www.pulse-jets.com

So....
Has this been done in the past?

I'm wondering if someone made a really long turbine and inside instead of a flameholder they had 5 pj's or ramjets.....must draw a pic to get my thought out I guess.


Imagine 5 chinese valveless's spaced around a shaft, with a compressor infront of them and a turbine behind. Yes it wud be exceedingly long, but the possibility to run a turbine cooler and cleaner should have a positive outcome. Hell spray some water on the comrpessor to help cool the pj's and make some STEAM POWER


Btw I'm back in the shop and really bored

Zippiot wrote: I'm wondering if someone made a really long turbine and inside instead of a flameholder they had 5 pj's or ramjets.....must draw a pic to get my thought out I guess.

The reality of your concept is, there are severe limits to the possible length of the shaft. Specific data is available to us at the amateur level, courtesy of the famous book by Thos. Kamps.

My initial look at the limits shows there may NOT be any potential "middle ground" where your concept might work. To make things even worse, the potential resonance issues created by a PJ combustor would enhance the problem.

What about ramjets, or is that just a less effective version of what a turbine already uses...

Zippiot wrote:So....
Has this been done in the past?

I'm wondering if someone made a really long turbine and inside instead of a flameholder they had 5 pj's or ramjets.....must draw a pic to get my thought out I guess.


Imagine 5 chinese valveless's spaced around a shaft, with a compressor infront of them and a turbine behind. Yes it wud be exceedingly long, but the possibility to run a turbine cooler and cleaner should have a positive outcome. Hell spray some water on the comrpessor to help cool the pj's and make some STEAM POWER


Btw I'm back in the shop and really bored

Hi Zippiot,

Here is something to answer your above question, which was taken out of our current patent application.

I tried a '' 1 '' engine setup once and got scared like hell when I did that trial for I was using an home made compressor and turbine before and after our engine, linked by a shaft and of coarse, everything unbalanced. The vibration was so horrible that the setup almost came off the stand by it self .

I then tried a '' 2 '' engines setup later on using the same shaft, turbine and compressor setup and still unbalanced (Did'nt learned from the first trial obviously), just to see more vibration and get more scared sooner

Overall and as bottom line, these tests were certainly and mostly revealing for we did get good rotation and nice flow from the compressor (If I may call what I had ... ''A compressor'') .

Hope this image answers your question,

Regards,

Its not only possible but it has been done in the past, the big engine companies have more or less given up with pulsejets and are moving towards pulse detonation combustors for turbine engines.

Hmm

This looks to be interesting. Luc how deathly scary was it

I'll see if I can dig up some more pics and info

True, a limiter to RPM is "shaft whip", which is essentially requiring you stay under the natural frequency of the unsupported shaft length, which is a simple calculation. This concept would need bearings all along the length of the shaft to keep that unsupported shaft length low and hence it's natural frequency higher than RPM/60. Spinning faster will fail the bearings or the shaft itself in short order.

Would a giant hydraulic bearing work? One that runs the whole shaft length.

Yes, but then viscous drag (proportional to speed) will eat up your power. Air bearing might be better, but at these speeds it would still be significant drag. Regularly spaced radial ball bearings would be the best bet.

A thought, Setup some piping so that the pj doesnt make the jet unnecessarily long, excuse the terrible picture



Could keep shaft length really short if the pipes didnt screwup the pj too bad, if it would I have another idea let me draw it out.

Slightly better pic to get my idea accross

To help alieviate the pulse "problem" and issues with resonance, set the PJ by itself in the airflow of the jet. You can keep the shaft very short and still use the wind produced from the PJ as useable power. My pic needs some major work I know, just gettin my idea out.

Zippiot wrote:Luc how deathly scary was it

Very very scary ...

The setup consisted of 4 inches long sliding tubes used as mounting provisions and of coarse, I did'nt think bolting this together was required ... BIG mistake ...

The intire compressor, shaft and turbine setup almost got off the stand while spinning ...

Very Very Scary ...

Regards,

Why not, instead of placing several engines around the shaft, compressor and turbine, simply run the shaft through the middle of the engine? I was under the impression that current turbojets did just this and used an almost toroidal combustion chamber open at both ends built around the central shaft connecting the turbine to the compressor. I was also under the impression that the compressor consisted of several sets of rotors and stators that drew in and compressed air by cramming it into a progressively smaller space as it is moved toward the combustion chamber. Perhaps this was a contributing reason to Luc's troubles?

I was also under the impression that the pulsation from a pulsejet could damage a turbine's rotors, is this correct? Would a possible solution be to add an afterburning ramjet to even the flow before the turbine stage of the engine? Perhaps a low-bypass single- or multi-staged fan could be attached to the front of the compressor to feed extra air into the ramjet. I'm curious as to just how much of the pressure gain provided by a pulsejet running on a compressor would be lost in a setup resembling the one I have attempted to describe here and how much extra thrust would a second-stage combustion chamber being fed exhaust and extra fresh air would provide. I'd be very interested to see any historical accounts of similar engines and their performance.

Hi 44,

Here are my comments or answers ...

Why not, instead of placing several engines around the shaft, compressor and turbine, simply run the shaft through the middle of the engine?

Simple ... PJs run very hot and it woulb be very costly to 1) keep that shaft cool so it don't warp, 2) supported at 3 place at least so it don't oscilate and finaly, lubricate and cool down that "Central" bearing or support. Designing such for a PJ is simply not worth it.

I was under the impression that current turbojets did just this and used an almost toroidal combustion chamber open at both ends built around the central shaft connecting the turbine to the compressor.

Also true ... but next to de combustion chamber's core center, they also do run much colder than PJs as for they mostly are using Annular (Donut shape), Reverse Annular and Can Annular (This one is disapearing) chambers which gives a cold central section to run the shafts.

I was also under the impression that the compressor consisted of several sets of rotors and stators that drew in and compressed air by cramming it into a progressively smaller space as it is moved toward the combustion chamber.

True again ... Ruffly described but true ...

Perhaps this was a contributing reason to Luc's troubles?

Naaaaa ... My troubles are more related somewhere else. But I beleive I (We) have an alternate solution for it ... Just din't think about it at first ...

I was also under the impression that the pulsation from a pulsejet could damage a turbine's rotors, is this correct?

It is true that PJs can be very destructive for some equipments (i.e : Sensors, gauges, electronics ... ect) and even tear steel in some case. But I have yet to see a PJ destroying axial rotor blades. For my self, the turbos I am using have centrifugal empellers which are even more tuffer.

Would a possible solution be to add an afterburning ramjet to even the flow before the turbine stage of the engine?

You can probably add anything you want as a "Possible" solution, But the main problem remains which is "How do you get that PJ/Ram Jet/Turbo combination to self start without using starters or blowers???. But I do have my "Crossair" lock on a very pontential solution that I am actually building. Will see how it goes ...

Perhaps a low-bypass single- or multi-staged fan could be attached to the front of the compressor to feed extra air into the ramjet. I'm curious as to just how much of the pressure gain provided by a pulsejet running on a compressor would be lost in a setup resembling the one I have attempted to describe here and how much extra thrust would a second-stage combustion chamber being fed exhaust and extra fresh air would provide.

Indeed ... Answers to these questions would be very interesting. But it also boils down to "What the goals are?" For our self, we are not aiming for additionnal thrust or design a low cost jet engine as they are plenty out there. Our goals are simply aimed at to things which are 1) Convert PJs thrust or combustion into torque and have a self stating (No starter, battries and blower) system ... The rest is simply of no interest for us.

I'd be very interested to see any historical accounts of similar engines and their performance.

Well ... This is a good place for that as long as peoples are publishing of coarse. Stay tuned anyway ...

Cya,

You know, I've taken a peak at some of the first gas turbine engines and it seems that one of the original attempts by Frank Whittle involved placing several small combustion chambers around the compressor/turbine. The compressor would force air into the combustion chambers and the exhaust would be recombined at the end when turning the turbine and exiting the assembly. Maybe Zippiot was onto something by placing several pulsejets around a super-sized turbocharger.