Search

Abstract: Experimental studies are conducted on extinction and autoignition of methanol and ethanol flames in laminar, nonuniform flows. Two flame types are considered: nonpremixed and premixed. The studies are performed in the counterflow configuration. The burner used in the experiments is made up of two ducts. Studies in the nonpremixed configuration are carried out by injecting a stream comprised of fuel vapors and nitrogen from one duct, and a stream of air from the other duct. In the premixed configuration a premixed-reactant stream made up of fuel vapors, air, and nitrogen, is injected from one duct, and a nitrogen stream from the other duct. Numerical calculations are performed using detailed chemistry at conditions corresponding to those used in the experiments. For the nonpremixed systems considered here, the calculated values of the critical conditions of extinction agree well with experimental data. At given values of the strain rate and temperature of the fuel stream, the calculated temperature of the oxidizer stream at autoignition is found to be higher than the measured values. In the premixed configuration the strain rate at extinction is measured for various values of the equivalence ratio of the mixture in the premixed-reactant stream, ϕ 1. The value of ϕ 1, at which the calculated extinction strain rate is the highest, is found to be larger than the value of ϕ 1 at which the measured extinction strain rate is the highest. Sensitivity analysis is carried out to test the influence of various elementary reactions on critical conditions of extinction. The structure of a nonpremixed methanol flame is investigated. Concentration profiles of stable species and temperature profiles are measured. The flame structure is calculated using detailed chemistry. The results of numerical calculations agree well with experimental data. [Copyright &y& Elsevier]

Abstract: Reduced chemical kinetic mechanisms for methanol combustion were investigated by evaluating ignition delay magnitudes and combustion in a continuously stirred reactor. Unsteady computations were made to study the characteristics of the kinetic mechanisms proposed in the literature and to compare the dependence of various parameters on methanol combustion. All computations were done under isobaric conditions, and, to capture the influence of all the reactions involved in the mechanism, a very small time step was used. Finite-difference methods were used to solve the coupled differential equations. The five-step mechanism developed by C.M. Mueller and N. Peters [in: N. Peters, B. Rogg (Eds.), Reduced Kinetic Mechanisms for Applications in Combustion Systems, Springer-Verlag, New York, 1993, pp. 143–155] for premixed flames and both the five-step mechanism and the four-step mechanisms developed by C.M. Mueller, K. Seshadri, J.Y. Chen [ibid, pp. 284–307] for non-premixed flames were considered. It was found that the Mueller et al. five-step mechanism, with some modifications, best supported the spontaneous ignition and continuous stirred reactor combustion. The results were validated by comparing calculated ignition delays with available experimental data of C.T. Bowman [Combust. Flame 25 (1975) 343–354], and calculated final steady-state concentrations with chemical equilibrium calculations [J.-Y. Chen, Combust. Sci. Technol. 78 (1991) 127]. Initial temperature and concentration and the operating pressure of the system have a major effect on the delay of methanol ignition. The residence time of the continuous stirred reactor affects ignition delay and also changes the transient characteristic of chemical composition of the fuel–vapor mixture. The computations are intended to guide and explain many combustion studies that require a methanol kinetic mechanism. [Copyright &y& Elsevier]