Flash Atomization: A New Concept to Control Combustion Instability in Water-Injected Gas Turbines

The objective of this work is to explore methods to reduce combustor rumble in a water-injected gas turbine. Attempts to use water injection as a means to reduce NOX emissions in gas turbines have been largely unsuccessful because of increased combustion instability levels. This pulsation causes chronic fretting, wear, and fatigue that damages combustor components. Of greater concern is that liberated fragments could cause extensive damage to the turbine section. Combustion instability can be tied to the insufficient atomization of injected water; large water droplets evaporate non-uniformly that lead to energy absorption in chaotic pulses. Added pulsation is amplified by the combustion process and acoustic resonance. Effervescent atomization, where gas bubbles are injected, is beneficial by producing finely atomized droplets; the gas bubbles burst as they exit the nozzles creating additional energy to disperse the liquid. A new concept for effervescent atomization dubbed “flash atomization” is presented where water is heated to just below its boiling point in the supply line so that some of it will flash to steam as it leaves the nozzle. An advantage of flash atomization is that available heat energy can be used rather than mechanical energy to compress injection gas for conventional effervescent atomization. 1. Introduction The injection of water into gas turbines is not a recent concept. As early as 1903, ？gidius Elling (Bolland and Veer [1]) came up with the idea of spraying water into the air stream before and during the compression process. Wilcox and Trout [2] have also described the benefits of water injection for jet engines. As the pressure to reduce emissions and increase efficiencies and power outputs has mounted in more recent years, further studies have been carried out on ways to inject water by atomizing/spraying. A number of publications based on work by Lefebvre et al. [3–6] have described a method of liquid fuel atomization commonly referred to as “effervescent atomization”. In effervescent atomization, a gas (air in combustion applications) is introduced directly into a flowing liquid upstream of the nozzle exit orifice to create a bubbly two-phase flow. As the liquid flows through the discharge orifice, it is squeezed by the gas bubbles into thin threads and ligaments; the entrained gas bubbles burst as they are released to combustion pressure. Several researchers have linked insufficient fuel atomization to combustion instability. Chin and Lefebvre [7] demonstrated that in order to achieve better combustion stability, one could