Evaluation of Transport Line Effects on PM Size Distribution for Aircraft Exhaust for Different Flow Regimes and Dilution Methodology

This study is part of an ongoing European Aviation Safety Agency (EASA) programme (‘SAMPLE’). The effects of gas stream flow regimes in the sample transport line and dilution strategies for removal of the volatile fraction on measured PM size distribution are evaluated behind a simulated aero-derivative gas turbine exhaust using a fast mobility DMS500 particle sizer. The PM size distribution and concentration within the primary transport sample was found to be relatively insensitive to flow regime, with conditions of turbulent flow (lowest residence time) providing the highest number concentrations, and hence least losses. However, given the natural variation of PM production from the combustor source the statistical certainty of these observations require consolidation. A ‘bespoke’ volatile particle removal system based on the European automotive PMP protocol was constructed to allow the effects of dilution ratio and evaporation tube residence time to be investigated. It was shown that both strategies of increasing dilution ratio and residence times in the evaporation tube did not affect the size distribution at the two distinct nucleation and accumulation modes to any statistical certainty. When using high (420:1) dilution ratios in the VPR, a third larger (200nm) mode appears, which requires further investigation.