This engine was my third attempt to make a regeneratively cooled, liquid propellant rocket engine.  My first attempt was to work it up out of sheet stock.  It was a dismal failure.  My second attempt was to machine the engine out of bar stock.  It worked somewhat better, but I was concerned about the thin wall structures in the cooling jacket.  Also, it was originally machined out of 6061-T6 Aluminum, but I had to have the fuel inlets for the cooling jacket welded in which destroyed the hardness and temper of the metal.  I never test fired it because I was afraid it would fail in a spectactular manner.

So I designed and built engine A-3.

This image is taken from a solid model of the engine.

The engine consists of a 316 Stainless Steel combustion chamber inside a 7075-T6 Aluminum Cooling jacket.  The injector face plates are made of 316 Stainless and have a single impinging pentet injector in the center of the injector face.  The injector nozzles are a unique design that allows the nozzles to be precisely tuned for propellant flow rates.  The injector nozzle has a threaded body with an o-ring seal at the top which seals inside the propellant dome.  Fuel and oxidizer injectors are not interchangable so it is impossible to mix them up.  Each nozzle opening is formed from a length of 316 Stainless hypodermic needle tubing brazed into the threaded adapter.  This allows the ID of the nozzle to be selected from a broad array of standard hypodermic tube ID's.  The length of the tube can be ground to balance the flows of all 4 fuel injectors.  Very precise flowrates can be obtained this way.

This is a partial cut-away view of the EA3-1 engine.  You can see the way the holes for the injectors are drilled in the injector face.  The fuel dome is the large area above the injector face, the LOx dome is actually very tiny and is inside the center part of the injector face that protrudes up through the top cover of the engine.  The coolant passage around the combustion chamber is also visable.  The coolent flows tangentially around the combustion chamber.

The initial tests of this engine were plagued with low frequency combustion instabilities. After a number of tests I determined that this was due to vaporlocking in the relatively long propellant lines. The problem was primarily in the LOx lines. The lines were 1/8" OD by .090 ID which gives them a fairly heavy wall thickness. These lines caused the LOx to vaporize in the lines giving a burst of high pressure GOx through the injectors. The high pressure GOx also forced the LOx back up into the propellant tanks. Once the GOx pressure subsided, the LOx would flow back down into the line starting the process all over again. Not unlike a coffee percolator. Had much the same effect. Weasly little drips of burning Kerosene interspersed with great popping gouts of flame.

I'm now working on using ultra thin wall 316 SS hypodermic tubing as propellant lines. These have a wall thickness of aproximately .005" and have much lower coefficients of thermal conductivity. Plus I'm wrapping the lines in insulation, and making the lines as short as possible. I'm also going to cool the lines with LN2 prior to tests to pre-cool the lines as much as possible.
 
 

Updated 18 March 2004