Smart valve innovation boosts aircraft safety
Decreasing the aviation sector’s environmental and social impact is not just a question of improving engine efficiency. Every aspect of airflight needs to be re-examined, including the use of toxic chemicals across a range of applications. For example, halogenated hydrocarbons – or halons – have traditionally been used in aircraft fire extinguishers. The fumes however are toxic, and the chemicals harmful to the ozone layer. Replacing halon-based extinguishers with a safer, greener alternative has become an industry priority.
Preventing formation of explosive mixtures
The EU-funded VISTAC project sought to advance emerging technology that would produce inert gases capable of preventing the formation of explosive mixtures in the fuel tank. More specifically, the project addressed the need for valves to control gas flows. “To be economically viable and scalable for the aviation industry, these valves need to be reliable, low cost, low weight and with a small carbon footprint,” explains VISTAC project coordinator Cynthia Rawyler from Equip’Aero Technique in France. The project set out to design a valve that could be used in next-generation, halon-free fire extinguishing systems called On Board Inert Gas Generation Systems (OBIGGS). These work by allowing inert gases into the fuel tank and cargo bay, in order to prevent fire from spreading. Inert gases work by removing oxygen from the potentially hazardous areas. “A multi-position valve is needed to regulate the OBIGGS, to provide just the required amount of nitrogen-enriched air to inert the fuel tank or cargo bay,” adds Rawyler.
Applying shape-memory alloys
The valve was designed to be operated by an actuator made of shape-memory alloy (SMA) wires. SMAs are intelligent materials that change their properties or behaviour when exposed to an external stimulus. The electromechanical actuators used in the VISTAC project were thermally activated. “What this means is that heat is converted into mechanical force,” notes Rawyler. “This technique enabled us to reduce the number of parts needed for the actuator, helping us to achieve less weight, use less parts and make the equipment more reliable.” The valve was designed around this new actuator. The SMA wires were tested in representative environments, such as hot and cold temperatures, along with vibrations and shocks. “Fluidic behaviour was also characterised,” says Rawyler. “This helped us to see how the valve would open and close to reflect various flow rates.”
Scalability to other industries
The success of the project could lead to the replacement of electromechanical actuators for OBIGGS with a cheaper, simpler SMA-based actuator. The project also enabled Rawyler and her colleagues to increase their understanding of SMA actuators, from their conception and design to manufacture and integration into a workable valve system. “The scalability of the design means that the actuator technology we developed could be adapted for other industrial applications as well,” she adds. “These include not only the aerospace sector, but other sectors that use an actuating valve as well, such as the food industry and pharmaceuticals.” More tests and studies are required to fully assess the performance and potential of this innovation. “This technology will be matured in another project,” Rawyler says.
Keywords
VISTAC, aircraft, fuel, airflight, chemicals, aviation, SMA, alloy, electromechanical
