【作者】 李浩；

【导师】 宋崇林；

【作者基本信息】 天津大学 ， 动力机械及工程， 2017， 博士

【摘要】 后喷技术是目前降低柴油机污染物排放的有效手段之一,而不同的后喷策略对柴油机性能及排放具有重要的影响。本文选用纯柴油、生物柴油及F-T柴油,在一台高压共轨的柴油机上系统地开展了后喷策略对柴油机性能及排放影响的研究,研究成果对于深入认识颗粒物本质、揭示后喷策略下颗粒物生成机理及指导污染物净化技术的应用,具有重要的理论参考价值。主要研究内容及结果如下:1.后喷策略的引入对缸内燃烧状况有显著影响。与单次喷射工况相比,柴油机燃用纯柴油、生物柴油和F-T柴油时的缸内瞬时放热率均出现明显的后喷燃烧放热峰;在其他后喷控制参数为定值的条件下,其峰值位置随着主后喷间隔增大后移,峰高随着后喷油量增加上升;累积放热率则出现明显台阶状。后喷策略引入后,缸内平均温度在后喷燃烧阶段有明显上升。2.在其他后喷控制参数为定值的条件下,随主后喷间隔增加,燃用三种燃料柴油机的后喷燃烧热效率逐渐下降;随后喷油量增加,燃用三种燃料柴油机在选定的实验工况内后喷燃烧热效率逐渐升高。相同条件的主喷+后喷工况下,燃用三种燃料柴油机后喷燃烧热效率为:柴油<生物柴油<F-T柴油。3.在其他后喷控制参数为定值的条件下,随主后喷间隔的增加,燃用三种燃料的柴油机CO和THC排放呈上升趋势,NOx排放呈下降趋势;随后喷油量的增加,柴油机CO、THC和NOx排放均逐渐增加。相同条件的主喷+后喷工况下,燃用三种燃料柴油机的CO和THC排放为:纯柴油>生物柴油>F-T柴油,NOx排放为:F-T柴油>生物柴油>纯柴油。4.在其他后喷控制参数为定值的条件下,随主后喷间隔的增加,三种燃料PM排放呈先减小后增加的趋势;随后喷油量的增加,PM排放逐渐增加。相同条件的主喷+后喷工况下,燃用三种燃料柴油机的PM排放为:纯柴油>生物柴油>F-T柴油。5.存在最优化的后喷策略,柴油机在最优化的后喷策略下工作时,能够保证后喷燃烧有着较高的热效率,同时兼顾柴油机的排放性能。最优化的后喷策略:柴油,后喷油量在循环总喷油量中占10¹6%,主后喷间隔12°CA;生物柴油,后喷油量在循环总喷油量中占10¹6%,主后喷间隔14°CA;F-T柴油,后喷油量在循环总喷油量中占10¹6%,主后喷间隔15°CA。6.后喷燃烧生成碳烟量主要受到后喷结束时缸内未燃气体温度(T_{ug EoI})和喷油持续期（DoI,duration of injection）与表征燃烧时间的比值（DoI/ACT）影响。后喷燃烧能否生成碳烟存在明显阈值,如果T_{ug EoI}或DoI/ACT低于阈值条件,则后喷燃烧没有明显碳烟生成,T_{ug EoI}和DoI/ACT两个阈值因燃油不同而小幅变动。此外,拟合了一个包含变量T_{ug EoI}和DoI/ACT的函数公式,通过此公式可以计算后喷燃烧过程中生成的碳烟量。7.在其他后喷控制参数为定值的条件下,碳烟颗粒表面碳氢官能团随主后喷间隔的增加呈先减小后增加的趋势,随后喷油量的增加呈上升趋势,碳氢官能团当量比介于0.202⁰.520之间。在其他后喷控制参数为定值的条件下,三种燃料颗粒的O/C比、羟基和羰基官能团含量以及sp3/sp2杂化比均随主后喷间隔的增大呈先减小后增加的趋势,随后喷油量的增加而增大。相同条件的主喷+后喷工况下,上述特性参数的大小顺序均为:生物柴油>柴油>F-T柴油。8.后喷策略引入后,三种燃料所产生碳烟颗粒的起燃温度和燃尽温度分别介于439⁵26.9℃和592.5⁶33.5℃之间,表观活化能介于153.6¹69.4 kJ/mol之间。在其他后喷控制参数为定值的条件下,碳烟颗粒氧化活性随主后喷间隔的增加先下降后上升,随后喷油量增加而下降。相同工况下,三种燃料产生的碳烟颗粒氧化活性的大小顺序为:生物柴油>柴油>F-T柴油。更多还原

【Abstract】 Post injection is currently one of the effective approaches to reduce the exhaust emissions of diesel engines,which significantly influences the engine performance and exhaust emissions.In the present study,a diesel engine with high pressure common-rail system was used to explore the effect of post injection strategy on the engine performance and exhaust emissions.The fuels used were neat diesel,biodiesel and F-T diesel,respectively.The results obtained possess not only theoretical significance to understand the nature and formation mechanism of diesel particulates under post injection conditions,but also potential to guide the purification technology applications.The major work and achievements of this dissertation are listed as follows:Post injection has significant effect on the in-cylinder combustion process.The heat release curves are unimodal for the single injection conditions,while the heat release curves are bimodal for the post injection conditions.When the rest control parameters of post injection are held constant,increasing the main-post interval（MPI）retards the appearance of the heat release peaks of post combustion,and the peak value increases with the post injection mass（PIM）.Due to the introduction of post injection,the accumulated heat release curves show an obvious sidestep shape,and the in-cylinder gas mean temperature increases markedly during post injection combustion period.When the rest control parameters of post injection are held constant,for all the tested fuels,the increase in the MPI brings about a gradual reduction of combustion thermal efficiency.The increase in the PIM improves the combustion thermal efficiency under some specific engine operating conditions.Under the same main/post injection conditions,the combustion thermal efficiency of post injection fuel followed the sequence:neat diesel<biodiesel<F-T diesel.When the rest control parameters of post injection are held constant,for all tested fuels,increasing the MPI results in an increase in the CO and THC emissions and a decrease in NOx emissions.The CO,THC and NOx emissions gradually increase with the PIM.When neat diesel,biodiesel and F-T diesel are used under the same engine operating conditions,the CO and THC emissions follow the sequence of neat diesel>biodiesel>F-T diesel,and the NOx emissions are in the sequence of F-T diesel>biodiesel>neat diesel.When the rest control parameters of post injection are held constant,the PM emissions for the three fuels first decrease and then increase with the MPI,and increase with the PIM.Under the same main/post injection conditions,the PM emissions for all three tested fuels are in the sequence:neat diesel>biodiesel>F-T diesel.There is an optimal post injection control strategy,under which the post injection combustion efficiency and the exhaust emissions reduction are improved.The strategies aforementioned are 10¹6%post injection rate（ratio of post injection mass to the total injection mass）and 12°CA of MPI for neat diesel,10¹6%post injection rate and 13°CA of MPI for biodiesel and 10¹6%post injection rate and15°CA of MPI for F-T diesel.The soot quantity generated from post injection combustion is related to the unburnt gas temperature(T_{ug EoI})and the ratio of the duration of post injection to the apparent combustion time（DoI/ACT）.There are soot thresholds for the post injection combustion.That is,the post injection combustion cannot generate soot when the T_{ug EoI} or DoI/ACT is lower than the threshold.The thresholds for T_{ug EoI} and DoI/ACT show marginal change for different test fuels.Moreover,the soot quantity generated from post injection combustion can be calculated by an empirical correlation of T_{ug EoI} and DoI/ACT.When the rest control parameters of post injection are held constant,the amount of aliphatic C–H surface functional groups（SFGs）decreases and then increases with the MPI,while it increases with the PIM.The equivalent ratios of C-H SFGs are in the range of 0.202⁰.520.The O/C ratio,the amount of hydroxyl SFGs and the sp3/sp2 hybridization ratio decrease first then increase with the MPI,and they increase with the PIM.The values of these three soot parameters are in the sequence of biodiesel>neat diesel>F-T diesel under the same engine operating conditions.For all three fuels,the light-off temperatures,burn-out temperatures and apparent activation energies of soot particles are in a range of 439⁵26.9℃,592.5⁶33.5℃and 153.6¹69.4 kJ/mol,respectively.For the constant post injection parameters,the soot oxidation reactivity decreases first and then increases with the MPI and decreases with the PIM.Under the same engine operating conditions,the sequence of soot oxidation reactivity for the fuels is biodiesel>neat diesel>F-T diesel.更多还原