In attendance: Tim Brandon, Eric Hettinger, Brian O’Neel, Evan Waymire
We got a bit of work done at the meeting. Eric brought over the low-pressure plumbing for the nitrogen purge system. We adapted the Spartan Scientific solenoid with the right fittings and hoses to connect it to the nitrogen regulator. We did a switching test at 80psi. It worked great except we realized our solenoid switching diagram was backwards. The nitrogen should go from the regulator into port#1 on the Spartan solenoid, not port#2 like the diagram says. This caused venting to the atmosphere.
The preliminary nozzle design is done. We now have a ballpark estimate of what our nozzle throat and expansion ratio should be. We cut the graphite stock to machine two additional nozzles so that we will have three to try at the first static fire. We will start with a diameter 0.200” over the design target and step down to the correct throat diameter in successive tests. This will be to hopefully insure we wont blow the combustion chamber due to a miscalculation.
We also modified the Tescom high-pressure regulator with the appropriate fittings to adapt it to the oxygen tank. We tried it out on the small welding oxygen tank and all the fittings worked fine except there was a small amount of oxygen being vented from the regulator itself. We are not sure why this is and are going to contact the supplier to see what they have to say.
Discussion centered on injector design and metering orifice.
Since we are using gaseous oxygen in the prototype hybrid, atomization via the injector is not an issue. Our only concern (warranted or not, we don’t know) is the possibility of the incoming oxygen stream having sufficient velocity and focus that a percentage of the gas may pass too quickly through, and out, of the combustion chamber without reacting with the paraffin. We need an injector that will diffuse the oxygen inside the chamber yet not introduce a large pressure drop at the end of the oxygen feed system. We have decided to investigate two potential solutions. 1) A pintle injector used in the oil furnace industry 2) A flat plate impinging scheme we can build ourselves. We will most likely try both to check their performance.
The metering orifice still has not got much attention. We hope to make some progress by next meeting. The situation requires some research on our part. And it’s still not quite certain how we are going to gauge our oxygen flow rate. We can calculate it directly from the pressure drop across the orifice but it is not certain what the inlet of the pressure to the orifice will be since we maybe running through some restrictions up stream (i.e. Solenoid, check valves, small diameter braided hose) and we are not sure what the pressure needs to be on the downstream side of the metering orifice to allow for a possible pressure drop across an inject to end up with a final chamber pressure of 500psi. None of this is too hard we just need to spend the time doing the analysis and in the end it may be that we need to put a couple of pressure transducers in the system to make sure our calculations are correct.
One big issue that came up is that our oxygen solenoid may not work. It is rated at 150 psi. We were assuming that it would function given a 500 psi chamber pressure vs. a maximum 650 psi oxygen regulator output. This may still be true, we have not tested it, but we had not thought it through very well :) If oxygen inlet to the solenoid is at 650 psig then before we ignite the motor the chamber pressure will be 0 psig. It will most likely not open at that pressure differene. We don’t even know if the solenoid physically can handle that sort of pressure difference. We have decided to look for either a higher pressure solenoid or a way of automatically turning a manual valve.
Besides the small complications things are looking good. We are still targeting a late December static fire date. But there is still much to do. This includes:
To Do List:
- Metering orifice design and fabrication
- Injector fabrication
- Bolt and weld analysis
- Plumbing connections
- Static test stand fabrication
- Combustion chamber flange welding
Continue investigating metering orifice and doing calculations
- Talk to contacts about doing TIG welding of flanges till we get more practice
Talk to dealer about pintle orifice
Research servos to turn manual oxygen valve and high-pressure solenoids
Finish machining the 3 nozzles
- Acquire fuel grain initiator rings
Make replacement flange for injector side of combustion chamber this time putting the o-ring groove in the right place :)
Continue with orifice research
Continue with bolted and welded connection analysis
Continue with static test stand fabrication
The next hybrid meeting will be in 2 weeks.