I've been learning to TIG weld now for a few months. Most of the welding done in class is on 6 inch strips of metal [mild, stainless, aluminum]. I want to venture a little, so I've come up with a project of my own - I'm going to build a pulse jet engine.
I'm following the Lockwood Hiller design, and drew up the plans right from the patent. I'm going to build a small one, as creating tons of thrust isn't important to me right now - I just want to see if I can get the thing to run.
The limiting factor on how small I can make it is the size of the mandrel bend - the smallest I could find in 304 SS is 1.5" 16 gage]. From this I drew up plans in SolidWorks and made a 3D model. I'm going to purchase a sheet of .020" thick 304 SS to make the rest of the engine from. I am experimenting here - the material may be too thin, but I have NO way of bending 16 gage stainless if I purchased it to match the thickness of the mandrel bend. The overall length is about 3 feet.
Materials are going to run me around $80-$100 probably. I will probably use LPG for fuel. I have no idea how to build a 555 timer circuit, but I'm going to scour the net and see if I can put one together for the cheap. Another thing I'm having difficult with is the bung for the spark plug - From what I gather the typical Honda plug has a thread size of M14 x 1.25 mm - I can't find any nuts of this size on McMaster-Carr. Does anyone know where I can find a nut this size or probably even better an alterntative spark plug and its thread size?
I ended up going with a different spark plug with smaller threads and found a jam nut to match those threads so now I have a spark plug bung. I'm using either a D8EA or a CR7HS NGK plug - the threads on the D8EA are M12 x 1.25 mm, and the threads on the CR7HS are M10 x 1.0 mm.
I'll probably purchase the steel and the jam nut after the first of the year.
For a nozzle I found some 316 SS tubing in our shop at work with .125" ID and .25" OD [.0625" wall thickness]. I'm debating on whether I should just use a single tube with holes drilled in it or an "X" shaped set of tubes with holes drilled in them. This is the only part of the design I'm not too clear on. I don't know if I should place the holes in the tube(s) perpendicular or parallel to the length of the combustion chamber. Anyone have any ideas?
I got in my sheet metal finally! I cut out the stencils and am going to weld up the combustion chamber tonight in welding class. Here's a shot of me getting ready to cut out the stencils.
I have decided to go with the smaller CR7HS spark plug. I've also decided to change how I'm going to inject fuel. I'm going to attempt to use parts from a Nitrous Oxide injection kit. I will probably start out running it on LPG, just for ease of operation, but I'd eventually like to move toward a diesel / gasoline mixture. I'm thinking of using a nitrous fuel jet to atomize the fuel into the combustion chamber.