Patent Application
20230066103
Fire protection is required in several areas of the aircraft, including the cargo compartment and the engine/auxiliary power unit (APU). Currently these two systems use the same agent (Halon 1301) but are separate. This adds weight to the overall system as separate containers for the agent are required. Furthermore, the cargo compartment comprises two distinct phases: an initial high-rate discharge (HRD) to knock the fire down, followed by a subsequent low-rate discharge (LRD) to keep the fire suppressed or contained until the aircraft can land safely. The agent, Halon 1301, is an ozone depleting substance (ODS) and is being phased out. Production ceased in 1994 in the developed world and in 2010 in developing countries. In addition, the aviation industry is facing “cut-off” dates (i.e. do not use Halon 1301 after this date) and “end dates” (Halon 1301 must no longer be used and must be replaced with an alternative agent, including retrofit, after this date). The aviation fire protection community has been searching for a replacement for Halon 1301 for the last 20 years, without success.
A number of options to replace Halon 1301 in cargo compartments have been suggested, including hydrofluorocarbons (HFCs), and 2-bromo-trifluoropropene (2-BTP). None of these is ideal for the following reasons.
HFC's and 2-BTP fail a key performance test (a simulated exploding aerosol canister) in that, if tested at a concentration below the inerting concentration, they can in some circumstances make the explosion worse than if no agent was employed at all. Inert gas and water mist pass this test but are inefficient fire extinguishing agents and the resulting size and weight of the fire protection system has been deemed to be unacceptable by aircraft original equipment manufacturers (OEMs).
A number of replacements for HFCs in the refrigerant industry, based on hydrofluoro-olefins (i.e. contain carbon, (chlorine) fluorine and hydrogen and a carbon-carbon double bond (denoted C═C)), have been proposed as they offer similar physical properties to the HFC. However, due to reactivity of the C═C bond, they have much shorter atmospheric lifetimes. HCFOs have also been tested against the simulated exploding aerosol canister, and they also exacerbate the explosion if tested at a concentration below the inerting concentration.
A promising Halon replacement agent, trifluoroidomethane or CF3I, does not fail the aerosol can test. However, when tested recently, it failed another test, the bulk load fire test. In this test the fire load is cardboard boxes filled with shredded paper, which gives rise to deep-seated fire that is difficult to extinguish. CF3I is less thermally stable than Halon 1301, and the agent decomposed in the “preheat zone”, i.e. en route to the fire.
A fire suppressant blend comprises CF3I, at least one hydrofluoro-olefin (HFO) or hydrochlorofluoro-olefin (HCFO), and carbon dioxide.
CF3I is an efficient fire suppression agent, so it serves as the primary basis of the fire suppression blend. Cooling agents are added to the blend to lower the temperature of the cargo compartment and prevent excessive decomposition of the CF3I. A mixture of one of more HCFOs/HFOs with and carbon dioxide is used as the cooling agent in the blend with CF3I.
Example HCFOs include:
Example HFOs include:
The CF3I quantity may range from 20 mol % to 80 mol %.
The HCFO/HFO agent quantity may range from 1 mol % to 50 mol %.
The CO2 quantity may range from 20 mol % to 80 mol %.
Adding more CO2 increases the cooling, but requires more volume to store.
Adding more of the HCFO/HFO agent improves the toxicity of the blend and also reduces its cost.
To determine the effectiveness of CF3I:HCFO/HFO:CO2 fire suppressant blends, CF3I:HCFO:CO2 fire suppressant blends, or CF3I:HFO:CO2 fire suppression blends, two categories of inerting tests were performed: sub-inerting tests and peak inerting tests. Testing was performed against propane-air explosions in 42 liter spherical test vessel 10.
Previous work has defined the stoichiometric (theoretically most explosive) propane-air mixture as 4% propane in air. Therefore, this concentration is used to assess the relative performance of extinguishing agents and blends thereof.
A first step in the procedure for a peak inerting test is to evacuate the sphere. Then, while monitoring pressure transducer 32, propane is added to a pressure of 0.04 atm (i.e. 4% in the final mix), and then the agent or agents are added at the desired concentration. For example, if a blend of 3.2% CF3I, 1.6% HCFO1224yd and 4.8% CO2 were to be the subject of the peak inerting test, CF3I is added until the pressure reaches 0.072 atm (4% propane+3.2% CF3I). Then, HCFO1224yd is added until the pressure reaches 0.088 atm (4% propane+3.2% CF3I+1.6% HCFO1224yd), and CO2 is added until the pressure reaches 0.136 atm (4% propane+3.2% CF3I+1.6% HCFO1224yd+4.8% CO2). Finally, air is added to raise the pressure in the sphere to 1.00 atm. Long enough equilibration time or fan mixing is used to ensure that all the gases are mixed homogeneously throughout interior chamber 14 before the test is initiated. At test, the spark is ignited, and the pressure rise monitored by a data logger. A pressure rise of 1 psi or lower is designated as a pass.
Sub-inerting testing uses 2.5% propane in air, and 0.3-0.5 fractional peak inerting concentration of agent, to predict if the agent/blend would enhance explosion in aerosol can test. Sub-inerting tests use the same procedure as the peak inerting tests, except 2.5% propane is used in the final mix. A pressure rise that is less than the baseline test pressure rise predicts that the agent (blend) will not generate explosion in aerosol can test, and therefore passes of aerosol can test.
When assessing blends, the concept of Fractional Inerting Contribution (FIC) is helpful. This is defined as
It has been demonstrated that successful inerting should be attained when FIC is close to 1 (i.e., 0.95+), where effectiveness of the blend is equal to the summation of effectiveness of each component. When a successful inerting test has an FIC less than 1 (0.9 or less), the effectiveness of the blend is higher than the summation of effectiveness of each component. That indicates that a synergy of the components of the blend has a positive effect on suppression efficiency.
CF3I serves as the primary component of the fire suppression blend. Cooling agents (HCFO/HFO and CO2) are added to the blend to lower the temperature of the cargo compartment to prevent excessive decomposition of the CF3I. CO2 is an efficient physical cooling agent, but has drawbacks of low molar efficiency and suppressor volume penalty. The purpose of the HCFO/HFO agent(s) is to provide extra cooling beyond CO2, and reduce volume penalty brought up from CO2. A minimum level of CF3I and CO2 is required to ensure that HCFO/HFO component in the blend does not enhance explosion in sub-inerting tests, and thus cause an aerosol can explosion.
HCFO1224yd is an example HCFO used in the tests. In the sub-inerting test data shown in
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/018217 | 2/16/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62976806 | Feb 2020 | US |
