Experimental and Computational Investigation upon Combustion Characteristics of Liquid Fuel in a Novel Combustor with Hybrid Swirl and Recirculation Bowl.

In the present study, a novel hybrid swirl combustor is designed to reduce the size and complexity of a conventional gas turbine combustor. In this combustor, a dual-swirl pattern is adopted by providing the central vane swirler (45° vane angle) and circumferential tangential injection scheme to achieve higher recirculation of heat and combustion products inside the combustor. Numerical and experimental studies are carried out to understand the flow patterns and combustion characteristics in this high mass-heat interacting environment. Initially, computational studies were carried out to find the optimum geometry for greater recirculation and interaction among the reacting species inside the combustor. Liquid fuel (kerosene) is sprayed into the combustor for two thermal inputs of 25 and 50 kW. Three cases were studied to analyze the effect of bowl recirculation and tangential air inputs in addition to the swirlers. The hybrid swirl, formed by the counter-flow pattern, helps in achieving low and uniform temperature throughout and assists in flame anchoring. The tangential air flow provides a push to the combustion products from the downstream to the central recirculation zone of the combustor. The combined effect of central and tangential swirlers helps in attaining a more distributed combustion. The CO and NO emissions reduced with the use of hybrid swirl.

Atomization characteristics and instabilities in the combustion of multi-component fuel droplets with high volatility differential.

We delineate and examine the successive stages of ligament-mediated atomization of burning multi-component fuel droplets. Time-resolved high-speed imaging experiments are performed with fuel blends (butanol/Jet A-1 and ethanol/Jet A-1) comprising wide volatility differential, which undergo distinct modes of secondary atomization. Upon the breakup of vapor bubble, depending on the aspect ratio, ligaments grow and break into well-defined (size) droplets for each mode of atomization. The breakup modes either induce mild/intense oscillations on the droplet or completely disintegrate the droplet (micro-explosion). For the blends with a relatively low volatility difference between the components, only bubble expansion contributes to the micro-explosion. In contrast, for blends with high volatility differential, both bubble growth as well as the instability at the interface contribute towards droplet breakup. The wrinkling pattern at the vapor-liquid interface suggests that a Rayleigh-Taylor type of instability triggered at the interface further expedites the droplet breakup.