VII-7, 1 Numerical Simulation and Experimental Measurements of Soot and Organic Nanoparticles in Opposed-Flow Diffusion Flames of Methane, Ethylene and Propane A. D’Anna 1 , M. Commodo 1 , M. Sirignano 1 , P. Minutolo 2 , R. Pagliara 2 1. Dipartimento di Ingegneria Chimica - Università Federico II, Napoli - ITALY 2. Istituto di Ricerche sulla Combustione – CNR, Napoli – ITALY 1. Introduction In recent years attention of researchers has been focused on the combustion generated particles in order to have a deeper knowledge on their formation and develop combustion systems with higher efficiency and lower environmental impact [1,2]. Opposed-flow configuration allows to study behavior and sooting tendency of fuels, avoiding fluidodynamic problems fundable in diffusion flames laminar or turbulent. On the other hand, for co-flow flames, the study of particles inception and growth is much more complex than the opposed- flow system because the co-flows are intrinsically two dimensional compared to a quasi-one dimensional opposed-flow [3]. Moreover, soot formation in opposed-flow diffusion flames has been extensively investigated because of its relevance to turbulent flames in the laminar flamelet model. In the present work, three different fuels: ethylene, methane and propane, in comparable conditions, have been investigated, experimentally and by numerical simulation. The experimental detection of combustion-byproducts is attempted by UV laser induced emission spectroscopy. The fourth harmonic of a pulsed Nd:YAG laser (266 nm) is used, in order to enhance fluorescence from molecular particles within the flame and also allows larger soot particles to heat up and emit incandescent radiation [4]. Modeling of particulate concentration is performed by using a detailed gas-phase chemical kinetics coupled with aerosol dynamical equations using a discrete size spectrum [6-8]. The Comparison of model results with laser induced emission signals, is proposed, in order to contribute to understanding of the process of particle inception and dynamic in diffusion controlled conditions. 2. Experimental conditions The opposed-flow burner system was the same as that of Olten and Senkan [5]. Methane, ethylene and propane diffusion flames were stabilized between two opposed jet nozzles (ID 2.54 cm). The oxidizer stream, oxygen and argon, was introduced from the upper nozzle; the fuel streams, containing fuel and argon, were introduced from the lower nozzle. All gases used were of high purity. Screens were used at the exit of each jet to establish uniform gas flow velocities and to generate stable, flat flames. Using a mild vacuum through the holes in the annular section of the bottom burner, combustion products and shield gas were vented out of the system. Using a translation system (0.1 mm), sampling position within the flame was changed by moving the entire burner assembly up or down with respect to the fixed sampling volume. In all the flames investigated velocity of oxidizer and fuel stream were kept constant at 16.1 and 13.2 cm/s, respectively. Therefore, the global strain rate, defined as the sum of the fuel and the oxidizer nozzle exit velocities divided by the nozzle separation distance, was maintained constant at 37.7 s -1 for the three flames. Percentage of hydrocarbon in fuel stream was fixed at