Thunderchine starting problems

[zohrke]

Hello everyone, allow me to introduce myself to you:
My name is zohrke and I'm from Germany. I was active before in Eric Becks Forum, that seem to exist no more and have sucessfully build his FWE Engine together with a friend of mine. (Just to give you a bit of background about me, as I am new here.)

Our next project was the Thunderchine which now sadly wont start, and I would kindly ask for some advice from you. (Especially Grim and M. who seem to have already run this engine.)

My setup is a 5kg propane tank with direct fueling to the injectors (old brake pipes)
and compressed air (~ 10bar/ 140 psi) for starting.
The only success i had so far was when the engine was flaming out of the other intake or the tail and I gave it some compressed air it detonates once with a pleasant "Pfomp" sound, but thats all.

My questions are:
Where should the end of the injector be placed in the intake (front, middle, all the way down)? If someone who has sucessfully run this engine could supply mesures that would be great.

I read that it may help to cover the other intake for starting. Should I just put some (wet) cloth in it? (Holding my gloved hand on seems to be no good idea. It gets very hot.)

Any tips and suggestion for the starting procedure are thankfully welcome.

Greetings

zohrke

[Mike Everman]

Welcome!
How about a picture while we wait for an answer?

[zohrke]

I am not too proud of the pictures, because of my poor craftsmanship. The welds look terrible Nevertheless I will upload the pictures here, but not before tomorrow morning (~ 10-12 hours from now). The reason for this is, that there is a baby asleep in the room where my laptop is. It took ages to get it to sleep and i dont want to wake it up now. And I cant upload the pictures on this computer, because it has no bluetooth.
So goodnight for now to everyone. (At least the ones in my timezone )

zohrke

[metiz]

I read that it may help to cover the other intake for starting. Should I just put some (wet) cloth in it? (Holding my gloved hand on seems to be no good idea. It gets very hot.)

zohrke

Don't know about your other problems but I can tell you that putting some sort of blockade in a intake will do wonders for your starting. I have a realy big engine with 3 intakes wich i could not even start with a hand leaf blower so i put a stick with a wet rag wrapped around it in one intake and this allowed me to get enough compression to start it right up. after it starts it just blows the stick and rag out of the intake and breaths 100% again

[GRIM]

Hi Zohrke , welcome ,
I am very pleased to hear there is another Thunderchine in existence,

I only have one run under my belt so far , second run pending, (soon) ,

I did have trouble starting this engine too , but that is normal for a new design , one has to find the correct combination of injector type, position , gas flow, air flow, and duct temperature ,

I used a 45 kg gas cylinder , 115 psi static gas pressure @ 30 deg C , no regulator just the cylinder fitting and a ball valve , 3/8 bore hose from the ball valve down to my manifolded injectors ,

The injectors (3 point style 5/16” od ) had 3 x 1.5mm holes drilled in each one , (total of 6 x1.5mm holes) ,
I had the engine running with the cylinder valve fully open , and there was no sign of a flameout ,

The injectors were situated 149 mm in from the flare, this is not necessarily the best place , but It will run with them there , see .pdf,

I used a small air compressor for starting , this had a ¼” od x approx 18” long copper tube fitted to the end of the air gun ,

I tried blocking one inlet and found it only increased the tendency to flame out at the tail,

I found that the air tube needed to be pushed into the inlet at an angle of approx 45 degrees , less than this it tended to flare from the other inlet ,

With the setup described above , the following is how I managed to get it to start, there is likely a much better way ,

I found that I needed to allow the compressor to build up to full pressure , give it about half air , open the gas slowly , there is a point where it will grumble, maintain this for as long as the air will allow , to get the duct hot , once the air pressure drops and it flames out, shut off the gas ,

Allow the compressor to build to pressure again , and repeat ,

There appears to be a critical temperature , once reached there is a definite “lock in” and you can immediately remove the air ,

My next attempt will be with a blower , waiting for the compressor is a pain,

From your post , I can say that you need a bigger gas cylinder ,
It is quite likely cold in germany at this time of year , your gas pressure will be much lower than I had , you may need to warm your cylinder,

You don’t say much about your injectors , a photo of them would be a big help ,

Good luck and video everything !

G

[HPSCL]

I'm new to this hobby, but have been thinking about fueling problems for the past few days...

Fluidity (for lack of a better word) is defined as the physical property of a substance that enables it to flow. The Thunderchine has two injectors, each "a 3 point style", with three 1.5mm holes drilled in each one.

If each one of the holes were drilled into a slightly irregular surface, the propane gas would not flow smoothly, out of that hole... Also, if each one of the holes were drilled at a slightly different angle from one another, gas would flow irregularly.

Using the same 5/16" O.D. tubing, a taper could be hand-formed (with a small ball-peen hammer) at the end of the tubing. The hole is made to be much smaller than your intended nozzle orifice size, then the end is filed flat. A single 3/32" hole would then be drilled in the end of the taper, or you could carefully work the hole to this diameter, using an awl.



The crude drawing above, depicts fuel-flow out of a possibly irregular 3-point system. It also depicts a theoretical improved flow, from a single tapered point... In a discussion on another forum (several years ago) we were throwing ideas back-and-forth about laminar flow;

Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. In fluid dynamics, laminar flow is a flow regime characterized by high momentum diffusion, low momentum convection, pressure and velocity independent from time. It is the opposite of turbulent flow. In nonscientific terms laminar flow is "smooth," while turbulent flow is "rough."

I read on this forum (somewhere?) that any disturbance in the flow of the incoming air, OR the exhaust, could cause a flame-out. The Thunderchine's injector setup, with the possibility of the orifice angles being slightly off from one another, along with the possibility of a slightly irregular surface (pinching three sides together) could (theoretically?) cause such a disturbance.

The Thunderchine's internal fuel-nozzle supports, could also slightly disrupt the air flow? I believe that if a tapered nozzle was used, with the end of the taper filed as flat and as close to a 90-degree angle the the outside walls of the tubing, as possible... you could be that much closer to "laminar-flow", out of the orifice.



I also believe that there could be a possibility, that the total nozzle diameter area could be a little too large? If you wanted to run the same 3-sided setup, try using a #55 drill bit (for each hole), instead of the larger #53, being currently used.- Or, as stated previously, as single 3/32" hole (close to a #42 drill bit) in a tapered-end... If anything, the smaller holes would (could?) generate a higher velocity at a given pressure, as the gas exits the nozzle.

[zohrke]

Hello everyone,

as promised here is the first photo of the engine.
Thank you all for you comments, I will try them today as I will make a second attempt to start the engine. Except for the tip with the bigger gas cylinder, as I am already quite broke because of this engine, and I have no money to buy a bigger one.
I will also try to make some pictures of the injector, which might be tricky, because it is already welded in. (But adjustable.)
To give you some info in advance of the pictures: The injectors are made out of brake pipes. The end of the brake pipe that is in the engine is left as it was. (Mushroom-like head with a single 1-2mm hole in it.)
Today will also be the last day that I can try the engine, since I will travel home tomorrow to where I study, and i dont have a workshop there.
So wish me luck, I will report back to you when I have snapped the photos/tried the engine this afternoon.

zohrke

[zohrke]

I quickly snapped a picture of one of the injectors and the "T-connection" of the injectors. The orange tube goes directly to the gas tank and the injector can be moved in the welded nut to adjust its position. (I pulled it out all the way for the picture.)

[milisavljevic]

Hello Zohrke --

The injectors are made out of brake pipes. The end of the brake pipe that is in the engine is left as it was.
Mushroom-like head with a single 1-2mm hole in it.

One immediate problem is this: assuming you have sufficient propane pressure, two orifice ports 1-2 mm
in diameter present at best 40% of the injector area required and at worst only about 10% of this area.

And your description of the propane bottle makes it clear that you probably don't have sufficient pressure.

Thus, if we further assume that your Thunderchine is reasonably close to spec, you may not be supplying
enough fuel (likely < 15% of ideal) to attain even a minimally stable running point: self-sustaining, at idle.

In brief: you need more injector area, much more.

For what it's worth (in light of the above), try positioning your injectors ca. 38-57 mm inside each intake.

Good luck with your studies!

Cheers,
M.

[zohrke]

Thanks for the tip with the ejector M. I have measured them now as it is still raining and I cant test the engine right now. They are 3mm inner diameter. If I understood you correctly the ideal injector area would be around 31 mm² which places me with two 3mm injectors at 45%. This really seems a bit problematic. What confuses me is that Grim is takling about 6x1.5mm holes which would give about 10mm² injector area. So from this it seems that 3mm are more than enough Nevertheless I will have to try the engine today (once it stops raining) with the fueling setup I have, as I have no time to get the material for some new injectors today. Instead of that I will try the injector setups proposed by M. and Grim and also covering the second intake. By the way the Gas Tank is labelled to have a Pi of 30 bar but I dont know if it can sustain that once the gas is flowing and the bottle cooling.

zohrke

[milisavljevic]

Hello Zohrke --

I corrected my post; hope you see the new numbers. If you have 3 mm ports, then you probably
have ca. 50%-60% of the injector area that you need. The six (6) 1.5 mm ports that GRIM had
are too small; he has already upsized these to 2.0 mm. My estimates also include the likely gas
pressure (range) in that small propane bottle once the valve is opened up; not an exact science!

Hopefully, you are able to put enough fuel into the pulsejet to warm it up and attain resonance.

Good luck!
M.

[milisavljevic]

Oh my, where to begin...

Fluidity (for lack of a better word) is defined as the physical property of a substance that enables it to flow.

I believe the word you were looking for is "viscosity"; however, its definition stems from a different perspective.

The Thunderchine has two injectors, each "a 3 point style", with three 1.5mm holes drilled in each one.

This is simply not true.

The specification for Thunderchine contains no fuel injection system, at all. The Thunderchine that GRIM
built has the injectors you have described...the difference between generalisation and specific instance.

I read on this forum...that any disturbance in the flow of the incoming air, OR the exhaust, could cause a flame-out.

Even if someone did post this here, it is pure FUD. If any disturbance could cause a flameout to occur, then
we could never hope to start pulsejets, much less run them. Disturbance is intrinsic to pulsed combustion.

That said, unnecessary obstructions/disturbances in the intakes are undesirable and can reduce efficiency.

And as you have noticed, here is a specific example of unnecessary intake obstructions:

The Thunderchine's internal fuel-nozzle supports, could also slightly disrupt the air flow?

Btw., Joe (GRIM) has already moved away from in-duct centering for his fuel injectors.

Now, for the sake of expediency, let's take the two following quotes and consider them together...

The Thunderchine's injector setup ... could (theoretically?) cause such a disturbance.

You could be that much closer to "laminar-flow", out of the orifice.

No. Centering tabs aside, the injectors used by Joe will not cause undesirable disturbances in the intakes.

We do not want laminar flow injectors. Pulsejets are not cutting torches or bunsen burners. The plume of
fuel vapour introduced into each intake must be thoroughly (and to the extent possible, homogeneously)
mixed with the fresh air "charges" transferred into the combustor during each cycle (approx. 170-180 Hz).

In the case of Thunderchine, its twin intakes can easily pump in air at rates of 1500 lbs per hour or more.

Which leads us to our conclusion by way of this comment, hidden behind a question mark:

I also believe that there could be a possibility, that the total nozzle diameter area could be a little too large?

The original set of six (6) 1.5 mm ports used by Joe (GRIM) were too small, once adequate accounting for
ambient temperature, decreasing bottle pressure and backpressure in the intakes was made. These ports
have subsequently been upsized to 2.0 mm, a tidbit not mentioned on Joe's build thread. Sorry about that.

Cheers,
M.

[zohrke]

Hi there everyone, I'm back from testing.
Bad news first: I could not get the engine to self sustain.
But it did sound a lot better when I put a wet cloth into the other intake. Then i could get the sound produced in this video. Which sounds very similar to how my small pulsejet sounds before starting up. (Without the cloth I only get the one-time detonation I mentioned above.) Maybe some of you with more experience can tell something from the video.
I think at the moment the most probable cause of not-starting are the too small injectors in connection with the propane tank, which result in not enough fuel beeing delivered to the engine. By the way the propane tank had already ice on it when I stopped testing.
So when I get at this engine again (Eastern Holidays) I will most likly try to build a new pair of injectors, like the ones Grim used.
Although I will not be able to test them right now I would be glad if you have any tips or thoughts after watching the video, please post them here, I will consider them for my next run.

And thanks for the great support so far.

zohrke

[GRIM]

Yes thats the grumbling sound , you are nearly there,
I agree the small propane tank and low pressure are likely the main problem , try to borrow a larger tank , and get it refilled ,

One thing that you might want to look at is the mounting of the engine , you really need to anchor it down good , or when you get it to fire , it will crash right back into that cage ,

I should get another run or two in before easter, I will post as much info as possible,

Great try , dont be disappointed , this is a big step up from a Fwe ,

G

[zohrke]

Yes thats the grumbling sound , you are nearly there,

Really glad to hear that. I really hope I will get this beast running eastern, maybe then there will already be new information from other test runs available.
And considering the mounting of the engine: It is not just put on the ground and weighted with the stone and train track, as it may appear on the pictures. It is also bolted into the ground with different 20-60 cm rails which cant be seen because they are on the other side of the engine under the combustion chamber or concealed by the front mount. Safety first!

And by the way I am not dissapointed at all, as I have hope this engine will run, thanks to you.
In fact I cant wait to fire this thing up again.
Again, thanks alot for instructions and support!

zohrke

PS: For whoever is interested here is a video of my first engine running (Eric Becks FWE): http://www.youtube.com/watch?v=y1zEgRgm14Y