The use of fossil fuel in gas turbine engines results in combustion products within the exhaust. These combustion products consist of carbon dioxide, water vapor, oxides of nitrogen, carbon monoxide, unburned hydrocarbons, oxides of sulfur and particulates. Of these above products, carbon dioxide and water vapor are generally not considered objectionable. In most applications, governmental imposed regulations are further restricting the remainder of the species, mentioned above, emitted in the exhaust gases.
The majority of the products of combustion emitted in the exhaust can be controlled by design modifications, cleanup of exhaust gases and/or regulating the quality of fuel used. For example, particulates in the engine exhaust have been controlled either by design modifications to the combustor and fuel injectors or by removing them by traps and filters.
The principal mechanism for the formation of oxides of nitrogen involves the direct oxidation of atmospheric nitrogen. The rate of formation of oxides of nitrogen by this mechanism depends mostly upon the flame temperature and, consequently, a small reduction in flame temperature can result in a large reduction in the nitrogen oxides.
Attempts to control NOx emissions by regulating the local flame temperature have adopted the use of water or steam injection. This system increases cost due to the additional equipment, such as pumps, lines and storage reservoir. Furthermore, in areas where a supply of water is not readily available the cost and labor to bring in water basically makes this option undesirable.
In an attempt to reduce NOx emissions without incurring increase in operational cost caused by water or steam injection, gas turbine combustion systems have utilized a variety of approaches including premix systems and various fuel injector designs. These premix system and injectors used therewith are examples of attempts to reduce the emissions of oxides of nitrogen. The systems and injectors described above although reducing the emissions of oxides of nitrogen emitted from the engine exhaust still produce significant amounts of oxides of nitrogen in the engine exhaust.
As stated above, NOx typically forms in high temperature environments. Two ways of solving this problem each involve reducing the temperature of combustion. For example, exhaust gas recirculation (EGR) reduces the flame temperature during combustion. Another solution, used mainly in gas turbines, increases the air flow into the combustor reaction zone. Hence, reducing flame temperature of oxides of nitrogen.
The present invention is directed to overcome one or more of the problems as set forth above.