**Description**
This article presents one approach to the mathematical modeling and analysis of a turbojet engine as a speed-control object. Extensive research on turbojet engine dynamic parameters in the time and frequency domains has been presented. The turbojet engine transfer function was defined based on the operation characteristics and experimental test data, which included fuel flow, turbine rotation speed, and exhaust gas temperature. For the turbojet engine, where the turbine rotation speed was defined as a controlled parameter, fuel flow was used as a control parameter. The total gain of the control object and the time constant parameters were determined as nonlinear functions, which primarily depend on turbojet engine mechanical characteristics and thermodynamic processes. Using the Simulink digital simulation platform, a dynamic turbojet engine simulation was performed. In limited operational conditions on the ground test cell, turbojet engine acceleration and exhaust gas temperature parameters were simulated in response to the throttle handle position step command. Under the same initial conditions, the simulation results were analyzed and compared with the experimental test data. With regard to dynamic behavior, the study reveals that the presented turbojet engine mathematical model has high fidelity, where simulation results exhibit a numeric accuracy better than 1.5%. In conclusion, following flight test data from turbojet engine operations at high altitudes and dynamic performance analysis, this study reveals that fuel flow as an input control parameter cannot be considered an independent variable. For these reasons, the turbojet engine cascade speed control concept has been proposed, in which the engine fuel system has an executive fuel metering function. The personal motivation for this study has come as a problem investigation in which several turbojet engines have severe failures in exploitation. In all cases, turbine blades were heavily damaged due to excessive heat exposure. Before any technical solution was implemented, the very first step was turbojet engine mathematical modeling and dynamic analysis. For future studies, the presented technical approach and results can be used in turbojet engine predictive maintenance planning and health monitoring concept development.

**Author(s) - ranked in descending order of contribution / as it should appear when published**
Neno Novakovic



Mathematical Modeling and Analysis of the Turbojet Engine Dynamic Parameters Based on Ground Test Mode of Operations

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