Date of Award
Doctor of Philosophy
G. M. Colver
A unique combustion test facility was designed and built for the purpose of measuring quenching distance, flammability limit and burning velocity of powdered fuels. A uniform density particulate cloud of aluminum or coal particles was generated at atmospheric pressure between two parallel plate electrodes utilizing the concept of an electrostatic driven suspension. A spark discharge was used to ignite the particle/air mixture, and the burning velocity was measured using high speed movies.;The effects of particle size, concentration, and particle shape on the quenching distance and the burning velocity of aluminum powder and coal were studied. In addition, the effect of volatile content on the quenching distance and the burning velocity of coal powder was studied for five different types of coals.;The results show that generally the quenching distance, lean flammability limit, and minimum quenching distance increase as the particle size increases while quenching distance of coal decreases as the volatile content is increased. The burning velocity of both aluminum and coal was found to increase as the particle size was decreased. Batch aluminum particles from the can were tested to have a higher quenching distance compared to mono-sized particles of same mean diameter. The quenching distance of irregular aluminum was found to be lower than that of spherical aluminum particles smaller than 25 [mu]m in mean diameter, but the reverse was true for particles larger than 27 [mu]m.;A non-dimensional correlation equations for each of the coal and aluminum types was obtained using a polynomial least square multiple regression method. The correlation equations predicted the experimental data very well within ±7% for aluminum and ±5% for coal powders.;A one dimensional time-dependent homogeneous model of flame propagation of aluminum powder was developed using a Lagrangian transformation and finite difference method. The effects of particle size and particle concentration on burning velocity of aluminum powder was investigated with this model. The results matched reasonably well with the experimentally measured burning velocity.;Also a one dimensional model of flame propagation of coal powder (BYU, FLAME code) was tested based on a heterogeneous model of time-dependent non-linear partial differential equations. The numerical prediction of detailed flame structure and flame velocity could be predicted. The predicted variation of flame velocity with particle concentration of coal powder shows the same trend as the experimental data.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Kim, Se-Won, "Theoretical and experimental studies on flame propagation and quenching of powdered fuels " (1989). Retrospective Theses and Dissertations. 9058.