New PJ Designs and Feedback

Mark · Post by **Mark** » Fri Apr 16, 2004 1:29 pm

Nice to see some pictures and experimenting. Obviously you've made a "wave" engine. And I see you don't have to worry about denting it. Must to be quite deafening.
You engine has an interesting shape. Good work.
Mark

Rossco · Post by **Rossco** » Fri Apr 16, 2004 1:38 pm

I havnt used methanol ever, and don't know where to get it from?
Its an aircraft fuel or addative isnt it?

Anyway, ive not got this Biggun running any longer than its maiden 10 sec run (unasisted).

I gave it a blast the other evening at the race shop that keeps wanting me to take them down there. (they would be able to get me some different fuels!)
Its got a massive rumble and actualy shakes and rattles all the sheds in the industrial complex. And sets alarms off!

BUT it wont sustain again. Ive not had much time to try changing through much of a range of intakes, as soon as i couldnt get it to run with the second intake, they wanted me to get my "little" one out again.

Ive found some good party tricks with the "digeridoo" as theyve all dubed it. I can "pump it up" by giving it a blast of compressed air and cranking the fuel up a bit at the same time. Itll then sustain at this level. I can do this about 5 times with noticable power step ups. I got it glowing white hot at the CC and red half way down the tail by doing this! Not bad for an engine that is supposed to just be a test rig for different intakes, and its 7' long and 3" CC necked sharply and then 3" tail. Intakes only 1".

They also love it when i go the big start blasts too. Crank the gas right up, full air into the intake and the spark rate right down so it gives an almighty boom every second or two!

But running it on dirty old sump oil is the favorite. They just cant get that it runs!

Rossco

I promise, again, that ill get some running pics of them both soon.

tufty · Post by **tufty** » Fri Apr 16, 2004 2:08 pm

Well, I finally gave myself an hour (which turned into a couple once I tried firing it up) and squashed myself a baby 'rosscog kazoo'. 80cm long with a 15cm cc, made from 15mm id and a 5mm id inlet, inlet is brazed to a standard brass pipe constrictor and the front of the cc is threaded to take it. The constriction is squashed down to 1.5mm (or thereabouts) and the exhaust flares out to round at the end.

Of course, I have no spark plug small enough to fit. I fired it up with some methanol, given a bit of air at the front and a blowtorch I managed to get some bangs and (twice) some very shrill squeals as it actually fired up. Yay. Now I need to figure out a proper ignition system, and fit a fuel feed (probably a methanol drip into the inlet, although I'm also considering butane) and try to get it to sustain. If it ever does, I suspect it'll deafen all the dogs in the neighbourhood.

Any ideas for tiny ignition systems?

Simon

Rossco · Post by **Rossco** » Fri Apr 16, 2004 2:10 pm

I have gone over everything. Its got to be the CC restriction.
This should further restrict and focus the blast as well as deflect and focus the returning wave and or gas for reignition away from the intake.

Yes i know the funell down from the CC is a very long slope! Thats deliberate, also for focusing the blast. I have found that the steeper the slope in this type of engine the more shock out the intake. Im thinking from a reflection off the slope back at the intake mouth.

Rossco

Rossco · Post by **Rossco** » Fri Apr 16, 2004 2:17 pm

Simon

did you notice the spark plug in the tail as well as the CC?

My biggun starts there better (nicer) than at the CC. It flames, then howls then explodes into resonance!

The CC spark with air and gas going fairly hard to get it to ignite, makes one hell of a boom! I much prefer the tail ignition!

Thanx for trying this, its good to see a different method and direction of something that ive been battling away at for a while on my own!

For once tho, ive had much less success with the biger engine!?? You just cant predict anything with these engines!

Rossco

larry cottrill · Post by **larry cottrill** » Fri Apr 16, 2004 2:21 pm

Rossco wrote:I havnt used methanol ever, and don't know where to get it from?
Its an aircraft fuel or addative isnt it?

Rossco -

Around here, I've seen methanol packaged basically two ways, both as de-icers: As a winter fuel additive [it will actually dissolve ice from fuel lines - where water gets there as condensation and then freezes, blocking the fuel flow], which is put up in small plastic bottles [Heet is the most famous brand name]; and in pressurized spray cans for dissolving ice on windshields, door handles, locks, etc. - many 'store brands' are available. Very handy stuff; at the end of winter you can sometimes get overstock on sale for 10 spray cans to the dollar. Its only real disadvantage as a fuel is that its energy value per unit volume is somewhat lower than more commonly used motor fuels. Of course, I have no idea where you'd get it in the large quantities your mighty engines will demand.

The pictures are wonderful. I copied them to my drive here, and used MS Photo Editor to bump up the gamma significantly, so the machine is clearly visible. Man, that looks like a thing that will move some air! I can see from the "surfin'" picture that you're exactly the kind of bloke to be doing this!

Obviously, you don't have a shot that shows a direct comparison of the intake to the exhaust nozzle section. From the front view, though, my gut feel is that the intake is a bit small for the size of the chamber volume, and way small for the conical inlet shown. Experimentally, I'd like to see an intake throat about 75 or 80 percent of the nozzle ID, and an inlet bell not more than twice the diameter of the intake throat, to see what that would do.

On the other hand, I think the tail end is wonderfully proportioned - should be plenty of gas mass for good pumping, as discussed earlier. Similar in basic layout to the Chinese rear end, although I think your engine has far better proportions than the classic Chinese plan, which I've always thought had a very undersized chamber. [Bruno has pointed out that reports on the Chinese in action make it sound pretty suboptimal.] Does that 'second' spark plug seem to do anything for you? [I suppose you haven't had a chance to try it yet, but just thought I'd ask.]

As I said, these observations are just intuitive, and may be way off base. In my tiny engines, I have always made the mistake of making the air inlets too small and restrictive.

L Cottrill

Rossco · Post by **Rossco** » Fri Apr 16, 2004 2:39 pm

No, i think that you are on the same wave length exactly!

I had decided thisarvo with a mate that i would have to go up nearly an inch with the intake, and this reduces the conical section of the intake in the same move!

My strongest gut feeling on the thing tho is that the exhast restriction zone is too big? I dont know where im getting this from as its proportioned to my smaller "digeridoo" engine with a shorter fatter CC.
Ill have to give both these changes a go, and ill make them both adjustable so i can get them balanced.

Yep ive had a couple of blasts with the thing, as you can imagine, im fairly restricted with the place and time that i can run it! The tail plug is for softer starts. Its much nicer, and gives evryone a bit of warning that something is about to happen with a masive fire ball! rather than a heart stopping BOOM that is totaly unpredictable as i muck with the mixtures to get it to start up.

Funny how you get the feel for different engines! This one i am so rough with, just wind the gas on and give it a masive gutfull of air and whoomf, howl bbbbbbrrrrrr were away. Whereas my other of the same design im cearfull with the gas, bring it up with a constant air flow and its just an instant start!

Ive had a lot of fun with it over the last couple of days!
And i now have (unofficial) sponsoring from a steel yard!

OH, and i had a play with a big mig for the first time! WOW Man its so much easier and quicker than the arc. I welded those plugs in in two strokes with out blowing or leaving one hole, and they were the loosest fit with about a 2mm gap on one side! I gotta get me one!

Rossco

PS. it gets down to about 20C here in winter on an average day, so thats probably why i havnt seen much methanol around!

tufty · Post by **tufty** » Fri Apr 16, 2004 2:46 pm

Heh. My problem is not 'where to put the plugs' but 'I don't have small enough plugs' ;-)

Maybe I'll rig a fuel feed and then try the old 'bit of steel wool shoved up the exhaust and connected to a car battery' starting trick this evening. If that works and I can get the damn thing to make some noise, I'll do it again with some sound (maybe even video) recording gear and try to get some shots and noises up asap.

Hell. I love a new toy!

Oh, and Ross. Love the photos. That thing looks bloody brutal.

Simon

Bruno Ogorelec · Post by **Bruno Ogorelec** » Fri Apr 16, 2004 3:44 pm

A great-looking beast. I am holding my fingers crossed that it develops into as impressive a performer as it is a looker. That way, I would end up looking not so stupid after all, too. You work amazingly quickly.

tufty · Post by **tufty** » Sat Apr 17, 2004 4:19 pm

tufty wrote:If that works and I can get the damn thing to make some noise, I'll do it again with some sound (maybe even video) recording gear and try to get some shots and noises up asap.

Well, it made some noise. Butane is a no-go until I can get a decent fuel feed rigged, and for that I need some _tiny_ pipe. Maybe I'll go tear the brakelines off one of the wrecks at the local garage for that. Feeding from a butane canister with a wd-40 top and bit of old busted aerial into the inlet got me a flame out the 'zorst and a freeze burn on my index finger ;-)

In the end, I used my MAPP torch against the inlet and managed to get howling mode combustion (burning just after the constriction) along with the occasional pops and bangs. It wants to run, but I don't have enough hands to do it all. I changed to a bigger diameter inlet for a bit, but that didn't want to play (other than howling) at all. I guess it took up too much of the CC.

So, I reckon I need to get a decent (hands free) fueling setup, probably methanol, add some gentle air to the inlet and light the thing at the exhaust. By playing with air, I think I should be able to get it to run.

And no, no sounds or video yet.

Simon

Rossco · Post by **Rossco** » Thu Apr 22, 2004 1:47 pm

Tufty, how you going with that engine?

Ive been busy on my welder, but im off to a new test site this weedend to scare some new niebours so ill take as many pics as poss! Of the engines and maybe of any amusing scared niebous!

Rossco

tufty · Post by **tufty** » Thu Apr 22, 2004 3:48 pm

Rossco wrote:Tufty, how you going with that engine?

Was just playing with it, new inlets and the suchlike. I'm still trying to source some tiny copper tube for the fuel feed...

As far as running it goes, I had it pulsing for about 2 seconds this arvo, but then it flamed out. Mainly it runs in howling mode ;-(

Still, it _will_ run.

Simon

Axt · Post by **Axt** » Tue May 18, 2004 4:22 pm

Rossco, couldnt it be somewhat improved if one was to add small intakes/exhausts into the main intake.

My thoughts -

1. It would allow air to quickly fill the chamber.

2. They will restrict blast out the front, as its being shot back down through it.

3. blasting gas down the intake will help draw in more air.

4. An enlarged intake will push an excess of air through the exhaust ... inbuilt augmentor!

Note that I just put about 5min worth of thought into this, so it may not work at all, but seems to have good points and isnt hard to try.

Im no Larry Cottrill, but the ms paint picture attached shows an example of what im talking about.

Bruno Ogorelec · Post by **Bruno Ogorelec** » Tue May 18, 2004 6:53 pm

An interesting idea! Maybe the entire intake could be a series of conical rings spaced a little apart from each other, to give the effect of circular slats or gills. I'll have to draw this to make myself clear I guess. Very unusual, this. I don't know what the hell it might do to teh acoustics of teh thing, but it sure looks interesting.

Bruno Ogorelec · Post by **Bruno Ogorelec** » Tue May 18, 2004 7:16 pm

Here's what I had in mind. A setries of nestling cones. They would have to be very close to each other, much closer than in the picture, which is drawn only to explain the principle.