In the modern world, unmanned aerial vehicles (UAV) capture an ever-increasing part of our daily operations. This is especially true for small scale UAVs, which are commonly powered by micro-gas turbines. These micro jet engines have thrust rating below 1 kN and have disproportionate cost that varies between 30,000 to 150,000 USD. For both disposable and re-usable platforms, this inflates the system cost dramatically. Moreover, in multi-mission platforms, significant efforts are invested towards prolonging the service life of these small yet expensive engines, and maintenance becomes an important subject, which involves long chain of suppliers and overall work expenditures that have the potential to even surpass the base price of the engine.
Instead of relying on these paradigms, extremely cheap limited-life micro-jet engines have the potential to eliminate supply chains, warehousing of replacement parts, maintenance procedures, and all expenses associated with it. However, despite the relatively simple design of a conventional micro-turbojet engine, its manufacturing involves long and costly processes due to presence of numerous parts, different manufacturing methods, logistics of various subcontractors and collaboration of different departments that assemble and qualify the product. Instead of relying on this conventional process, the proposed concept here entails development of a non-conventional engine design that can be additively manufactured in its final topology through a single uninterrupted print that encompasses both the rotating and stationary components. Requiring only a metal printer and an operator, the cost of the engine will be diminished to capital equipment depreciation and raw material, with an expected cost reduced merely to a small fraction of the current engine market prices.
Considering the print volume of the currently available metal 3D printers, the target engine design will have a diameter of up to 30 cm, thrust rating of 650 N and air mass flow rate of about 1.4 kg/s. The proposed manufacturing method also mandates a reduction in number of components. Thus, the engine will include only two major parts – static casing with embedded combustion chamber and a rotating shell structure. This rotating part will include compressor and turbine impellers connected by a thick hollow shaft that will enhance the rotordynamic performance. The hollow shaft connecting the compressor and the turbine will also serve as a fuel driven hydrostatic bearing. The fuel will subsequently evacuate through perforated media towards compressor-diffuser region and mix as an aerosol with incoming air flow. In a pursuit to reduce engine size, porous media combustor will be used to burn the premixed fuel-air mixture. The rotating component of the engine is designed to be balanced after the manufacturing process only through external ad hoc removal of mass from the surfaces.
This project involves sophisticated multidisciplinary optimization of aerodynamics, thermodynamics, heat transfer, rotordynamics and stresses for turbomachinery and hydro-static/dynamic bearing components under 3D manufacturing limitations. Although the performance of the final design is anticipated to be inferior to state-of-the-art micro-turbojets in terms of both thrust to weight ratio and thrust specific fuel consumption due to design constraints associated with incessant printing, the expected disruptive change in cost and availability is expected to create a market for such products.