@article{PEI2025, 
author = {Xitong PEI and Bing WANG and Chenglu QI and Qiumeng QIAN and Qiaofeng XIE and Ziwan LI and Xinyu WANG},
title = {Research progress in mode transition technologies for turbine-based combined cycle engines},
year = {2025},
journal = {Journal of Tsinghua University (Science and Technology)},
volume = {65},
number = {12},
pages = {2410-2448},
keywords = {combined cycle engines, mode transition, thrust trap, intake and exhaust system, integrated integration},
url = {https://www.sciopen.com/article/10.16511/j.cnki.qhdxxb.2026.26.008},
doi = {10.16511/j.cnki.qhdxxb.2026.26.008},
abstract = {SignificanceTurbine-based combined cycle (TBCC) engine is an ideal propulsion system for hypersonic flight, with a wide-speed range, large flight envelope, and horizontal takeoff and landing capability. The TBCC engine, comprising an air-breathing gas turbine and a ramjet, has become a key aspect of current and future aerospace research. When the TBCC engine operates across a wide-speed range (Ma 0-7.0), it undergoes a mode transition between the gas turbine and the ramjet. This transition requires coordinated operation among various components and subsystems, involving a broad disciplinary scope, high technical complexity, and significant implementation challenges. Consequently, the mode transition has become a critical bottleneck in the development of TBCC engines.ProgressThis study systematically reviews the development progress of TBCC engines across various countries and analyzes the "thrust gap" phenomenon and the multi-component matching challenges that occur during mode transition. The review encompasses four key aspects: (1) Intake system design and regulation technology: Current mature approaches, such as boundary layer bleeding and vortex generators, offer limited adjustability, making precise and rapid flow control challenging. Axisymmetric intakes, favored for their simplicity in series-configured TBCC engines during mode transitions, still require enhanced variable-geometry capabilities to improve performance. Additionally, two-dimensional and three-dimensional inward-turning intakes provide greater regulation flexibility and effectively suppress inlet coupling interference; however, their control strategies within intake systems demand further in-depth investigation. (2) High-performance turbine and ramjet engine design, as well as rocket-assisted boost technology: Modified high-speed turbine engines utilizing inlet pre-cooling show greater potential, compared to newly developed ones, though their advancement hinges on the creation of lightweight pre-coolers that can operate across wide temperature ranges. For wide-speed ramjet technologies, methods such as rotating detonation combustion, advanced inlet designs, and combustion optimization can effectively extend the operational Mach number range. However, integrating these technologies into combined-cycle engines requires further in-depth research. While rocket-assisted thrust augmentation directly addresses the "thrust gap, " incorporating an additional rocket engine may introduce significant structural complexity. (3) Exhaust system design and regulation technology: Future directions focus on efficient aerodynamic profile design and active control of shockwave-boundary layer interactions. Regarding nozzle configurations, both two-dimensional and three-dimensional nozzles can satisfy the exhaust expansion requirements of combined-cycle engines. Two-dimensional nozzles offer simpler structures but pose significant challenges for aerodynamic integration. In contrast, three-dimensional nozzles provide superior performance and better integration potential with the overall propulsion system; however, they involve greater design, manufacturing, and control complexities. (4) The combined-cycle engine system integration, mode transition control, and experimental testing technologies: The United States has conducted relatively comprehensive research, having completed integrated engine model-level mode transition tests and comparative analyses of various control algorithms. Nevertheless, most existing studies remain theoretical or limited to model validation.Conclusions and ProspectsMany conducted mode transition experiments have not fully addressed the variable-geometry adjustment of the inlet and exhaust systems or the dynamic cooperative control of the fully integrated engine. Consequently, future research should prioritize cross-system integrated cooperative control for combined-cycle engines, the development of advanced test facilities capable of simulating wide-range flight environments, and full-scale engine validation of mode transition processes. Key future research directions include optimizing off-design performance and multi-physics coupling in intake system design, advancing rotation detonation combustion technology, developing three-dimensional nozzle control and multi-duct collaborative matching techniques, and establishing a full-chain research and development system for TBCC engines.}
}