An aircraft cabin is a unique environment due to the extremely high density of occupation and the limited available air volume. Typically, half of the air is exhausted and the other half is mixed with outside air (in most aircraft, supplied through the engine -bleed air-) and re-circulated into the passenger cabin, with a complete cabin air exchange every 2–3 min. This situation leads to the dispersion of germs and viruses and the accumulation of pollutants. Among them, Volatile Organic Compounds (VOCs) include not only internal pollutants (e.g. from materials present in the cabin or related to the presence of passengers) but also outdoor pollutants which can be present on the ground at very low altitudes (including gases from reactors and auxiliary power units).
In the majority of aircraft, the recirculated air passes through High Efficiency Particulate Air (HEPA) filters to trap contaminants suspended in the air (particles, bio-contaminants). However, these systems are not able to remove chemical pollutants (i.e. VOCs, ozone) and, since bio-contaminants (such as bacteria, viruses or fungi) are not inactivated, they can remain in the filter or even grow, thus representing a possible health risk. Only a small proportion of aircraft currently in service have implemented air treatment systems for VOCs/odour removal such as adsorbers. Moreover, these systems usually have high weight and cost, short life span (saturation) and septic conditions due to growth of microbial matter such as fungi and bacteria. Other technologies include electrostatic passive filters/precipitators based on the use of wires to remove pollutants, but the high voltage usually generates ozone. UVC lamps can also be used for air treatment and disinfection, but their efficiency for chemical pollutant removal is usually limited and they can also generate ozone. There is a great need for new alternative and innovative solutions that can surpass these limitations in current air treatment systems, capable of removing pollutants and bio-contaminants under aircraft environmental conditions while fulfilling constraints imposed by the size, weight and energy consumption.
To surpass those limitations, Breeze project propose to develop a new air purifier, connectable to the environmental control system ECS of aircraft to treat the recirculated air. The solution investigated is based on a composite filter that combines adsorption and photocatalytic technologies. The R&D program includes the design of the reactor and its testing for VOC, ozone and microorganism removal. Moreover, constraint regarding the incorporation of the prototype in real environment (TRL 6) is taken into account. In this regard, the tests are conducted at aircraft conditions (high flow rate and low humidity), and pressure loss of the system is monitored. The main objective is to achieve at least 85% VOCs removal without generating harmful by-product with a filter span life of at least 3000 hours of flight.
At the end of the project, a reactor compatible with the current ECS system, combining a low pressure drop HEPA filter for particle removal with a photocatalyst coated activated carbon filter was delivered. The adsorption properties allowed to achieve the objective of VOC removal with a filter’s span life evaluated around 4500 flight hours. However, the photocatalytic activity of the filtering media tested was not significant under experimental conditions representative of the ECS system.
