The impact of fuel composition, engine power (idle and full power) and operation mode (cold and hot idle) on the gaseous emissions, particle number and mass concentrations and size distributions from an aircraft auxiliary power unit (APU) was investigated. A re-commissioned Artouste MK113 APU engine was used. The engine was run at three operational modes: i.e. approximately 6 minutes at idle (cold idle) after stabilized from start, 6 minutes at full power and then returning to idle again (hot idle) for 6 minutes. All operating parameters of the engine were monitored and recorded. The engine exhaust particle measurements and gaseous emissions were taken at three operating modes.

Five alternative fuels/blending components were tested and compared to neat conventional JetA1 fuel either in pure or blended forms. These fuels varied in their compositions in terms of H/C ratio, density and other properties. A Scanning Mobility Particle Sizer (SMPS) with a Nano-Differential Mobility Analyzer (NDMA) was used to determine the number and mass concentration and size distribution of engine exhaust in the size range from 5 nm to 160 nm. The influence of fuel elemental ratio (H/C), engine power and cold/hot operation on particle number and mass size distribution was investigated. The results show that there was a good correlation between fuels H/C ratio and particle concentrations, particle size and distributions characteristics. The engine at hot idle produced ∼20% less particles compare to the results at cold idle. The alternative fuel blends produced less particles than JetA1 fuel. The testing fuels produced similar levels of NOx, slight reductions in CO and remarkable reductions in UHC compared to JetA1.

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