Numerical Studies of Spray Combustion Processes of Palm Oil Biodiesel and Diesel Fuels using Reduced Chemical Kinetic Mechanisms

Spray combustion processes of palm oil biodiesel (PO) and conventional diesel fuels were simulated using the CONVERGE CFD code. Thermochemical and reaction kinetic data (115 species and 460 reactions) by Luo et al. (2012) and Lu et al. (2009) (68 species and 283 reactions) were implemented in the CONVERGE CFD to simulate the spray and combustion processes of the two fuels. Tetradecane (C₁₄H₃₀) and n- heptane (C₇H₁₆) were used as surrogates for diesel. For the palm biodiesel, the mixture of methyl decanoate (C₁₁H₂₀O₂), methyl-9-decenoate (C₁₁H₁₉O₂) and n-heptane was used as surrogate. The palm biodiesel surrogates were combined in proportions based on the previous GC-MS results for the five major biodiesel components namely methyl palmitate, methyl stearate, methyl oleate, methyl linoleate and methyl linolenate. The Favre-Averaged Navier Stokes based simulation using the renormalization group (RNG) k-ε turbulent model was implemented in the numerical calculations of the spray formation processes while the SAGE chemical kinetic solver is used for the detailed kinetic modeling. The SAGE chemical kinetic solver is directly coupled with the gas phase calculations by renormalization group (RNG) k-ε turbulent model using a well-stirred reactor model. Validations of the spray liquid length, ignition delay and flame lift-off length data were performed against previous experimental results. The simulated liquid length, ignition delay and flame lift-off length were validated at an ambient density of 15kg/m³, and injection pressure conditions of 100, 200 and 300 MPa were utilized. The predicted liquid length, ignition delay and flame lift-off length agree with the trends obtained in the experimental data at all injection conditions.