Aussie project

[Chook]

Hi everyone.
I have been trawling through this forum for a while now and really enjoy what people have been doing and sharing here.

I have been interested in pulsejets from when I was in school and built a very small valved jet in the late 70's.
A very serious sporting injury called "marriage" put me out of action for a good while.
Now the kids have gone their own ways, earlier this year I built a small Chinese pulse jet and had a lot of fun getting it running on LPG.
The second line that is at right angles to the intake was going to be for petrol but I never drilled it out or got it set up.

It was quite entertaining and got the neighbours attention. I'm lucky enough to live on the very outskirts of town, on some acreage. So all the neighbours were invited over to see the first run.
The info I found here helped me a lot, as I am no scientist by any stretch of the imagination.
This is the first run of the Chinese thermo pulse. I don’t know how much thrust as I‘m excited enough that it starts and runs really well. It’s made out of 1.6mm galvanized mild steel (I have just used the offcuts I had laying round) and automotive exhaust pipe. It was a great little project.

Once I had this under my belt I moved onto a larger Lockwood that I found plans on here for. I had to change a few little things as some of the sizes are not available here in Australia. It too is made out of 1.6mm galv sheet. It took a bit of effort to hand roll the tapers on a large 75mm x 1400mm slip roller and finish them off. A motorized set would have been really good.

Then I started thinking what it could be used for and just mounted it on the back of one of the land yachts I built.

With the extraction of 4 bolts and take the turn buckle off the front, it can be removed and I’m back sailing in 10 minutes.

The fuel system was a bit of a guess really. I used a hydraulic needle valve for the idle circuit and a ball valve for power.
All the gas lines are 3/8” 10mm copper, with the intake line being 10mm stainless steel. It has a brass fuel nozzle (from a drawing on this forum) I made on the lathe, pinned to it with 12 x 1mm holes around it facing forward at 15 degrees and mounted right in the middle of the first transition cone.

I had lots of problems with the ignition system, I made using an automotive coil and a relay. It works every time at home and as soon as it’s really needed it breaks down.

So in desperation I bought some party sparklers and throw 5 twisted together and lit into the intake.
It needs a whiff of air from a leaf blower to get it cycling and then it’s away.
It will run for a couple of minutes and then the 8.5 kg bottle freezes up.
I have inverted the bottle and had it running for 20 seconds or so but my fuel control needle valve is too coarse (I reckon?????) and it over fuels and freezes the lines and quits. Boy it has a lot more grunt on liquid LPG though.
I’m open to any ideas as to how to solve the freezing with an inverted bottle as it has much more potential than on vapour.
Here is a very scratchy video of a run I did and it freezing up.
http://www.youtube.com/watch?v=Vdf30S-gEI0
Thankyou everyone who has posted info on here. You have no idea how much it has helped me.

[metiz]

Hey Chook, welcome to the forum!

Nice couple of engines you build, good work. Usually when new members appear here they start asking about plans right away but you have done your homework it seems
There's no easy (portable) way of dealing with the tank freezing up. you could try to get an electric blanket, 12 volt battery and an inverter. Wrap the blanket around the tank to prevent freezing. One other more drastic option would be to pre-heat the tank to a maximum safe temperature. It will still freeze but take a lot longer to do so. (also: more pressure = more thrust ) Use a propane burner to get the tank nice and toasty.

[John Hasler]

Could you be more specific about what is freezing when you invert the bottle?

[Chook]

Thanks metiz for your ideas.
The radiant heat from the jet does put some warmth into the top of the cylinder while it's going which I guess must help. It's the last 100mm of gas, left in the cylinder that ices up, so that’s not too bad really. It’s burning 1.5 kgs a minute.

John it has only run for 20 seconds on liquid, so it's a bit hard to comment where it's going wrong.
When it cut out, the copper lines were covered in ice from the needle valve to the preheating coil around the motor. It was just spraying icy frozen liquid out the exhaust before I turned off the valve.
I didn't have a chance to experiment with different needle valve settings as the run was too quick. The ball valve fuel circuit wasn't even used for this run.
I'm curious as to what the difference in volume is, between vapour and liquid. I'm sure I was well and truly over fuelling it. Would a much finer needle valve sort this problem and regulate it better.
Another thought was that I didn't give the motor time to get to operating temperature before increasing the fuel supply.
I just got too excited with the extra power and didn’t monitor it well enough.
I would definitely have be a divorcee, if I had done another run on liquid here at home.

Later on I'd be interested in changing it to run on either diesel or petrol. What would be the advantages????

Thanks for your time fellas,
Chook

[John Hasler]

When it cut out, the copper lines were covered in ice from the needle valve to the preheating coil around the motor.

Sounds like evaporation is occuring at the needle valve rather than in the preheater or at the nozzle.

I'm curious as to what the difference in volume is, between vapour and liquid.

Depends on pressure and temperature, of course. At STP the density of the liquid is about 250 times that of the gas (but the gas will flow faster because of its lower viscosity).

Would a much finer needle valve sort this problem and regulate it better.

I think you need a much smaller nozzle so that there is enough back pressure to keep the fuel liquid until it hits the preheater.

[Jutte]

Gidday Chook,
Nice one mate - good engines - I'm across the ditch from you in NZ. I just used to use a coil , and spark it directly from the battery
- bit of a drama trying to do that and fiddle with the air etc.
A very serious sporting injury called "marriage"...
LOL... that is funny..unfortunately that same 'injury' and not having a very good paying job
has sort of slowed down my pulse jetting for awhile now.
However in saying that , a few months back I fired up the scooter pulse jet that I
donated to the NMIT Aviation Engineering School. My former tutors and the current students
were all wowed, and deafened - and you could see the cogs whirring around in heads of some of the students.
Had to cut it short as the School is on the Air Force Base.
The other cool thing is that tomorrow I am off to the local Aero Club as they are covering Jet Engines for the Young Aviators
Club - with me in the starring role as the madman doing the demo of the Pulse Jet - wohoo and all that sort of thing.
I will endeavour to bend them to the "Dark Side" of Pulse Jetting - or at least try .
Good stuff Chook - and you're doomed for sure - you'll start seeing pulse jets in all sorts of things.

[Chook]

Ah thats the go.
Fuel nozzle size. My fault here as I was told that the gas expands only 62 times. Big difference to 250 times!!!!
I should have checked it out further myself.
I makes much more sence now that you have explained it thanks heaps John.

I'll make up a new nozzle when I get more time. Maybe an adjustable nozzle????
I have a list of jobs to do round the home as I've been a bit distracted by this build.

Sound like the young ones are in for a lesson that they will never forget Jutte.
Thats fantastic that you are taking the time to get them involved and thinking.
My part time job at the Agricultural College, is working with Yr 10 students and I just love it.
They also loved the stationary engine test run I did at the workshop there.
Many thanks, Chook

[John Hasler]

My fault here as I was told that the gas expands only 62 times. Big difference to 250 times!!!!

Well, it depends on temperature and pressure, of course. 250 (approx.) is going from liquid to atmospheric pressure and room temperature. The pressure inside your tube will be much higher than atmospheric and so the density will be higher as well. You still want to keep the propane liquid until it reaches the preheater, though, and I think that the way to do that is to use a more restrictive injector. Perhaps you should try a Roscojector: they are supposed to be easy to make and easy to adjust.

Nice looking engines. I hope mine look that good when I finally finish one. I'm bogged down in simulation software now.

[Chook]

Sorry for not replying I've been out of town.

John, I will certainly have a play around with a rosco injector as they are such a simple design.
Aren’t all good inventions simple??

Would anyone like to guess as to the size I would require for the outlet, as a starting point?
On vapour it's running really well using 12 x 1mm holes on the radial injector.
Here is the injector just stuck onto a scrap bit of 10mm copper tube.

I used a 10mm ball valve rather than the 6mm/1/4", in the photo for the power circuit.

It's a fantastic learning curve.
Thanks Chook