- Ali Tarraf
I designed a combustion chamber with optical quart glass access and instrumentation ports for my research during graduate school. The chamber had to be leak proof in vacuum and when pressurized up to 200psig. Previous design were complicated with many parts, so the new design was simplified to have 3 main blocks bolted together and housing the quart glass as seen in the CAD model below.
I decided to go with stainless steel material SS304 for its low thermal conductivity, high strength, and good corrosion properties. The main challenge was the fabrication of the big parts: 16"x5"x4.5" are the rectangular dimensions of the chamber. Starting from 3 stainless steel blocks, milling everything was proving to be time consuming, especially that I did not have the capability of milling the small rectangular cut in the front which stands at 16" tall sitting on a machine vise. So I outsourced the cutting of the rectangular parts to a local water jet cutting company and then proceeded to milling the other rectangular parts, oring grooves and drilling the holes. These are the results starting with the raw material blocks on the left to the assembled chamber on the right.
Initially I was planning to only have Orings as the seal interface between the blocks and glass but upon vacuum and pressure testing there was still leakages. I think this was due to inadequate compression ratio for the Oring, I designed the groove depth to provide 20% compression which might not be enough. Additionally my oring cross section of (0.139") might be providing too small of a surface contact area to provide adequate sealing. To solve this problem I fabricated a gasket made from Aramid/Buna material that is sandwiched between the outside blocks and the middle block. You can see a slight green line on the top surface of the combustion chamber.
More work is on going to instrument the chamber and to develop adequate dynamic sealing with a rotating interface. I will update my progress when available.