Four lean premixed prevaporized (LPP) combustor concepts have been identified which utilize variable geometry and/or other flow modulation techniques to control the equivalence ratio of the initial burning zone. Lean equivalence ratios are maintained at high power engine operating conditions for low NOx emissions, while near stoichiometric conditions are maintained at low power for good combustion efficiency and low emissions of carbon monoxide and unburned hydrocarbons. The primary goal of this program was to obtain a low level of NOx emissions (≤3 g/kg fuel) at stratospheric cruise conditions; additional goals are to achieve the currently proposed 1984 EPA emission standards over the landing/take off cycle and performance and operational requirements typical of advanced aircraft engines. Based on analytical projections made during this conceptual design study, two of the concepts offer the potential of achieving the emission goals. However, the projected operational characteristics and reliability of these concepts to perform satisfactorily over an entire flight envelope would require extensive experimental substantiation before an engine application can be considered.

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