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Oxygen GENERATORS are chemical devices that generate O2 by mixing two or more chemicals, usually in a very spirited exothermic reaction. They need to be properly installed and insulated to manage the heat. Having a few dozen loose ones in the cargo hold is what brought down ValuJet. Oxygen GENERATORS are usually used in emergency situations where oxygen is needed for a short duration (a few tens of minutes). The only use I am aware of is in aircraft cabins to provide oxygen during emergency descent after a depressurization.
Oxygen CONCENTRATORS are mechanical devices that concentrate oxygen from the ambient atmosphere. They work by pumping high pressure air into what you can think of as a filter. The nitrogen is absorbed in the filter and the oxygen comes out the other end. After a few seconds, the filter needs to be vented to release all the absorbed nitrogen and then the cycle is repeated. Basic systems have two or more filter elements that are pressurized alternately so that one of the elements is always producing oxygen.
Oxygen CONCENTRATORS are safer than oxygen cylinders because you are not dealing with large quantities of oxygen at high pressure. Small concentrators are increasingly being used instead of tanks for patients on home oxygen therapy and for smaller welding operations. Large concentrators can be found in industrial applications.
At ground level (0 to 5,000 MSL), it typically requires about 16 CFM of clean, dry, oil-free, room-temperature air at about 45 PSI to produce one CFM of 95% Oxygen (the remaining 5% is Nitrogen and other atmospheric gases). To use one in an aircraft, you need to compress the ambient air without introducing any oil in it, cool it down to "room temperature" and plumb it through various check valves & solenoids to the filters. Using an oil-less compressor is a requirement because even minuscule quantities of oil will damage the filter material as well as your lungs. All of that is quite doable using existing technology, it just requires some analysis and engineering. If done properly, it can be a perfectly safe system built out of mostly COTS components.
Based on the power requirements of currently available home oxygen therapy units, I believe that it will not be practical to run a 4 passenger system off aircraft batteries. The compressor will have to be engine driven or powered by a dedicated engine driven alternator.
This approach has one major problem: When your engine quits, you also loose your oxygen. This requires having a redundant tank based system -- one that can be brought online easily during an emergency. In other words, you still need to install and maintain a conventional oxygen system. The only thing you save is not having to refill it as frequently and the weight saving from a smaller tank. Is that saving worth the extra cost, weight, volume, performance and complexity of an oxygen CONCENTRATOR? Everyone who has looked at the problem so far has concluded NO.
Otherwise there is no technical reason not to built one.
Regards,
Hamid
Ted Noel wrote:
It appears that there is a semantic issue here. The oxygen generators in the ValuJet crash used a highly exothermic process that created and fed the fire. The device used in the Diamond is almost certainly an oxygen /concentrator/, not oxygen generator. Wikipedia has a nice article on the mechanism. Concentrators are less hazardous in some ways than oxygen cylinders, and are certainly safe in aircraft.
Ted Noel
On 6/1/2012 2:12 PM, Colyn Case wrote:
re: oxygen vs. pressurization
If you are solo maybe it's workable but I find generally passengers question my decision to fly higher when we have to get the hoses and cannulas out. Then you either need to invest in your own refill station or always arrange with the nearest FBO that has oxygen. ...a 30 minute trip away in my case.
re: bottles vs. generators
I don't know the issues. I just remember an airliner that went down when oxygen generators it was carrying as cargo started burning.
On Jun 1, 2012, at 12:12 AM, sales@newmanaviation.com wrote:
I was reading the latest edition of FLYING Magazine, and I noticed an article about Diamond's new 6 passenger turbodiesel twin. What really caught my interest was the statement "Diamond is not planning on pressurizing the airplane; instead, it will be equipped with an oxygen generator."
As a builder of a non-pressurized Lancair IV, this was interesting to me. I've long wondered why I've never heard about oxygen generators being used in small planes.
Is an oxygen generator really a substitute for pressurization? Is the main disadvantage to not having pressurization really the price of bottled oxygen?
I've attached the short article for anyone who is interested.
Pete <DA52.jpg>--
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