A combined computational and experimental investigation to examine temperature and soot volume fraction in coflow ethylene-air diffusion flames was presented.A numerical simulation was conducted by using a relatively detailed gas-phase chemistry and complex thermal and transport properties coupled with a semi-empirical two-equation soot model.Thermal radiation was calculated using the discrete ordinates method.An image processing technique and a decoupled reconstruction method were used to simultaneously measure the distributions of temperature and soot volume fraction.The results show that the maximum error for temperature does not exceed 10% between the prediction and the measurement.And the maximum error is 6.9% for soot volume fraction between prediction and measurement.Additional simulations were performed to explore the effects of global equivalence ratio on diffusion flames and the soot formation.The results display that the soot formation increases with decreasing the coflow air velocity.And the soot formation in each case appears in the annular region,where the temperature ranges from about 1 000 K to 2 000 K and the profile becomes taller and wider when the coflow air is decreased.
This paper investigated the influence of assumptions in soot volume fr action measurement by thermocouple particle densitometry (TPD) method in laminar nonpremixed ethylene/air diffusion flame. TPD method is based on an extension o f the theoretical treatment of Eisner and Rosner, who assumed that the particle deposition to a cold surface immersed in a flame is dominated by thermophoresis. They developed a formulation for the soot particle mass flux to thermocouple be ad to infer soot volume fraction by inserting the thermocouple to flame rapidly. However, in their formulations, some important parameters were neglected, such as the radiation from soot to thermocouple bead. We added the parameter into the formulation and analyzed its impact. The results show that the ignored paramete r had significant influence for the calculation of thermocouple bead emissivity and thermophoresis is not the dominant mechanism during the initial stage of soo t particles deposition to bead, whose real causes should be studied further.
