pulse jet fever

1fastneonrt · Post by **1fastneonrt** » Tue Jan 15, 2008 8:41 am

Hello everyone in the pulse jet world; well where to start. I have been fascinated over pulse jets for some time now. I know the general concept of how they work and I think that it's amusing. With that said I am under way in making the advanced fwe according to the free plans by http://www.beck-technologies.com/freeplans.html. So far I have made a paper mock-up of the engine, which is pictured below. I have got my templates made and should be welding one up here in a couple of days.

Now onto my next creation which is ugly. I wanted to experiment a bit so I built an "ugly stick" pulse jet. The dimensions are based on (I think) acoustical lengths of the intake and exhaust pipes, for i.e. - Exhaust dia. is 1/2 of CC dia. and intake length is 1/7 of the over-all acoustic length etc.....but theres a problem!
I had to use what was available to construct the engine, which doesn't match the mathematical equations that I came up with.

O.K. my dimensions for my engine goes as is (picture below):
CC dia.: 1-1/2"
CC length (from front plate to rear bell): 4-1/2"
Intake dia.: 3/8 sch. 40
Intake length: 3-3/4"
Exhaust dia.: 1/2" sch. 40
Exhaust length: 18"

The engine is being fueled by a rosscojector straight from a 20lb. propane tank. I tried fueling the engine through the intake with no luck. I then tried to fuel it by directly injecting the fuel into the CC, which seemed to worked better. When I introduce a little fuel, air, and spark all I get out of it at first is a few loud pops and bangs similar to rapid gunshots. If I give it a little more air, it will start to rumble, add a little more fuel and rumbling gets a bit louder. Now if I take the air supply away the engine quits rumbling. I have noticed that if you leave the air supply on and let it continuously rumble, the end of the exhaust pipe gets red hot. I am just looking for some insight and pointers so I can get this engine to self-sustain if possible.
Sorry guys for writing a bible here but I thank you for reading and helping out.

larry cottrill · Post by **larry cottrill** » Tue Jan 15, 2008 7:59 pm

1fast -

Everyone will say I always fall back to harping on this, but here goes anyway: I think you are probably feeding too much air. You're running as a forced-air burner; the red hot zone is where mixing is complete enough for combustion to happen.

Try advancing the fuel up very slowly as you gently "puff" the air into the intake. Yes, you will get some pops and bangs, but as you increase fuel flow and get a feel for the right air input, you'll likely hit a zone where real pulsejet action will occur. Of course, that doesn't guarantee it will sustain, because the tuning of the lengths has to be very close for that to happen. But at worst, you'll have a good idea of what starting should be like. And at best, she may take off and run!

Good luck!

L Cottrill

Vermin · Post by **Vermin** » Wed Jan 16, 2008 12:21 am

Larry is right
start with small air and small fuel then build up from there......
V

1fastneonrt · Post by **1fastneonrt** » Fri Jan 25, 2008 8:44 pm

O.K. thanks for the advice guys; I'll have to give it a try. While in the mean time I had just finished welding up my Advanced FWE out of some 16ga. mild steel. I've got some final sanding to do and I've got to fix some small holes. In the pictures below the silver tape on the intake tube is covering up some small burn through holes from welding. I had just enough propane left to get the engine to run for about 5 seconds. Boy what a loud little thing it is though. Also in the photos you can notice the discoloration of the steel from the short test run. After I finish sanding and fixing the small holes I will post a video of it running.
One question I have is - "What is the average temperature in the CC of a pulse jet"?
The reason being is that I would like to use a ceramic coating on the inside and outside of a pulse jet. The ceramic coating would act like a thermal barrier so you could have longer static runs on engines constructed of mild steel. Basically I am looking for an alternative for stainless steel.

Jutte · Post by **Jutte** » Sat Jan 26, 2008 2:05 am

Nice!

Jim Berquist · Post by **Jim Berquist** » Sat Jan 26, 2008 2:15 am

Wow, Good start!

C.C. temp could be dependent on all kinds of factors, Fuel used, Engine Design, Size, Materials used. Static or other wise ! Expert I are Not.

Look around in TOOLS AND CONSTRUCTION! Some one even built one out of ceramics one time. Don't know if he followed up on it or not.

http://uk.youtube.com/watch?v=aO7uRjez_vY

1fastneonrt · Post by **1fastneonrt** » Sat Feb 02, 2008 7:17 am

Thank you guys, I'm glad you like it. Yes berquistj I have seen that particular ceramic pj on this forum before. I think he made a Lady Ann Boleyn all out of a ceramic material and or clay. What I want to use is a "ceramic coating" that is applied much like how a powder coating is applied. I know they use ceramic coatings in and on car headers, cylinder heads, piston, and valves. Basically I would be putting a ceramic-coated paint job in and outside of the PJ.
Now for the good news, at the moment, I finally got some propane and went out to run my engine but walked away shaking my head. I for some odd reason cannot get my pj to run properly. Below is some video footage of the engine running or aahhhhhh at least doing something. The engine isn't very loud; it much resembles a torpedo heater in noise level. Is it running properly, that is the question?

Oh let me see, ah well I start the engine by igniting a little bit of propane at the intake (no spark plug). I increase the gas slightly till it starts to rumble, and then it pretty much does what it does in the videos. I try to blow some air into the intake but all that does is extinguishes the flame. I am using a 30psi max regulator (set to max) along with a rosscojector. Any ideas will be very appreciative. I think the cure is to mess around with it some more till I get it right. Thank you guys

Mr.B · Post by **Mr.B** » Sat Feb 02, 2008 1:20 pm

Get rid of the fuel regulator!!!!
Really.....

Post by **Mike Everman** » Sat Feb 02, 2008 3:27 pm

Yeah, lose the regulator, you've got the perfect fitting on your tank. Use the tank valve with a very light touch. Also, very very easy touch on the air for starting. Look to the Faq for starting tips.

1fastneonrt · Post by **1fastneonrt** » Sun Feb 03, 2008 2:46 am

OH really lose the regulator. O.K. sounds easy enough, can I still use the needle valve for thottle-bility? Also I was wondering, should I still use a crimped fuel line (a rosscojector) running into the engine with that 3/16" brake line. I have seen some where on the forum that someone was running their engine on a straight open piece of 1/8" tubing.??? HHMMM
But yeah I will toss the regulator and go ahead and give it another try. Thanks

Post by **Mike Everman** » Sun Feb 03, 2008 6:10 am

A straight 1/8" tube will probably work in the right place. You may not get enough fuel through a 3/16" rossco without opening it up a good deal.
Your needle valve may be fine, tough to say.

1fastneonrt · Post by **1fastneonrt** » Mon Feb 04, 2008 12:44 am

Yes yes yes yes yes thanks guys for all your help. I finally got my engine to run today. WOW that thing is absolutely loud. HA HA all the dogs in the neighbor hood had finally shut upped once I fired up the engine. I was a amazed by the size of the flame or jet coming out of the intakes though. I have seen other pictures and videos of engines that have a small flame or jet coming out of the intake. I guess it must be injector placement or the design of my engine. All I did was tossed the regulator, opened the up injector a little, and put the injector 2.5" down the intake. It seems to take abit of air to get it to run, though I am only using a raft inflator with a coned nozzle. Below are some pictures and later tonight I will post up a video of the thing running. Once again thanks for your help. I must say this is the beginning of a fun adventure. Hehehehehe

Eric · Post by **Eric** » Mon Feb 04, 2008 1:10 am

Nice build.

You can get a little less flame out of the intake with a deeper injector placement but you'll pretty much always get a flame out of a FWE on full throttle.

Eric

Post by **Mike Everman** » Mon Feb 04, 2008 3:59 am

Congratulations! That color gets addicting, you know...

1fastneonrt · Post by **1fastneonrt** » Mon Feb 04, 2008 5:38 am

Well here you go. Here is the video.
If you notice in the pictures the test stand is buried a little in the gravel. On the first run it was just sitting on top of the gravel. This little engine was rocking and moving the stand forward at a rate of 1 inch every 30 seconds. I must say that the stand weights at least 5lbs. without the engine attached. I don't know, but I think that is pretty impressive. Yes it does Mike, almost like candy. I can see the mild steel is starting to take a beating though - next one STAINLESS.

*The video is longer but I had to shorten' it up to put it on the forum.