Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Measurement of the Regression Rate in a Lab-Scale Hybrid Rocket Motor by Acquiring the Helmholtz Frequency in the Combustion Chamber
Submission Author:
Isabel Matos , SP
Co-Authors:
Isabel Matos, Rodrigo De Melo Silveira, Lia Pimont, Leonardo Henrique Gouvêa, Pedro Lacava
Presenter: Isabel Matos
doi://10.26678/ABCM.COBEM2021.COB2021-0883
Abstract
Hybrid rocket propulsion provides an attractive alternative to the conventional liquid or solid rockets. Compared to liquid bipropellants rockets, hybrids have less complexity and lower costs, due to less piping and valves. And compared to solid rockets, they have controllable thrust, shutoff and restart capability, and are safer, since the fuel is not reactive by itself and can be manufactured, transported, and handled safely, avoiding the explosiveness of the propellant. Despite its advantages, hybrid rocket propulsion has never attained mainstream adoption. A strong reason for that stems from its inherently low fuel regression rate, that limits its applications in relatively lower thrust levels rocket motors. The low thrust is a consequence of the difficulty in quickly mixing the fuel and oxidizer, which is characterized by a low rate of regression of the fuel grain (assuming a liquid or gaseous oxidizer), which indicates the speed at which the fuel is consumed during combustion. Therefore, the measurement of this parameter is of great importance in studies that aim solutions for this deficiency in hybrid rocket motors (HRM). Several studies evaluate the average regression rate over time, measuring the total mass of fuel before and after a burn. An alternative and least expensive method to measure instantaneous regression rate is by acquiring the Helmholtz resonance frequency of the combustion chamber, as the internal volume increases with grain consumption. This non-intrusive technique has already been demonstrated by another research group on a large-scale HRM (oxygen mass flow rate from 2 to 6 kg/s), and the present work aims to evaluate its applicability on a laboratory-scale HRM (oxygen mass flow rate from 20 to 50 g/s). Using an existing laboratory scale test bench with high-density polyethylene (HDPE) and gaseous oxygen, the objective of this work is to use a piezoelectric pressure transducer to obtain the Helmholtz frequency mode of the combustion chamber, in order to calculate the instantaneous regression rate of the fuel grain. The average values of the regression rate will also be obtained, by measuring the mass of the chamber and propellant before and after each motor firing. These two measurements of the regression rate will be compared in a series of tests, determining the feasibility and accuracy of the instantaneous regression rate measurement by the Helmholtz frequency method.
Keywords
Aerospace engineering, hybrid rocket propulsion, Regression Rate, hybrid rocket motor, test bench
