【作者】 于群；

【导师】 孙万臣；

【作者基本信息】 吉林大学 ， 动力工程及工程热物理， 2018， 硕士

【摘要】 压燃式发动机具有良好的动力性和经济性,但NO_x和碳烟排放较高。通过燃用含氧燃料、优化喷油参数、引入EGR分层等方法,并借助先进的光学测试技术,多角度深入研究影响发动机燃烧和排放过程的核心问题,对实现压燃式发动机高效清洁燃烧具有重要意义。本文搭建了定容弹喷雾特性试验平台和光学发动机试验平台。借助高速摄像法综合研究燃料特性、喷油参数以及EGR分层对压燃式发动机喷雾特性、燃烧和碳烟排放过程的影响。主要研究内容分为三部分:1)制取煤基F-T合成柴油及其分别掺混5%碳酸二甲酯(D05)、10%碳酸二甲酯(D10)和15%正丁醇(B15)共四种燃料,在定容弹试验平台上进行燃料喷雾特性试验研究,分析燃料特性对贯穿距离、喷雾锥角和喷雾面积等喷雾特性参数的影响。2)在光学发动机中试验研究喷油参数及燃料特性对于燃烧与火焰发展历程的影响规律。从特定燃烧时刻、不同曲轴转角、火焰面积和红色单通道火焰图像四个角度分析不同条件下的燃烧过程。揭示燃料含氧量及含氧官能团对燃烧特性的影响规律。3)利用双色法对燃烧火焰图像进行数值解析计算研究燃料特性、EGR率和EGR分层方式对燃烧过程温度场以及碳烟KL因子的影响,探究缸内燃烧过程中燃料氧组分和环境氧组分对燃烧及排放的复合协同作用机理。主要研究结论如下:1)定容弹喷雾特性试验结果表明,贯穿距离、近场锥角、远场锥角和喷雾面积均随喷油压力的增大而增大,适当提高喷油压力能够改善燃料雾化混合过程。F-T合成柴油中掺混含氧燃料DMC能够改善燃料雾化效果;由于正丁醇黏度大,F-T合成柴油掺混15%正丁醇后,混合燃料雾化混合效果变差。2)喷油参数对火焰发展规律影响的试验结果表明,随着喷油压力增大,亮点状火焰减少,大面积的片状火焰增多,燃烧迅速,但滞燃期变化不大;随着喷油提前角的增加,着火滞燃期略有延长,着火点数量减少,火焰亮度降低,火焰面积几乎不变;随着喷油脉宽的增加滞燃期不变而燃烧持续期有所增加,着火点增多,火焰面积及火焰亮度增大,燃烧更加剧烈。3)不同燃料燃烧特性试验研究结果表明,随着DMC掺混比例的增加,燃料含氧量增加,燃烧滞燃期略有延长,速燃期燃烧加剧,后燃期燃烧平缓,燃烧压力峰值降低,着火点数量增多且更均匀地分布于气缸之中,R通道值降低,集中高亮火焰转变为更均匀的低温火焰。相同含氧量不同含氧官能团的D05和B15含氧混合燃料燃烧过程的区别是B15后燃期燃烧过程更平缓,火焰面积较大且火焰亮度较暗。F-T合成柴油掺混含氧燃料后可以降低燃烧过程中碳烟生成量。4)EGR对不同燃料燃烧火焰发展历程的双色法研究结果表明,随着DMC掺混比例的提高,燃料含氧量增加,缸内燃烧温度逐渐降低,火焰温度梯度减小。燃烧过程中碳烟生成量随DMC掺混比例增加而减少。掺混相同含氧量的正丁醇和DMC相比,B15燃料的碳烟生成量较低。随着EGR率的增加,燃烧温度逐渐降低。燃用含氧燃料后EGR的引入能够在一定程度上降低燃烧温度及NO_x排放,同时对碳烟排放影响不大。五种EGR分层方式下火焰温度从高到低排序为均质EGR>螺旋导管分层>螺旋分层>切向导管分层>切向分层。五种分层形式的碳烟排放量的大小与温度场的高低相吻合。5)含氧燃料和EGR分层的协同作用能够同时降低NO_x和碳烟排放。燃用含氧燃料能够降低燃烧过程碳烟生成量,采用螺旋进气道EGR分层方式形成中间浓四周稀的径向分层有利于降低NO_x生成量同时对碳烟生成量影响较小。更多还原

【Abstract】 CI engine has excellent dynamic and economy performance as well as poor NOx and soot emission performance.By using oxygenated fuels,optimizing fuel injection parameters,using EGR stratification,and utilizing advanced optical testing techniques,the research on the key issues that affect the process of engine combustion and emissions is significant for achieving high efficiency cleaning combustion in CI engine.In this paper,a constant volume bomb test platform and an optical engine test platform were built.Comprehensive study was carried on the effect of fuel characteristics,injection parameters and EGR stratification on the spray,combustion and soot emission in CI engine by high-speed imaging method.The research can be divided into three parts:1)F-T synthesis diesel(F-T)and its blended with 5%DMC(D05),10%DMC(D10)and 15%n-butanol(B15)were used in the study on fuel spray characteristics in constant volume bomb test platform,analyzed the penetration,spray angle and spray area.2)Did Research on the effect of injection parameters and fuel spray characteristics on combustion flame propagation process in optical CI engine.And then conducted experimental research on the effect of fuel characteristics on combustion process in CI engine,analyzed the effect of fuel characteristics on combustion process from four aspects by specific combustion position,different crank angle,flame area and Red channel flame image.The influence of fuel oxygen content and oxygen-containing functional groups on combustion characteristics was studied.3)Studied the effect of fuel characteristics,EGR rate and EGR stratification method on the temperature and KL factor of combustion process.The main conclusions are as below:1)Spray characteristics test result showed that spray penetration,near field spray angle,far field spray angle and spray area were increased with the injection pressure increases,the reasonable increase of injection pressure could optimize the spray atomization.F-T diesel blended with DMC can also optimize the spray atomization.But F-T diesel spray atomization was worsened after blending with 15%butanol.2)Experimental results of the influence of fuel injection parameters on the development of macroscopic flames showed that with injection pressure increased,bright spot-like flame decreased,flake flame increased,ignition delay was almost unchanged while burning duration increased obviously.Injection angle was advanced gradually resulted in the rising of ignition delay,the decrease of ignition points,dark flame and the invariant flame area in the late combustion.And the increase of injection duration resulted in the increase of combustion duration but had almost no effect on ignition delay,the flame area and flame brightness increased at the same time.3)Study on the effect of fuel characteristics on combustion characteristics indicated that with the increase of DMC blending ratio,ignition delay increased and combustion pressure decreased,ignition points increased and distributed in the cylinder evenly,R channel value decreased so that bright flame changed into even low temperature flame.The difference between the combustion processes of D05 and B15 with the different oxygen-containing functional groups was that the combustion process of B15 was more gradual in the late combustion,and the flame area was larger in B15 and the flame brightness was darker.The blending of oxygenated fuel with F-T diesel can reduce soot production during combustion.4)With the increase of DMC blending ratio,both the combustion temperature and the combustion temperature gradient in the cylinder gradually decreased.The amount of soot produced during combustion decreased with increasing DMC blending.With the increase of EGR rate,the combustion temperature decreased gradually.EGR could reduce the combustion temperature,reduced NO_x emission and had little effect on soot emission.There were obvious differences in the combustion flame temperature,which sorted from largest to smallest was homogeneous>spiral catheter>spiral>tangential catheter>tangential.The sort of soot emission amount in five stratified forms was consistent with the sort of temperature field.5)The cooperation of oxygenated fuel and EGR stratification could reduce NO_x and soot emissions simultaneously.The use of oxygenated fuel could reduce the amount of soot generation during the combustion process.The spiral EGR stratification which form the radial stratification of thick in the middle and diluted around help to reduce the amount of NO_x generation,and had little effect on soot generation at the same time.更多还原