Research On The Stability Of Fuel Control System For Small Turbojet Engine

In this thesis, in order to solve the unstable working problem of a small turbojetengine during low rotate speed to meet the requirements of engineering, modeling of theengine, the stability analysis and design of the fuel control system, the effects of sidewardadjuster on the stability of the engine were studied.Firstly, the mathematical models of the fuel pump in turbojet engine, the motor in thefuel in the fuel pump, the turbojet engine, the fuel line and the sideward adjuster in the fuelsystem were established by combining the mechanism modeling method and theexperimental modeling method. These models were validated by the experimental and thesimulation, which laid the foundations of further study of the stability of the fuel controlsystem of the engine. Secondly, the stability analysis of the fuel control system was madeto find out the differences between two different fuel control systems. And theexperimental results of the engine using these two fuel control systems were analyzed andcompared in detail. On the basis of the analytical model, the instability of the rev is studiedby simulation method, and the analytical model can be confirmed in further. Nextly,Matlab software was used to carry on the frequency domain analysis of the control systemfor the turbojet engine. Then the dynamic character of the engine was obtained, theperformance of the fuel control system was analyzed and the unstable rev range wasdetermined by using the Bode figure and the pole zero figure. According to the results ofthe frequency domain analysis, the mechanism of the instability of the engine wasinvestigated to find out the physical mechanism which can result in the instability of therev of the engine, which can be the basis of the further design of the control system. Fromthe point of view of the design of the control system, the design of the control system canbe carried on through investigating the current engine to find out whether there were idealparameters to ensure the stability of the system, or the condition under which there areparameters that can meet the requirement of the stability of the system and the basicrequirements to guarantee the stability of the engine, and verifying it with the help of theclose-loop simulation method of the engine control system. According to the analyticalresults, refine scheme of the fuel control system of the turbojet engine was established byadjusting parameter of the sideward adjustor. Finally with simulation method, effect of thevariety of the elastic modulus of the spring, the preload, the original displacement of thepointer and the friction of the ring on the stability of the engine were analyzed and the key parameters of the system were found.