ANALYSIS OF LIQUID ROCKET ENGINE COMBUSTION INSTABILITY

This report develops a nonlinear model which can be used to predict combustion instability zones in liquid rocket engines. The model is developed by combining a nonlinear instability model with a steady-state vaporization model. Such an analysis determines the zones of an engine in which a tangential mode of high frequency instability is most easily initiated. A rocket engine can be analyzed by incrementally dividing the combustion chamber into annular nodes in the r and z directions. Steady-state properties at each annular node or position in the chamber are computed from the steady-state vaporization computer program. The steady-state program is capable of computing combustion profiles in thermally unstable propellants of the monomethylhydrazine/nitrogen tetroxide type. This model describes droplet vaporization with vapor phase decomposition. Using the computed steady-state properties and the stability limit curves from the instability computer program, stability at each node is determined. This process is repeated for each node to determine a stability map of the entire engine.