Development of ultra-compact combustors for low-carbon technology using trapped vortex concepts

到2040年，能源需求将增加四分之一以上[国际能源署数据]。鉴于燃烧在满足这一需求方面的主导地位，开发低碳、高效的燃气轮机(GT)发动机以减少排放影响和应对《巴黎协定》设定的全球变暖势在必行。近年来，稀油预混技术因其具有减排和高效的潜力而引起了人们的兴趣。然而，稀薄燃烧很容易发生不稳定，可能会导致不必要的振荡、火焰熄灭和闪回。氢等低碳或零碳燃料的使用也受到限制，因为防止高低热值(LHV)导致的闪回所需的高速可能会破坏涡旋动力学的稳定。因此，为了实现更高的效率和更低的排放，需要进一步的发展，而有效的火焰保持技术对这一发展至关重要。在超紧凑型燃烧室设计中，捕集涡(TV)系统被安装在主区或涡轮间区域，以增加燃烧气体的停留时间，从而获得更好的混合，从而提高效率和降低排放。更长的停留时间也意味着燃烧室更短，因此发动机更轻，燃料消耗更少，这也有助于多循环设备中的混合动力过程。电视被稳定地锁在一个腔内，因此即使在高速下对外部干扰也不那么敏感，从而允许使用具有高LHV的低碳或零碳燃料，如氢气。然而，由于剪切和边界层涡动力学、壁面强烈的换热以及火焰传播和自燃过程的同时发生，火焰稳定过程相当复杂。对火焰动力学的有效控制需要对这些过程有深入的了解。该项目旨在更好地理解用于超紧凑型燃烧设计的电视系统中控制火焰稳定的基本过程，以及它们在稀薄预混技术的背景下在高速(亚音速)条件下提供更好的火焰稳定性和低排放的潜力。特别地，电视物理将被研究：i)当燃烧室入口处存在代表旋流动力学的径向加速流时；以及ii)当腔体位于靠近燃烧室出口的收敛管道内时，存在轴向加速流。旋转和轴向加速都会破坏涡旋动力学，因此在电视系统可以有效使用之前，必须了解这种动力学。分析将通过高保真大涡模拟(LES)进行，与昂贵的实验研究相比，这是一种成本效益高的工具。这样，就可以通过参数研究来详细地研究湍流、当量比和空腔几何形状的影响。此外，不同替代燃料的性能以及它们在火焰保持和模型性能方面的含义可以针对不同的电视设计进行评估。将开发一个改进的模型，其中包括基于混合火焰片/完全搅拌反应器的假定PDF方法，以解释上述物理现象。对这一发展的基本理解将从前所未有的详细的直接数值模拟(DNS)中提取出来，并使用项目合作伙伴提供的实验验证数据。该项目的成果将极大地帮助现代低碳发动机的开发，并提高对这些设备中基础物理的理解。此外，该项目还将导致开发可用于工业设计周期的CFD代码和模型。因此，该项目对罗尔斯-罗伊斯等英国领先行业和其他新兴行业具有及时和强烈的相关性，并将帮助它们保持在发电行业的领先地位。

Energy demand will be up by more than a quarter by 2040 [International Energy Agency data]. Given the dominance of combustion in meeting this demand, it is imperative to develop low-carbon, efficient gas turbine (GT) engines to reduce emissions impact and tackle the global warming as set by the Paris Agreement. In recent years lean premixed technology has attracted interest due to its potential of reduced emissions and high efficiency. However, lean combustion is prone to instabilities that may lead to unwanted oscillations, flame extinctions and flashbacks. Use of low or zero-carbon fuels like hydrogen is also limited because the high speeds needed to prevent flashbacks due the high low-heating values (LHV) can destabilise the vortex dynamics. Further development is thus required to achieve better efficiency and lower emissions, and effective flame holding techniques are crucial for this development. In ultra-compact combustor design, trapped vortex (TV) systems are implemented either in the primary zone or in the inter-turbine region to increase the resident time of combusting gases, resulting in better mixing, thus higher efficiency and lower emissions. Higher resident times also imply a shorter combustor, thus a lighter engine and less fuel consumption, also helping the process of hybridisation in multi-cycle devices. TV are locked stably within a cavity and thus are less sensitive to external disturbances even at high speeds, allowing use of low or zero-carbon fuels with high LHV like hydrogen. However, the process of flame stabilisation is rather complex because of the shear and boundary layer (BL) vortex dynamics, the strong heat transfer to the wall and the simultaneous occurrence of flame propagation and auto-ignition processes. The effective control of the flame dynamics requires a deep understanding of these processes.This project aims to develop improved understanding of the fundamental processes governing flame stabilisation in TV systems for ultra-compact combustion design, and their potential to deliver improved flame stability and low emissions at high speed (subsonic) conditions in the context of lean premixed technology. In particular, the TV physics will be studied i) in presence of a radially accelerating flow representing the swirled flow dynamics at the entrance of the combustion chamber; and ii) in presence of an axially accelerating flow when the cavity is located within the converging duct near the combustor exit. Both swirled and axial acceleration can destabilise the vortex dynamics, so this dynamics has to be understood before TV systems can be effectively employed. The analyses will be conducted through high-fidelity large eddy simulations (LES), which represents a cost-effective tool as compared to expensive experimental investigations. In this way the effect of turbulence, equivalence ratio and cavity geometry can be explored in details via parametric study. Moreover, the performance of different alternative fuels and their implication in terms of flame holding and model performance can be evaluated for different TV designs. An improved model involving presumed PDF approaches based on mixed flamelets/perfectly stirred reactor will be developed to account for the aforementioned physics. The fundamental understanding for this development will be extracted from unprecedented detailed direct numerical simulation (DNS) and by using validation data from experiments provided by the project partners.The outcomes of this project will significantly help the development of modern, low-carbon engines, and improve the understanding of the fundamental physics within these devices. Moreover, the project will lead to the development of CFD codes and models that can be used in industrial design cycles. Thus, this project is timely and strongly relevant for leading UK industries such as Rolls-Royce and other emerging industry, and will help them to maintain their leading role in the power-generation sector.