Experimental study of aeronautical ignition in a swirled confined jet-spray burner
Abstract
Aeronautical gas turbine ignition is still not well understood and its management and control is mandatory for new lean-burner designs. The fundamental aspects of swirled confined two-phase flow ignition are addressed in the present work. Two facilities enable the analysis of two characteristic phases of the process. The KIAI-Spray single-injector burner was investigated in terms of local flow properties, including the air velocity and droplet fuel (n-heptane) size-velocity characterization by phase Doppler anemometry (PDA), and the study of local equivalence ratio by means of planar laser induced fluorescence (PLIF) on a tracer (toluene). The initial spark location inside the chamber is vital to ensure successful ignition. An ignition probability map was elaborated varying the location of a 532 nm laser-induced spark in the chamber under ultra-lean nominal conditions (phi=0.61). The outer recirculation zone (ORZ) was found to be the best region for placing a spark and successfully igniting the mixture. A strong correlation was found between the ignition probability field and the airflow turbulent kinetic energy and velocity fields. Local equivalence ratio enhances the importance of the ORZ. Once a successful ignition is accomplished on one injector, the injector-to-injector flame propagation must be examined. Highspeed visualization through two synchronized perpendicular cameras was applied on the KIAI-Spray linear multi-injector burner. Four different injector-to-injector distances and four fuels of different volatilities (n-heptane, n-decane, n-dodecane and jet-A1 kerosene) were evaluated. Spray branches and inter injector regions changed with the inter-injector distance. Two different flame propagation mechanisms were identified: the direct radial propagation and the arc propagation mode. Ignition delay times were modified with the injector-to-injector distance and with the different fuels.