Flame stability characteristics of a flame spray pyrolysis burner

Abstract

The stability characteristics of an established flame spray pyrolysis (FSP) burner are quantified in order to determine viable operating conditions and map the structure of FSP flames. The primary novelty of this work lies in exploring a large parameter space which is necessary to explain the dependence of visible flame emissions on input variables. Using high-speed flame luminescence imaging (1–120 kHz), we demonstrate that the input pilot heat release and the flowrates of liquid and dispersion gases are primary control variables that dictate combustion quality. Indeed, variation in these input conditions allows the qualitative identification of four flame types: (i) stable, (ii) lifted, (iii) unstable and (iv) low intensity. Quantification of these flame types is derived via statistical analysis of the temporal luminosity fluctuations. Key metrics such as the mean and standard deviation effectively describe the behaviour of the aforementioned flame types and act as classifying parameters for FSP flames. High normalised mean intensities and coefficients of variation are characteristic of stable flames. However, flame extinction events in the ignition region and throughout the entire flame are characteristic of unstable flame configurations. In this case, poor combustion efficiency and significant intensity fluctuations are quantified by significantly lower mean intensities and higher coefficients of variation. Further insight is given via the implementation of phase-Doppler anemometry (PDA). It is demonstrated how variation in the input flowrates - and therefore variation in gas and droplet-phase velocities - correlate with the identified flame structures. This analysis demonstrates how input parameters can be varied in order to configure the combustion mode and control combustion stability during FSP. Both of which are relevant for understanding the boundary conditions for nanoparticle growth using FSP.