Hydrocarbon on-line detection from atmospheric pressure flames at different C/O ratio B. Apicella 1 , X. Li 1 , X. Wang 2 , M. Armenante 1 , N. Spinelli 3 1. Institute of Research on Combustion - C.N.R., Napoli - ITALY 2. Istituto Nazionale per la Fisica della Materia - C.N.R., Napoli – ITALY 3. CNISM and Dipartimento di Scienze Fisiche, Università di Napoli Federico II– ITALY 1. Introduction A novel apparatus based on Time of Flight Mass Spectrometry (TOF-MS) was recently developed and applied for the on-line analysis of combustion products from atmospheric pressure combustion systems [1, 2]. In the present work, TOF-MS apparatus, improved and optimized, have been used for on-line detection of combustion gases from hydrogen up to benzene and the profiles of these species have been evaluated along two ethylene flames, one slightly fuel-rich and the second very fuel-rich. The profiles have been also compared with the same profiles measured in similar condition with conventional gas chromatographic techniques and reported in the literature [3, 4]. The comparison has been used for validating the TOF-MS apparatus before its use as detector for species like soot precursors, whose structure and concentration profiles are still unknown. 2. Experimental 2.1. Set-up An innovative set-up specifically designed for the on-line detection of combustion products of high masses has been used for the analysis of PAH in an atmospheric-pressure ethylene flame. The experimental set-up is deeper described in a previous work [1]. Basically, it is composed of: (i) a combustion system, (ii) a sampling probe and transfer line, (iii) a supersonic molecular beam, and (iv) a reflectron TOF-MS instrument, designed and built by Kaesdorf s.r.l., where different types of ionization sources can be used. The TOF-MS system can be operated with a mass filter, a disposal where a pulsed electric field is used to deflect the lowest mass ions. In these conditions, saturation of the MCP due to the very high signal intensities produced by the most abundant low-mass ions is avoided and the dynamic range of the detector is preserved. The ionization has been performed by electron impact (EI), which consists of an electron beam produced by a hot tungsten loop filament. In the present experiment a pulse duration of 2 microseconds with a repetition rate of 20 Hz was used for EI. 2.2. 2.2 Hydrocarbon source As combustion pollutant source, a fuel-rich ethylene/oxygen laminar premixed flame was used, produced by a McKenna burner. The burner can be translated allowing the sampling at different positions in the flame. A water-cooled stainless-steel probe (2mm i.d.), connected to a suction pump, was used for the sampling of combustion gases. The probe is also equipped with a second jacket for the 1