Study On Oxygen-enriched Combustion Characteristics And Soot Formation Of Propane In CO₂/H₂O Atmosphere

Under the background of realizing the development goal of“double carbon”in our country,the share of natural gas and renewable energy in the energy consumption structure is increasing year by year,but the fossil energy dominated by coal and oil still accounts for the main share.Soot is an important product of traditional fuel combustion,which has a great negative impact on human health,air quality and the service life of combustion devices.Because of its advantages in strengthening combustion and reducing pollutant emissions,oxygen-enriched combustion is considered as a potential clean combustion and carbon capture technology,which is widely used in the industrial field.Liquefied petroleum gas（LPG）with propane（C₃H₈）as the main component has been used in many combustion devices,and its soot particulate emission level is worthy of attention.Previous studies mainly focused on soot formation in various fuel structures such as methane,ethylene and syngas.The soot formation mechanism in propane laminar diffusion flame needs to be further studied.Therefore,the combustion characteristics and soot formation of propane,the main component of liquefied petroleum gas,were studied in this paper.The main research contents include:Firstly,based on the experimental platform of laminar diffusion flame combustion,a non-contact detection method based on CCD（Charge Coupled Device）camera and solid thermal radiation imaging was used to measure the soot volume fraction and temperature two-dimensional distribution of propane laminar diffusion flame in air atmosphere.At the same time,the propane laminar diffusion flame was numerically simulated by Fluent software coupled with GRI-Mech3.0 gas phase reaction kinetic mechanism,and the accuracy of experimental reconstruction data and numerical results were compared to verify the reliability of the model.Secondly,based on the above model,the effects of flame temperature,flame height and soot formation of propane co-flow diffusion flame in O₂/CO₂and O₂/H₂O atmosphere were studied,and the step-by-step decoupling method was used to separate the density effect,transport effect,thermal effect and chemical effect of CO₂or H₂O in the oxidant,and to explore the effects of CO₂or H₂O on propane flame structure and soot formation.The results show that the addition of CO₂or H₂O can effectively inhibit soot formation,but the inhibition pathway is different.CO₂affects soot nucleation and surface growth rate mainly by reducing flame temperature and H mole fraction,but not by promoting soot oxidation,while H₂O inhibits soot formation mainly by increasing OH concentration by chemical effect.Finally,the effect of dilution of CO₂or H₂O or dilution on the fuel side on the combustion characteristics of propane co-flow diffusion flame was studied.The virtual species FCO₂and FH₂O were introduced to explore the effects of different effects on propane flame soot formation,and whether there was a synergistic effect when two diluents were added simultaneously.The results show that dilution effect and chemical effect are the main factors that inhibit soot formation when CO₂and H₂O are added to the fuel side,while the thermal effect has little effect.The effect of adding CO₂and H₂O diluent on propane flame temperature and soot volume fraction is greater than that of adding CO₂and H₂O alone.The peak flame temperature and soot peak volume fraction were reduced by 5.2%and 42.0%by adding CO₂and H₂O at the same time.Combined with the change trend of soot precursor acetylene and soot mass nucleation rate and surface growth rate,it is further confirmed that when CO₂and H₂O are added to the fuel side at the same time,there is a certain synergistic effect between them.