Characterisation of particulate matter emitted from aviation gas turbines and spray-guided direct injection gasoline engines

Particulate matter (PM) emissions from combustion processes are of concern as evidence increasingly shows the negative impact that airborne concentrations of ultra-fine particulates can have on human health, environmental damage and global climate change. Aviation gas turbine and automotive engine exhaust contain a polydisperse mixture of solid and liquid, volatile and non-volatile particles in a hot, highly turbulent flow. In recent years it is the potential health implications of these combustion generated particulates which has become the driving force for more stringent PM emission regulations and improved sampling methodologies. This Thesis explores the characterisation of PM produced by current fleet aviation gas turbines and direct injection gasoline (GDI) automotive engines. Both the automotive Particle Measurement Programme (PMP) which dictates the European regulatory sampling system and the system currently being developed for international aviation industry regulation only consider non-volatile PM in recorded measurements to increase both reliability and repeatability of results. Experiments were performed to evaluate the performance differences between a volatile particle remover (VPR) which adheres to the specifications within the automotive PMP sampling methodology and that of a system which does not. Two sample aerosols were considered; these consisted of an aerosol containing solely volatile particles and another which consisted of solid core volatile coated particles. Mono-disperse size distributions (100, 50, 30 and 15nm) of each aerosol were employed as ‘challenge’ aerosols during VPR testing where particle size distributions and number concentrations were performed upstream and downstream of the VPR. GDI engine technology is becoming more prominent in the automotive market primarily due to the potential for increased operation flexibility and fuel reduction benefits. Regulations governing the output of PM from light duty GDI engines will come into force in 2014 resulting in a new phase of research into GDI engine PM vii emission and potential reduction or mitigation methodologies. This Thesis examined how PM emissions varied in response to changes to key engine operational parameters at homogeneous and stratified charge combustion modes and multiple engine loadings. PM produced by aviation gas turbines is currently regulated using SAE Smoke Number (SN). The main shortfall of SAE SN is that it gives little or no indication of PM size, number or mass; particle parameters which would greatly improve the sensitivity and understanding of an exhaust emission assessment. In order to address these inadequacies the International Civil Aviation Organisation (ICAO) plans to implement a new regulatory standard for the sampling and measurement of non-volatile PM in 2016 through the Committee on Aviation Environmental Protection (CAEP). Appointed with the development of this new methodology is the SAE E-31 Committee, a broad consortium which includes academic institutions, aircraft manufactures, aircraft operators, engine manufactures and Government agencies. During the development of the new standard, multiple large scale PM emission sampling tests have been and are continuing to be performed in order to validate the performance of the sample transfer mechanism and the measurement apparatus being considered as replacements for SAE SN. Analysis of PM emissions gathered during European Aviation Safety Agency (EASA) funded research projects (SAMPLE projects) is presented in this Thesis with a focus on how PM varies as a result of sample conditioning (i.e. dilution, line temperature and length), sample line loses, and the emission source. Gas turbine designers and manufactures are continually researching new combustion technologies as they strive for a competitive advantage in the industry. The introduction of lean-burn combustion regimes into engine combustor design is one such advancement which can provide a significant reduction in pollutant emission formation. In this Thesis analysis of PM emissions generated from the combustor sections of a modern large civil aviation gas turbine, operating in rich and lean burning combustion modes was performed. The use of a traversing sample probe system to acquire exhaust emissions at the exit of the combustor allowed fully annular sample measurements to be made.