As environmental protection is more and more important, pollution emission in aircraft combustors should be low. The RQL (rich-quench-lean) technique is one of the promising ways to control NOx emissions from combustors. In RQL combustors, NOx is mostly produced in quench zone. So the optimization of quench zone is very important to control NOx emissions.
According to thermal NOx mechanism, NOx emissions are determined by residence times. For a RQL combustor all the mainflow fuel should be burned out in quench zone. Then the maximum residence time is the time for the flame to transport the longest distance. Based on the first-principle analysis of the flow and combustion in the quench zone, the FMT (flame mixing time) criterion for the optimization of quench jets has been proposed.
There are two typical quench ducts. One is the annular shape and the other is the can shape. The two types of ducts are similar but there are some differences between them. In this paper both of them were analyzed in terms of the FMT criterion. The maximum residence times calculated by FMT criterion were compared with the experiments by Chiappetta et. al.  and Holdeman & Chang for annular and can combustors, respectively. The comparison shows the very good agreement between the maximum residence times calculated by FMT criterion and the experiments. That means the FMT criterion can be validated by both annular and can shape combustors. And the FMT criterion could be used to optimize the configuration of quench zones.