Particle Transport and Losses when Sampling Aircraft Engine Combustion Emissions

Theme: Aerosol Technology

Start date: Cohort 2: 2020

Supervisors: Dr. Paul Williams, Dr. Amanda Lea-Langton, Dr. Adam Boies, and Dr. Mark Johnson

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.