A fundamental understanding of soot formation in practical systems is still a daunting challenge and laboratory flames remain a better setting to make progress in the field. The research has the realistic objective of examining the structure of laminar counterflow flames in the pressure range 1-40 atm under conditions of incipient sooting. It entails the characterization of temperature, stable gas species, including soot precursors and growth species, and soot in flames as a function of pressure. The selected pressure range is of relevance to gas turbines and engine applications. The project represents an ambitious, comprehensive and unprecedented effort with potentially transformative impact in the context of the environmental footprint of combustion. The counterflow diffusion flame is selected as an optimal environment because of the unparalleled level of control that it provides on the soot formation process. The flames are treated essentially as ?flow reactors? with well defined temperature time-histories. Furthermore, this flame configuration is very convenient for modeling purposes since the system is one-dimensional, which is advantageous for fuels with a very large chemical mechanism. Fuels to be considered include liquid fuels, such as heptane and toluene, that would be prevaporized at modest concentrations and introduced in such environments either individually or in combination as a perturbation of baseline gaseous flames. The approach is both experimental and computational in nature. Deliverables of the program include: 1) a test-bed experimental system to study the structure of high-pressure laminar diffusion flames of gaseous and liquid fuels of different sooting propensity and their sooting behavior under well-defined and well-controlled conditions; 2) a validated code with a comprehensive model of soot formation/oxidation, allowing for detailed transport and a semi-detailed chemical kinetic mechanism; and 3) a comprehensive database that will be made available to other modelers.
Combustion-generated soot particulates from land-based sources are now acknowledged to pose a significant health risk and have been the subject of stringent new EPA regulations. Moreover, the contributions of aircraft flights to atmospheric aerosol levels via high altitude soot emissions and their impact on the mechanisms of long term global climate change and ozone depletion are also receiving great attention and face the likelihood of tightened regulation. All these issues are exacerbated by the high pressures at which new combustors are operated, because soot production is very sensitive to the pressure. If soot and the problems associated with it are to be controlled, quantitative understanding of the soot growth and oxidation mechanisms in the form of experimental measurements supported by computational models is essential and is the primary goal of the project.
