In-flight measurement of aircraft CO and nonmethane hydrocarbon emission indices

Emission indices were derived from in-flight measurements of CO, nonmethane hydrocarbons (NMHCs), H2O, and nonvolatile condensation nuclei in the exha ust plumes of the Deutsches Zentrum fur Luft- und Raumfahrt VFW 614 (ATTAS) and NASA DC-8 experimental aircraft. CO emission indices, EIs(CO), of the ATTAS Rolls Royce M 45H Mk501 engines were determined concurrently by two i ndependent techniques: monitoring of exhaust emissions using a customized F ourier transform infrared spectrometer (FTIR) and by simultaneous continuou s fast CO and CO, measurements. The EIs(CO) determined by FTIR were systema tically 28% lower than those derived from the CO/CO2 concentration ratios. The EIs(CO) of the newer and larger CFM 56-2C1 engines, used on DC-g, were substantially smaller than those of the ATTAS engines. The emission behavio r of CFM 56-2C1 engines is very similar to CFM 56-3 engines frequently used on Boeing 737 aircraft. Tn-flight derived EIs(CO) of the ATTAS engines wer e strongly dependent on the fuel flow rate and agreed well with those calcu lated from ground-based measurements. Emission indices for individual NMHCs were determined fi om the concentration ratios of NMHC/CO in the plume of ATTAS and DC-g and from the EIs(CO) determined by FTIR or derived from the concentration ratios of CO/CO2. The EIs(NMHC) are highest for alkenes and a lkynes generated by a cracking of larger fuel molecules and for benzene fro m unburnt fuel, and they depend strongly on the power setting of the engine s. As with EIs(CO), the EIs(NMHC) of the CFM 56-2C1 engine tend to be small er than those of the Rolls Royce M 45H Mk501.