Detailed Gaseous and Particulate Emissions of an Allison 250-C20B Turboshaft Engine

Abstract

Aviation is known to be one of the most significant contributors to air pollutants. This includes gaseous emissions, like carbon dioxide (CO2) and nitrogen oxides (NOx), and also particulate matter (PM), especially in the form of soot. This study conducted emission measurements on an Allison 250-C20B turboshaft engine operating on Jet A-1 fuel with a focus on gaseous compounds (e.g., ozone precursors) and PM. The different engine loading points were chosen based on the percentage thrust ratios of the International Civil Aviation Organization LTO-Cycle. A standard FTIR/O2/FID system to measure general gaseous combustion compounds, e.g., CO2, carbon monoxide (CO), unburned hydrocarbons (UHC), and NOx. For the investigation of the volatile organic compounds (VOC), which are known to act as ozone precursors, a gas chromatograph was applied. Different measurement methods were used to characterize the PM emissions. For the particle size distribution (PSD), we used two types of electrical mobility analyzers and an aerodynamic aerosol classifier. All measurement systems yielded comparable PSD results, indicating reliable results. The particle measurement methods all show increasing aerosol diameter modes (electrical and aerodynamic) with increased engine loading. The aerosol diameter modes were shifting from 29 nm to 65 nm. The size and shape of different individual particles were evaluated with a scanning electron microscope. A correlation between the injection system and the particle formation was established. Gaseous turboshaft engine emissions show high CO and UHC values at Ground Idle level. NOx levels were the highest at Take-Off conditions. Acetylene and ethylene were the most significant contributors to ozone formation.