A Design Approach for Piccolo Tube Fuel Diffusers to Meet Airworthiness Requirements

Electrostatic discharge is one of the ignition sources that cause aircraft fuel tank fires and explosions. The airworthiness regulations and advisory circulars propose the design of a piccolo diffuser to limit the fuel flow velocity to prevent the occurrence of sparks or arc discharges in fuel tanks due to fuel flow. However, the airworthiness regulations and advisory circulars do not provide specific guidance on how to carry out the design of piccolo diffusers, and at the same time, the current perforated tube design method cannot be used to obtain a diffuser that meets the airworthiness technical requirements. Therefore, combined with the knowledge of fluid mechanics, the design method of piccolo tube diffuser is analyzed and discussed in this paper. Taking the design of piccolo tube diffuser for a certain type of aircraft as an example, the structural parameters of piccolo tube such as the diameter of the holes, the method of distributing the orifices, and the position and height of the baffle plates are optimized based on the computational fluid dynamics (CFD) method, and the design result that meets the requirements of fuel flow velocity limitation is obtained. The results show that the diffuser design method with built-in baffle plates can regulate the pressure inside the tube and solve the problem of uneven distribution of outlet flow velocity, compared with the current design method of perforated tubes. Based on the calculation results, the design principle of built-in baffle plates is concluded, and a universal design method of piccolo tube fuel diffuser with built-in baffle plates is proposed, which can meet the double requirements of high refueling efficiency and low flow velocity limitation at the same time. It makes up for the lack of design details in AC 25.981-1D and provides useful guidance for the design of piccolo tube diffusers that meet airworthiness requirements.