Test cell emission measurements of commercial aircraft engine: CFM56-7B26

Abstract

In this study, the results of a test cell emission measurement campaign for overhauled CFM56-7B26 series engines are presented. The emissions are measured for specific power settings representing the main operating modes of aircraft, during the functional and performance tests of the engines. The measured emissions are carbon dioxide, carbon monoxide, total hydrocarbons and nitrogen oxides (NO and NO2), the observations of which are consistent and repeatable. Unlike other emission measurement campaigns, where the sample probe is conventionally located downstream of the exhaust, in this study it is installed inside the engine, immediately behind the final stage of the low pressure turbine rotor. Therefore, the results are obtained without the interference of by-pass air which may lead to significant uncertainty. The idle emissions between the beginning (cold idle) and the end (hot idle) of the engine operation reveal measurable differences leading to the conclusion that treating the same emission indices at both the taxi-in and taxi-out phases may result in inaccurate determination regarding the true impact of the aircraft emissions. It has also been found that the low power CO and HC emissions are significantly higher compared to the corresponding ICAO values, while the NOx emissions are found to be lower.