Fuel, Vol.145, 50-62, 2015
Numerical investigation of localised forced ignition of pulverised coal particle-laden mixtures: A Direct Numerical Simulation (DNS) analysis
Localised forced ignition of mono-disperse pulverised coal particle-laden mixtures has been analysed based on three-dimensional Direct Numerical Simulations for the carrier phase with simplified chemistry for the combustion of volatile gases. The coal particles are treated as point sources and tracked in a Lagrangian manner. The coupling between Eulerian gaseous and Lagrangian particulate phases has been achieved by appropriate source terms in the mass, momentum, energy and species conservation equations. A detailed parametric analysis has been carried out to analyse the effects of particle equivalence ratio Phi(p) (which is defined based on the total available primary volatile fuel in the particulate phase), root-mean-square of turbulent velocity u' and particle diameter d(p) on the early stages of combustion. Both non-premixed and premixed modes of combustion have been observed in the reaction zone for the flames resulting from localised ignition. An increase in Phi(p) is found to be detrimental for sustaining combustion, whereas a reduction in particle size may adversely affect the extent of burning. It has been found that an increase in u' increases the rate of mixing of devolatilised fuel with the surrounding air, which, though beneficial for sustaining combustion, increases the heat transfer rate from the hot gas kernel, thus leading to flame extinction for high values of u'. Detailed physical explanations have been provided to explain the observed effects of Phi(p), root-mean-square turbulent velocity fluctuation u' and particle diameter d(p) on combustion of coal particle-laden mixtures following successful localised forced ignition. (C) 2014 Elsevier Ltd. All rights reserved.
Keywords:Direct Numerical Simulations;Coal combustion;Localised forced ignition;Root-mean-square turbulent velocity fluctuation;Particle equivalence ratio