STORING AND DISCHARGING DRY CHEMICAL FIRE EXTINGUISHING AGENTS

A system includes a pressure vessel defining an interior space with a discharge outlet. A valve or burst disc is connected in fluid communication with the discharge outlet. Discharge piping is included in fluid communication with the valve or burst disc to receive discharge from the interior space. One or more discharge nozzles are in fluid commination with discharge piping for issuing a spray from the discharge piping into the environment external of the pressure vessel. A mixture of liquid Carbon Dioxide (CO2) and a dry chemical fire extinguishing agent is housed under pressure within the interior space.

BACKGROUND

The present disclosure relates to fire extinguishing, and more particularly to dry agents for fire extinguishing.

2. Description of Related Art

The conventional engine nacelle fire extinguishing agent was traditionally a gas (Halon 1301). It is, however, and ozone depleting gas and thus there is a need to find alternatives. Dry chemical agents are one possible alternative.

Achieving an efficient and robust dispersion of dry chemical fire extinguishing agent throughout the designated fire zones (DFZs) in aircraft engine nacelles and auxiliary power units (APUs) can be challenging. Dry chemical agents are generally stored with compressed gas in a bottle. A piping system connects the bottle to the DFZ. Upon discharge of the bottle, the compressed gas expands and carries the agent through the piping system and sprays it into the DFZ. The agent then aerosolizes and disperses throughout the DFZ. Unlike gaseous agents, dry chemical agents tend to adhere to surfaces. This tendency to lose agent to surfaces is exacerbated by the fact that many modern DFZs are highly cluttered. Thus, efficiently delivering adequate concentrations of airborne agent to every region of the DFZ is challenging.

The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved systems and methods for storing and discharging dry chemical fire extinguishing agents. This disclosure provides a solution for this need.

SUMMARY

A system includes a pressure vessel defining an interior space with a discharge outlet for fluid communication from the interior space to an environment external of the pressure vessel. A valve or burst disc is connected in fluid communication with the discharge outlet. The valve or burst disc is configured to block flow through the discharge outlet in a first state of the valve or burst disc, and to allow flow out of the discharge outlet in a second state of the valve or burst disc. Discharge piping is included in fluid communication with the valve or burst disc to receive discharge from the interior space with the valve or burst disc in the second state. One or more discharge nozzles are in fluid commination with discharge piping for issuing a spray from the discharge piping into the environment external of the pressure vessel with the valve or burst disc in the second state. A mixture of liquid Carbon Dioxide (CO2) and a dry chemical fire extinguishing agent is housed under pressure within the interior space with the valve or burst disc in the first position.

The dry chemical fire extinguishing agent can include Sodium Bicarbonate (NaHCO3) particles. The particles can be sized in a size range from 0.1 micron to 50 microns, inclusive of endpoints. The liquid CO2can fill into interstitial spaces between the particles. The NaHCO3particles can include additives. The dry chemical fire extinguishing agent can include potassium bicarbonate (PKP).

A method of fire extinguishing includes discharging a pressure vessel housing a mixture of liquid Carbon Dioxide (CO2) and a dry chemical fire extinguishing agent through one or more nozzles. The method includes freezing a coating of the liquid CO2around particles of the dry chemical fire extinguishing agent by cooling from passage of the mixture through the one or more nozzles so that the particles are coated in dry ice. The method includes extinguishing a flame with the particles coated in dry ice.

Discharging the pressure vessel can include bouncing the particles coated in dry ice off of surfaces downstream of the one or more nozzles. Discharging the pressure vessel can include maintaining pressure in any lines feeding the one or more nozzles during discharge so CO2in the line or lines remains in liquid state while discharging the pressure vessel.

The method can include sublimating the dry ice off from the particles coated in dry ice. The method can include filling an aircraft compartment with a mixture of CO2gas sublimated from the particles coated in dry ice and with the particles of the dry chemical fire extinguishing agent after the CO2has sublimated off of the particles coated in dry ice.

Extinguishing the flame can include depriving the flame of Oxygen with the mixture of CO2gas and particles of dry chemical fire extinguishing agent in the aircraft compartment. Extinguishing the flame can include lowering heat in the aircraft compartment by absorbing heat into the mixture of CO2gas and particles of dry chemical fire extinguishing agent in the aircraft compartment. Extinguishing the flame can include lowering heat in the aircraft compartment by breaking down the particles of dry chemical fire extinguishing agent in endothermic reactions. Extinguishing the flame can include catalytic radical scavenging that chemically inhibits the combustion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an embodiment of a system in accordance with the disclosure is shown inFIG.1and is designated generally by reference character100. Other embodiments of systems in accordance with the disclosure, or aspects thereof, are provided inFIGS.2-5, as will be described. The systems and methods described herein can be used to store and discharge dry chemical fire extinguishing agents, e.g. for use in extinguishing fires onboard aircraft.

The system100includes a pressure vessel102defining an interior space104with a discharge outlet106for fluid communication from the interior space104to an environment108external of the pressure vessel102. A discharge control device such as a valve or burst disc110is connected in fluid communication with the discharge outlet106. The valve or burst disc110is configured to block flow through the discharge outlet106in a first state of the valve or burst disc, e.g. when there is no fire to maintain the contents of the interior space104under pressure. The valve or burst disc110is also configured to allow flow out of the discharge outlet106in a second state, i.e. upon detection of a fire needing to be extinguished. The discharge is actuated by opening the valve or burst disc110upon receipt of a discharge signal, e.g. from the cockpit, upon detection of a fire, or discharge can be actuated automatically. Discharge piping112is included in fluid communication with the valve or burst disc110to receive discharge from the interior space104when the valve or burst disc110is in the second state for extinguishing a fire. One or more discharge nozzles114are in fluid commination with discharge piping112for issuing a spray116from the discharge piping112into the environment108external of the pressure vessel102when the valve or burst disc released the pressure of the vessel102for extinguishing a fire. A mixture of liquid Carbon Dioxide (CO2)118and a dry chemical fire extinguishing agent particles120or crystals is housed under pressure within the interior space104when the valve or burst disc is in its closed, normal position. Technically the CO2will be a two-phase fluid within the pressure vessel102, with most of it being in the liquid phase. If the pressure vessel102gets hot enough during flight the CO2might become a supercritical fluid.

The dry chemical fire extinguishing agent includes particles120of Sodium Bicarbonate (NaHCO3) particles, potassium bicarbonate (PKP), and/or particles of any other suitable dry chemical fire extinguishing agent plus any applicable additives. The particles120are sized in a size range from 0.1 micron to 50 microns, inclusive of endpoints. The liquid CO2118inside the interior space104fills into interstitial spaces between the particles120, e.g. 70% of tank volume is available for liquid CO2storage in close-packed interstices of the particles120. To reach the liquid state, the interior space104can be filled with CO2to a pressure about 800 psi (54.43 atm) or more. Depending on the required low temperature operating range, an additional pressurizing gas like N2, He, or Argon, may be added in small quantities to the extinguisher to ensure sufficient discharge pressure.

With continued reference toFIG.1, a method of fire extinguishing includes discharging the pressure vessel102through the one or more nozzles114, e.g. by opening the valve or burst disc in response to detecting a fire. As the mixture of liquid CO2and particles120pass through metering orifices of the nozzles114, the mixture passing through the nozzles114cools significantly. During discharge, the liquid CO2expands and evaporates thus dropping the fluid temperature to the triple point. At this point the CO2begins to freeze and makes a coating122dry ice frozen from the liquid CO2around the particles120of the dry chemical fire extinguishing agent. As shown inFIGS.1and2, the particles120near the nozzles114are coated in a coating122of dry ice. As the coated particles120travel further from the nozzles114, the dry ice coating122sublimates way from the particles120, as indicated inFIGS.1and3, becoming CO2gas124.

With reference now toFIG.4, the method includes extinguishing a flame126with the particles120coated in dry ice. While the particles120are still coated with dry ice (as shown inFIG.2) they coated particles120bounce off of surfaces128downstream of the one or more nozzles114, as indicated inFIG.4with the trajectory arrows. Discharging the pressure vessel102includes maintaining pressure in the line or lines112feeding the one or more nozzles114during discharge so CO2in the line or lines112remains in a pressurized two-phase state while discharging the pressure vessel102.

After the dry ice coated particles120(as shown inFIGS.1-3) have traveled some distance from the nozzles114, and have persisted for some time, the dry ice coating122sublimates off from the particles122of dry chemical fire extinguishing agent (as shown inFIG.3). The method includes filling an aircraft compartment130, e.g. a designated fire zone (DFZ), with a mixture of CO2gas sublimated from the particles120, and with the aerosolized particles120of the dry chemical fire extinguishing agent after, i.e. distributing the gaseous CO2and particles120substantially evenly within the compartment130as indicated schematically inFIG.5by the clouds representing the mixture132of CO2gas and aerosolized particles of dry chemical fire extinguishing agent inFIG.5.

This extinguishes the flame126ofFIG.4by depriving the flame of Oxygen with the mixture of CO2gas and particles of dry chemical fire extinguishing agent in the aircraft compartment, i.e. the expansion of the mixture132into the compartment130displaces air out of the compartment130. This also extinguishes the flame126by lowering heat in the aircraft compartment130by absorbing heat into the mixture132, as well as by breaking down the particles120(labeled inFIGS.2-3) of dry chemical fire extinguishing agent in endothermic reactions. These constituents can also chemically combat the flame126(labeled inFIG.4) via catalytic radical scavenging.

Systems and methods as disclosed herein provide various potential benefits including a more efficient distribution of the dry-chemical agent than in previous methods as a result of the following. The solid CO2can physically shield the dry-chemical agent from contacting surfaces upon impact (to reduce coating the surfaces). The tendency is reduced for particles to impact surfaces due to the sublimating dry ice coating providing a gas cushion to the dry-chemical agent. Dispersion and diffusion of the agent due can be improved to the expanding carbon dioxide displacing more ambient air than the equivalent system charged with compressed gas (N2, He, or Argon). Dispersion and diffusion of the agent can also be improved due to the transient nature of the sublimation and resulting expansion of the carbon dioxide, e.g. as opposed to standard compressed gas driven systems that are fully expanded at or shortly after the nozzle exit.

The methods and systems of the present disclosure, as described above and shown in the drawings, provide for storage and discharge of dry chemical fire extinguishing agents, e.g. for use in extinguishing fires onboard aircraft. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.