Particle Transport and Losses in Sampling Aircraft Gas Turbine Engine Combustion Emissions

飞机燃气轮机通过燃烧产生碳烟排放。烟尘被认为对公众健康和环境都有负面影响。为了应对这些影响，ICOA引入了法规，并由EASA等国际监管机构执行。这些法规--特别是APR6320--规定了如何采样和测量烟尘颗粒，这导致发动机制造商、监管机构和大学之间合作开发了采样系统。目前，采样系统使用气溶胶仪器来测量发动机出口平面上的烟尘颗粒的数量和质量。然而，由于整个系统都出现了损失，烟尘的采样在很大程度上仍然没有量化--特别是在探测器上。穿透曲线表明，较小的颗粒没有被采样，因为它们没有穿透样品系统足够远。虽然已经开发了各种损失模型(LLCA、UTRC等)，但由于模型外推了小于15 nm的颗粒，因此小颗粒(直径小于15 nm)的损失仍然是不确定的。由于烟尘颗粒的尺寸损失以及热排放和采样系统之间的温度梯度，推测损失主要是由于扩散和热湿损失机制造成的。为了充分研究微小的烟尘颗粒损失，需要将采样点移到燃烧室外。从这一点开始采样将在小煤烟颗粒凝聚和凝结形成长链(直径大于15 nm)之前将其隔离，并允许更好地了解燃烧室附近的煤烟颗粒形成过程。由于该地区以前没有进行过采样，因此将面临几个挑战，主要是开发一种能够承受恶劣环境(1100 K温度)的探测器。该项目将分为两个主要目标：对靠近燃烧区采样时的烟尘损失和传输进行实验量化，以及开发2020/2021年费格斯-利德斯通-莱恩有效模型来解释小的烟尘颗粒。实验将使用各种气溶胶仪器进行--CPC用于数字浓度，LII和MSS用于质量测量，DMA和ACC用于尺寸测量。试验将主要在各种燃烧试验台上进行，在这些试验台上更容易隔离特定的燃烧条件，并允许直接进入燃烧区。对于建模，将开发当前的损失模型来解释小的烟尘损失，以及更先进的3D CFD模型。建模过程的第一步将是用理论和实验结果挑战当前的假设--例如，假设所有煤烟的密度为1g/cm3--以检查考虑小煤烟颗粒时模型的有效性。随着新的实验结果的获得并输入到模型中，这个过程将变得迭代。由于对排放的担忧，在整个项目中需要考虑负责任的创新是关键。主要的担忧是，排放的未量化的小煤烟颗粒数量比预期的大得多。导致政策变化，这可能对发动机制造商造成潜在损害，或者更有可能导致更高效发动机的设计变化。

Aircraft gas turbine engine produce soot emissions through combustion. Soot is considered to have negative impacts on both public health and the environment. To combat the impacts, regulations have been introduced by the ICOA and enforced by international regulators, such as EASA. The regulations - specifically APR6320 - stipulates how to sample and measure the soot particles, and this has led to collaborations between engine manufacturers, regulators, and universities to develop a sampling system. Currently, the sampling system uses aerosol instrumentation to measure the number and the mass of soot particles at the exit plane of the engine. However, the sampling of soot is still largely unquantified due to losses witnessed throughout the system - especially at the probe. Penetration curves indicate that smaller particles are not sampled as they do not penetrate far enough through the sample system. Although there has been various loss models developed (LLCA, UTRC, etc..), small soot particle (below 15 nm in diameter) loss remains uncertain, as the models extrapolate for particles below 15 nm. Due to the size of the soot particles being lost and the temperature gradients between the hot emissions and the sampling system, it is speculated that the losses are mostly due to diffusion and thermophoretic loss mechanism. To fully study small soot particle loss, the sampling point will need to be moved to just outside the combustion chamber. Sampling from this point will isolate small soot particles before they agglomerates and coagulates to form long chains (larger than 15 nm in diameter) and allow a better understanding of soot particle formation processes near the combustion chamber. As sampling from this area has not been done before, there will be several challenges, mainly developing a probe that can withstand the harsh environment (temperatures of 1100 K). This project will be split into two main objectives; experimentally quantifying the soot losses and transport when sampling close to the combustion zone and the development of an 2020/2021 Fergus Lidstone-Lane effective model to account for small soot particles. The experimentation will be conducted using various aerosol instrumentation - CPC for number concentrations, LII and MSS for mass measurements, and DMA and ACC for size measurements. Experimentation will mostly be conducted on various combustion test rigs, where it is easier to isolate specific combustion conditions and allows direct access to the combustion zone. For the modelling, there will be both development of current loss models to account for small soot losses and more advanced 3D CFD models. The first steps of the modelling process will be to challenge current assumptions - such as, assuming all soot has a density of 1 g/cm3 - with theory and experimental results to check the models validity when considering small soot particles. This process will become iterative as new experimental results are obtained and feed into the models. Due to the concerns around emissions, it is key that throughout this project responsible innovation needs to be considered. The main concern is that the unquantified amount of small soot particles being emitted is significantly larger than expected. Resulting in policy change which could be potentially damaging for engine manufacturers, or more likely result in design change for more efficient engines.