The impact of representative paths of engine degradation on aircraft cruise NOx emissions was investigated. Engine cycles corresponding to older, current, and future subsonic and supersonic technologies were developed and used to determine the sensitivities of combustor conditions to various changes in component efficiencies and flow capacities due to aging. Estimates of relative changes in NOx emissions levels were made using established empirical correlations that relate emissions to combustor flow parameters. The analysis methodology was validated through comparisons to test data where available.It was found that the sensitivity of specific fuel consumption (SFC) and combustor flow parameters to component aging is enhanced by increases in cycle temperatures and pressures. This ultimately results in a higher sensitivity of NOx emissions to engine degradation for cycles representative of more advanced technology. At constant thrust, turbine degradation typically acts to decrease NOx emissions while compressor aging results in an increase in NOx emissions; both occurring at the expense of SFC. Sample degradation scenarios were used to highlight the balance between turbine and compressor aging effects. Changes in NOx emissions in the −1% to +4% range were predicted for typical aging scenarios. The applicability of these results to the formulation of aircraft emissions inventories is considered.Copyright © 1997 by ASME

Effects of Engine Aging on Aircraft NOx Emissions

A comparative probabilistic maintenance reliability and economic analysis is presented with the object of quantifying the potential economic impact of aircraft engine component parameter aerothermal variability. A representative parametric aerothermodynamic cycle-deck is established for the Pratt & Whitney JT8D-9 model engine and utilized throughout the study. Open literature degradation data on this exemplar is employed in establishing functions of the second moment characteristics of the dependent parameter of interest, thrust specific fuel consumption (TSFC). Mean degradation data on component performance parameters are also presented in the literature and an approach is introduced to derive their variabilities from that of the dependent parameter. The practicality of a matching off-design analysis, as opposed to the design-point approach, is also validated and adhered to while using a commercially available gas turbine thermodynamic cycle analysis software, GASTURB. Maintenance criteria are established based on industry practices of exceeding predetermined TSFC and/or exhaust gas temperature (EGT) margins. By varying the second moment chararcteristics of the component performance parameters, the response of fleet operating maintenance reliability and economics is studied. Thesis Supervisor: David L. Darmofal Title: Associate Professor of Aeronautics and Astronautics A miracle is in actuality the manifestation of presently incomprehensible science, which is why ignorance is so blissful; of that which one is ignorant, everything is a miracle. RozzTz

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B. R. Arnold

Papers

A Cooperative Airline Program to Evaluate Engine Parts Aging Effects on a Current Turbofan Engine Model