5 years ago

chapter 5 turbulent diffusion flames - FedOA

chapter 5 turbulent diffusion flames - FedOA


1.4 HUMAN HEALTH AND ENVIRONMENTAL ASPECTS The increase of instrumental capability in measuring smaller and smaller particles has been accompanied to the revelation of new potential adverse human health and environments effects related to fine and ultrafine particles in ambient air. Furthermore these compounds are prevalently generated by combustion sources and are typically characterized by a complex mixture of different particles type: elemental and organic carbon, metals, and inorganic compounds such as sulfates. On the other hand particles composition varied noticeably if different particles size ranges are taken in consideration. Sardar et al. [36] sampled for a period of 3 years size-fractionated ambient particulate matter with diameter below 10 μm (PM10) founded that the ultrafine particle mode mostly consisted of organic carbon, with higher wintertime levels at the source sites due to increased organic vapour condensation from vehicles at lower temperatures. The organic carbon that dominates the ultrafine aerosols is comprised of primary aerosol that is emitted directly from combustion sources and of secondary aerosol that is produced by atmospheric processing of carbon compounds. Adverse health effects of combustion-generated fine and ultrafine particles are well resumed in terms of current understanding and knowledge in recent papers by Kennedy [37], by Donaldson et al. [38] and by Oberdoster et al. [39]. The authors report a significant literature that demonstrates the link between exposure to these compounds in the atmosphere and adverse health effects. Fine and ultrafine particles, in fact, are able to penetrate much deeper into the lung. Therefore, when inhaled by people, the particles can be taken-up by cells in the lung and eventually penetrate into the circulatory system and lodge in organs such as the liver and heart. Moreover nanoparticles generated during combustion constitute a cause of concern also for their direct or indirect, as cloud-condensation-nuclei, effects on radiative transfer in the atmosphere as showed by Jacobson [40] and by Novakov and Penner [41]. 28

CHAPTER 2 COMBUSTION SYSTEMS AND EXPERIMENTAL TECHNIQUES In this section a brief description of three combustion systems used and the fundamental of the physical principles to the base of the diagnostic techniques employed during the thesis will be given. 2.1 OBJECTIVES The objectives of the PhD thesis are focused on the experimental characterization of total particulate produced from combustion processes. To this purpose in-situ optical diagnostics: laser induced fluorescence, laser induced incandescence, light extinction and elastic light scattering are extensively employed in numerous combustion configurations with the aim to produce a complete, qualitative and quantitative, description of the kinetic evolution of the particulate in combustion. Moreover it is well know that the techniques normally used for particle measurements in flames can be divided into two categories: ex-situ and in-situ. To this purpose optical techniques are used for in-situ particle characterization (size and volume fraction). Their advantages over the ex-situ techniques include non-intrusion in the flame and real time analysis. However, the main drawback of the optical techniques is that they need to exactly know the refractive index of the particles to reproduce the data correctly [43]. Particular efforts in this thesis have been focused on particles inception, the formation of the first particles nuclei (NOC) and to follow their evolution in different flame conditions. The current state of the knowledge on these species, in fact, came from numerical and experimental works 29

DNS of Turbulent Nonpremixed Ethylene Flames
Heat release rate measurement in turbulent flames