Experimental And Simulation Study On Flame Lift-off Of Diesel Engine

The proportion of emissions of vehicles in diesel exhaust emissions,accounting for 43% of the total NOX,accounting for 83% of the suspended particles.The combustion process of internal combustion engine has great effects on the performance and emission characteristics.A reasonable organization is to improve the combustion dynamics,improving the economy,reduce harmful emissions and reduce the noise of the decisive factor.For direct injection diesel engine,the combustion process performance depends largely on the cylinder mixture formation,fuel injection and in-cylinder flow field parameters directly affect the quality of the air mixture is formed.So the study of combustion process of diesel spray to find ways to reduce soot emission and improve emission characteristics has important significance.This paper mainly uses the method of experiment and numerical simulation of a combination of research and analyzes the process parameters of flame lift-off length and its influencing factors in a direct injection diesel engine turbulent diffusion combustion process.The experiment part of the main work is: to build a constant volume combustion bomb system which is suitable for the experiment requirements of environmental conditions,the rational design of the experiment procedure.In the selection of nozzle and cylinder after comprehensive consideration,selection of injection pressure,cylinder temperature,cylinder pressure,fuel quality on combustion most key factors were studied,and then adjust the parameters and experiment work.In this study,the temperature and pressure sensor to measure the real-time change of temperature and pressure values of the flame lift-off length and the image data for specific measurement analysis software of diesel oil.Finally based on the analysis of the constant volume combustion bomb in ambient temperature,ambient pressure and injection pressure on the flame lift-off length effect,and to analyze the impact of changes in trend to get a different proportion of fuel's flame lift-off length,may provide reference for different fuel diesel emissions.Numerical simulation part main contents are: based on the STAR-CD software,the constant volume combustion bomb internal injection pressure,different oxygen concentrations,different environment temperature and turbulent combustion model of the spray and combustion process simulation,obtain a time within the working state of combustion in the bomb,and comparing the results obtained from the simulation calculation of two turbulent combustion models with the test data,finally concluded that the effect of parameters on combustion and flame lift-off length effect.The results show that the probability density function(PDF)model simulation results better than the eddy breakup model(EBU)to get the real value;under the low temperature,the EBU simulation results compared with experimental values differ greatly,with the temperature rising,gradually approaching the test value.The ambient temperature is 1000 K,the oxygen concentration is 21%,EBU and PDF to calculate the flame lift-off length is approximate,but the turbulent flame structure is quite different;for low temperature environment(such as environmental temperature is 850 K,the oxygen concentration is 21%),the difference between the model of PDF with EBU in particular significant.In all simulations under different conditions,compared with the PDF model,EBU model of the turbulent flame brush is more narrow,more consistent high Reynolds number turbulent flame and turbulent flame brush and test of PDF model in the broader observed.Finally,the flame floatation conditions of the kerosene and diesel fuels under different environmental conditions are summarized,the main factors affecting the flame lift-off length size and trends;and use the PDF simulation of turbulent combustion model of diesel and kerosene,through the comparative analysis of test results to further verify the reliability of the PDF model.Considering the fuel molecular structure and the number of carbon atoms,to make a simple prediction for different quality diesel flame lift-off length,i.e.the higher the average carbon atom number of diesel,at lower ambient temperatures and pressures,the flame lift-off length is smaller,the change is not obvious.