System and method for reducing combustion dynamics in a combustor

A system for reducing combustion dynamics in a combustor includes an end cap having an upstream surface (42) axially separated from a downstream surface (44), and tube bundles (24) extend from the upstream surface (42) through the downstream surface (44). A divider (32) inside a tube bundle (24) defines a diluent passage (34) that extends axially through the downstream surface (44), and a diluent supply (58) in fluid communication with the divider (34) provides diluent flow to the diluent passage (34). A method for reducing combustion dynamics in a combustor (10) includes flowing a fuel through tube bundles (24), flowing a diluent through a diluent passage (34) inside a tube bundle (24), wherein the diluent passage (34) extends axially through at least a portion of the end cap into a combustion chamber (26), and forming a diluent barrier in the combustion chamber (26) between the tube bundle (24) and at least one other adjacent tube bundle (24).