Investigation of the influence of the bluff-body temperature on a lean premixed DME/air flame approaching blowoff

Abstract

In flames stabilized by a two-dimensional (2D) bluff body, the lean blowoff (LBO) limit can be extended by increasing the bluff-body temperature, which is verified experimentally in premixed dimethyl ether (DME)/air flames in this work. Two bluff-body temperatures of 573 K and 773 K are tested, respectively. High-speed OH* chemiluminescence (CL) imaging is applied to record the spatial distribution of the heat release. Particle image velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) are performed simultaneously to explore the flow field and the combustion characteristics. Based on the results of OH*-CL, the heat release of the area near the bluff body is strengthened in the case of higher bluff-body temperature, and the enhanced chemical reactivity will further influence the downstream area. The turbulent flame speed obtained by OH-PLIF is increased in the entire area of interest. Due to the higher velocity gradient adjacent to the bluff body in the upstream region (y < 35 mm), the flame surface density (FSD), brush thickness, and flame wrinkling ratio are not sensitive to the bluff-body temperature. However, in the downstream region (y > 35 mm), a noticeable change can be found in these three parameters due to a higher turbulent flame speed and a much lower velocity gradient. Based on the PIV results, a limited effect on the velocity field by increasing the bluff-body temperature by 200 K. Furthermore, the probability density functions (PDF) of the vorticity and strain rate on the flame front are computed. The results indicate that the enhanced flame stability leads to a more pronounced overlapping between the flame front and the high-vorticity region, further increasing the values of these two parameters.