Gas turbine engines are combustion-based machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to this energy conversion process. Air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor, thereby converting into the mechanical energy.
In that combustion is a critical aspect of the operation of a gas turbine engine, various efforts are made to control the combustion to a desired level and location. A variety of combustor designs exist, each having a specified combustion zone as an area for combustion to occur. Aspects of combustion that must be balanced in modern gas turbine engines are the potential for flashbacks, operational efficiency and ease of operation, and emissions from the combustion process.
Flashback is undesired and potentially damaging combustion that occurs when a flame travels upstream from a combustion zone and approaches, contacts, and/or attaches to, an upstream component. Although a stable but lean mixture is desired for fuel efficiency and for environmentally acceptable emissions, a flashback may occur at times more frequently with a lean mixture, and particularly during unstable operation that may occur during lean operations. For instance, the flame in the combustion chamber may progress backwards and rest upon, for a period, a base plate that is disposed perpendicularly to the flow-axis and defines a partial flow barrier. Less frequently, the flame may flash back into a fuel/air mixing apparatus, positioned upstream of the base plate, damaging components that mix the fuel with the air. In addition to damaging combustion system components, flashback often results in unloading or shutdown of the engine.
Gas turbine technology is evolving toward greater efficiency, in part to accommodate environmental standards in various nations, and in various approaches this results in the use of leaner gas air mixtures for the main fuel/air mixing apparatuses. This approach provides for increased efficiency and decreased emissions of NOx and carbon monoxide. However, a richer fuel/air mixture often is used in a centrally disposed pilot flame that is provided to maintain combustion. Notwithstanding the overall low emissions objective, combustion of over-rich pockets of fuel and air, such as from the pilot flame, leads to high-temperature combustion that produces high levels of unwanted NOx emissions. In view of the low NOx objective, gas turbine engine systems are designed to minimize such over-rich pockets.
However, as noted lean operating conditions may lead to a greater risk of flashbacks due to flame instability and operational fluctuations. Various approaches to reduce or eliminate flashback in modern gas turbine combustion systems have been attempted. Since the prevention or elimination of flashbacks is a multi-factorial issue and also relates to various aspects of the design and operation of the gas turbine combustion area, a range of approaches has been attempted. These approaches often inter-relate with, and at times supplement one another.
The inventors of the present invention have appreciated the importance of improving flow patterns near the base plate as a valuable approach to reduction of specific flashback damage. They have appreciated a need to improve such flow patterns, and have sought to effectuate appropriate solutions to address this need.