| Summary: | This research experimentally investigates the exhaust gas characteristics of a methane-air lifted-jet flame with elevated stream temperatures up to 450 K. Emission indices of NOx and CO were measured by direct gas sampling using a gas detector tube. The index of NOx decreased or did not change with increasing stream temperature up to 350 K, and then increased with further temperature increases. The index of CO changed in an opposite manner to that of NOx with increasing stream temperature. These tendencies demonstrated that the generation of emission gases did not monotonically increase with stream temperature. These non-monotonic properties of the emission indices were caused by particular variations in the lift-off height of flame and flame length. In order to examine these flame characteristics, we measured the flame curvature with OH-PLIF and related it to the lift-off height of triple flame. These flame properties could explain the unique emission characteristics of a lifted-jet flame with stream heating.
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