Abstract:

When simulating combustion in a combustion chamber, the associated chemical reaction mechanism is extremely complex and computationally intensive, complicating its widespread use. To meet the requirements of engineering design, simulation is an effective method to determine the combustion mechanism of surrogate fuel. Based on the directed relation graph with error propagation and sensitivity analysis, 40 species and 234 reactions were involved in the mechanism obtained by high-temperature (> 1100 K) simulation with 180 species and 1962 reactions of n-dodecane. Simplified and detailed mechanisms were used to simulate ignition delay times for different equivalence ratios and pressures. At the same pressure and equivalence ratio, the ignition delay times decreased with increasing temperature. At different equivalence ratios, the simulation results agreed with the experimental data, especially at high temperatures. At constant temperature and equivalence ratio, the ignition delay times decreased with increasing pressure, and the simulation results accurately reflect this trend. Because the mechanism was simplified for the high temperature conditions, the calculated data for ignition delay times of the simplified mechanism have a larger error at low temperatures, with a maximum of 23.86%, compared to the detailed mechanism. Between 1100 and 1250 K, the average error was 8.89%. The flame propagation speed at different initial pressures and temperatures was simulated using the simplified and detailed mechanisms. As the initial pressure increased, the flame propagation speed continuously decreased, while the propagation speed increased. These simulation results are in good agreement with the experimental results, verifying that the simplified mechanism can accurately reflect the combustion characteristics of n-dodecane. Using the concentration data of C₁₂H₂₆/OH/H₂O/CO₂ and other important species over time, it was revealed that the simplified mechanism can accurately describe the reactant consumption, radical changes, and product generation during the combustion process. The temperature has a significant influence on the pyrolysis of C₁₂H₂₆. At 1390 K, C₁₂H₂₆ is almost completely consumed within 0.1 ms. At different temperatures, two peaks were observed in the OH radical concentration. The detailed and simplified mechanisms can reflect the variation characteristics of the OH radical concentration and the maximum value of the peaks. Both the simplified and detailed mechanisms accurately reflect the characteristics of H₂O and CO₂ concentration that initially slowly increased and then were generated rapidly. Using the simplified mechanism, a numerical analysis of the Bunsen burner was performed. The simulation results accurately reflected the changes of the temperature and species of the flame in the axial and radial directions and reproduced the combustion process of the Bunsen burner flame. Simulation results of Bunsen burner showed that this mechanism can be applied to numerical calculations and produced good simulation results. Comprehensively, the simplified high-temperature mechanism of n-dodecane correctly reflects the physical and chemical properties and can be used for 3D numerical simulation, which has good engineering and application prospects.

Key words: n-Dodecane, Combustion mechanism, Mechanism reduction, Bunsen burner, Surrogate fuel