The fuel ring

The fuel ring mounts to the aft of the combustion chamber, encircling the flange which grips the NGV. This helps pre-heat the fuel. A single brass line delivers kerosene to the ring from one of the service ports.

For all of the internal plumbing, I chose to use drawn copper tube rather than brass, as copper bends and handles far easier.

(Note: Mike Murphy from Wren Turbines has since informed me that copper is not a good choice, as it may work harden from subtle vibrations and eventually split, releasing fuel and potentially causing an immediate and catastrophic overspeed! Be warned!)

The rear of the combustion chamber was used as a guide to bend and cut the fuel ring shown. The "T" and the fuel delivery pipe was also a simple bend job. Distance front to rear is important.

The ring is brazed to the delivery pipe, which in turn is braced to a service connector. Like so much else in this project, I tossed it in the nickle tank prior to drilling the holes for the twelve 316SS needle fuel injectors. The nickle is very resistant to corrosion, and will help preserve the piping in this extreme environment.

The 12 holes were drilled #76, and the needles cut and inserted. Great care was taken to keep the needles clear of dust and debris. They were inserted roughly 1/2 way through the diameter of the ring tubing.

Brazing the ring was tricky. The copper absorbs heat, and it is easy to exhaust the flux at the joint to be brazed. Use plenty of flux, and direct the flame so that as little as possible impinges directly on the needles. Try to do all 12 in one sitting.

After cleanup, the ring was connected to a propane source and the needles tested. All passed with flying colors!

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