Finite Rate Chemistry Effects in Highly Sheared Turbulent Premixed Flames

Abstract

Detailed scalar structure measurements of highly sheared turbulent premixed flames stabilized on the piloted premixed jet burner (PPJB) are reported together with corresponding numerical calculations using a particle based probability density function (PDF) method. The PPJB is capable of stabilizing highly turbulent premixed jet flames through the use of a small stoichiometric pilot that ensures initial ignition of the jet and a large shielding coflow of hot combustion products. Four lean premixed methane-air flames with a constant jet equivalence ratio are studied over a wide range of jet velocities. The scalar structure of the flames are examined through high resolution imaging of temperature and OH mole fraction, whilst the reaction rate structure is examined using simultaneous imaging of temperature and mole fractions of OH and CH 2 O. Measurements of temperature and mole fractions of CO and OH using the Raman-Rayleigh-LIF-crossed plane OH technique are used to examine the flame thickening and flame reaction rates. It is found that as the shear rates increase, finite-rate chemistry effects manifest through a gradual decrease in reactedness, rather than the abrupt localized extinction observed in nonpremixed flames when approaching blow-off. This gradual decrease in reactedness is accompanied by a broadening in the reaction zone which is consistent with the view that turbulence structures become embedded within the instantaneous flame front. Numerical predictions using a particle-based PDF model are shown to be able to Submitted to the Special Issue of Flow, Turbulence and Combustion dedicated to S.B. Pope. 622Flow Turbulence Combust (2010) 85:621-648 predict the measured flames with significant finite-rate chemistry effects, albeit with the use of a modified mixing frequency.

Application of a laser induced fluorescence model to the numerical simulation of detonation waves in hydrogen–oxygen–diluent mixtures

“…Although a more complex LIF model [66,67,68] cycle [28,63,69,70]. In order to extract reliable LIF data from the experiments, the image stripes analysed were located within the second half of the cell cycle so that the velocity is closed to the CJ detonation and the LIF field is not affected by 3-dimensional effects.…”

A Combined Experimental and Numerical Study of Laminar and Turbulent Non-piloted Oxy-fuel Jet Flames Using a Direct Comparison of the Rayleigh Signal

“…In these tests, we used the helium and the oxidizer image sets. The raw pixel signal, Sraw, for each case can be defined as [13]:…”

Large-eddy simulation of a piloted premixed jet burner

“…The elemental mass fractions of carbon and hydrogen are denoted by y C and y H , respectively. In this context it is noted that the expressions for Z 1 and Z 2 are identical to the variables n 1 and n 3 , defined by Dunn [15]. With the variables defined above, the solution of the flamelet equations, Eq.…”

“…in which the independent FPV-state-space variables, denoted by the superscript ''Exp,'' are evaluated from the single-point scatter data [4,15]. Table 2 Prescribed species mass fraction composition at the inlet.…”

“…Of interest to the current study is the Sydney piloted premixed jet burner (PPJB) that was investigated by Dunn et al [4][5][6]. This burner configuration was designed with the objective to resemble conditions relevant to partially-premixed gas turbine combustors, but without the additional complexity of geometrical confinement, swirl, or recirculation.…”