Soot formation in n-heptane/air laminar diffusion flames: Effect of toluene addition

The mixture of n-heptane and toluene is regarded as surrogate fuel for diesel. Under the premise of a certain carbon flow rate, the particle size, nanostructure, microcrystalline size and soot deposition morphology of three kinds of fuel laminar diffusion flames were studied by Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), X-ray diffractometer (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The three fuels were pure n-heptane (T0), toluene / n-heptane blends with 5 vol% (T5) and 10 vol% (T10) toluene, respectively. Thermophoretic probe sampling and SiC fiber deposition were used to obtain soot samples. The results showed that with the increase of toluene content, the flame height increased and the temperature decreased at the same height. The addition of toluene increased the content of PAHs, which promoted the formation of soot, and increased the number and particle size of soot. At HAB = 30 mm, with the increase of toluene content, the graphitization degree of soot increased, which showed a larger soot fringe length and a smaller fringe tortuosity, and microcrystalline width (La) of soot particles increased gradually. It is worth noting that the size of a new structure in the soot deposition is counted for the first time, and it is found that its size is negatively correlated with the fringe length and microcrystalline width of soot.