Temperature response of turbulent premixed flames to inlet velocity oscillations

Abstract

Flame-turbulence interactions are at the heart of modern combustion research as they have a major influence on efficiency, stability of operation and pollutant emissions. The problem remains a formidable challenge, and predictive modelling and the implementation of active control measures both rely on further fundamental measurements. Model burners with simple geometry offer an opportunity for the isolation and detailed study of phenomena that take place in real-world combustors, in an environment conducive to the application of advanced laser diagnostic tools. Lean premixed combustion conditions are currently of greatest interest since these are able to provide low NO (x) and improved increased fuel economy, which in turn leads to lower CO(2) emissions. This paper presents an experimental investigation of the response of a bluff-body-stabilised flame to periodic inlet fluctuations under lean premixed turbulent conditions. Inlet velocity fluctuations were imposed acoustically using loudspeakers. Spatially resolved heat release rate imaging measurements, using simultaneous planar laser-induced fluorescence (PLIF) of OH and CH(2)O, have been performed to explore the periodic heat release rate response to various acoustic forcing amplitudes and frequencies. For the first time we use this method to evaluate flame transfer functions and we compare these results with chemiluminescence measurements. Qualitative thermometry based on two-line OH PLIF was also used to compare the periodic temperature distribution around the flame with the periodic fluctuation of local heat release rate during acoustic forcing cycles

Comparison of 2D and 3D density-weighted displacement speed statistics and implications for laser based measurements of flame displacement speed using direct numerical simulation data

“…For the present flame conditions the suitability of OH-PLIF to mark the reaction zone has been extensively validated [50][51][52][53][54][55][56][57] and found optimal, yielding high signal levels and exhibiting only a weak dependence of signals to changes in curvature and strain rate.…”

Simulation of the flame describing function of a turbulent premixed flame using an open-source LES solver

“…1. This is described in detail by Balachandran et al [5,6], and has featured in other studies of turbulent flames [41,42,43,44]. A long tube emerges from a plenum chamber, within which is a conical bluff body with diameter d = 25mm.…”

Heat release rate markers for premixed combustion

“…[OH][CH 2 O], where [A] indicates the molar concentration of species A, has been used in a number of studies, for example [9][10][11][12][13][14][15][16][17], as the de facto standard to infer heat release rate related information in laminar and turbulent premixed flames irrespective of the fuel mixture composition and stoichiometry.…”