Measurements of soot and response optimisation of laminar pool and prevaporised jet flames for various oxygenated biofuels

In this study, the generation of soot from the combustion of biodiesels and their blend with fossil diesel are investigated under laminar pool flame and prevaporised diffusion jet flame conditions. Neat biodiesels from eight feedstocks including carotene palm, palm, soy, coconut, rice bran, waste vegetable oil, duck, and goose, alongside two methyl esters of methyl laureate and methyl myristate are blended with fossil diesel at 20% volumetric intervals to form 51 different blends. The soot volume fractions for the combustion of all blends are determined using continuous-wave laser cavity extinction (CW-LCE) calibrated 2D laser-induced incandescence (2D-LII) technique. Results show that biodiesels with higher degree of saturation produce less soot, as reflected in both laminar pool and prevaroprised diffusion jet flames. The experimental data is further analysed using design of experiments (DOE) methodology. The mixture design model (MDM) following the simplex design is used to focus on the soot generating effects arising from the chemical compositions by classifying the chemical components into hydrocarbons and saturated, monounsaturated and polyunsaturated fatty acid methyl esters (FAME). The results from the Cox response trace plot associated with DOE elucidate the effects of the individual chemical group within the fuels. Both laminar flame types for the all 51 biodiesel-diesel blends exhibit the same trends with differing magnitudes. Saturated FAME has the largest singular effect on soot generation followed by hydrocarbons. However, when only neat biodiesels are considered, the laminar pool flame and laminar diffusion jet flames show differing trends for all the chemical groups. Monounsaturated FAME and saturated FAME have the greatest influence on neat biodiesel-generated soot for laminar pool flame and laminar diffusion jet flame, respectively. From the mixture design model, an optimum synthetic biodiesel mixture containing 16.1%, 34.6% and 49.3% of saturated, monounsaturated and polyunsaturated methyl esters is recommended for the lowest soot generation.