Imaging measurements and LES-CMC modeling of a partially-premixed turbulent dimethyl ether/air jet flame

Abstract

Turbulent dimethyl ether (DME) jet flames provide a canonical flame geometry for studying turbulenceflame interactions in oxygenated fuels and for developing predictive models of these interactions. The development of accurate models for DME/air flames would establish a foundation for studies of more complex oxygenated fuels. We present a joint experimental and computational investigation of the velocity field and OH and CH 2 O distributions in a piloted, partially-premixed turbulent DME/air jet flame with a jet exit Reynolds number, Re D , of 29,300. The turbulent DME/air flame is analogous to the well-studied, partially-premixed methane/air jet flame, Sandia Flame D, with identical stoichiometric mixture fraction, n st = 0.35, and bulk jet exit velocity, V bulk = 45.9 m/s. Measurements include particle image velocimetry (PIV) and simultaneous CH 2 O and OH laser-induced fluorescence (LIF) imaging. Simulations are performed using a large eddy simulation combined with conditional moment closure (LES-CMC) on an intermediate size grid of 1.3 million cells. Overall, the downstream evolution of the mean and RMS profiles of velocity, OH, and CH 2 O are well predicted, with the largest discrepancies occurring for CH 2 O at x/D = 20-25. LES-CMC simulations employing two different chemical reaction mechanisms (Kaiser et al., 2000 [20] and Zhao et al., 2008 [21]) show approximately a factor of two difference in the peak CH 2 O mole fractions, whereas OH mole fractions are in good agreement between the two mechanisms. The single-shot LIF measurements of OH and CH 2 O show a wide range of separation distances between the spatial distributions of these intermediate species with gaps on the order of millimeters. The intermittency in the overlap between these species indicates that the consumption rates of formaldehyde by OH in the turbulent DME/air jet flame may be highly intermittent with significant departures from flamelet models.

LES flamelet-progress variable modeling and measurements of a turbulent partially-premixed dimethyl ether jet flame

“…Additionally, radial velocity distributions at different axial locations were obtained using stereoscopic particle image velocimetry (SPIV). Initial computational results using LES-CMC for the velocity, CH 2 O and OH fields were also presented in [23]. This investigation showed characteristic separations of CH 2 O and OH distributions in DME flames.…”

“…The rapid DME pyrolysis leads to increased levels of formaldehyde (CH 2 O) in fuel-rich regions [21], levels which are two orders of magnitude larger than for CH 4 flames. Besides higher amounts of CH 2 O, the interplay with OH radicals showed varying separations in the distributions of the two species, which were detected by LIF measurements [23]. The experimental results by Coriton et al [23] and Fuest et al [24] provide a comprehensive data set including velocity, species and temperature data, which we use for comparison with the LES results.…”

“…Further studies considered a series of partially-premixed DME/air flames in the Sydney/Sandia piloted jet burner [22]. Coriton et al [23] analyzed the topology of CH 2 O and OH fields using laser-induced fluorescence (LIF). Additionally, radial velocity distributions at different axial locations were obtained using stereoscopic particle image velocimetry (SPIV).…”

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

“…Quantitative evaluation of OH-LIF signal is not straight-forward and thus sometimes qualitative comparisons are performed that normalize the OH-LIF signal [7,28], which must be mirrored in the simulation, e.g. [9,22]. Thus, Fig.…”

“…Connelly et al [8] applied the procedure to NO-LIF and luminosity measured from laminar sooting and non-sooting flames. A similar approach has been applied to a turbulent DME flame in order to investigate the CH 2 O-and the OH-LIF signal [9], where the turbulent simulation was performed with an LES-CMC approach. Further, a first investigation and validation of the incorporation of different experimental signals into the flamelet/progress variable (FPV) model is given in [43] for the same DME flame.…”