Soot particle size distribution measurements in a turbulent ethylene swirl flame

There is a need to better understand particle size distributions (PSDs) from turbulent flames from a theoretical,
practical and even regulatory perspective. Experiments were conducted on a sooting turbulent nonpremixed
swirled ethylene flame with secondary (dilution) air injection to investigate exhaust and in-burner
PSDs measured with a Scanning Mobility Particle Sizer (SMPS) and soot volume fractions (f v ) using ex-
tinction measurements. The focus was to understand the effect of systematically changing the amount and
location of dilution air injection on the PSDs and f v inside the burner and at the exhaust. The PSDs were
also compared with planar Laser Induced Incandescence (LII) calibrated against the average f v . LII provides
some supplemental information on the relative soot amounts and spatial distribution among the various
flow conditions that helps interpret the results. For the flame with no air dilution, f v drops gradually along
the centreline of the burner towards the exhaust and the PSD shows a shift from larger particles to smaller.
However, with dilution air f v reduces sharply where the dilution jets meet the burner axis. Downstream of
the dilution jets f v reduces gradually and the PSDs remain unchanged until the exhaust. At the exhaust,
the flame with no air dilution shows significantly more particles with an f v one to two orders of magnitude
greater compared to the Cases with dilution. This dataset provides insights into soot spatial and particle size
distributions within turbulent flames of relevance to gas turbine combustion with differing dilution parameters and the effect dilution has on the particle size. Additionally, this work measures f v using both ex situ
and in situ techniques, and highlights the difficulties associated with comparing results across the two. The
results are useful for validating advanced models for turbulent combustion.