Simulation Research On Flame Temperature Measurement And Soot Deposition Process By Thermocouple

With the rapid development of economy of China, the situation of energy supply is becoming tighter and tighter, and the environmental pollution produced by burned fuel is becoming more and more serious. Soot is one of pollutants produced by burned fossil fuel, and it represents unrealized chemical energy of fuel. The emission of soot by combustion processes is a source of atmospheric pollution and, due to its association with mutagenic and carcinogenic polycyclic aromatic hydrocarbons (PAH), has been affecting human health. Soot particles also affect the environment in many other ways including their contribution to the formation of photochemical smog and atmospheric acids. Soot particle presented in the atmosphere scatter and absorb solar radiation that can impede atmospheric visibility. Therefore, it's critical to understand the physical and chemical mechanisms about soot formation, and make it possible to control the processes of soot nucleation, surface growth, and oxidation. More and more scholars analyse the characteristic of soot formation by measuring the soot volume fraction.This paper introduces the used methods of the soot measurement home and abroad in detail, emphasis was put on the characteristic and applications of direct sampling technique. It firstly analyses the influence of the flame radiation and wire conduction for the temperature measurement without considering the soot deposition. According to the numerical simulation result of the axisymmetric laminar coflowing ethylene flame, the correlative gas temperature field, velocity, flame radiation field and soot volume fraction can be obtained. Our work is to simulate the process of the thermocouple being inserted into the flame by numerical calculation. The result shows that at the bottom of the flame where the temperature is low enough, the radiation of the flame to the junction is larger than the radiation loss, the energy gained is larger than the loss, so the temperature of the junction will be higher than the gas temperature in this district. The influence of the wire conduction is also very large for the temperature measurement. Since the thermal gradient existed in the thermocouple , the cross-sectional area of the 100μm thermocouple is large enough to allow significant heat conduction along its axis. Conduction through the wire will remove energy from the junction at the maxima, but add it at the local minimum, so the junction temperature will be lower than the gas temperatre where the gas temperature is high enough, and higher at low temperature area. The influence of the wire conduction will be different when the thermocouple moving in the different way.When the thermocouple is inserted into a soot-containing flame, particle will deposite on the junction. We simulate the process of soot deposition onto the junction by using thermophoresis theory. The curve of the junction temperature changing with the soot deposition can be obtained. We has analysed the influences of the wire conduction, different initial temperature, soot deposit density, wire diameter and soot aggregate diameter for the junction temperature as soot deposit.