Ancient pulse jets?

[Dave367]

Please forgive me, I am a complete noob here. I've read the FAQ, and spent half a dozen hours browsing the forii and referenced sites, so I probably have just enough information to be dangerous. ;-) I don't even honestly know whether this post belongs in the valved or valveless forum--or even in Off Topic. Anyhow, here's my quandry:

I'm doing a paper on ancient technology--that never was. The current question is: could ancient engineers have conceivably (not in fact, but just conceivably) invented pulsejets and used them for useful work? I must stress that I am NOT suggesting this was actually done, but only asking if it was technically feasible.

Applications might incluide Hero's c.1000BC invention of the steam turbine (and a number of other "modern" mechanisms), in which he theoretically could have substituted a pair of pusle jets for steam jets, used the whirling dervish to power a set of wheels, and invented the automobile 3000 years ago. Another might be Leonardo DaVinci's adding one or more pulse jets to the rim of his helicopter concept and invented heavier-than-air flight 400 years before the Wright brothers.

OK, OK, I know it's a waste of time, but it's intertesting to me, eh? A number of questions more or less immediately arise:

Could a pulse jet be built of copper, bronze, tin or perhaps zinc, as steel wasn't available? How about iron? Could it be built riveted together, without welding? Perhaps cast? (how much pressure is there in a pulse jet's combustion chamber?)

Could a valveless version possibly have been invented first, or could useful valves have beeen built conceived and built, without carbon steel?

Is it reasonable that a society which was familiar with the theory of resonance (church organs were well known in 500 BC +/-), wood gas, vegetable oil, (methanol?), but not with high temperature combustion, welding or high carbon steels have possibly stumbled across the concept (say via a Reynst pot??), then improved it to the point of both reliability and sufficient power to do useful work? (a tip-jet helicopter can fly with jets capable of as little as 5-10 lbs of thrust)

I am (perhaps naively) assuming such a jet could be started pyrotechnically, using either wood or biogas, or maybe methanol, then run on either vegetable oil (bio-diesel?) or animal fat via carburation rather than fuel injection, and might be useful for a few minutes' run during an important battle, or for short flights in heavier-than-air craft (history suggests, in addition to Da Vinci's helicopter, also his gliders, as well as man-carrying kites in ancient Japan. There's evidence these might have been capable of being "cut away" and flying as gliders for short distances.

I offer also the knowledge that Hero--and presumably some his collegues or students--knew enough about thermodynamics not only to build the steam turbine he's known for, but also many cylindered and valved devices, such as water pumps, air-powered toys, self-opening doors. He knew to build power transmissions, cog-controlled clockwork robots, etc.

My first--and recurring--thought is that this is all a pipe dream on my part, but I keep coming back to the just *possible* idea that this was a golden missed opportunity--and maybe one of a number of similar ones.

Or am I just nuts?

thanks!

Dave

[Anders Troberg]

Well, there has been some talk of ceramic Reynsts here, and I don't see any reason why that would not work.

Perhaps not for propulsion, but it would work for heating. Perhaps it would be a possible way to get higher temperatures than an ordinary furnace, which would make it possible to get higher quality steel much earlier in history (the problem for a long time was that insufficient heat meant uneven coal distribution and unpredictable properties).

Perhaps they could also be used as a sound device, for example fog horns or warning alarms.

Perhaps simple coconut Reynsts could be used as fireworks or ceremonial devices. Loud, flaming, spectacular, even if they'd probably only last seconds.

By injecting some kind of flammable fuel into the exhaust, they may be able to use them as simple flame throwers, but that would probably only be practical in naval warfare and at short distances where you certainly don't want a burning ship, even if it is an enemy vessel. They also had other alternatives for this which were more practical, so I doubt it would catch on.

I doubt other types of jets would be practical, as metal was too expensive and difficult to work for the short lifespan the metals known at the time would have. Ceramic pulsjets would be to heavy (or brittle if they were made light) to be practical for propulsion, so propulsion is probably not practical either.

It is possible that they would be able to build a putt-putt boat, but with effective sails and cheap labour for rowing, I doubt it would be practical.

[paul skinner]

I've often wondered this myself (ancient applications of modern technology). Personally, I can't see pj's being manufactured anytime before the early industrial age (17th-18th century). There just wasn't enough basic engineering, material science, fuel, or precision tools available to create a workable pulsejet.
Look how long it took to work out the basics of a practical chronometer.

[Eric]

I would have to disagree on that, but its all just speculation anyway so its not like it really matters. The romans definately had the finances and precise enough building to make a pulsejet. Hell if Mike E. can make an engine out of a crushed pipe the romans, egyptians, greeks and chinese definately could have.

Another thing is the wooden pulsejet. I have discovered a type of south american tree called the Fatwood tree. Its got so damn much pitch in it its like burning a sponge soaked in tar. Once you get it burning it vaporizes the pitch and creates a ton of flames.

If it werent for the dark ages we probably would be of colonizing other planets... :(

Eric

[Mark]

It would probably be easy enough to nail or screw some 2 X 4s together to fashion a rectangular duct of some sort, maybe choke down the "exhaust pipe" with some strips of plywood. Or even just use plywood for the whole enchilada.
A Logan side-ported pulsejet is an easy shape to get to rev up with a priming of methanol, just light the tail. I have found the Logan shape to be very forgiving in proportions. For a spark plug, you could just use a couple of nails hammered into the sides, wood acting as the insulator.
I was going to look for some small wooden tubing the other day but forgot about it.
Mark

[mk]

Quite interesting topic.
Reminds on the ancient Chinese or Japanese folks building kind of swords, which implied the usage of techniques that cannot be copied even inawadays with the equipment available. E.g. those masters knew when a klinge needed to be put out of the fire just by looking at it. Most impressive.

Back to the topic.

By some event of chance, it appears possible that pulsating combustion was known. And maybe used for heating or so, but for propulsion? I don't think so. The overal ducts would have been pretty havy and sufficient fuel delivery differing from evaporation appears almost impossible to my eyes.
However, rember those "Inca stoves", commonly sold as at least? Weith some friends we somehow got a nice pulsating combustion out of it. Any other burner featuring a combustion zone and some sort of a chimney caries the possibility of pulsating combustion with it.
Thus I may summarize:
Prinziple of pulsating combustion known: maybe.
Ancient pulsjets: most likely a no go.

But any prove or fact pointing me wrong would be appreciated.

[paul skinner]

I would have to disagree on that, but its all just speculation anyway so its not like it really matters. The romans definately had the finances and precise enough building to make a pulsejet. Hell if Mike E. can make an engine out of a crushed pipe the romans, egyptians, greeks and chinese definately could have.

Another thing is the wooden pulsejet. I have discovered a type of south american tree called the Fatwood tree. Its got so damn much pitch in it its like burning a sponge soaked in tar. Once you get it burning it vaporizes the pitch and creates a ton of flames.

If it werent for the dark ages we probably would be of colonizing other planets... :(

Eric

Interesting.

So how do you provide enough air to keep it running? How would you even supply enough compressed air to start it?

//asked without hostility, just pure curiousity. :)

[Mark]

I just read the Chinese had distilled liquors in the 7th century. As for lighting a pulsejet without compressed air, you can prime it and then light the tail. Logans are very good at this. And if only some fellow had taken notice when lighting a near empty bottle of spirits. Surely someone must have come close to the jam jar effect.
Heck a straight pipe that is primed and closed at one end will make an interesting sound if you light the open tail end. From that they could have picked up the trail with experimentation. Surely someone must have played cannon or potato gun with the effect. Other things might have occured in the process.
Mark

[Jim Berquist]

Why would they go that rought when they had the B.P.???

They as fare as I know they made the first rockets!

I seem to Think there alchemist was ahead of the game!

How they fell so fare behind I just can't fathem!!!

They may have set charges to pulse?? Less charge and more go!!

Your talking materials at hand and that was clay and bambo!

They had bronse and later mild Iron steel...


I'm just a thinking person!

Most likely wrong!!

[Mark]

I believe in pulsejet gods. There is no other explanation for all the suffering I have seen. And they don't have apples that imbue you with insight, which by the way don't really grow in certain climes and probably evolved in translation. Maybe it was a Granny Smith or Red Delicious, I can't quite figure out which would hold more information. ha
Mark
http://www.bestapples.com/varieties/

[Hank]

Hello- About the closest reference to a pulsed combustion duct I know of for certain, as used in the ancient world are two:
The Romans used massive ducting in conjunction with combustion for heating and cooling.
Mines were ventilated by pipes that were led into the mine, running back to a firebox at the enterance of the shaft. The air in the pipes was sucked into the firebox and created a low pressure condition in the shaft. This drew in fresh air.

[Jim Berquist]

Like Drafting in a fire place?

[Viv]

Well back on topic, its pretty certain they must have come across pulsating combustion at one time or another, I say this purely as its so unlikely not to have happened at one time or another given all the types of fires and chimneys they had in those times.

A typical roman hypo-cast (spelling) would have a chance of resonating given the right circumstances along with stoves and chimneys popular at the time

The problem is and exemplified by the chinese you need a certain amount of social complexity and a reasonable level of civilization to allow people time to ponder questions such as, hey that went bang I wonder why? let alone hey it went ba ba bang:-)

If food on the table (if you have one) is more important than the odd bang from the stove then the question goes to the bottom of the pile and does not get answered.

The romans would fit those conditions and have a reasonable life style and material wealth to accomplish any experiments needed, but as a slaver society would the guy at the top have gone near a stove or hypo-cast to wonder what all the noise was about?

You also have to consider that metal was expensive and to have it worked in to a tube was even more expensive, would they have played around in the fire with what to them had a high cost?

I also have to wonder from a cultural stand point weather a roman of sufficient wealth and social standing to achieve any type of rudimentary pulse jet would have gone any wear near the project in the first place, would roman society tolerate one of there own doing what amounted to the work of a slave?

Viv

[El-Kablooey]

I think I remember reading somewhere about a guy who threw some oily rags or something into his wood stove. His stove began buzzing really loud and the vent pipe was glowing red hot.

[Bruno Ogorelec]

I think we are all in agreement that the principle could have been discovered easily. The problem is in developing it for practical application. One has to ask, what possible application, followed by questions about the materials and the fuel.

What application? Space heating doesn't look likely. First, people in general just didn't do much space heating until the 20th century. They just dressed heavily. Besides, the advanced civilizations all sprung up in warm climates. (Which really does make you wonder about Canadians, doesn't it?)

A pulsejet burner for smithery is also unfeasible. The exhaust temperature is far too low because of the mixing with sucked-back air. A pulsejet blower is just not worth the trouble, compared to ordinary bellows.

That clearly leaves propulsion. On the ground, jet propulsion was certainly not something you'd consider without the great expanses of highways, supermarket parking lots and old airfields, so that one's out. For flying, you need a flying machine, and the ancients just didn't have one. So you have to postulate not just one wonderful invention but two.

It could have happened, mind you. They could easily have built hang gliders, the easiest flying machine of them all, but the idea obviously didn't occur to anyone. As for Leonardo’s helicopter, look at the drawings and you'll see that it would not really have worked, with jet power or without it. It would just have made a lot of wind.

But, it leaves us with the likeliest candidate – watercraft. Before the 18th century, shipbuilding was arguably the most advanced form of engineering. It was vital to normal life and prosperity for a number of ancient cultures. It united the best in the financing, engineering, logistical and other resources of the ancient nations. What better place for a technological leap?

Another factor making the whole thing more likely is the fact that the power-to weight ratio is the least important in ship propulsion. Wooden ships habitually carried tons and tons of rocks in their bilges to make them more stable in the seaway.

A pulsejet made of wrought iron or terracotta or whatever could have weighed a ton or two without affecting a ship adversely. A pulsejet with valves can be made to pump water, rather than air, so that the ancients could have had jet power to tide them over the windless periods and save them from the need to have two or three or four score rowers that had to be fed and tended to in other ways. Not to mention the psychological effect on the enemy of having a roaring warship hurtle towards him with nothing visible propelling it.

The biggest problem I can see (apart from the process of developing the thing) is fuel. What the hell could the ancients have used? We have to consider China, ancient Persia, and Rome for the likeliest candidates, I guess. There must have been some oil available on the surface in Mesopotamia, I guess, but I doubt the feasibility of using it as fuel for such purposes. It was a curiosity back then, rather than a resource for anything of major proportions.

Olive oil? Could the ancient Greeks have produced enough olive oil to power a dozen warships for, say, an hour a day? Sounds like an awful lot of olive oil to me.