Development of efficient and accurate skeletal mechanisms for hydrocarbon fuels and kerosene surrogate

In this paper,the methodology of the directed relation graph with error propagation and sensitivity analysis（DRGEPSA）,proposed by Niemeyer et al.（Combust Flame 157：1760-1770.2010）.and its differences to the original directed relation graph method are described.Using DRGEPSA,the detailed mechanism of ethylene containing 71 species and 395 reaction steps is reduced to several skeletal mechanisms with different error thresholds.The 25-species and 131-step mechanism and the 24-species and115-step mechanism are found to be accurate for the predictions of ignition delay time and laminar flame speed.Although further reduction leads to a smaller skeletal mechanism with 19 species and 68 steps,it is no longer able to represent the correct reaction processes.With the DRGEPSA method,a detailed mechanism for n-dodecane considering low-temperature chemistry and containing 2115 species and8157 steps is reduced to a much smaller mechanism with249 species and 910 steps while retaining good accuracy.If considering only high-temperature（higher than 1000 K）applications,the detailed mechanism can be simplified to even smaller mechanisms with 65 species and 340 steps or48 species and 220 steps.Furthermore,a detailed mechanism for a kerosene surrogate having 207 species and 1592 steps is reduced with various error thresholds and the results show that the 72-species and 429-step mechanism and the66-species and 392-step mechanism are capable of predicting correct combustion properties compared to those of the detailed mechanism.It is well recognized that kinetic mechanisms can be effectively used in computations only after they are reduced to an acceptable size level for computation capacity and at the same time retaining accuracy.Thus,the skeletal mechanisms generated from the present work are expected to be useful for the application of kinetic mechanisms of hydrocarbons to numerical simulations of turbulent or supersonic combustion.

Reduced Methane Combustion Mechanism and Verification,Validation,and Accreditation(VV&A)in CFD for NO Emission Prediction

In order to obtain a reduced methane combustion mechanism for predicting combustion field and pollutants accurately in CFD simulations with a lower computational cost,a reduced mechanism with 22 species and 65 steps of reactions from GRI-Mech 3.0 was obtained by direct relation graph method and sensitivity analysis.The ideal reactor calculation and VV&A(Verification,Validation,and Accreditation)in CFD were carried out using the proposed mechanism.The results showed that the proposed mechanism agrees well with the detailed mechanism in a wide range of operating conditions;the temperature field and species can be predicted accurately in CFD simulations(RANS and LES models),and the NO prediction error of an industrial gas turbine combustor outlet is less than 2×10-6.The proposed mechanism has high engineering values.