With the rapid developments in the military technology, there’s a growing demand for high performance variable cycle gas turbines. Variable cycle technology could make engines meet supersonic and subsonic flight requirements and improve the propulsion system’s performance in the whole envelope of symmetrical and asymmetrical flight.
Previous efforts by the US Air Force Research Laboratory, General Electric, and Rollo Companies have led to the development of the adaptive engine equipped with an adaptive fan and three streams. The project was labeled the adaptive engine technology development. This type of engine is designed to keep the inlet flow constant by varying internal and external flows to reduce the engine’s fuel consumption, and achieve high thrust-weight ratio and longer flight range. The engine’s by-pass flow effectively suppresses and conceals the engine’s infrared intensity.
A successful operation of military fighters is contingent upon the aircraft’s ability to remain undetected by infrared guided missiles. High temperature engine exhaust gas, hot metal turbines, and metal surfaces in contact with the hot exhaust cause the engine to emit high levels of infrared energy. This is why to minimize the chances of infrared detection, many devices including the variable cycle engine have been designed to reduce the engine’s infrared radiation.
As the threat of infrared detection system and infrared guided missiles become even more serious, it’s becoming extremely necessary to study the low-infrared technology of a variable cycle engine. Traditional engine control system design didn’t take into consideration infrared radiation characteristics. To ensure stable and safe engine’s operation at the worst operating point in the flight envelope, a larger safety margin is normally retained in the design process. Fortunately, performance seeking control can help calculate the engine’s performance parameters and optimize the engine’s working point in real time, which would utilize the potential of the engine performance. Although several previous studies have focused on the role of performance seeking control in improving specific fuel consumption and thrust, not all consider the optimization of infrared radiation intensity through performance seeking control.
In light of this, Nanjing University of Aeronautics and Astronautics researchers Dr. Haoying Chen, Dr. Qiangang Zheng, Mr. Yuan Gao, and Professor Haibo Zhang established an infrared prediction model on the exhaust system based on the real-time component-level model of double bypass variable cycle engine. The model enabled them calculate the infrared radiation intensity in real-time. Their research work is currently published in the journal, Aerospace Science and Technology.
The authors used Feasible Sequential Quadratic Programming with local and global superlinear convergence characteristics to investigate the performance seeking control of double bypass variable cycle engine, minimum specific fuel consumption mode, minim infrared characteristics mode, and maximum thrust mode.
The researchers established a component-level model of double bypass variable cycle engine whose error was less than 2%. The established model has high credibility and can be extended in the study of optimal control. They observed that the infrared radiation intensity of the exhaust was related to the exhaust system’s section temperature and the detectable area. The infrared radiation intensity declined with a decrease in the nozzle throat area and fuel consumption.
Feasible Sequential Quadratic Programming algorithm enabled the variable cycle engine to satisfy the constraints and achieve the optimal solution in each optimization mode. The authors observed that the engine thrust increased in the maximum thrust mode while specific fuel consumption decreased in the minimum specific fuel consumption mode and infrared intensity decreased in the minimum infrared characteristic mode. The newly proposed algorithm could help obtain the operating conditions of double bypass variable cycle engine in various working condition, thereby achieving the steady-state performance seeking control of the engine.
Haoying Chen, Qiangang Zheng, Yuan Gao, and Haibo Zhang. Performance seeking control of minimum infrared characteristic on double bypass variable cycle engine. Aerospace Science and Technology, issue, 108 (2021), 106359.