Combustion Technology for Low-Emissions Gas-Turbines:Selected Phenomena Beyond NO_x

Since recent reviews cover the issues in NO_x formation under gas-turbine canditions, and since regulations essentially dictate use of the premixed mode of combustion for minimum NO_x, this review concentrates on phenomena that can arise in premixed combustion. Specifically, 1) the initial unmixedness in a fuel-air premixer has been shown to make overall lean mixtures autoignite sooner than might be expected based on the overall fuel-air ratio, because the richer portions of the mixture lead the process;2) combustion pressure oscillations caused by the interplay between acoustic waves and unsteady heat release in a one-dimensional system can be calculated in good accordance with measured data, and set the stage for multi-dimensional CFD;3) carbon deposition arising from the flow of liquid fuel over metal surfaces such as found in fuel injectors and swirl cups has been described as a function of temperature and of surface composition; and 4) quenching and subsequent emissions of carbon monoxide can be minimized by preservation of a boundary-layer rather than an impingement type of flow over combustor liners.