Numerical simulation of ignition in pulverized coal combustion with detailed chemical reaction mechanism

Abstract

A two-dimensional direct numerical simulation with a detailed chemical reaction mechanism that considers 158 species and 1804 reactions is applied to pulverized coal combustion occurring in a mixing layer and the ignition phenomena is investigated in detail. The pulverized coal particles which are initially heated up to 2000K are distributed in a fully developed mixing layer. The distributions of temperature and various chemical species concentrations in terms of the mixture fraction are analyzed during ignition. The results show that the ignition occurs in the rich mixture fraction condition (ξ∼0.2), as the gas temperature is also high in this condition because of the high initial temperature set for the central coal particles. However, once ignition occurs, the combustion reaction dramatically takes place in the condition indicating ξ=0.03–0.06, which is a slightly lean value compared with the stoichiometric value and shows the shortest ignition delay time in the calculation for autoignition of homogeneous mixtures of volatile matter and air (zero-dimensional calculation). In addition, in the combustion reaction zone, high OH radical mass fraction is observed around the conditions of stoichiometric mixture fraction, whereas high CH radical mass fraction is observed in the rich mixture fraction conditions.