Pulse Jet Engine: Project Diary

Pulse Jet Project Diary

Updated: 23 January 2001
In response to the number of emails I'm receiving from people who have designed their own pulse jet or built one from the many plans that are available on the Internet and are having trouble getting it to run I have added The Pulse Jet Troubleshooting Guide and an explanation describing how these engines actually work.
Updated: 22 January 2001
I have just completed the latest prototype of the 45KG (90 lbs) thrust pulse-jet engine and given it its first run.
The power output seems to be a little more than was predicted and it has excellent starting and throttling characteristics. I hope to post some pictures and video to the site in a week or so.
I will also be fitting it to the gokart which is currently nearing completion. Many visitors to this site have asked how fast a gokart with such an engine would go -- we will soon find out!
Also note that due to the astonishing demand (which presently exceeds my capacity to manufacture them) for the pulse-jet kits I will shortly be offering plans and instructions for people who are prepared to build their own engines from scratch and have (or have access to) the necessary equipment. Included will be a CDROM containing the plans, documentation and about 20 minutes of video in MPEG format, showing the construction and operation of these engines.

My First Pulsejet Project
Note: This material was written shortly after I had set up my workshop and was just getting to grips with the skills and techniques required to build these engines.
Not having had any formal training in metalworking or engineering, this meant I had a steep learning curve ahead of me. Fortunately, almost two years later, I'm now significantly more competent and capable in this area.
Updated: 16 October 1999
Horray! At last I've fired it up and got the bugs out of it. You'll find the details of my test-bench and final assembly on this page.
There'll be another installment shortly when I hope to add the streaming video and talk about the next version -- which will be bigger, louder and hopefully -- a constructional project with plans for those who want to also build one of these really interesting little engines.
Updated: 26 September 1999
The front end of the engine is now almost complete. I have cut out the reed valve, turned up a retaining washer/seat and tapped the hole in the back of the venturi section to accept a 4mm hex-head machine screw that holds it all together.
More details of this part of the project can be found on the reed valve page
Note that I'm going to re-organise this site a little so as to put each weekend's work on a separate page to avoid ending up with pages that are so large they take ages to load.
In the meantime, please feel free to tell me what you think of the project and this website. I'm always keen to hear of good ideas as to how I can do a better job of either. Just drop me a note.

Updated: 18 September 1999
Today I finished turning up the body of the intake assembly -- a process which involved center-drilling and tapping the back face so that the intake reeds and retainer can be bolted on.
The front-end of the intake body has a tapered hole which creates a venturi section where the fuel jet will sit. The initial size of this air-intake hole may be a little small for maximum power but I've decided to err on the side of better fuel draw by having a higher air velocity through the venturi.
Once I have this version of the engine running I'll be playing around with the construction of a tuneable intake venturi and a throttle.
I also turned down a lip on the intake by the wall thickness of the combustion chamber tube so it will fit inside. The intake assembly will be affixed to the combustion chamber by 4 machine screws around the circumference which will screw into tapped holes.
More pictures of the intake body can be found on the components page.
The combustion chamber is of a larger diameter than the exhaust tube so it becomes necessary to create a tapered section to match the two tubes.
I had considered using a separate piece of stainless sheet to make a funnel section to join the two tubes but decided this was too much work so I simply cut some triangular slots in the back end of the combustion chamber and I'll try to form this in to a tapered section -- welding along the seams that it creates. Not pretty -- but quick and functional (I hope).
Tomorrow I hope to MIG up the stainless sections and start work on the reed-valve system.

13 September 1999
After fixing my lathe I trued up both ends of the aluminum rod that is to be the intake venturi and reed-valve seat.
I marked and drilled the eight holes which carry the air-fuel mixture into the combustion chamber.
These holes were drilled at a 30 degree angle -- a procedure I was not too sure about because I thought the drill might wander a little when addressing the face of the work so far off-square.
The method I finally used was to punch the hole positions then lightly counter-sink the punch-marks with a drill perpendicular to the surface before rotating the table of the drill press to 30 degrees and drilling the pilot holes. The final 6mm holes were then drilled to a depth that meant they all joined up at a focal point in the center of the bar.
You may note the lack of measurements at this stage -- I have to admit that when I'm designing and developing I tend to fly by the seat of my pants and use the "looks about right" technique for deciding on dimensions. I can hear you cringing from here :-) Rest assured that I do carefully measure things when it's necessary to ensure that holes line up and components fit together though.
I'll go back and measure things when I know it all works so as to provide those interested in building their own pulse jet with a set of working blueprints.
Please remember I'm new to this stuff so if you have any comments or criticisms about the methods or techniques used then please feel free to throw them at me.
Later this week I hope to finish this part of the engine by drilling a hole from the other end of the unit to join up with the eight intake port holes then turn that out into a venturi on the lathe.

September 12
Today has been very frustrating! My lathe has been behaving erratically for a few weeks and just as I sat down to turn up the aluminum intake venturi and reed-valve seat/retainer for the pulse jet, the damned lathe stopped completely.
As you'll see from the accompanying picture -- I have delved into the atrociously constructed electronics of the beast and found the relay to have an open-circuit winding. And, wouldn't you know it -- amongst the myriad of boxes of electronic componentry accumulated over the last 20 years I don't have, a double-poll 20K ohm, 220V relay so that puts an end to this weekend's construction work.
I guess I'll just go back to work and try to claw back the hours mid-week once I've had a chance to get a replacement.
Oh.. but I did get around to unpacking and assembling my new drill press and it's a beauty. Not even Chinese! (unless the Republic of Taiwan counts :-)
I also took a few minutes to update the links page with some more interesting sites.
5 September 1999
Today I put up the first incarnation of this web site after taking some pictures of my bits and pieces using video captures from my Sony handicam.
Start here I've also collected all the raw materials (right) I think I'll need and started clearing the junk off my workbench. Given the nature of this project I also checked that my fire extinguisher was fully loaded and ready for the operational trials.
I've collected together the following materials at this stage:

2.5" dia stainless steel tubing. This will be used for the combustion chamber and was obtained from the local exhaust and muffler shop. It's seam welded but I hope it will be strong enough. I notice that some of the other pulse jet plans on the Net have seam welds in the construction of their tubes so -- fingers crossed.

1.5" dia stainless steel tubing. This will be the tailpipe section.

Stainless sheet. I may use this to fabricate the conical shaped section that connects the combustion chamber area to the tailpipe -- or I may simply put some triangular slits in the tail-end of the combustion chamber pipe and then weld the fingers created so as to provide a tapered end. Any suggestions?

2.5" dia aluminum rod stock. This will be drilled and turned to make the intake venturi.

0.006 shim steel. I had a hell of a lot of trouble finding this stuff -- it seems that everyone "used to stock it" but I only found one place that still had the stuff on the shelf. This will be used to fabricate the intake reed valves.

3/8" dia Brass rod stock. This will be used to build the fuel jet and metering valve that sits in the venturi ahead of the reed valves.

1" dia steel rod stock. I'm not quite sure yet how I'm going to affix the spark plug to the combustion chamber but at this stage I'm thinking I'll probably turn up a threaded tube that will be welded(?) into the combustion chamber and into which the plug will screw. Does anyone know how well stainless welds to plain steel with a MIG?

I also have some lumber to build a test stand and a plastic fuel tank and flexible plastic piping to connect it to the engine. I will probably add some kind of thrust measuring facility to the test stand using a spring and graduated scale.
Unfortunately labor day here in New Zealand isn't until late October so I don't have the benefit of a holiday weekend to do much more on this project today -- and it's now late Sunday afternoon so you won't see any additions to this page until next weekend.