Thrust Regulation System Medium Test: Nozzle Passes Pressure Testing

In March 2019, the thrust regulation system of Jiuzhou Yunjian① successfully completed its medium-condition test assessment, and the thrust chamber nozzle passed the pressure test evaluation. This marks another solid step forward in the development of the Lingyun engine.
A fundamental prerequisite for applying liquid rocket engines to the commercial space market is their ability to be recovered and reused. Only through recycling and reusability can launch costs be gradually reduced, paving the way for widespread commercial adoption. From the very beginning of its design, Lingyun Engine has been specifically tailored to meet the demands of commercial aerospace—namely, being recoverable and reusable. After thorough analysis and validation, the thrust adjustment range of the Lingyun Engine was set at 30% to 100%. At the heart of achieving this wide-range thrust modulation lies the advanced thrust regulation valve system, which enables stepless adjustment of valve opening to precisely control the propellant flow rate. This capability allows the engine to dynamically adjust its thrust output across the entire 30%–100% range, enabling critical functions such as rocket recovery. Indeed, the thrust regulation valve and associated technology employed in pump-fed liquid rocket engines represent a truly cutting-edge innovation—a remarkable feat of engineering that underscores the advanced nature of this propulsion system.

This test evaluated the control characteristics, flow performance, and control logic of the thrust regulating valve system, comprehensively verifying the rationality of the design scheme, the adaptability of the variable-thrust control logic, and the compatibility between the controller and the measurement/collection system. The thrust regulation system successfully passed the medium testing assessment, marking another critical milestone in Jiuzhou Yunjian's independent breakthrough of deep thrust adjustment technology for engines. Moving forward, we will continue to optimize and refine the thrust regulation control logic, while further enhancing the reliability of the system through various methods such as hardware-in-the-loop simulation and medium tests, aiming to minimize any potential technical risks that the variable-thrust system may pose to the engine.

Closed-loop Adjustment Curve for Medium Test Pressure

The role of the liquid rocket engine nozzle is to expand and accelerate high-temperature, high-pressure gases before ejecting them outward, thereby generating a reaction force—the final stage in producing engine thrust. To simplify manufacturing processes, engineering practice typically divides the thrust chamber structure into two sections downstream of the throat (at an expansion area ratio of 5–8): a short-nozzle thrust chamber and a nozzle extension segment. These two components can be connected either by welding or flanged joints.

To enhance technical adaptability in the commercial space market, the nozzle extension section of the Lingyun engine from Jiuzhou Yunjian underwent detailed research and validation during the conceptual phase. It was determined that an inner-and-outer double-layer structure would be adopted, a solution that significantly reduces manufacturing complexity and costs compared to the conventional tube-bundle design. Moreover, domestic private enterprises are well-positioned to achieve this innovative approach. The Lingyun engine's nozzle extension section is designed with a regenerative cooling scheme, utilizing a relatively simple and reliable milling-groove sandwich welding process. This segment is connected to the short-nozzle thrust chamber via flange joints, facilitating rapid iteration and iterative development in the early stages of the project. After thorough reliability assessments, the connection method will be transitioned to direct welding with the thrust chamber, further reducing structural weight. As part of Jiuzhou Yunjian's pioneering exploration within the private aerospace manufacturing ecosystem, the Lingyun engine's nozzle extension section successfully overcame numerous design and process-related challenges throughout its development. Ultimately, the team achieved breakthroughs in the efficient welding technology required for both the inner and outer layers of the nozzle. The first completed nozzle extension section of the Lingyun engine has now successfully passed pressure testing, demonstrating that Jiuzhou Yunjian's design concept for large-scale thin-walled sandwich structures is both rational and feasible, while also confirming the reliability of the associated manufacturing processes. Moving forward, this innovative approach will be applied to the design and fabrication of nozzles featuring even higher area ratios.

Since its establishment just over a year ago, the JiuZhou YunJian team has continuously innovated and put innovation into practice, steadily nurturing the technological "tree" of liquid oxygen-methane rocket engines. With dedication and hard work, we have diligently cultivated this tree, believing that, through the persistent efforts of China's aerospace pioneers, it will continue to thrive, drawing nourishment from the fertile ground of military-civilian integration. Ultimately, we hope this technology tree will take deep root in this rich soil, bearing abundant fruits that belong uniquely to China's commercial space industry.