Chapter 5 – Lean Combustion in Gas Turbines

Publisher Summary This chapter discusses gas turbines for both stationary power and aircraft propulsion applications, as well as the aircraft auxiliary power unit (APU), which has features of each. Aircraft propulsion engines focus first on safety and reliability, while ground-based systems can relax the demands in these categories slightly and push toward higher efficiency and lower emissions by operating close to static stability limits. Tremendous progress has been made in the area of lean combustion as applied to gas turbines. This has been a principal strategy for achieving ultra-low emissions performance for both stationary and aviation engines. With the shift away from traditional “diffusion” -type combustion systems, a wide variety of technologies that attempt to lower the peak combustion temperatures found in the reaction zone have appeared. As a result, improved stability (both static and dynamic), avoidance of flashback and autoignition, good ignition characteristics, and good turn down are all key design aspects. Relative to future needs, the shift from fossil fuels to alternative fuels coupled with low emissions requirements will call for increased understanding of the fundamental behavior of these potential fuels. Understanding how fuel composition affects flame speeds, reaction rates, and kinetics is one important requirement. Additionally, the desire for higher firing temperatures in order to achieve higher efficiencies means that further research is needed to fill the gaps in our comprehension of lean-burn gas turbine combustion.