Turbojet direct-thrust control scheme for full-envelope fuel consumption minimization

Abstract

Purpose Reducing fuel consumption of unmanned aerial vehicles (UAVs) during transient operation is a cornerstone to achieve environment-friendly operations. The purpose of this paper is to develop a control scheme that improves the fuel economy of a turbojet in its full operating envelope. Design/methodology/approach A novel direct-thrust linear quadratic integral (LQI) approach, comprised by an optimal observer/controller satisfying specified performance parameters, is presented. The thrust estimator, based in a Wiener model, is validated with the experimental data of a micro-turbojet. Model uncertainty is characterized by analyzing variations between the identified model and measured data. The resulting uncertainty range is used to verify closed-loop stability with the circle criterion. The proposed controller provides stable responses with the specified performance in the whole operating range, even with after considering plant nonlinearities. Finally, the direct-thrust LQI is compared with a standard thrust controller to assess fuel economy and performance. Findings The direct-thrust LQI approach reduced the fuel consumption by 2.1090% in the most realistic scenario. The controllers were also evaluated using the environmental effect parameter (EEP) and transient-thrust-specific fuel consumption (T-TSFC). These novel metrics are proposed to evaluate the environmental impact during transient-thrust operations. The direct-thrust LQI approach has a more efficient fuel consumption according to these metrics. The results also show that isolating the thrust dynamics within the feedback loop has an important impact in fuel economy. Controllers were also evaluated using the EEP and T-TSFC. These novel metrics are proposed to evaluate the environmental impact during transient-thrust operations. The direct-thrust LQI approach has a more efficient fuel consumption according to these metrics. The results also show that isolating the thrust dynamics within the feedback loop has an important impact in fuel economy. Originality/value This study shows the design of an effective direct-thrust control approach that minimizes fuel consumption, ensures stable responses for the full operation range, allows isolating the thrust dynamics when designing the controller and is compatible with classical robustness and performance metrics. Finally, the study shows that a simple controller can reduce the fuel consumption of the turbojet during transient operation in scenarios that approximate realistic operating conditions.

Turbojet Thrust Augmentation through a Variable Exhaust Nozzle with Active Disturbance Rejection Control

“…Small-scale turbojets applications usually involve operating in environments with different sources of disturbances, from wind gusts and variations in the ambient conditions to more complex situations, such as variations in the effective payload [4] that modify the required throttle turbojet setting. These turbojet disturbances translate into disturbances in both the nozzle input and nozzle output, since the turbojet thermal state directly affects the input nozzle gas-path properties [5].…”

“…Turbojet control, on the other hand, has been a subject of interest of many researchers and different methods to overcome its difficulties have been developed. For instance, H ∞ synthesis algorithms [7], single neural adaptive propositional-integral-derivative PID controllers [8] and non-linear controllers based on a linear control-loop with an exogenous non-linearity [4] have been developed to handle the process non-linearities. On the other hand, model uncertainty has been handled through model predictive control in [9,10].…”