Study On Laminar Premixed Combustion Characteristics Of C₁-C₄ Alkane Fuels With Dilutions

The continuous industrial and economic development increased urbanization and fuel consumption.To meet the demand for energy growth and reduce carbon emissions,the energy structure of China is being continually improved.At present,natural gas?NG?,considered as one of the cleanest sources of energy carrier of conventional fossil fuels,offers high energy efficiency and low-emissions with the potential of transport facilitation.It has gradually become an important part of energy used in industry and transportation.The composition of natural gas varies with its origin,but the overall proportion of the C₁-C₄?methane,ethane,propane and butane?alkane fuels in natural gas is about 95%and play an important role in the combustion community.In recent years,some studies have shown that the addition of hydrogen to methane and propane can effectively promote its burning velocity and extend its ignition limit.Moreover,addition of hydrogen has a significant effect on the combustion performance and can reduce emissions from engines fueled with natural gas.In addition,a series of studies have reported that adding diluted gases?such as N₂,CO₂,H₂O?to hydrocarbon fuels can effectively reduce the related pollutants emission.Therefore,in this paper,four alkanes C₁-C₄,which are the main components of natural gas,are taken as the research objects.Using H₂,N₂,CO₂ and H₂O as diluents,based on ChemkinII/Premix Code and modified detailed chemical reaction mechanism:GRI 3.0*-Mech and San Diego*-Mech?introducing five hypothetical substances of FH₂,FO₂,FN₂,FCO₂ and FH₂O?,the physical and chemical effects of four diluents on laminar burning velocities,adiabatic flame temperatures,net heat release rates and elementary reactions responsible for temperature changes of C₁-C₄alkanes under different equivalence ratios were analyzed and determined.Results showed that the chemical effect of H₂ promotes the laminar burning velocities and adiabatic flame temperatures of C₁-C₄,while the physical effect decreases the two parameters.The physical and chemical effects of N₂,CO₂ and H₂O all decrease the laminar burning velocities of CH₄,C₂H₆ and C₃H₈,while for C₄H₁₀,the laminar burning velocity of C₄H₁₀0 increases due to the chemical effects of CO₂and H₂O during lean combustion.Under a few conditions,the chemical effects of CO₂and H₂O increase the temperature of C₁-C₄ adiabatic flame.In addition,the physical effects of H₂,N₂,CO₂ and H₂O inhibit the chemical reactions of C₁-C₄ combustion,resulting in the decrease of net heat release rates.The chemical effect of H₂accelerates the process of chemical reaction and obviously increases the net heat release rates of C₁-C₄ laminar premixed combustion,while the chemical effects of N₂,CO₂ and H₂O decrease the net heat release rates.Sensitivity analysis of the important elementary reactions responsible for temperature change of C₁-C₄ by adding H₂,N₂,CO₂ and H₂O show that the two most important elementary reactions that play a leading role in promoting the temperature increases of C₁-C₄ are H+O₂<=>OH+O and CO+OH<=>H+CO₂,and the important reactions responsible for inhibiting the temperature rise of C₁-C₄ are H+CH₃?+M?<=>CH₄?+M?and H+O₂+H₂O<=>HO₂+H₂O or H+O₂?+M?<=>HO₂?+M?.