Do i need a venturi?

[Barramundi]

Is it necessary to have venturi if the pulse jet is direct injected? and do i need to make the valve hole bigger than usual?

[Hank]

Hello- The purpose of the venturi is to create low pressure in the intake tract in order for the atomised fuel to enter. You would not need this feature if you are direct-injecting into the diffuser/combustion chamber. I'd certainly consider it in an engine injecting before the valves.

The pulse jet engine is a constant volume engine. You can only admit so much fuel-air mixture for each operating cycle. Some of the more successful of this engine type, such as the McDonnell type produced to power the Gorgon C series of research/stand-off bombs in the 1940's, used an end cap that admitted air from the sides. Ram induction is not usful in pulsed combustion, at least in the valve types. It will blow the flame front away from where it is needed in order to sustain combustion.

[Mark]

I wonder what the gizmo is at the bottom of the aircraft with the line of holes in a pipe of some sort. Perhaps it dispensed silver nitrate to seed clouds or maybe it was a way to drop mind controlling substances over overpopulated areas of Canada . Any other guesses?
Mark

[Mark]

Does anybody remember way back when there was a discussion about pulsejets flip-flopping into a ramjet mode. One fellow said it was illegal to export technology related to this subject, some fancy governmental code/agency that had a high and mighty ring of truth to it. I believe he sighted the phraseology used in export regulations.
It would be fun nevertheless to make a toy, perhaps flown as you would a Dynajet with a control line, then switch it over to subsonic ramjetting and get really dizzy perhaps if it picked up speed. I wonder how hard it would be to make a reed bypass channel when it got up to speed, that is have the intake divert around the valve grid.
Mark

[larry cottrill]

Does anybody remember way back when there was a discussion about pulsejets flip-flopping into a ramjet mode. One fellow said it was illegal to export technology related to this subject, some fancy governmental code/agency that had a high and mighty ring of truth to it. I believe he sighted the phraseology used in export regulations.
It would be fun nevertheless to make a toy, perhaps flown as you would a Dynajet with a control line, then switch it over to subsonic ramjetting and get really dizzy perhaps if it picked up speed. I wonder how hard it would be to make a reed bypass channel when it got up to speed, that is have the intake divert around the valve grid.
Mark

Mark -

Maybe this [one of Bruno's favorites] could be re-styled to do the job. The area marked 'Combustion zone' would become the subsonic diffuser as combustion shifts rearward. Would probably take some careful shaping of the area marked 'Tail tube', which would need to carry the combustion [add a few flameholdrs in there].

I don't show a transverse section, but there are supposed to be a lot of radial webs which the valves rest on when they shut, each web carrying two adjoining valve edges.

L Cottrill

[Hank]

Hello- The keel with the holes in it is an early yaw sensor hooked up to an equally primitive electrical control system. As the airframe slipped sideways it changed the pressure in the ports and actuated a variable resistor that compared go/not go and rate. State of the art until inertial navigation. Thanks to Bruno for including this photo some years ago on the "old" Forum. I was lucky enough to meet some of the ancients who knew what it was a while back.
Perhaps a pulsejet could transition into a ramjet. Fold the valves out of the way and extend the valve stop into the combustion chamber to act as a flame holder.
Hank

[Mark]

Thanks Hank, that seems to make sense. I wonder if it could be thought of as a kind of lateral line, as fish have, man imitating nature.

Mark

[Glenn Olson]

A few years back I talked to an old pulse-jetter who described what he called (as I recall) an afterburner for pulsejets. What he described was basically a sleeve or tube that engulfed the pulsejet turning it into a pulsejet-powered pressure jet. That is, the exhaust of the pulsejet entrained air inside the tube with the result of a lower exhaust velocity but higher mass flow. I suspect that the heat off the pulsejet body also created a slight ramjet effect.

With this in mind, one can visualize a ramjet with a pulsejet inside to give the vehicle thrust at zero speed. Then, as the speed increases, the ramjet begins to produce thrust and, at some point, the pulsejet is turned off. The flame holder for the ramjet would have to be aft of the pulsejet, of course.

Or the pulsejet could be placed in front of the ramjet so that it's exhaust inducts air into the inlet of the ramjet. This would leave the ramjet inlet relatively open for higher speed operation.

An alternative would be to have a rectangular inlet to the pulsejet. The valves could be integrated into a trap door that swung out of the way when ramjet speed was achieved.

Another would be to have moveable inlet doors into the combustion chamber aft of the valve body. During pulsejet operation the doors would be closed. During ramjet operation the doors would be open and the combustion chamber would act like a dump-combustor. A sleeve valve arrangement rather than doors might also work. This could be incorporated into a Katydid-like front end.

The most simple system, though, would be to have both a pulsejet and ramjet on the air vehicle. This way each engine could be optimized for it's own function and flight regime. And, if you're looking for top-end performance, the pulsejet could be parachuted to the ground after it shut off, sort of like rocket-assisted takeoff.

The variations and possibilities are probably endless.

[Bruno Ogorelec]

In the early 1970s, the German Messerschmitt company (part of the Messerschmitt-Bölkow-Blohm conglomerate) developed a valveless pulse ramjet. It would segue from pulsating combustion at low speeds, at which ram pressure is poor, to constant combustion at high speeds, at which the ram pressure alone is sufficient to contain combustion. The task required a deflector that would be efficient in redirecting the reverse flow coming from the intake, but would not represent too much of an obstacle to the entry of fresh air. Here’s what they came up with.

The broadest part is the pulsating combustion chamber and the narrower tube behind it is the ramjet combustion chamber. They found it necessary to interpose a variable diameter (irising) restrictor between the two, as the thing would not work too well with fixed geometry.

[Pieter van Boven]

Oh yes, I saw this jet in the "Viva la France" post today, wich is GREAT!
Did it run?!?

Pieter.

[Bruno Ogorelec]

Oh yes, I saw this jet in the "Viva la France" post today, wich is GREAT!
Did it run?!?

Yes it did. I am not sure how well, as my French is only sufficient for shopping and saying 'no' to ladies of the night on the Pigalle. But, it did work. However, Messerschmitt apparently found no good application for the thing.

[Hank]

Thanks Hank, that seems to make sense. I wonder if it could be thought of as a kind of lateral line, as fish have, man imitating nature.

Mark

Hello- A neat comparison. I am going to Mote Marine lab later today and will be looking at lateral lines in the flesh. Hank

[Hank]

In the early 1970s, the German Messerschmitt company (part of the Messerschmitt-Bölkow-Blohm conglomerate) developed a valveless pulse ramjet. It would segue from pulsating combustion at low speeds, at which ram pressure is poor, to constant combustion at high speeds, at which the ram pressure alone is sufficient to contain combustion. The task required a deflector that would be efficient in redirecting the reverse flow coming from the intake, but would not represent too much of an obstacle to the entry of fresh air. Here’s what they came up with.

The broadest part is the pulsating combustion chamber and the narrower tube behind it is the ramjet combustion chamber. They found it necessary to interpose a variable diameter (irising) restrictor between the two, as the thing would not work too well with fixed geometry.

Hello- I've been thinking on this one and the geometry problem of the duct came up. There are different requirements for pulsating constant volume and constant stream. Do you have any schematics of the "iris" or fuel metering controls, Bruno?

Hank

[tufty]

Do you have any schematics of the "iris" or fuel metering controls, Bruno?

Available on the 'vive la france' site, image_01b_0067.jpg

Simon