| At present,a lot of theoretical research and experimental analysis have been carried out on the fuel consumption rate and NOx emission of marine four-stroke diesel engines using EGR systems at home and abroad.However,the experimental studies and theoretical analysis have not been sufficient for the particulate emissions that have not been restricted by laws and regulations.Based on this,this paper carries out the following work:Firstly,a low-pressure EGR system test-bed is designed and established for a marine four stroke medium and high-speed diesel engine.On this basis,the performance and emission data of diesel engine under different loads and EGR rates were obtained by using ordinary diesel as fuel.Experimental results show that the introduction of EGR can effectively reduce NOx emission,but at the same time,it will cause the decrease of power,exhaust temperature,exhaust pressure and other parameters and the increase of fuel consumption.EGR alone can meet the requirements of the IMO Tier III emission regulations,but the EGR rate is greater than 30%.The analysis method based on quantity,mass and composition was used to study the particles produced by EGR.It was found that the number concentration and particle size distribution curve of particles showed multi peak distribution,and with the increase of load,the peak value gradually increased,the total quantity concentration increased,and the average particle size increased.With the increase of EGR rate,the amount and concentration of particulate matter increase,the mass specific emission increases gradually,and the carbon content(OC + EC)increases.Secondly,the working process simulation model of the test object is established based on the experimental data,and the influence of EGR on the combustion and emission of the engine is analyzed by using the converge software.The calculation results show that with the increase of the EGR rate,the average pressure,average temperature,cumulative heat release rate and instantaneous heat release rate in the cylinder all decrease to different degrees,and the combustion duration is lengthened.Although the EGR rate equal to 20% can effectively reduce the NOx production,it still does not meet the tier III emission standard,and the soot production increases,which shows a clear trend of growth and decline.The research results of this paper can provide basic data for the design of the EGR system and the design of the key component of the EGR cooler,and can also provide theoretical support for the subsequent black carbon emissions of the engine. |
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