A method of assembling a feed injector is provided. The method includes providing a feed injector tip that includes an inlet, a tip end, a flow passage that extends longitudinally through the feed injector tip from the inlet to the tip end, an annular cooling channel that substantially circumscribes the flow passage, and a buffer region that separates the annular cooling channel from the flow passage. The method further includes coupling the feed injector tip to the feed injector to enable a fluid to be channeled through the flow passage, such that the fluid flows past the inlet, at which the buffer region has a first width, before flowing past the tip end, at which the buffer region has a second width, the first width wider than the second width, and coupling a cooling assembly to the feed injector to enable a flow of cooling fluid to be channeled into the annular cooling channel.