"The Millenium Lance" Project Build

[Zippiot]

I have stood infront of one of those blowers before and IT BLOWS HARD (couldn't resist), so I assume that when you duct it down it'll easily pass 200 mph winds at super high cfm. I saw leaf blowers that hit 220 mph but had less than 200 cfm airflow. If your jet isnt getting enough air I would only assume a super high cfm blower could help.

Many different shapes and configs, search northerntool.com for blowers and take a look around.

Motor burnout...no idea dont make it work too hard I guess.

[Irvine.J]

Cool thanks zippiot...

In my last run I got good blue inside but nothing but yellow outside. I had 8 larger diameter holes then I probably should have, and could tell instantly it was suffering for it. I think the next thing I'll try is having very small holes, just more of them, so I still have the high pressure injection, but can give it all the tank has got to give. I also think once I get it running again like before, I'll add a 1cm wide curved circle all the way around and welded to the blades holding in the aerospike. Giving equal distance between aerospike and the wall, I think the airflow may not be disrupted as much as it should be.

[Irvine.J]

Well, i've pretty much concided myself to thinking that this ramjet is designed for "Megahypersonic" use only...the fact I got an excellent blue flame burn without the flames shooting back out the front like the second scene in the video after some tweaking was promising...however, I think there might be something I can do to make it run a little more standard. Here are some photos of what i've been thinking, I love cone designer, makes life so easy.

What do you guys think???

[Zippiot]

I'm still tying to figure out to to not lose my plastic mold piece while making my cone...stupid epoxy!

Is the tank giving it all that its got or are the fuel injectors restricting flow?

That is why I love liquid fuels, if your cc is too long use kerosine, if it is too short use alcohol or gasoline, and if it is way way to short, use ACETONE!!! haha

Its 230 am here, my chocie is work through the night and sleep away the daylight or try to sleep and work all day (chronic insomnia...), gotta make a run to the hardware store at some point. Ran out of welding wire again, gas too!

[larry cottrill]

Yes, James, that's fabulous. The only thing I note that's not to like is that you still sporadically get some jetting forward into the diffuser section. My question is, what kind of area ratio did you end up with? The diffuser section is pretty short, AND the spike is increasing velocity significantly going in ... I wonder if the diffuser is providing as much pressure as you'd like.

You're getting serious, now; you should try rigging up a couple U-tube water manometers side-by-side so you can measure the pressure difference. It wouldn't take much effort - you could build the whole instrument out of clear vinyl tubing (say 1/4-inch ID) and a simple frame to hold it with an inch or cm scale up the middle of the U. Then, tap one side of one U into the diffuser near the front end and the same side of the other U at the rear end of the cone, with the 'other' side of each U sensing free air. This would let you judge the pressure rise. Providing the taps into the cone would be the only "hassle" to it - you would need to make sure there is NO roughness on the inside where they cut in.

Great work !!!

L Cottrill

[larry cottrill]

As to these great fans, guys, you're neglecting one consideration - power. Axial fans have a very poor "fan curve" for elevated pressure applications. In other words, they will drag down BADLY (and heat up badly, if the motor power is low) when a lot of back pressure is forced upon them, which it WILL be when you try to make them drive a large area ratio nozzle. This is true no matter how long and "gradual" you make the nozzle cone. A centrifugal fan will do much better in this regard, believe it or not.

If you find this hard to imagine, try this: Take a little "breeze box" window fan, run it up to speed and gently tip it over face down on the floor. Don't do this for long - the little motor will get VERY hot VERY fast! That's the problem you're up against. It takes very little power to move a lot of air when it's truly "free flowing"; a LOT more if you're working against significant pressure.

Remember that any "nozzle" (like your long cones) is the opposite of a diffuser - the pressure coming OUT will be equal to atmospheric but at high speed; the pressure going IN to the large end will be elevated. The velocity gain in the cone is not free - it requires significant power! These fans are relatively cheap because the motors are pretty small and low power (note the modest current requirement at 120V).

L Cottrill

[Irvine.J]

Ok, Larry, so i'm going to return to my high pressure injectors, and use that thin steel round flameholder config but drill a few holes through it, so not to impede airflow too much. Like you said when feeling the incoming airflow during setup running over the inlet spike it was really under significant pressure. I would consider that the inlet cone may not be long enough too, but do you think the addition of that flameholder ring will help things out a bit?

My areas are as follows.

CC : D= 5" = 19.625 inches.
Inlet spike max D = 3" = 7.06
Diff= 12.565sq/in.
Inlet (around spike) is equal to 12.565 till reaching the cc.

Exit nozzle.
D = 3.5 inch
Area = 9.62

Inlet / outlet diff
12.565
-9.62
=2.945sq/in

After adding flameholder ring...
outer D=4.25" = 14.18sq/in
inner D=3.75" = 11.04sq/in

area diff (after flameholder addition) = 3.14sq/in

Therefor with addition of flameholder ring (with maybe a hole or two drilled through it
will be

Inlet
12.565-3.14 =9.425
Exit Nozzle =9.62

Hmmm, these figures sound a little better. What do you think larry? That small flameholder section
might do the trick you think? Also i keep breaking my tiny drillbits,anyone else find silver solder
is impossible to drill through?!

[Irvine.J]

This should do the trick...

[larry cottrill]

Hmmm, these figures sound a little better. What do you think larry?

Um ... actually, no. Now that I see the numbers and go back thru the photos and video, I actually don't think you're getting what you really want. Where you say:

Inlet (around spike) is equal to 12.565 till reaching the cc.

I think what you're saying is that it's a constant passage section between the two cones. What that leaves you with, then, is no diffuser! AND, this is after you've increased the flow speed with the "exposed" part of the spike. There is no possibility that you're developing elevated static pressure at the rear edge of the spike.

You're basically trying to do what I'll call a "velocity jet" rather than a ramjet: you're overcoming whatever chamber pressure you develop with a high speed stream, i.e. dynamic velocity head, rather than static pressure. This is not totally unworkable, but instead of smooth diffusion, what you're getting is "rough nozzling"; i.e. your slowing of the stream is in the form of turbulence behind the spike.

Ideally, what you want is for the passage size (area) at the cone inlet to be significantly smaller than the passage into the chamber. Not only that - you want it to be significantly smaller EVEN WITH THE FLAMEHOLDER AREA SUBTRACTED OUT! This would ensure that you have fairly low speed high pressure flow into the combustion zone.

What you've got isn't really bad - the video clearly shows that the combustion is taking place where you want it - but it probably isn't capable of good power development over a useful range of speeds.

That small flameholder section might do the trick you think?

As to the flameholder, the ring isn't a bad idea, either, but as you've proposed, the flameholder area needs to be reduced significantly. The main thing is you wouldn't want it to kill the action of a carefully designed diffuser. Since you're "nozzling" into the engine anyway, a reduced area version of what you show in your photo should work fine.

Of course, you'll hate the suggestion, but what I would do is re-design the front inlet cone to about twice its current length, and more "blunt" shape so that real diffusion is obtained. Get the inlet plane area down to a figure somewhat less than the exhaust nozzle area, certainly. And, of course, I would make just a SLIGHT flare all around the inlet rim.

A different approach, if you want to build a new version, would be to use a short nozzling (not diffusing) cone as an inlet "flare" and make a "back end" to the spike that tapers inward, making a diffuser section that way. That would lengthen the straight cylinder part of the engine, though (and the engine as a whole, of course). Just another way of getting there. At the same time, you could develop your multiple "blade" flameholders as in your drawing - a design detail that I really liked!

Anyway, just my opinion - not to take away anything from your achievement of a running engine, just trying to goad you into wringing everything out of it that you can. (Some forgiveness required, perhaps ;-)

EDIT: I wrote this before seeing James' latest photos showing the perforated flameholder - he just beat me to the mouse click!

L Cottrill

[Irvine.J]

Larry,
you don't need ever to be forgiven for you most helpful insights. That information was pure gold.

You know what... I had considered whilst watching the running videos, that the reason combustion seemed to be concentrated around the Lance was exactly as you said, the rolling vortex off the back of the spike was providing the mixing for the burn...great stuff. I totally understand what you mean by velocity jet and it makes perfect sence, Infact I'm quite glad I managed to achieve it in my back yard!

Larry I had intended to make 2 versions of this jet, and will definantly make the blades like you said, however the only difference is the inlet cones diameter is 2.5 inches instead of 3. Still 9 inche long inlet spike though...

So you think I should dull the tip of the spike a bit? That could be tricky.

I could, I think on the current jet, make another inlet cone extention that forms the same profile and extend it another 2/4 inches and just weld it on...I might just start from scratch and make it a little smaller though this is one seriously big engine, though I'd love to see it absolutely roaring.

Are you happy with that perferated section, I can easily remove it with a quick dremel session?

I'll begin plans on that bladed one shortly, took me a few good solid days for the last one. Its 3am and i'm about to start fixing my injectors, hell of a job, but I gotta work out a better way then breaking small drillbits as they cost nearly 2 bucks each for No 61/68 drills.

Instead of flaring it initially which will be tough as hell on this 1.6mm steel, I bought a huge amount of blue-tack (like plasticine) and will form a small flare, then coat it in silicone spray so its nice n smooth, after I run it as is with the new flame holder. That will save me a good hour or two in hammering, if it burns off but runs well, I'll flare it properly.

[larry cottrill]

So you think I should dull the tip of the spike a bit?

No, not the spike - the inlet cone around the spike. By "blunting the cone" I meant a "harder" slope, so the area of the passage between it and the spike would start small (at the flare) and increase as you go back to the flameholder plane.

This could be done with an "add on" cone, but again you'll have a lot less of the spike visible out in front of it. You're not really there until you have less passage area at the inlet throat than the area of the exhaust outlet. You want the area increase to be equivalent to a simple cone diffuser - in that design, a good guess might be 12 or 13 degrees included angle, max. You'd calculate the length of that based on the angle and the difference between inlet and outlet area, then "wrap" that design around your central spike so the length and passage areas come out the same. It will end up more "blunt" than the simple cone because of the slope of the spike.

On a very fast engine, the inlet can be MUCH smaller than the exhaust port, with a very long but very high ratio diffuser. You can't get away with that at low speeds, but the included angle can be larger without getting separation, so the whole thing can be much more compact.

L Cottrill

[larry cottrill]

Are you happy with that perferated section, I can easily remove it with a quick dremel session?

I don't think there's anything terrible about the design; I'd just drill it out more to reduce the area even further. It really shouldn't take much area, and the more blocking area you have the more drag it produces, all other things being equal.

L Cottrill

[Irvine.J]

I have several printouts I've made and are ready to go, having drilled only 2 or 4 more holes in the flameholder...
This is a picture of a 4inch D to a 3.25 inch D over 1 inch, to an area (not minusing the spike) to 8.3 sq/in. (I believe it would be about 6.5/7 square inches if we took the spike into account.)

To be honest it still looks very neat with the extention, I don't think the angle is too great either, but has a significant area reducing effect with that spike. I'm going to do a 4inch D to 3.1 and 3.0 inch D over 1 inch now, but i think the 3.25 is pretty good. I feel bad for making asking alot of this stuff Larry, hope you don't mind. Check it out, the included angle like you said isn't to rediculous but is noticable, I just hope it shows up in this pic.

I'll post a picture of the 3.1/3.0 in a sec.
Your call Larry, can't wait to give it a go! I'll also run to the gas place and try and get some multi hole nozzles.

Zippiot rolling paper and having it stay in shape sucks, I fully know what your talking about LOL :-)

[larry cottrill]

I'd say that looks really good - I bet you'll find the net area is even smaller than you're estimating; but I think that's OK, because you can only go so far in reducing the flameholder area with it already in place. Yes, give that a shot, definitely!

L Cottrill

[Zippiot]

About cones, do you think they should be a "real cone" or should they slowly become a cylinder? I am wondering which ones smoothes the airflow entering the engine whilest still increasing the pressure...

Larry do you have a big centrifugal fan in mind, I think I saw one lemme see

http://www.northerntool.com/webapp/wcs/ ... _200324137

or

http://www.northerntool.com/webapp/wcs/ ... _200306875