Combustors are commonly used in industrial and power generation operations to ignite fuel to produce combustion gases having high temperatures and pressures. Various competing considerations influence the design and operation of combustors. For example, higher combustion gas temperatures generally improve the thermodynamic efficiency of the gas turbine. However, higher combustion gas temperatures also promote flashback or flame holding conditions in which the combustion flame migrates towards the fuel being supplied by nozzles, possibly causing severe damage to the nozzles in a relatively short amount of time. In addition, higher combustion gas temperatures generally increase the disassociation rate of diatomic nitrogen, increasing the production of nitrogen oxides (NOX). Conversely, lower combustion gas temperatures associated with reduced fuel flow and/or part load operation (turndown) generally reduce the chemical reaction rates of the combustion gases, increasing the production of carbon monoxide and unburned hydrocarbons.
In a particular combustor design, a plurality of tubes may be arranged radially in an end cap to provide fluid communication for a working fluid to flow through the end cap and into a combustion chamber. A fuel may be supplied to a fuel plenum inside the end cap. The fuel flows over the outside of the tubes before flowing through a plurality of fuel injection ports and into the tubes to mix with the working fluid. The enhanced mixing between the fuel and working fluid in the tubes allows leaner combustion at higher operating temperatures while protecting against flashback or flame holding and controlling undesirable emissions. However, in certain combustor designs, the fuel may leak from the fuel plenum and become trapped in a volume within the end cap, and the working fluid velocity may be insufficient to purge the trapped fuel from the end cap. As a result, the working fluid and fuel may create conditions conducive to flashback and/or flame holding events. Therefore, an improved combustor and method for purging fuel from the combustor that minimizes the risk of a flashback event would be useful.