Comprehensive characterization of sooting butane jet flames, Part 2: Temperature and soot particle size

The present work investigates the effect of jet-exit Reynolds number (Re) on soot particle size and flame temperature in n-butane jet flames. Correlation of temperature with soot volume fraction (f(v)), soot precursor (polycyclic aromatic hydrocarbons or PAH), and reaction zone (OH) is also examined. The investigated flames (Re = 50 00-21,500) are identical as of the companion work (Part 1). The temperature was measured in a low-sooting region using a fine-wire thermocouple. The soot particle size distribution was obtained using a scanning mobility particle sizer (SMPS). Temporal evolution (with 0.1 s resolution) of f(v) in the extracted aerosol sample was monitored with a Pegasor particle sensor (PPS). f(v) from LII and PPS are compared, and the reasons for differences are discussed in detail. The radial location of peak temperature is biased towards the fuel-rich side. At Re 500 0, peak-PAH occurs at 650 K, whereas in lifted turbulent flame (Re 21, 500), peak-PAH shifts to 940 K. PAH formation temperature is influenced by air/fuel mixing. Despite the variation of turbulence level (Re = 5000 -21, 500), peak-f(v) in the soot inception region occurs at a nearly identical temperature of 1400 K. Peak-f(v) shifts towards lower temperature with increasing height, likely due to oxidation by diffused OH. The soot mode diameter (D-m) was measured along the axis. D-m increases with height and reaches a maximum near peak-f(v) region. D-m at moderate Re (5000 -7200), varies between 12 and 28 nm along the flame axis. At high Re (21,500), D-m range decreases to 12 -24 nm. The decrease in peak-D-m with Re is likely due to reduced residence time and enhanced reactant mixing. The comprehensive database containing a wide range of parameters from the present and companion (Part 1) papers will aid in the development and validation of turbulence and soot chemistry models, especially for fuels of practical relevance. (C) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved.