Multi-diagnostic approach to characterize the onset of formation of nanoparticles in a premixed laminar ethylene/air flame

The onset of formation of nanoparticles in a premixed laminar ethylene/air flame was studied using optical and non-optical diagnostic techniques. The optical techniques (Visible Imaging, Spectroscopic analysis of optical emission, Laser Induced Incandescence and Optical Extinction) were checked against the direct measurement of particles size distribution done with a commercial sampler. The diagnostic techniques were set up on a standard burner (McKenna). The combustion conditions were varied by tuning two experimental parameters: the equivalent ratio Φ and the cold gases velocity v. Values of Φ were investigated in the range 1.3 to 2.2, in combination with cold unburned gas velocities of 5, 7 and 10 cm/s. By varying the combustion conditions, a transition in the signal detected by the different techniques was observed. The transition was put in correspondence with the sensitivity of the given technique to the onset of the nanoparticles formation. A comparison of the sensitivity of the different techniques was performed.