Influence of alternative fuel properties and combustor operating conditions on the nvPM and gaseous emissions produced by a small-scale RQL combustor

Abstract

Non-volatile Particulate Matter (nvPM) from aircraft gas turbine engines are harmful to both human health and the environment, but can be significantly reduced by using low aromatic Sustainable Aviation Fuel (SAF). As part of the Horizon 2020 funded JETSCREEN (JET fuel SCREENing and optimisation platform for alternative fuels) project, nvPM and gaseous emissions were characterised using regulatory compliant sampling and measurement methodologies for a small-scale (<250kW) non-proprietary RQL combustion rig, at pressures ranging from 1.0 to 2.4 bara. The impact of flow conditions, air to fuel ratio and fuel composition was investigated for a selection of conventional aviation Jet-A1 fuels, SAFs, and blended fuels. Measured concentrations were corrected for particle-size-dependant system losses using particle size measurements, to be representative of combustor exit concentrations.Across the range of fuels (hydrogen contents 13.51%-15:31%), system-loss-corrected nvPM mass, number, and size were shown to decrease with increasing fuel hydrogen content, in agreement with previous studies. Inverse power law correlations are proposed as the best descriptors of these trends. Average reductions in nvPM mass, number, and sizes of 73%, 54% and 17% respectively, were observed for a near-zero aromatic ATJ fuel compared to a reference Jet A1 fuel, with minimal changes to measured gaseous pollutants. It is noted that without size-dependant system loss corrections, nvPM number reductions were overreported (∼6% for the ATJ fuel) due to the smaller particle sizes with increasing fuel hydrogen content. It was hypothesised that observed nvPM deviations from the fuel hydrogen content trends were due to fuel physical properties affecting atomisation, however no correlations were found greater than the measurement uncertainty and combustor rig variability.This study provides a unique dataset intended to facilitate combustion model validation, providing full details of combustor geometry, flow conditions and rig conditions, along with the representative combustor exit nvPM and gaseous data.