Experimental and Numerical Study of MILD Combustion in a Cyclonic Burner

Cyclonic mixers could represent a very effective system in realizing mixing processes in very short time and compact size while allowing for a reasonable long residence time for the development of combustion reactions. This is particularly of interest in the case of high inlet temperature and diluted conditions, typical of MILD and HiTAC combustion, where the fast mixing process is a need, chemical kinetics and fluid-dynamical characteristic times are comparable and the residence time play a central role in the achievement of satisfying reaction progress. In addition this configuration can be of interest also for more fundamental studies since it allows a very detailed control of the fluid-dynamic process and the study of the interaction of fluid-dynamics and chemical kinetics in well defined conditions. For these reasons a lab-scale facility has been designed and built. The core of the facility is a rectangular prismatic chamber with a typical volume of 2 cubic dm. Oxidant/diluent (preheated up to 1400K) and fuel streams, independently adjustable, are injected from two opposite sides of the chamber allowing for the realization of various cyclonic flowfields. Inlet temperatures (up to 1400K), equivalence ratio (lean to reach mixtures), residence times and mixture dilution levels are the main operating parameters of the system. Temperature measurements, sampling and inline chemical analysis as well as optical access are built-in. The main reaction chamber is made of an easily machinable refractory material thus allowing for the realization of different geometries. A detailed numerical simulation of fluid dynamics and reactive processes in the chamber is currently under development and will allow for a side-by-side analysis of the numerical and experimental results. For the time being, Numerical simulations are based on RANS in which combustion chemistry is accounted for by the flamelet-generated manifold (FGM) approach. RANS results will give clues about more detailed LES studies.