Operation micro Thermojet on liquid fuel!

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mag
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Operation micro Thermojet on liquid fuel!

Post by mag » Sun Dec 05, 2010 9:20 pm

Hi folks, it´s quite a long time I have been around here but time did not permit me to build any pulsejets for a long time. Maybe the old forums members will remember me!

But last week I got infected again by the noise virus and decided to put a small thermojet together! Now the project, I want this to be used for a small RC plane! It run´s very strong on propane vapor but this is not suitable for RC need´s as you all know.

So I started experimenting with a liquid fuel supply. I made a vaporiser coil as seen in the pic and a tank which i can pressurize! I use a clamp on the hose to adjust the flow which works very well from a drop per minute to shooting out diesel 4m wide... ;-)

In the pic the injectors for the diesel are pinched and located in front of the intake, this position has not been tested yet.

I tested the injectors inserted through the intakes so they are located directly at the end of the intakes.

When starting the unit on propane it starts very easy and I regulate the propane down so it´s idling very slow. When I now switch on the diesel supply very slowly the engine starts to run strong for very short bursts and after that it stops self sustained running! I also did a test with gasoline but this does not work, vaporates too fast and not smooth enough.

Now the big question! Any suggestions on what to try? I know that running these small valveless on liquid fuels might be a PITA but it must be possible. The engine want´s to run but just does´nt on it´s own. I´m sure it´s just a small adjustement that it´s needed but I can´t figure out what to do.

Any help appreciated!
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Jutte
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Re: Operation micro Thermojet on liquid fuel!

Post by Jutte » Mon Dec 06, 2010 7:47 pm

Hi Mag,
"..switch on the diesel supply very slowly the engine starts to run strong for very short bursts and after that it stops self sustained running"

OK - it could be that the engine is using up the fuel in the heated vaporiser coil (think of it as a fuel tank ) -hence the 'very short bursts' running -it drains the vaporised fuel then the next flow has to be heated up etc .Perhaps just as it really starts to get going the unvaporised fuel floods the combustion chamber and it stops.
Try making a longer ( or thicker vaporiser coil ) - to in effect a big "fuel tank".Just be cautious that with a bigger vaporiser coil the engine will still run a little while after you turn off the fuel at the primary tank - as there will fuel in the vaporiser coil to burn out.
Some where here on the board there is a similiar thermojet but it has an outer vaporiser shell completely covering the combustion chamber. That engine seemed to run alright - so perhaps a bigger vaporiser coil could remedy the problem.

OK Mag just my two cents worth - I hope it helps.

mag
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Re: Operation micro Thermojet on liquid fuel!

Post by mag » Tue Dec 07, 2010 9:12 am

That may be possible! The coil now is 50cm in length and when the engine stops runinng vaporized diesel is coming out of the nozzles fo around 10 sec´s! (quite a lot of white fog in the shop... hehe).

I have a slightly bigger brass pipe here which I will turn into a bigger volume vaporizer! I´ll give it a try and let you all know!



Regarding the injection position, where is it best? For propane I found it best to be just at intake level. Any recommendations?

The engine realy is quite small and I think that this maybe is a problem, even though it starts easy and runs well on propane! (the plug is a CM6 size NGK, so you can estimate size!) On full power this engine is loud as hell, i´ve thought that an engine this small is not so loud but the noise don´t allow me to test it like I want, just from time to time when the neighbours are gone... ;-)


Could you provide me a link to the other engine?

Greets, Mag
Trust me, I know what I´m doing... o_O

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