Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Figure 7-18: Combustor development process.
It is important to note that the intrinsic complexity of the combustion process and limitations of current analytical tools lead to considerable uncertainty in prediction of
emissions from new combustor designs. Mongia (1997a) estimates that even with analytical models that have been "anchored" to measured data-a process to
systematically calibrate a model so that it reproduces measured emissions results-prediction accuracy is only about ±15% for NO x and ±30% for CO and HC. The
uncertainty in prediction is even higher for smoke.
One of the clear lessons that emerged from early emissions reduction programs was that changes to reduce NOx emissions could produce adverse effects on other
performance characteristics, leading toward tradeoffs in design. Tradeoffs can be attributed to the engine cycle selected or the combustor design itself. Tradeoffs
based on engine cycle reflect changes in overall pressure and bypass ratios, which, in turn, affect fuel burn rates and the conditions at which combustion occurs (see
Section 7.4.1.1). Tradeoffs generated by design changes affecting the combustor can influence major combustor performance parameters, including operability,
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