Mixture ratio control of liquid propellant engines

Purpose - Development and application of a new systematic approach for design of a control system in order to control the mixture ratio of liquid propellant engines. Design/methodology/approach - The design approach is based on a full nonlinear dynamic model of the engine, and the controller design method is based on describing function models of the engine coupled with the factorization theory. The presented systematic design procedure is comprised of five primary steps. The developed software for the design approach is in the MATLAB environment. Findings - It is found that the presented design approach may successfully be used to control the mixture ratio of a class of liquid propellant engines whose control loops are decoupled. The performance and robustness of the designed controller is found to be satisfactory. Research limitations/implications - At present, the research is limited to liquid propellant engines whose control loops are decoupled. Practical implications - The major outcome of this research is that complicated hydromechanical control valves that are used to control the mixture ratio may be replaced by simple microprocessor based servomechanisms that drive simple valves. This will allow for the engine to accept various set point values for mixture ratio as is required in multi-regime engines. Originality/value - This is the first paper in the area of mixture ratio control of a liquid propellant engine that is based on the application of describing function approach coupled with the factorization theory.