Cant start pulse jet

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Pulse_Man
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Cant start pulse jet

Post by Pulse_Man » Thu Jul 13, 2017 4:23 am

Ive built this pulse jet at my school work shop and was testing it today and i couldn't get it to start. im not sure what im doing wrong. it runs on propane and then i use a small leaf bower to try and start it. i cant seem to get it going. any help would be so helpful. heres a video of the test run https://youtu.be/d76tePxCKls

PyroJoe
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Re: Cant start pulse jet

Post by PyroJoe » Thu Jul 13, 2017 9:18 pm

Looks like the tail is a bit short. It might be helpful to look at the topic in the Valveless section called 'PyroJoes Recipe for Beginners'. I put that up to help show what dimensions are likely to work, and to help out folks new to the pulse jet experience.

As always, happy combustion!

Mark
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Re: Cant start pulse jet

Post by Mark » Thu Jul 13, 2017 9:33 pm

I was thinking the same thing, a longer tail - more confinement.
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Pulse_Man
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Re: Cant start pulse jet

Post by Pulse_Man » Fri Jul 14, 2017 3:55 am

So i increased the length of the tail pipe from 22cm to 77cm and i managed to get two separate bangs from it but nothing more. im not sure what im doing wrong..

PyroJoe
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Re: Cant start pulse jet

Post by PyroJoe » Fri Jul 14, 2017 2:02 pm

Bangs are a good thing, and it can take over half a minute of fire to heat the tail up to running temperature.
I don't think it's a matter of doing right or wrong. What we see is that there are sets of dimensions that lend themselves to resonant combustion. Size, shape and length of the resonant chamber(usually called the combustion chamber). Size, shape and length of the tail pipe, (tail pipe works as an inertial air pump). The diameter ratio of the intake to the tail pipe for aerodynamic valving. Length and flaring of the intake pipe. The recipe helps to show where things can be adjusted.

Those are the important ones. Looking at the video, it may become important to look at the propane source, it takes considerable fuel to keep up with the rates of consumption.

If we had some current dimensions I could probably work out some adjustments if needed.

Mike Everman
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Re: Cant start pulse jet

Post by Mike Everman » Fri Jul 14, 2017 5:24 pm

Lengths and area ratios must be in a range, intake almost always needs a flared inlet. When using a leafblower, farther away from the intake is best. wave back and forth in various amounts of dead-on. It may be just the little fringe of the blower stream going in from a foot away. When you push it right on there it will only make a blowtorch.
Then there is fueling and where you put it. what have you done there?
Mike
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Pulse_Man
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Re: Cant start pulse jet

Post by Pulse_Man » Sun Jul 16, 2017 12:09 am

so you reccomend that i let it run for a little bit to warm up the tail pipe. anything else??

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