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

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.

Aerosol science has a significant impact on a broad range of disciplines, extending from inhaled drug delivery, to combustion science and its health impacts, aerosol assisted routes to materials, climate change, and the delivery of agricultural and consumer products. Estimates of the global aerosol market size suggest it will reach $84 billion/year by 2024 with products in the personal care, household, automotive, food, paints and medical sectors. Air pollution leads to an estimated 30-40,000 premature deaths each year in the UK, and aerosols transmit human and animal infections. More than 12 million people in the UK live with lung disease such as asthma, and the NHS spends ~£5 billion/year on respiratory therapies. Many of the technological, societal and health challenges central to these areas rely on core skills and knowledge of aerosol science. Despite this, an Industrial Workshop and online survey (held in preparation for this bid) highlighted the current doctoral skills gap in aerosol science in the UK. Participating industries reported that only 15% of their employees working with aerosol science at doctoral-level having received any formal training. A CDT in aerosol science, CAS, will fill this skills gap, impacting on all areas of science where core training in aerosol science is crucial.

Impact on the UK aerosol community: Aerosol scientists work across governmental policy, industrial research and innovation, and in academia. Despite the considerable overlap in training needs for researchers working in these diverse sectors, current doctoral training in aerosol science is fragmentary and ad hoc (e.g. the annual Fundamentals of Aerosol Science course delivered by the Aerosol Society). In addition, training occurs within the context of individual disciplines, reinforcing artificial subject boundaries. CAS will bring coherence to training in the core physical and engineering science of aerosols, catalysing new synergies in research, and providing a focal point for training a multidisciplinary community of researchers. Working with the Aerosol Society, we will establish a legacy by providing training resources for future researchers through an online training portal.

Impact on industry and public-sector partners: 45 organisations have indicated they will act as CAS partners with interests in respiratory therapies, public health, materials manufacturing, consumer and agricultural products, instrumentation, emissions and environment. Establishing CAS will deliver researchers with the necessary skills to ensure the UK establishes and sustains a scientific and technical lead in their sectors. Further, it will provide an ideal mechanism for delivering Continuing Professional Development for the existing workforce practitioners. The activity of CAS is aligned to the Industrial Strategy Challenge Fund (e.g. through developing new healthcare technologies and new materials) and the EPSRC Prosperity Outcomes of a productive, healthy (e.g. novel treatments for respiratory disease) and resilient (e.g. adaptations to climate change, air quality) nation, with both the skilled researchers and their science naturally translating to long-lasting impact. Additionally, rigorous training in responsible innovation and ethical standards will lead to aerosol researchers able to contribute to developing: regulatory standards for medicines; policy on air quality and climate geoengineering; and regulations on manufactured nano-materials.

Public engagement: CAS will provide a focal point for engaging the public on topics in aerosol science that affect our daily lives (consumer products, materials) through to our health (inhalation therapeutics, disease transmission and impacts of pollution) and the future of our planet (geoengineering). Supported by a rigorous doctoral level training in aerosol science, this next generation of researchers will be ideally positioned to lead debates on all of these societal and technological challenges.