In situ measurements of soot formation in simple flames using small angle X-ray scattering C. Gardner a , G.N. Greaves a, * , G.K. Hargrave b , S. Jarvis b , P. Wildman b , F. Meneau a,c , W. Bras c , G. Thomas a a Institute of Mathematical and Physical Sciences, University of Wales, Aberystwyth SY23 3BZ, United Kingdom b Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough LE11 3TU, United Kingdom c Netherlands Organisation for Scientific Research (NWO), DUBBLE CRG/ESRF, P.O. Box 220, F38043 Grenoble Cedex, France Available online 1 September 2005 Abstract Direct SAXS measurements of soot formation from ethylene have been made using laminar pre-mixed flames for the first time. The slot burner was configured to maximise the signal from particulates. The geometry also enabled the ther- mal background from the surrounding hot gasses to be accurately removed. With cold flame speeds of 40 cm s 1 we have been able to identify particle sizes and densities from moderately sooty to rich flame conditions. By adjusting the height of the burner in the beam, the development of particles as a function of position above the flame tip and therefore as a function of time from ignition have been obtained. These reveal evidence for bimodal particle nucleation and growth at different stages in the continuous combustion of ethylene. Ó 2005 Elsevier B.V. All rights reserved. PACS: 60.10.Eq; 61.46.+w; 81.05.Uw Keywords: Soot; Flame; Particle size; Nucleation; Aggregation; SAXS 1. Introduction Understanding soot generation in simple hydro- carbon fuels is fundamental to establishing practi- cal strategies for increasing combustion efficiency, at the same time as limiting particulate emissions. Quantitative knowledge of the processes from soot inception to the generation of visible particles has, until recently, relied on in situ static and dynamic optical techniques [1,2] and ex situ transmission electron microscopy (TEM) [3–5]. Optical tech- niques, however, are insensitive to particle sizes below 100 A ˚ and therefore to the primary soot particles that nucleate as well as the smaller 0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.06.072 * Corresponding author. Tel.: +44 1970 622802; fax: +44 1970 622826. E-mail address: gng@aber.ac.uk (G.N. Greaves). Nuclear Instruments and Methods in Physics Research B 238 (2005) 334–339 www.elsevier.com/locate/nimb