System analysis of low frequency combustion instabilities in liquid rocket engines

In this paper we propose an analysis of low frequency combustion instabilities, taking advantage of the software EcosimPro. We implement a specific module based on the double time lag model and investigate the coupling of combustion chamber and feed line oscillations by using a complete set of non-linear equations. We identify the characteristic time lags following two approaches: (i) a constant time lag approach and (ii) a variable time lag approach based on correlations available in open literature. To prove the module capabilities we reproduce an experimental set up consisting of a combustion chamber decoupled from the upstream feed lines. For this configuration we generate a stability map, comparing our results with literature data from both experiments and a linear double time lag model. The stability boundaries obtained with the chug module are in good agreement with those obtained in open literature, and the first characteristic frequency of the engine is well predicted. Finally, we study the influence of the feed lines on the system stability, verifying that the lines extend the stable regime of the combustion chamber and that the propellant domes play a key role in coupling the dynamics of combustion chamber and feed lines.