Turbojet Engine Parameters Calculation Based on Fuel Flow and Exhaust Gas Temperature (SAE Paper 2021-01-0029)

Abstract

The aircraft jet engine is one of the most complex multivariable systems with multiple inputs and multiple outputs. To attempt to optimize control functions or to address diagnostic problems, a detailed knowledge of all jet engine design parameters and performances is required. Although jet engines have been around for almost a century, there are only a few companies in the world presently designing and manufacturing them; as such these companies possess detailed knowledge of all relevant design characteristics and performance parameters. In the event where jet engine technical details are unknown, or only a few of them are known from manufacturer�s catalogues, the challenge becomes how to calculate and extrapolate critical performance parameters based on only fuel flow, jet exhaust temperature and total thrust. The brief engineering concept of calculation steps presented herein has the goal of identifying unknown turbojet engine parameters and design characteristics based on limited measurements and test data obtained at static conditions and single operating point. Test data included steady state fuel flow, turbine gas exit temperature and total jet engine thrust. For the purpose of jet engine parameters estimate and identification, the Rolls-Royce VIPER 11 Mk 22-6 jet engine was used. Calculated and estimated jet engine design parameters were evaluated and compared with measured parameters under the same initial conditions. The results show that calculation and identification processes are accurate with an overall error of less than 1 percent. The presented numeric algorithm combined with off design parameters calculation, can be used in jet engine health monitoring and fault detection processes.