波转子烟气回流机理及其对低污染燃烧条件的控制机制研究

The wave rotor is a flow device based on unsteady pressure wave mechanisms. There is an inherent phenomenon of the exhausted gas recirculation (EGR) in common wave rotors. The EGR phenomenon is usually treated as negative in the field of wave rotor research. However, we newly found that the high-temperature, low-oxygen conditions of the low-emission combustion positively required the EGR. For that purpose, this project starts with the research on the mechanisms how the EGR is driven and mixed, and then utilizes the controllable parameters in the wave rotor design or operation to adjust its EGR status, and finally controls the low-emission combustion conditions. After that, this project accomplishes the experiment on the EGR of wave rotors, which validates the knowledge of the wave-rotor-inner EGR mechanisms and the control of the wave rotor on the low-emission combustion conditions. Compared to the extant research on the wave rotor or the low-emission combustion, this project tends to discover the positive effects of the wave rotor inner EGR phenomenon, and thus proposes a method to control the EGR based on the unsteady pressure waves. The results would support the wave-rotor-inner EGR to become a stable and controllable technology to provide the low-emission combustion conditions in front of the combustor. It means an extension of the low-emission combustion technology from a component to the core engine system, which would be important to the emission reduction of gas turbines.

波转子是一种基于非定常压力波原理的流体机械，其内部流场普遍存在烟气回流现象。此现象在波转子领域一般被认为是一种不利现象；但申请人新近发现低污染燃烧所需的高温、低氧条件对烟气回流有积极需求。为此，本项目首先研究波转子烟气回流的驱动与掺混机理，并运用波转子设计、运行中可以直接控制的参数对烟气回流状态进行调节，进而控制烟气回流所形成的低污染燃烧条件；然后进行波转子烟气回流试验，验证波转子烟气回流的机理认识以及波转子对低污染燃烧条件的控制作用。与波转子或低污染燃烧的以往研究相比，本项目更侧重于发掘波转子烟气回流现象的积极作用，并且提出基于非定常压力波驱动作用的烟气回流控制方法。本项目研究结果将支撑波转子烟气回流逐渐发展为一种稳定可控的技术，用于在燃烧室外部预先形成低污染燃烧条件，使低污染燃烧技术从燃烧室部件层面拓展到核心机系统层面，对降低燃气轮机污染排放具有重要意义。

在能源环境危机背景下，燃气轮机行业对燃烧污染物NOx减排的要求不断提高，仅靠发展燃烧室技术难以兼顾低污染燃烧与热力性能的发展需求。而波转子作为增压部件，凭借其内部固有的烟气回流现象，则可以从燃烧室外部控制低污染燃烧条件，同时保持其增压性能收益。上述视角突破了波转子领域长期将烟气回流视为消极现象的局限性，从而发掘波转子烟气回流的积极作用。波转子烟气回流的流动机理以及对低污染燃烧的作用研究结果表明：.（1）结合CFD与实验方法，发现波转子运行中，凭借±10%范围的转速调节即可形成±40%以上的烟气回流流量变化，而且转速与流量呈近似线性变化规律，同时波转子增压比保持在2.0以上、而且变化比例小于3%，从而掌握了基于转速控制的烟气回流流量调节方法。.（2）基于波转子二维全环非定常CFD模拟，发现了波转子内部烟气/空气的掺混机理，掌握了基于扰流片的烟气/空气掺混主动控制的方法。.（3）波转子与驻涡燃烧室串联，发现烟气与空气的掺混过程从波转子内部开始、持续到下游联接的燃烧室内部，形成特定的非均匀流场，使驻涡燃烧室可以在温度、氧气浓度条件适当的位置组织喷油、燃烧。.（4）发现波转子-驻涡燃烧室系统输出的流场存在几个主频下的压力、温度波动，主要原因是波转子内部的非定常压力波与局部涡系扰动向下游传播，而驻涡燃烧也引入新的涡扰动，最终耦合作用在输出流场中。.本项目研究形成了波转子对烟气回流的流量、掺混状态的调控机理，并且论证了它对低污染燃烧条件的控制机制。研究成果将支撑波转子烟气回流逐渐发展为一种稳定可控的技术，使低污染燃烧技术从燃烧室部件层面拓展到核心机系统层面。