Prof. Madjid Birouk
In residence at
Dr Christian Chauveau
Spray combustion: on the vaporization process of micro droplets
Spray/Droplets formation and combustion are the processes which control combustion efficiency and emissions of power generation systems such as gas turbines, diesel engines, and other industrial burners. In the combustion chamber of these systems, upon its injection, liquid fuel breaks up into droplets to increase the mixing between the oxidant/air and fuel but more importantly to ease and enhance the vaporization (gasification) process of liquid fuel and hence the overall combustion performance. Therefore, understanding these processes is crucial for the design and development of these systems in order to meet the ever increasing stringent emissions limitations. Although the vaporization characteristics of a liquid fuel injected into a gaseous environment/ambient have been studied extensively in the open literature, there still remain many challenges. For instance, most of published research on liquid fuel gasification was based droplets that are way larger than those encountered in real combustion chambers. This is especially due to the technical difficulties in developing test rigs capable of replicating realistic conditions (e.g., droplet size, droplet surroundings composition and state and flow character – laminar or turbulent). An understanding of the interplay between these parameters when it comes to liquid fuel vaporization is lacking. This is why currently used computer codes employed by industry for modeling and designing spray combustion still rely on untested approximations especially on the effect of gas phase turbulence. The research project outlined below will lead to significant scientific advances where new knowledge and comprehensive data at realistic test conditions will be generated. The findings of this research will greatly aid the combustion research community to construct high fidelity computer simulation codes for modeling spray combustion and consequently benefit the industry in designing more efficient and less pollutant power generation systems.
Publications in relation with the research project
This paper presents an analysis of the effect of the droplet support fiber on the droplet evaporation process. This effect is evaluated for a droplet evaporating in a hot environment at atmospheric pressure using the experimental results of the present study and those in the literature. Selected published results are acquired using similar test conditions and experimental setups as the present data. The only main difference between these studies is the droplet support fiber diameter which varies between 14 µm and 225 µm. The ambient temperature explored in these studies ranges from room temperature up to 973 K. n-Heptane is selected because it is the most common fuel used in these studies. The main findings are that the cross-fiber technique, which uses 14 µm fiber diameters, induces no noticeable heat transfer into the droplet and consequently does not interfere with the evaporation process. In contrast, the classical fiber technique, which uses relatively larger fibers, greatly enhances the droplet evaporation rate as a consequence of increased conduction heat transfer through the fiber. A correlation is proposed to quantify the level of this increase as a function of ambient temperature and the fiber cross-sectional area.