in to the center of the radius.
You've restored my confidence that it will work eventually, despite my uhhhh improvements! Thanks!
EDIT:
I calculated the difference in CC volume, and my CC is about 78% of the original volume.
A 1-1/2" pipe is about 73% of the volume of a 1-3/4" pipe.
Well, both these pipe sizes are OD not ID, but close enough. So if it doesn't work with the bigger pipe, it might be a better match with the smaller.
70% chance of rain tomorrow.
I do have a feeling that besides the right injector in the right place, I may have to change out the pipes for a smaller diameter. That wouldn't be hard, I'd cut off the old ones leaving say a 4mm lip, then use that to weld to the 1-1/2" pipes. I could probably do it in 20 minutes. But I will try your injector, in the right place and at the right angle first.
I also just noticed that my inlet pipe is not centered in the radius of the big end of the oval. It is closer to the front edge -- away from the tailpipe. This gives less room for the injector. I think if I can't get it running as is, I should also move that pipe in to the center of the radius.
You've restored my confidence that it will work eventually, despite my uhhhh improvements! Thanks!
EDIT:
I calculated the difference in CC volume, and my CC is about 78% of the original volume.
A 1-1/2" pipe is about 73% of the volume of a 1-3/4" pipe.
Well, both these pipe sizes are OD not ID, but close enough. So if it doesn't work with the bigger pipe, it might be a better match with the smaller.
70% chance of rain tomorrow.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
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GRIM
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Re: Towards a wood fueled pulsejet
I built a slightly smaller version , using 1 1/2" pipe , I havent calculated the volume but I would guess that it was about 75-80%
heres the link
viewtopic.php?f=3&t=5003&st=0&sk=t&sd=a&start=15#p59505
This was more difficult to start , required a sparkplug and compressed air in fact , but did run ,
I put the difficult starting down to the funny shape of the cc , but maybe the volume is an issue , just the same it did go , and the little ones ran dead easy , with all kinds of crazy combinations of inlets and exhausts ,
heres the link
viewtopic.php?f=3&t=5003&st=0&sk=t&sd=a&start=15#p59505
This was more difficult to start , required a sparkplug and compressed air in fact , but did run ,
I put the difficult starting down to the funny shape of the cc , but maybe the volume is an issue , just the same it did go , and the little ones ran dead easy , with all kinds of crazy combinations of inlets and exhausts ,
Re: Towards a wood fueled pulsejet
Did you try with only the 1-1/2" insert pipe in the intake, and the draft pipe at full 1-3/4"(without insert)?
That may make her go. It is good advise trying a cold start, but I have seen the two extremes, sometimes they like to start cold and sometimes they like to be nearly glowing when they start. Kind of a bi-polar thing.
With the 1-1/2" intake try the injector at the side of the intake nearest the draft pipe, inserted about 1/2" into the intake. begin with the injector about 1/4" off the sidewall of the intake, it takes some strength to keep it there as it is cycling, as she locks in she will often pull the injector to the side of the intake. If she is locked in and pulled to the side like that, just let her warm up some. After she is good and hot, then the throttle range can be tested, and also get a feel for injector position.
Only about 1 in 5 injectors will work reasonably well, there are several reasons. One thing to check is if the injector will make a nice fast flame outside of the engine. If it can't make a nice flame plume outside the engine, it will have a tough time within. Keep trying, adjusting the injectors, getting a feel for throttling up when the pulses get stronger. Propane is a challenge the first few times.
Joe
That may make her go. It is good advise trying a cold start, but I have seen the two extremes, sometimes they like to start cold and sometimes they like to be nearly glowing when they start. Kind of a bi-polar thing.
With the 1-1/2" intake try the injector at the side of the intake nearest the draft pipe, inserted about 1/2" into the intake. begin with the injector about 1/4" off the sidewall of the intake, it takes some strength to keep it there as it is cycling, as she locks in she will often pull the injector to the side of the intake. If she is locked in and pulled to the side like that, just let her warm up some. After she is good and hot, then the throttle range can be tested, and also get a feel for injector position.
Only about 1 in 5 injectors will work reasonably well, there are several reasons. One thing to check is if the injector will make a nice fast flame outside of the engine. If it can't make a nice flame plume outside the engine, it will have a tough time within. Keep trying, adjusting the injectors, getting a feel for throttling up when the pulses get stronger. Propane is a challenge the first few times.
Joe
Re: Towards a wood fueled pulsejet
Thanks Joes!
I'm psyched for tomorrow.
ace, man, hold off on that rain!
I'm psyched for tomorrow.
ace, man, hold off on that rain!
No problem is too small or trivial if we can really do something about it.
Richard Feynman
Richard Feynman
Re: Towards a wood fueled pulsejet
It's started raining at 10 AM, but before that I got to make up a new injector with three pin sized holes using the GRIM Jacobs chuck method.
I also drilled a 1/4" hole in the CC for the injector. I tried out the injector in air and it seemed to work okay. Three small equal flames, and there was a good range of throttle.
And I got in a few tests before the rain started:
With 1-1/2" pipe inserts in the intake, intake and exhaust, no real improvement, though the sound was different. Mostly a yellow flame in the cc. Had to keep the injector retracted pretty far. More throttle and deeper injector meant flame out.
Best action seemed to be with no inserts. I got a pretty good roaring burn with mostly blue flame with the injector almost completely out of the CC hole, and the injector nearly horizontal. But giving it too much throttle would flame out. It sounded almost like I was getting a little liquid at that level, injector had an uneven spitting sound.
Then a couple times I would light the injector in air and throttle to what would look good, and slowly insert it into the CC hole. As i got very near, the flame would go into the CC, and as I got even even closer all of a sudden I got the sound of a pulsejet. But it would blow the flame out after a brief burp. I don't know if that was acting like a lip feed, or just that the injector needs to be further from the inlet pipe than my altered CC allows.
If you look at the photo you can see that the inlet pipe is too close to the front edge of the CC. I'm wondering whether it should be moved toward the tailpipe. Look at the distance of the inlet edge from the front of the CC, then compare that with the distance between the inlet and the side of the CC. They should be the same if it was centered. On the drawing, the inlet is at the center of the radius of the outside of the CC. However, this CC is shorter than the designed one, so moving the inlet to the center might make it too close to the tailpipe -- if that distance is critical.
If I do move the inlet, any suggestions how close I go toward the exhaust?
I also drilled a 1/4" hole in the CC for the injector. I tried out the injector in air and it seemed to work okay. Three small equal flames, and there was a good range of throttle.
And I got in a few tests before the rain started:
With 1-1/2" pipe inserts in the intake, intake and exhaust, no real improvement, though the sound was different. Mostly a yellow flame in the cc. Had to keep the injector retracted pretty far. More throttle and deeper injector meant flame out.
Best action seemed to be with no inserts. I got a pretty good roaring burn with mostly blue flame with the injector almost completely out of the CC hole, and the injector nearly horizontal. But giving it too much throttle would flame out. It sounded almost like I was getting a little liquid at that level, injector had an uneven spitting sound.
Then a couple times I would light the injector in air and throttle to what would look good, and slowly insert it into the CC hole. As i got very near, the flame would go into the CC, and as I got even even closer all of a sudden I got the sound of a pulsejet. But it would blow the flame out after a brief burp. I don't know if that was acting like a lip feed, or just that the injector needs to be further from the inlet pipe than my altered CC allows.
If you look at the photo you can see that the inlet pipe is too close to the front edge of the CC. I'm wondering whether it should be moved toward the tailpipe. Look at the distance of the inlet edge from the front of the CC, then compare that with the distance between the inlet and the side of the CC. They should be the same if it was centered. On the drawing, the inlet is at the center of the radius of the outside of the CC. However, this CC is shorter than the designed one, so moving the inlet to the center might make it too close to the tailpipe -- if that distance is critical.
If I do move the inlet, any suggestions how close I go toward the exhaust?
- Attachments
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- Note the intake proximity to the injector hole and the distance from center of the CC radius.
No problem is too small or trivial if we can really do something about it.
Richard Feynman
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ace_fedde
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Re: Towards a wood fueled pulsejet
It's kind of out of my hands now. Once started it's hard to control...vturbine wrote:ace, man, hold off on that rain!
I gave it a try though. If it works it should stop raining after an hour or so.
Your scepticism is fuel for my brain.
Re: Towards a wood fueled pulsejet
"the flame would go into the CC, and as I got even even closer all of a sudden I got the sound of a pulsejet. But it would blow the flame out after a brief burp."
You almost got it. Even good engines will do the burp thing before lock in. Just repeat that same operation several times until the draft pipe length is sufficiently hot. It will stop burping and lock in.
Joe
You almost got it. Even good engines will do the burp thing before lock in. Just repeat that same operation several times until the draft pipe length is sufficiently hot. It will stop burping and lock in.
Joe
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GRIM
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Re: Towards a wood fueled pulsejet
Yes real close , try the injector at different angles , and depths , If it still wont go, lengthen the exhaust , some thin steel sheet and some hose clamps work , the joint doesnt have to be totally airtight ,