Power generation and aeropropulsion gas turbines: From combustion science to combustion technology

In the 50 years since its introduction, the gas-turbine engine has become an essential component of our global society. One need only look at the nearest airport to realize its dominance of air transportation. It has also become a significant element of the power-generation industry. In the last decade, power-generating combined-cycle powerplants have increased in thermal efficiency to about 60%, while NO_x emissions have been reduced by an order of magnitude, to below 9 ppm (dry, at 15% O₂) in some cases. This paper reviews the ongoing transition from science to the needed technologies: new modes of combustion have been introduced in gas turbines, including lean premixed combustion, reheat and axially staged combustion, catalytic combustion, and rich-lean combustion: high-efficiency low emissions performance is being extended to nonpremium fuels such as coal gas and crude oil: new materials such as superalloys thermal harrier coatings, and ceramics have been incorporated into designs: and improved theories greatly dependent on advanced laser-based diagnostics of flame structure have led to design tools of increasing scope. Future challenges—such as viable propulsion for supersonic transports, powerplants fueled byrenewable resources, and extension of gas turbines to micropower applications—can be met only through further progress in the underlying aerothermal and materials sciences.