Investigation of flame propagation in a partially premixed jet by high-speed-Stereo-PIV and acetone-PLIF

Abstract

This paper presents an experimental study of flame propagation through a partially-premixed flow following ignition. A combination of simultaneous high-speed acetone planar laser induced fluorescence (PLIF) and stereoscopic particle image velocimetry (SPIV) was utilized for time-resolved measurements of mixture fraction, flow field and flame position. This provides access to the major quantities needed to characterize non-premixed flames. High quality mixture fraction measurements with signal-to-noise ratios up to 120 for unity mixture fraction were made feasible using a combination of a conventional high-speed laser at 10 kHz for LIF excitation and a wavelet based de-noising algorithm to reject camera noise. It was observed that flame propagation in the far-field of a partially-premixed jet takes place in a premixed mode, with the flame propagating through highly stratified mixtures until it approaches locations containing mixtures outside the flammability limits. In these areas the flame recedes and further propagation is controlled by mixing processes of air and fuel. Even though flame propagation is then mixing-controlled, the flame is not observed to switch into a non-premixed mode. Instead, mixing ahead of the flame takes place until locally premixed flammable mixtures are recovered for subsequent flame propagation.

Experimental Characterization of an Ethanol DI - Gasoline PFI and Gasoline DI - Gasoline PFI Dual Fuel Small Displacement SI Engine

“…The discrepancy between the combustion history of the DI with respect to the PFI and the DF configurations becomes more evident with the increase of the engine speed. The large presence of rich zones, typical of DI, slows down the propagation of the flame [14]. At the same way, also the effect of fuel is stronger with engine speed.…”

Experimental investigation into turbulent negatively buoyant jets using combined PIV and PLIF measurements

“…With a measurement of the power profile of the laser sheet for any individual pulse, the corresponding PLIF images in the region of interest could be corrected so that differences in the profile (in both magnitude and shape) between pulses were accounted for. After this correction, the PLIF images were filtered using a wavelet based denoising algorithm designed for CCD cameras (Weinkauff et al, 2015).…”

“…Equation 3 omits this assumption by including the laser power profile, P , which corresponds to the PLIF images I. The third method, equation 4, additionally includes applying the wavelet-based denoising filter (Weinkauff et al, 2015), denoted here by D{•}. All three methods rely on weak absorption (valid for low dye concentrations), and assume that light attenuation along the laser path is similar in I, Îc and Ĩc (Shan et al, 2004), which is discussed further in §4.4.…”

Single-shot imaging of major species and OH mole fractions and temperature in non-premixed H2/N2 flames at elevated pressure

“…To improve SNR, images are denoised using the wavelet adaptive thresholding (WATR) method described in [17,18]. This method is optimized to reject noise while preserving spatial resolution.…”