Study On Effect Of The Carbon Dioxide/Oxygen Environment On Diesel Combustion Characteristics

Diesel engine has the advantages of high thermal efficiency,good reliability,strong adaptability and good economy,which is widely used in construction machinery,transport vehicles and military equipment.However,diesel engine emissions of pollutants cannot be ignored,which contains a large number of carbon dioxide,nitrogen oxides and particulate matter.In particular,in closed environments such as tunnels,subways and underwater air circulation,emissions need to be strictly controlled.Liquid oxygen carbon sequestration closed cycle diesel engines can effectively reduce the impact of emissions on workers and meet the increasingly stringent emission requirements.When diesel is burned in this system,the background gas is a mixture of carbon dioxide/oxygen,so it is urgent to study the combustion characteristics of diesel under the environments.In this paper,the combustion characteristics of diesel oil in different carbon dioxide/oxygen environments are studied.First of all,based on combustion simulation software Converge,established the physical model of constant volume combustion chamber,diesel fuel characterization of n-heptane and chemical model of the diesel combustion flame in carbon dioxide/oxygen environments flame lift-off length and the distribution of flame temperature contours.Secondly,a test system combining a constant volume combustion chamber with a high-speed camera is built,and the system composition,operation process and test conditions are introduced in detail.The visual experiment of ignition process of diesel oil is carried out.Finally,the similarities and differences of ignition process and flame lift-off length of diesel oil under air atmosphere and different carbon dioxide/oxygen concentrations are discussed,and the changes of natural luminosity of the flame in the test and the distribution of flame temperature cloud maps in the simulation results are analyzed.The results show that the combustion characteristics of diesel oil in the air and carbon dioxide/oxygen environments are greatly different,and the simulation results of the flame lift-off length and flame temperature cloud maps of diesel oil in the carbon dioxide/oxygen environments are consistent with the experimental results,which proves that the calculation model established in this paper is accurate in simulation.When the carbon dioxide concentration is less than 43%,the flame lift-off length decreases with the influence of carbon dioxide concentrations.By comparing the temperature diagram,it can be seen that under different carbon dioxide/oxygen environments,the temperature distribution in the upstream region of diesel flame changes significantly.However,there was no significant difference in temperature distribution in the downstream region of the flame.The curves of the flame lift-off length show the same trend: first it goes down rapidly,then it goes down slightly,later on it goes up rapidly.With the increase of carbon dioxide concentrations,both the flame lift-off length and the natural luminescence of the flame increased and the peak value of the natural luminescence of the flame increased and lagged.