Turbulent mixing enhancement of compact swirl puffs

脉冲燃烧是一种间歇燃烧技术，其特点是伴随着温度、压力和速度场的周期性变化的振荡质量流量，但不像内燃机那样具有往复运动机制。它被认为是一种有前途的燃烧技术，它促进了可再生能源的发展，因为它可以燃烧不同质量的燃料，从高级天然气和丙烷到低级燃料，如沼气。与现代喷气发动机燃烧室中的传统稳定燃烧相比，它还具有更高的燃烧效率和更低的污染物排放。这些特点使其成为可持续发展（自然资源和环境）的理想候选者，而可持续发展是一项重大的全球挑战。在最近的一篇评论文章中，它提到，尽管有80年的研发历史，脉冲燃烧仍然是一种相对模糊的技术，需要从流体力学到化学等广泛学科的基础研究。虽然迄今为止的研究主要集中在整个系统的性能，系统的研究，许多子系统中的每一个仍然是很高的需求。与燃料喷射策略相关的流体力学就是其中之一，与脉冲燃烧相关的流场通常是高能的、紧凑的，其形式为湍流喷烟。它以相当大的自诱导速度传播。在非预混燃烧应用中，这导致燃料和周围氧化剂的不充分混合，并因此导致不期望的燃烧条件。为了解决这一问题，本项目寻求一种提高混合效率的方法，其目的和目标本项目从基本的非反应流体力学的观点出发，旨在通过在脉冲喷流上叠加各种强度的旋流分量来找到一种最佳的标量混合增强。这种混合注入方法将引入复杂的相干湍流结构，从而促进高混合效率。它结合了目前喷气发动机中普遍采用的旋流射流燃烧和脉冲燃烧的优点。还将探索一种可行的静态流动控制策略，以进一步增强湍流混合。为了实现这些目标，将利用先进的激光诊断技术进行系统的实验，以非侵入性方式同时测量速度场和标量场。脉冲燃烧技术的主要应用领域是脉冲燃烧，其主要优点是减少排放，促进可再生能源的发展。这两个要素对全球可持续发展，特别是对发展中国家而言至关重要。在英国，超过75%的能源需求由化石燃料的燃烧提供，每年排放超过3000 Kt的空气污染物。这些污染物加上温室气体排放每年额外增加160亿英镑。从NHS的医疗保健服务和产品。这些排放量的小幅减少将给英国经济带来巨大影响。

The context of the researchPulse combustion is an intermittent combustion technique, which is characterized by the oscillatory mass flow rate accompanied by a periodic variation in temperature, pressure and velocity field, but without a reciprocating mechanism as in IC engines. It is considered to be a promising combustion technique, which promotes renewable energy sources since it can burn fuels of different quality ranging from high-grade natural gas and propane to low-grade fuels like biogas. It also has higher combustion efficiency and lower pollutant emissions, compared to conventional steady combustions like it in modern jet engine combustors. These characteristics render it an ideal candidate for sustainable development (for natural resource and environment), which is a major global challenge. In a recent review article, it mentions that although with 80 years of R&D history, pulse combustion remains a relatively obscure technique, which requires fundamental research across a wide range of disciplines ranging from fluid mechanics to chemistry. While the research so far has mainly focused on the overall system performance, systematic studies on each of the many subsystems are still in high demand. The fluid mechanics associated with the fuel injection strategy is one of them.The flow field associated with pulse combustion is usually highly energetic and compact, which is in the form of a turbulent puff. It propagates at a considerable self-induced velocity. In non-premix combustion applications, this results in insufficient mixing of fuel and the surrounding oxidizer and hence undesirable combustion conditions. To tackle this problem, a method to enhance such mixing efficiency is sought in the project.Its aim and objectivesThis project, from a fundamental non-reacting fluid mechanics' point of view, aims to find an optimal scalar mixing enhancement by superposing a swirl component of a variety of strengths on to the pulsed puffs. Such a hybrid injection method will introduce complex coherent turbulence structures and hence promote high mixing efficiency. It combines the advantage of swirling jet combustion, which is commonly adopted in current jet engines, and pulse combustion. A feasible static flow control strategy will also be explored in order to further enhance turbulent mixing. In order to achieve these aims, systematic experiments will be conducted using advanced laser diagnostic techniques for simultaneous measurements of velocity and scalar fields in a non-invasive way. Its potential applications and benefitsThe main application of the research is pulse combustion, whose key advantage is to reduce emission and promote renewable energy sources. These two elements are crucial for global sustainable development, especially for developing countries. In the UK, over 75% of the energy demand is provided by the combustion of fossil fuels, at the cost of emitting over 3000Kt of air pollutant each year. These pollutant plus greenhouse emissions make extra £16 billion p.a. from NHS on health care service and products. A small reduction of these emissions will bring a huge impact to the UK economy.