A question about homemade ramjets

[Arman_awn]

That's exactly right! Congrats On you, My desing resembles your thought a lot, with a little bit difference.
I'm sure that it is possible. If this engine im working on will be successful, it will be a revolution in the propulsion world, A ramjet that works without any booster...when it is stationary...

You did'nt answer my question...

How fast the air coming out from the nozzle of a home made ramjet(by using a leaf blower to keep it running) travels?

[Najm]

How fast the air coming out from the nozzle of a home made ramjet(by using a leaf blower to keep it running) travels?

If you are talking about the ramjet's exhaust velocity then check out the program that I posted before, it will give you velocity(in mach) at various points in a ramjet, also the exhaust velocity varies with the air velocity you are putting into the ramjet so knowing the leafblower velocity is also a good thing(that is easy to calculate if you have information about how much air it blows out in a minute).

[Arman_awn]

Dear Najm,

The application you provided me can not calculate anything in subsonic speeds, and the values get a negative number when I try to do that.

I wanna ask that is it possible to return some of the exhaust gases to the inlet in order for them to be compressed for the next cycle? by using some kinda ducting...You know that the combustion inside the engine causes a vaccum and this in turn causes fresh air to be sucked into the engine.

I would be very happy to know your opinions....


Thanks

[Najm]

The application you provided me can not calculate anything in subsonic speeds, and the values get a negative number when I try to do that.

Open the attachments with RJSC, I get positive thrust values, its just putting in the correct values for all areas and the fuel ratio.


Can please present your idea in pictorial form (if you can) I have a bit of difficulty understanding it

[Arman_awn]

This is a simple diagram of what I have in mind. (See below)

1- Firstly, The engine is started by an air blower. The air goes through the diffuser and is compressed.

2- The compressed air is mixed with fuel, goes through the flame holder and then ignited.

3- The combusted gases expand through the nozzle. Here is the real trick! A portion of the exhaust gases is collected by a simple ducting at the nozzle, and is guided and forced through the outer ducting in the opposite direction of the exhaust gases, to the engines inlet.

4- The ducting delivers the returned air to the inlet and the air which has an initial velocity, is compressed without requiring an air blower to blow the air into the engine.

5- In the next cycle, because the combustion is done without air being flowed from outside, and while the exhaust gases are bled into the engine, a vaccume happens in the inlet. This vaccume causes fresh air to be sucked into the engine from the outside for the next cycle.

6- The cycle stated above is repeated and the Ramjet will be self sustaining without any air blower.

Isn't it really a very revolutionary design? A ramjet sustaining without any air being flowed into the engine?

[Najm]

Whats with the cyclic flow engine invented hundreds of times?

There ain't no such thing as a free lunch.

Nothing's 100% percent efficient so there will be power loss when the exhaust gases are cycled, though a workable engine cuold be made if designing is done carefully.The exhuast gases which are being cycled would have to be accelerated when they are coming out at the intake.
It can be compared to an automatic assualt rifle in its way of operation. Reloading a new charge of air after the exhaust phase.And then burning it.

[Arman_awn]

The exhuast gases which are being cycled would have to be accelerated when they are coming out at the intake.

The gases has their initial acceleration, because they come from the nozzle.

[tufty]

The exhuast gases which are being cycled would have to be accelerated when they are coming out at the intake.

The gases has their initial acceleration, because they come from the nozzle.

Nope, they have pressure and a certain amount of velocity.

The pressure you're going to see will be relatively low, you'll be lucky to get 1atm gauge (about off the combustion chamber and stealing enough working fluid to get a decent ram effect working will, at best, significantly reduce performance.

The better air amplifiers give between 10:1 and 25:1 ratio of entrained air to working fluid, but you need a lot of pressure and a significant amount of flow to get that, almost certainly more pressure than you will have available off the combustion chamber; the manufacturer's figures generally start at around the 2 atm range, at which point the graph is "going flat" - i.e. you will get very little useful entrainment below those levels.

It might be worth a shot, but I can't see it working very well, if at all, in all honesty.

Simon

[Arman_awn]

OK, So I'm adviced not to continue my working on this engine. but I still think that the design should work...

[Najm]

Velocity in the recycled air would be necessary to entrain more air into the ramjet.To increase the pressure and velocity of the air that is being cycled the air could be heated that would increase its pressure and velocity and if the duct is gradually thinned till it is at the intake and pointing into the ramjet then also the velocity would be increased though the pressure would decrease.
Even if this type of ramjet would not sustain without air being blown into it then it would make some kind of supercharged ramjet....

[Anders Troberg]

The first rule for any inventor is to not be discouraged by people saying that it can't be done.

That said, I agree that it will be hard to make it work. Basically, it has no natural front or back end, it all depends on which way you blow air into it as it starts (assuming the flame holder works both ways). My guess would be that the pressure in the CC will be similar at both ends (at the rear from the cumbustion, at the front from the ram pressure) and will cancel out.

On the other hand, I would not rule out that, with some careful fiddling with the geometry, the design might be able to work as a ram jet which works at hobbyist speeds. That would be a significant achievement, even if it still needs some speed/ram pressure to operate. Perhaps you'll be able to make something that works for a ram jet powered model aircraft!

I'm not a specialist at ram jets (or jets of any kind, I just try to pick up whatever wisdom I can from the guys here), so I may of course be wrong. I don't know where in a ram jet you find the maximum pressure, but I suspect that that's the point you should use as entry point to you feedback sleeve.

Hmm, I just got a flashback to some classes in telecommunication! Some background: At high frequencies, electrical currents behave less like current and more like waves. At some point, you stop using wires and instead use hollow tubes (usually square) through which the waves propagate, known as wave guides. As we are talking about waves here, it's very important that these tubes are properly tuned and of the proper length for the frequency we are using. By know, I think most of you are beginning to recognize some of this stuff. Just exchange the electromagnetic waves for acoustic waves and we almost have the same issues we face when designing a jet engine.

OK, here comes the interesting bits. When we have the wave in our controlled waveguide, we can do a lot of cool stuff by surprisingly simple means. We can divert part of it by placing another, similar tube next to it and drilling holes between them at specific distances, distances that correspond to the wave length that we want to get. I suspect, although I havn't seen that used, that you can filter out certain frequencies through similar means. It's not that different from, for example, a trumpet, where you affect the operating frequency by adding holes at different positions.

Could such a method be used in jet engines, to divert part of the flow as in this design, or to lock it at a certain operating frequency, supress overtones, to couple engines or to reduce/enhance noise? I have no really clear view of how it could be used, just a general feeling that it may be something we have overlooked.

If Sören Willmer ever reads this: I learned a lot from your lessons, even though I've had little chance of putting it to use. I bet you never though it would/could/should be used in jet engines!

[Arman_awn]

Anders Troberg,
Thanks, you gave a lot of hopefullness to continue my work. I have decided not to be disappointed again, and I'll keep on working on my engine untill I get my desired results.

by the way, I've a question: Can I use a 1400W home-vac as an air blower for testing my engine?

another question: what metrials am I supposed to use for the combustion chamber, the diffuser and the nozzle? will stainless steel suffice?

is there any need for a spike or something like a cone in the diffuser section? I know that such an element is mostly used on supersonic ramjets to control the shockwaves, but is it possible to use such a thing in order to get higher pressure ratios?


Thanks
Arman

[larry cottrill]

Arman -

You can check out a couple of prior cyclical flow ideas farther down in this forum:

http://www.pulse-jets.com/phpbb2/viewtopic.php?t=2123

http://www.pulse-jets.com/phpbb2/viewtopic.php?t=2187

Good luck!

L Cottrill

[Stuart]

Isn't it really a very revolutionary design? A ramjet sustaining without any air being flowed into the engine?

Actually, I've been working on this design for the last 15 years. Or at least what I think is a more practical version of it. Cottril has a version, and so did the foul Russian whose name escapes me. Trust me, there are problems getting it to produce thrust, though I have gotten a little out of it.

[Arman_awn]

Another Idea:

I place a fuel injector and a spark and somthing like a flamholder in the cycling duct, in order to re-accelerate the cycled air. will this do anything?

another question: how do I have to place the flameholder?