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On-Board Oxygen Generation Systems (OBOGS) HONEYWELL 16 Jan 2008
Honeywell developed OBOGS technology in the 1980’s to allow an aircraft to generate its own oxygen during flight. OBOGS takes advantage of a molecular sieve material, Zeolite, which traps nitrogen molecules when air is passed through it, allowing it to act as a molecular sieve. Figure 3 shows an OBOG concentrator with 2 zeolite-filled beds. The lower zeolite bed is currently producing oxygen.
Conditioned engine bleed air enters the lower bed, having first been filtered to remove particulate contaminants, and is then reduced to a suitable pressure by the Pressure-Reducing Valve. As the air passes along the zeolite bed, the nitrogen molecules within it are adsorbed by the zeolite.
At the far end of the bed, a product gas that is up to 95% oxygen is produced, the balance of the gas being made up of argon. The presence of argon has been widely shown to have no physiological effect on crew/pilots.
Over time, the bed becomes saturated with nitrogen, and oxygen production is switched to another bed that has been purged of nitrogen. The upper bed in Figure 3 is in the process of having the nitrogen removed, by using part of the product gas from the lower bed to ‘purge’ the nitrogen out of the bed to then be vented overboard. Once the upper bed is clean, oxygen production will be switched to it, whilst regeneration of the now nitrogen full lower bed is carried out, and so the cyclical process continues.
Typical System Architecture
A typical system is shown in Figure 4. The OBOGS is controlled by a solid state monitor/controller that monitors the PPO2 level of the OBOGS product gas, and adjusts the cycling of the beds to produce the desired level of oxygen concentration shown in Figure 2. This process is known as concentration control and means that
no air-mix, or dilution, of the product gas is required at the regulator.
The breathing gas then passes to the pilot’s breathing regulator, either a console/ panel-mounted, ejection seat-mounted or pilot-mounted device. The regulator is a demand flow regulator like those of GOX and LOX systems, differing only in the fact that they operate at lower pressures and do not air-mix. The final system element is a
back-up oxygen cylinder mounted on the ejection seat to provide oxygen during pilot ejection, or in the unlikely event of an interruption in the OBOGS supply.
Benefits of OBOGS compared to GOX and LOX...
...Breathing gas purity –
OBOGS regulators do not air-mix thus the pilot is not susceptible to smoke and fumes from the cockpit. Oxygen concentration is controlled inside the zeolite beds and is hence free from contamination...."
https://aerocontent.honeywell.com/ae...rt_Systems.pdf