Determination of major combustion products in aircraft exhausts by FTIR emission spectroscopy

The results of ground-based FTIR emission measurements of major combustion products such as CO2, H2O, CO, NO, and N2O of in-service aircraft engines are reported and compared to values published in recent literature. About 25% differences in the NO and CO emission indices at several power settings were found for two military bypass engines of the same type. In addition the measured CO emission index of (51.8 +/- 4.6) g kg(-1) at idle power of a CFM56-3 engine was about 27% lower than the value given by Spicer et al. (1984, 1994) for this engine type and about 27-48% higher than the ICAO data (ICAO, 1995) for the whole span of CFM56-3 engines. The CO emission index measured at idle power of a CFM56-5C2 engine of an Airbus A340 was (24 +/- 4) g kg(-1) and can be compared to the ICAO value of 34 g kg(-1). The N2O mixing ratios measured at a higher power setting of this engine was found to be 4 ppm and is in the range of reported literature values. Since the NO and CO emissions are strongly connected to the combustion process/efficiency and thus to the state of engine maintainance and/or the engine age, it can be concluded that there are significant engine-to-engine (of the same type) and possibly day-to-day variations in the emission characteristics of aero engines which cannot be neglected for the estimation of the overall air-traffic emissions. (C) 1998 Elsevier Science Ltd All rights reserved.