Start-up transient simulation of a liquid rocket engine

During the start-up of a liquid rocket engine most of the engine components are required to work at extreme operating conditions; this phase features very complex phenomena such as combustion instabilities, water hammer eFFects in feed lines, turbopumps operating far from design conditions and two-phase flows that cannot be neglected when design studies of an engine are to be performed or the assessment of the valve opening sequence has to be done. For these reasons simulations of the ignition transient phase become necessary in order to reduce the experimental tests and increase the engine safety and reliability. The subject of the present work is to develop an LRE transient model, to apply it to simulate the start-up transient and to validate the model with an existing liquid rocket engine (the RL-10). A system approach has been used, since it is necessary to take into account all the interactions between all the components of an engine. This choice is fundamental if a detailed estimation of the engine transient behaviour is the task. The system simulated by the code encompasses the complete feeding system from the tanks down to the the turbopump subsystems, the valves, the pipes, the thrust chamber's inlets, the flow ducts of the thrust chamber itself and the chemical reactions inside the combustion chamber. The engine model is built using ESPSS,5 the propulsion system library compatible with EcosimPro, an object oriented tool capable of modelling various kinds of dynamic systems. The engine model includes also original models developed by the authors and presented in previous works6 such as a new injector plate model, and more realistic heat transfer coefficient correlations. The transient phase of the Pratt and Whitney RL-10 engine has been taken as validation case. This engine has been chosen for several reasons, among which the good availability of engine construction data, performance and tests results in open literature.1-3 The main subsystem models of this engine will be described and their validation will be presented. Then the integrated model of the entire engine will be described alongside the comparison of the simulation with experimental data. © 2011 by F. Di Matteo.