BALRoG

The Bench for Advanced Liquid Rocket Engine Ground-testing (BALRoG) project aims to develop expertise for TUDSaT in the field of liquid-liquid engines. The project includes the construction of a test bench designed to supply propellants to engines up to 3 kN. The next step will be the construction of a suitable liquid-liquid engine that can later be used in liquid engine competitions. This engine is expected to replace the solid-fuel engine currently used by RAPID for the FRoDO series to reduce the environmental impact of the engine exhaust.

Test Bench

The test bench is designed as a stand-alone system to provide flexible testing capabilities and is equipped with a data acquisition and control system to allow for remote operation. In addition, the system is built as a compact setup for easy storage and transportation with standard vehicles. This allows for multiple test locations.

The main body of the test bench is supported by four legs to level the entire setup in the terrain. It contains the required piping, propellant tanks, etc. as shown in the P&ID below.

The main components of the piping are the nitrogen tank and the two propellant tanks. The propellant tanks have a similar architecture using an aluminum tube and two end caps that are bolted together. The tanks are designed for 200 bar according to Ad-2000 norm. A manual high pressure pump can be attached to the tanks and tested with water to test the pressure tanks. It is essential to test with an incompressible fluid due to the high risk involved when testing with combustible propellants. The tanks are equipped with safety valves to maintain a maximum pressure in the tank to prevent bursting. The operating pressure of the test bench is approximately 60 bar, depending on the propellant and the ambient temperature. Thus the safety valves have been chosen so that they open at 100 bar. Downstream of the tanks, mass flow meters, pressure and temperature sensors are installed to provide adequate test bench monitoring. The mass flow is controlled by the proportional main valves and supplies the engine with the required propellants. Nitrogen gas is used to pressurize the propellant tanks and provide sufficient purging of the system. This feature allows testing of injector designs using water, which requires fewer safety precautions.

The expected test bench specifications are listed below.

Liquid-liquid Engine

The first iteration of the BALRoG engine borrows the design and injector architecture from Half Cat Rocketry's MOJAVE SPHINX rocket engine. Due to the challenge of building the test bench and engine simultaneously, the first design must have a minimum number of controlled variables. As such, the first production engine is a "battleship design," meaning it is simple and robust at the expense of efficiency and performance.

The engine consists of 3 main parts: Injector head, chamber and nozzle. These parts are designed to slide into each other to stay concentric and sealed. From both sides, flanges compress the graphite gasket seals by pushing the nozzle and injector head.

The injector design utilizes the Scrintle (screw-pintle) / splash plate method. In this design, centrally injected N2O is diverted outward to the axial ethanol jets for combustion. The engine is ignited towards the injector from outside the nozzle and the resulting exhaust from the engine combustion throws the igniter away. The first iteration will be all aluminum and will not have cooling.