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This paper describes our recent research on vapor and particle deposition rate processes in combustion systems. Inorganic compounds which deposit on heat exchanger surfaces and gas turbine blades are formed when the fuel and/or ingested air contain inorganic impurities. A quantitative understanding of the deposition rate of inorganic oxides, salts or soot can suggest efficient test/control strategies. Accordingly, we have developed optical methods for precise, real-time measurements of the growth rate of deposits under laboratory conditions. To demonstrate these techniques, and provide data for theory development, a deliberately simple chemical system and target geometry are described; viz. BCl3(g) is added to a premixed C3H8-air flat flame and the B2O3(l) deposition rate on an electrically heated Pt ribbon is measured interferometrically or ellipsometrically over a range of fuel/air ratios and seed levels. The stability of B2O3(l) at present seed levels and surface temperatures (ca. 1200–1300 K) reveals kinetic restrictions on B2O3(l) gasification reactions. Measured deposition rates agree with predictions of our multicomponent mass-transfer boundary layer (BL) theory, with a constrained equilibrium ((HBO2)3precluded) boundary condition. These encouraging results suggest a more general applicability for the optical methods and BL theory outlined herein, and demonstrate the role of heterogeneous kinetic barriers in determining dew points and deposition rates in combustion systems.

Results of experimental and numerical studies of counterflow, partially premixed, flames burning methane in air are reported. Experimental data is obtained for the temperature profile, the axial velocity profile, the concentration profiles of various stable species and the critical conditions of the flame at extinction. The results are compared with numerical calculations performed at conditions identical to those used in the experiment. Experimental measurements and numerical calculations show that partial premixing of the reactant streams of a counterflow diffusion flame makes the flame less resistant to stretch. In addition, numerical calculations show that the reaction zone of a partially premixed flame exhibits a diffusion flame and a premixed flame-like structure. Both results are consistent with previous asymptotic analyses of the structure of partially premixed flames.