Conventionally, an APU compartment is a part of a rear end of an aircraft intended to house an APU and all the components and systems required for its functioning. The APU is a small turbine engine designed to provide electrical, hydraulic, or pneumatic power to some systems of an aircraft, such as the air conditioning system, the main engine starting system, and the anti-ice system.
The need of fuel and the high level of temperatures reached by the engine, converts the APU into a component susceptible of starting a fire. For that, the most likely areas of the APU to start up or suffer a fire, such as the combustion chamber, are conventionally monitored to achieve a prompt detection of fire. Typical fire detection systems involve the use of detector wirings extended around such critical areas of the APU and also around its compartment for detecting temperature.
Following the fire detection, the APU is conventionally shut down at the time that the fire extinction system of the APU compartment is started. Providing a quick and effective fire extinction is also a concern in the aeronautical industry.
For this purpose, APU compartments are conventionally provided with halon fire extinguishers. Such halon fire extinguishers have been used for years. Several patent documents deal with these halon fire extinguishers. For instance, patent application U.S. Pat. No. 4,625,808A describes a device to be coupled to a fire extinguisher containing a source of pressurized fire suppression chemical, such as halon compounds. This invention extends the use of the fire extinguishers provided in the aircraft, gaining access to inaccessible areas or to areas not equipped with fire extinguishers.
However, halon fire extinguishers contain substances harmful to the environment. For this reason, they are being replaced by other fire extinction systems. With this purpose, Patent Application US2013240218A1 describes the use of an organic blend of compounds to create a fire suppression agent. However, some of the organic compounds used by the invention, such as carbon dioxide, also pollute the environment. Besides, additional care should be taken in relation to the boiling points of the organic compounds involved in the blend, and also to the boiling point of the result of the mixture.
Therefore, it would be desirable to provide technical means for achieving fire suppression and extinguishing in an APU compartment, which in addition to be environmentally friendly, are able to provide a quick response against fire, and enable protecting the whole compartment.
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