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new engine won't run

Posted: Sat Aug 29, 2009 8:40 pm
by metiz
I'm getting a bit frustrated here. I've build 3 prototype engines with the sole purpose of selling the finished product. The engine itself is very simple. It consists of a SS cup, store bought, a flat front plate and an intake and exhaust that share the same D, made from a pipe.

Because of its simplicity and easy of construction, I can build one rather quickly and consequently sell it at a VERY low price. The engine is made for easy starting with a build in Rossco. each engine will be delivered with a cheap ignition circuit. It's also small enough to run with flow restrictor and can be started with a small airpump

At least, that was the plan.

I have made 3 engines now, 1 being the first and 3 being the current and I can not get then to run properly. The first one requires great effort to start and will only sustain on forced air. the second one will run but is still a pain to start. the third one, wich i made today, does not run at all, just a lot of machine gunning.

I have used the same Rossco on all the engines with all positions thinkable from 20mm outside the intake to 60% in the intake. the slit is 1mm, the fuel line used has an external D of 5mm and an internal D of 3mm.

The plans of all the 3 engines are posted below.

So what's the problem:

Something wrong with the geometry of the engine?
Rossco slit to big?
Rossco slit to small?
Rossco not neccecairy? (I want easy starting)

If anyone can give me some help here, that'd be great. I'm getting realy pissed here.

Re: new engine won't run

Posted: Sat Aug 29, 2009 11:49 pm
by vturbine
Looks like a draft engine sort of.

If it's anything like mine, longer tailpipe, shorter inlet by about 1/3, and try one size narrower insert tube in the inlet to choke it down.

Injector was Grim's three point coming through the corner of the plate/CC junction at about a 40 degree angle from the plate. Just barely in the CC. Your CC Joint is not as far away from the inlet so might be even more finicky. If you used a smaller ID inlet, you'd have a little more room.

Try propping the engine up vertical first, like a draft engine for as much assistance as you can get.

Please ignore all of this if someone with more experience says otherwise! :)

Re: new engine won't run

Posted: Sat Aug 29, 2009 11:59 pm
by vturbine
Okay I see you have different dimensions on each of the three.

So if it was me I'd try a 21 mm inlet, say 65 mm long, and a 25mm exhaust, say 500 mm long.

Or, whatever anyone else says, who knows more!

Re: new engine won't run

Posted: Sun Aug 30, 2009 1:37 am
by Jutte
The smaller engines I have made were the worst to get going.
I found that 10mm either way could really screw things up.
What I found helpful was the sliding bigger pipe trick - to get
a sort of adjustable tail pipe.
Just glancing at your one metiz - I think your tail pipe
could be too short and too small dia - ( don't take that as gospel ).
I have made some smaller pulse jets with ridiculous length tail pipes - way longer
than I thought - and it was only desperation that I tried the longer lengths.
Apart from that - cut and weld ( nice welds by the way) until you get it
going - good luck.

Re: new engine won't run

Posted: Sun Aug 30, 2009 4:09 am
by Eric
Where on earth are you getting thick wall stainless pipe cheap? If you got a bunch as scrap, you'd probably be selling the finished engine for not much more than the value of the pipe.

Re: new engine won't run

Posted: Sun Aug 30, 2009 8:31 am
by metiz
Eric wrote:Where on earth are you getting thick wall stainless pipe cheap? If you got a bunch as scrap, you'd probably be selling the finished engine for not much more than the value of the pipe.
I get all my SS from the scrapyard. 2.50/ kg. sometimes I'm in luck. I bought a long pipe, good for 5 or so engines for about 14 euro's

Re: new engine won't run

Posted: Sun Aug 30, 2009 8:32 am
by metiz
Eric wrote:Where on earth are you getting thick wall stainless pipe cheap? If you got a bunch as scrap, you'd probably be selling the finished engine for not much more than the value of the pipe.
I get all my SS from the scrapyard. 2.50/ kg. sometimes I'm in luck. I bought a long pipe, good for 5 or so engines for about 14 euro's

Re: new engine won't run

Posted: Sun Aug 30, 2009 8:34 am
by metiz
double post.

Re: new engine won't run

Posted: Sun Aug 30, 2009 8:36 am
by metiz
That said I need to use the 22mm pipe on both intake and exhaust if possible...

Re: new engine won't run

Posted: Sun Aug 30, 2009 1:11 pm
by milisavljevic
Hello Metiz,

As promised, I have re-dimensioned your pipe-jet into a running configuration, but be warned:
your choice of materials and offset combustor layout result in a product that is basically a toy.

Here are the dimensions you need to use; please follow them closely:

[1] intake ID 22 x length 112 mm (length includes an ID 31 mm flare)
[2] combustor ID 60 x length 64 mm
[3] tailpipe ID 22 x length 821 mm (yes you read that right: 821 mm)

These dimensions will look off to you, but you want an engine that runs, right? This is a runner.
Yes mate, a runner! If built to these dimensions, it will develop 454 grams of thrust at 236 Hz.

As for fueling, stick with a rosscojector for the moment; position the tip about 30 mm inside.
metiz wrote:I can build one rather quickly and consequently sell it at a VERY low price.
Please do not ask for more thrust, not from this arrangement. We always get what we pay for. :wink:

Cheers,
M.

Re: new engine won't run

Posted: Sun Aug 30, 2009 1:19 pm
by metiz
milisavljevic wrote: Please do not ask for more thrust, not from this arrangement. We always get what we pay for. :wink:
Cheers,
M.
hehe thrust was never an objective for this engine and 450 grams, or just about one pound, is exactly what I bargained for. I'll try the mods on the last prototype, Thanks M. The rather long tailpipe will force me to up the price by about 5 bucks though :)

*edit*

Wow, that IS long.... Is it because of the large D pipe? I did get a 21mm pipe engine running with roughly the same dimensions as the 2nd drawing a couple posts above

Re: new engine won't run

Posted: Sun Aug 30, 2009 1:35 pm
by milisavljevic
Hello Metiz,
metiz wrote:The rather long tailpipe will force me to up the price by about 5 bucks though.
I tried to give you a shorter tailpipe, but the Helmholtz modes were just too far out of synch.

I would appreciate you posting a video clip of the running engine for my, ahem, "payment". :D
And when you do that, be sure to provide the ambient temperature and test site elevation.

Cheers!
M.

PS: With you living in the Netherlands, I would guess your elevation is essentially sea level... :wink:

Re: new engine won't run

Posted: Sun Aug 30, 2009 1:47 pm
by milisavljevic
.
I missed this question:
metiz wrote:Is it because of the large D pipe?
The pipes are too small for the combustor you have selected. That, and you need a tailpipe expansion.
With an expanded tailpipe, the length comes down dramatically; but I know this is out of the question.

The "long-gun" configuration I gave you should run out well and with good throttle range and response.

Cheers,
M.

Re: new engine won't run

Posted: Sun Aug 30, 2009 6:33 pm
by ace_fedde
milisavljevic wrote:Hello Metiz,

.... be sure to provide the ambient temperature and test site elevation.

Cheers!
M.

PS: With you living in the Netherlands, I would guess your elevation is essentially sea level... :wink:
Would a negative elevation be a problem for your calculations? :lol:

Fedde

Re: new engine won't run

Posted: Sun Aug 30, 2009 7:28 pm
by metiz
yeah it's so freaking wet here all the time that you'd almost expect to be UNDER sea level :P

I'll just give barometric pressure then, see if that works....Also, M, don't take this as an insult but I´m going to try to lengthen the pipe on the existing engine incrementally firts - that tailpipe just looks so off! If I still don't get results after 2 or so attempts, ill increase to the 82cm specified and bolt the tailpipe onto yet another prototype. Good thing they are so easy to make :)

If I do get result, I'll ofcourse post the dimensions and the temp/elevation/ video of it