Design of a Fast Responding Start-Up Mechanism for Bi-Propellant Fueled Engine for Miniature UAV Applications

In this work a new design of a liquid fuelled combustion engine is proposed for small and light weight unmanned air vehicles (<10kg and 15-200N thrust). Ethanol and gasoline were selected as the potential fuels while pressurized air and hydrogen peroxide were used as the oxidizer. The engine combines features of both a common rocket and turbojet engine. The main features of the engine are the restart ability during flight, low cost, easy manufacturability, light weight, long operation time and high durability. The main difficulties that come along with this engine are the need for proper engine cooling (long term operation) and start-up ability at atmospheric conditions. The low temperatures and injection pressures are not favorable for the fuel atomization and ignition. The paper focuses on the design on low pressure injectors and a start-up mechanism for micro UAV's without the use of a large amount of additional fueling circuits or components.

Twin and triple nozzles and liquid, liquid-gas and gas injection were tested both in terms of atomization and combustion. The start-up injector makes use of the catalytic decomposition of hydrogen peroxide (HP) in order to mix and evaporate the fuel prior to injection. High speed shadowgraph imaging and thermocouples are used to investigate the performance of the HP injection and ignition. It has been found that temperature and contact surface - volume ratio between the catalyst and hydrogen peroxide are of great importance for the performance of the start-up mechanism. This simple technology demonstrates promising results for the considered application.