Mathematical Modeling of Water-Coal Fuel Droplets Ignition Under High Pressure Medium

Abstract

ABSTRACT The article presents the results of theoretical studies of the ignition process of a water-coal fuel particle under conditions of high-temperature heating at high pressures of the external environment. The authors have developed a new mathematical model of the water-coal fuel particles ignition under stress (pressure – Pg = 1–200 bar, and temperature Tg = 873–1273 K) heating conditions. The mathematical model differs from the known ones by a detailed description of the physicochemical processes occurring during the induction period of time, as well as the processes of phase transitions under high pressure conditions. Based on the results of numerical simulation of the ignition process, it was found that the pressure of the external environment (Pg) has a significant effect on the characteristics and conditions of ignition of water-coal fuel particles. It was shown that the tign(Pg) dependence is essentially nonmonotonic. The authors have established that when Pg changes in the range from 1 to 30 bar (for oxidizer temperatures (Tg = 873–1273 K), an increase in the ambient pressure leads to a nonmonotonic increase in tign. In this way such a dependence tign(Pg) is due to the joint influence of two significant parameters of the factor space, which significantly affects the dynamics of the thermal treatment of fuel. With an increase in the pressure of the mixture of oxidizer and combustible gases, the saturation temperature (the temperature of intense evaporation of water) increases, at the same time, the heat of the phase transition (QL) decreases and the rate of release of pyrolysis gases into the oxidizing environment decreases. Based on the results of the theoretical studies, it has been shown that for efficient combustion of water-coal fuel under the conditions of the combustion chambers of a GT at oxidizer temperatures Tg≥1073K, the pressure in the combustion chamber of the GT must be at least 50 bar.