FLAMMABILITY

& INERTING

The current On-Board Inert Gas Generation System (OBIGGS) and fire suppressant foams are the preferred methods for fuel tank protection and can be found on both military and commercial aircraft. Unfortunately, OBIGGS technologies require engine bypass air and are resource and weight intensive. In addition, the time required to reach the necessary Oxygen inerting levels is protracted. Fire suppressing foam have installation difficulties and repair issues that make them less than desirable.

 

ESI was asked to evaluate thesetechnologies and develop an alternative system if possible. As a result ESI has developed a new Reaction-Based Gas Inerting (RBGI) system that is capable of reducing ullage Oxygen levels below 9% by volume and does not require bleed air or other engine resources. Furthermore, the RBGI system provides rapid fuel tank inerting, has low unit installation and maintenance cost, and is easily retrofitted into existing aircraft fuel tanks.

 

Other advantages of the RBGI system over commercially available inerting systems are:

  •  Shorter time to fully inert an ullage

  •  Lower weight per mass of Nitrogen

  •  Higher inerting gas flow rates

  •  Lower electrical power requirements

  •  No pre-pressurized gas source required

A simulation based on an FAA model was used to predict the ullage Oxygen concentration for a given inerting condition and flight profile and indicated that 13.3 to 30 minutes was necessary to reach a 10% O2 level, depending on flow rate (Figure 1).  

In contrast however, ESI’s suggested RBGI system has been tested and has successfully demonstrated its capability to reduce the Oxygen level below 10% in less than 1.5 minutes. The following comparison (Table 1) demonstrates the performance of an RBGI system and compares it to an OBIGGS system when inerting an 800 gallon ullage space to below 9% Oxygen level.

Figure 1: Tank Oxygen Concentration Level as a Function of Time

Table 1: Inerting System Comparison for 800 Gallon Ullage

to Reach Oxygen Levels Below 9% by Volume

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