Turbulent Combustion in a Jet Stirred Reactor.

Abstract

The applicability of a jet stirred reactor for the study of constant volume turbulent flame propagation has been confirmed by generating combustion data for methane/air mixtures that agrees with that reported in the literature which employed a fan stirred reactor. For dust/air mixtures, measurements have shown the concentration and turbulence intensity are uniform and steady within the jet stirred reactor. The turbulent burning velocities have been measured for Mira-Gel, cornstarch (varying in particle size and moisture content), polyethylene, para-dichlorobenzene, graphite, corncobs, oil treated sweepings and Pittsburgh seam coal. The turbulence level inside the reactor was measured using a Laser Doppler Anemometer (LDA), and the results deviate slightly from the previously measured hot wire results. The LDA measurements show that the dust has little effect on the turbulence intensity. The values of the laminar burning velocity for coal dust obtained by this method, 6 to 25 cm/sec, are of the same magnitude, 10 to 30 cm/sec, as those obtained from open flame tubes. An increase in the turbulence intensity up to the maximum currently employed, u$\\sp\\prime$ = 3.3 m/sec, gives a continually increasing turbulent burning velocity for all of the dusts. Since all parameters are controllable with this apparatus, the combustion phenomena of cornstarch or graphite dust mixed with methane/air mixtures is also investigated. The hybrid mixture of methane and cornstarch has a much lower explosion limit than each substance alone. A small amount of methane greatly enhances the explosibility parameters of cornstarch. Graphite dust raises the explosion limit of methane slightly in a hybrid mixture, but it has little effect on the explosion parameters in a fairly fuel lean mixture of methane. Graphite also greatly lowers the explosibility parameters of methane at stoichiometric and fuel rich mixture ratios. Graphite dust in a premixed methan/air flame is an energy sink in the reaction instead of an energy source. The relation between the ratio of turbulent to laminar burning velocity and turbulence level for methane/air flame is obtained from the experiment and this matches with an other researcher's three-region model of a turbulent flame. This research has been conducted in order to obtain fundamental data under tightly controlled conditions and to attempt to underst and the basic mechanisms of heterogeneous combustion in order to prevent dust and hybrid explosions in industrial situations. (Abstract shortened with permission of author.)