new build with problem

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ddun
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new build with problem

Post by ddun » Mon Dec 01, 2003 11:15 pm

Hello,

I just tried to run a new valveless engine that I completed this weekend. It is an Escopette design with a 1"dia. chamber, a 0.75"dia. tailpipe 12" long and an intake 0.500"dia.
The problem I am having is with a blower on the intake the engine gives one report and then it turns into a bunsen burner with the primary flame in the combustion chamber and the secondary forms a large torch out the tailpipe. After each try the results are the same, after the first explosion the engin turns to a burner. I have experimented with adjusting the gas density (flow rate) and either it is too lean and I do not get ignition or once I get a report in a higher gas flow the flame is simply larger.
I have ran out of ideas. Does anyone have any ideas as to what to try next. Is there a design flaw or am I overlooking something. This is my first try at a valveless construction.

Thanks for any help.

hinote
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Re: new build with problem

Post by hinote » Tue Dec 02, 2003 12:17 am

ddun wrote:Hello,

I just tried to run a new valveless engine that I completed this weekend. It is an Escopette design with a 1"dia. chamber, a 0.75"dia. tailpipe 12" long and an intake 0.500"dia.

I have ran out of ideas. Does anyone have any ideas as to what to try next. Is there a design flaw or am I overlooking something. This is my first try at a valveless construction.
It's too small. There's a lot of support on this forum for tiny pulsejets, but they are VERY difficult to get to run properly. You are below the smallest limited previously published for success with a PJ.

Furthermore, you CAN'T just scale down an exisitng design--it won't work.

Look back through this forum for discussions about the subject.

OK Mark, I know you're going to chime in here--but let's give the guy a reasonable chance for success, OK?

Bill H.
Acoustic Propulsion Concepts, Inc.

Graham C. Williams
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Post by Graham C. Williams » Tue Dec 02, 2003 12:20 am

Hi.
where do you have the fuel injection? Drawing please.
What is the fuel?
Graham

Bruce
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Post by Bruce » Tue Dec 02, 2003 2:07 am

If you end up with a bunsen burner then obviously the fuel and air inside the engine are not mixing into a stoichiometric ratio properly.

This can be:

a) insufficient air (to much fuel)
b) insufficient fuel (too much air)
c) improper mixing (inadequate vaporization)

Work out which the problem is and then fix it.

Once you've done that, and providing your dimensions are roughly correct, it should run in pulsating combustion mode. If your dimensions aren't quite right it may not do so without continued forced air -- but at least you'll be on the way.

Mark
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Re: new build with problem

Post by Mark » Tue Dec 02, 2003 2:57 am

[quote="ddun"]Hello,

I just tried to run a new valveless engine that I completed this weekend. It is an Escopette design with a 1"dia. chamber, a 0.75"dia. tailpipe 12" long and an intake 0.500"dia.
The problem I am having is with a blower on the intake the engine gives one report and then it turns into a bunsen burner with the primary flame in the combustion chamber and the secondary forms a large torch out the tailpipe. After each try the results are the same, after the first explosion the engin turns to a burner. I have experimented with adjusting the gas density (flow rate) and either it is too lean and I do not get ignition or once I get a report in a higher gas flow the flame is simply larger.
I have ran out of ideas. Does anyone have any ideas as to what to try next. Is there a design flaw or am I overlooking something. This is my first try at a valveless construction.

What are you using for fuel, propane? If so it is exceedingly tricky to get it to MIX well on a small scale, just as gasoline or ether is. The window of opportunity is smaller for it to run, even mixed with air, propane has a more demanding critical ratio, than with methanol which will burn lean or rich on a much wider scale and is forgiving.
Somehow you have to get it to mix with air just right and then hope you can maintain that ratio from starting to running. I made plenty of flaming flames with my small 3/4 " diameter Logan with propane but never could get it to burn inside because mixing it just right with air inside the chamber is essential and if you don't preheat it with a regenerator and mix it with air, it just kind of streams out the tail in a billowing long flame, the flame won't wolf down the tube. A larger jet would be more forgiving too.
Mark

Mark
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Joined: Sat Oct 11, 2003 10:14 pm

Re: new build with problem

Post by Mark » Tue Dec 02, 2003 3:09 am

[quote="Mark"][quote="ddun"]Hello,

I just tried to run a new valveless engine that I completed this weekend. It is an Escopette design with a 1"dia. chamber, a 0.75"dia. tailpipe 12" long and an intake 0.500"dia.
The problem I am having is with a blower on the intake the engine gives one report and then it turns into a bunsen burner with the primary flame in the combustion chamber and the secondary forms a large torch out the tailpipe. After each try the results are the same, after the first explosion the engin turns to a burner. I have experimented with adjusting the gas density (flow rate) and either it is too lean and I do not get ignition or once I get a report in a higher gas flow the flame is simply larger.
I have ran out of ideas. Does anyone have any ideas as to what to try next. Is there a design flaw or am I overlooking something. This is my first try at a valveless construction.

Where did you get the design? I would think the exhaust tube is too wide or a little short in proportion to the combustion chamber if it is a straight tube 12 inches long. And you could choke down your intake tube a fraction too. That may confine the pressure waves enough to build a feedback. I've toyed with a lot of small valveless shapes, days on end. You just have to play around and you start to get a feel for probabilities. Just keep at it and eventually you will find something.
Mark

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