【作者】 毕小杰；

【导师】 乔信起； 李佳峰；

【作者基本信息】 上海交通大学 ， 动力机械及工程， 2014， 博士

【摘要】 本文以三维CFD（KIVA3V-R2）数值模拟为主，结合定容燃烧弹光学测试和发动机台架试验，系统研究了石化、生物柴油不同燃烧边界条件下的碳烟形成机理，揭示不同初始环境温度、环境氧浓度、生物柴油掺混比例、供油定时和EGR率下碳烟和燃烧中间产物的形成历程及空间分布。本文首先在定容燃烧弹中采用光源前置消光法（FILE）研究初始温度和氧浓度对石化、生物柴油燃烧和碳烟形成的影响。研究发现初始温度降低，预混燃烧比例增大，燃烧由以扩散燃烧为主的双峰放热转变为以预混燃烧为主的单峰放热，碳烟净质量降低；初始温度700K时，全程碳烟质量（NTISM）趋近于0，接近无烟燃烧。高温环境下，随氧浓度降低生物柴油碳烟净质量升高；低温环境下，随氧浓度降低碳烟净质量降低。与石化柴油相比，生物柴油燃烧压力峰值小，碳烟净质量少。为进一步阐释容弹中石化柴油碳烟形成历程，本文改进了石化柴油现象学碳烟模型，考虑了表面氧化反应对碳烟数密度的影响，并利用不同初始温度和氧浓度条件下高时间分辨的定量碳烟测量数据对模型进行广泛验证，并与Hiroyasu-NSC碳烟模型的预测精度进行比较。结果表明，改进的碳烟模型耦合KIVA3V程序计算所得碳烟浮起长度、碳烟净质量及其空间分布均与试验结果吻合较好，且其预测精度优于Hiroyasu-NSC碳烟模型。氧浓度降低，氧化反应是影响碳烟变化的决定性因素，低氧浓度下氧化反应速率降低，石化柴油碳烟净质量、净个数和燃烧中间产物净质量峰值升高，碳烟平均摩尔质量减小。初始温度降低，碳烟生成反应受到梯级抑制：碳烟生成反应速率首先开始降低，随后碳烟前驱物生成反应速率亦降低；最终，碳烟净质量和净个数峰值降低，碳烟平均摩尔质量增大。700K初始温度，整个燃烧室内当量比均低于2，碳烟生成质量趋近于零。在改进的石化柴油现象学碳烟模型基础上，耦合生物柴油官能团结构对碳烟形成的化学作用，提出了生物柴油现象学碳烟模型，并应用不同初始温度和氧浓度的容弹燃烧和碳烟结果进行广泛验证。将该模型耦合KIVA3V程序对容弹中生物柴油碳烟形成历程进行机理分析表明：该模型可以很好预测由温度和氧浓度改变引起的燃烧压力、放热率及碳烟净质量的变化；氧浓度降低，不同温度环境的碳烟质量变化趋势相悖是因为主导碳烟变化的机理不同：高温环境下，碳烟生成反应速率增大，氧化反应速率减小，生物柴油碳烟净质量、净个数峰值升高；而低温环境下，生成和氧化反应速率同时降低，但生成反应是影响碳烟变化的决定性因素，碳烟净质量、净个数峰值降低。不同氧浓度下乙炔净质量变化不明显，这是因为乙炔生成反应的温度界限和浓度界限更宽。初始温度降低，生物柴油碳烟及燃烧中间产物变化与石化柴油类似。对燃烧过程、燃烧中间产物及碳烟的分析表明，生物柴油化学特性对碳烟形成的影响要大于其物理特性。基于所提出的石化、生物柴油现象学碳烟模型，构建了可计算混合燃料碳烟形成的石化-生物柴油碳烟模型，并构建了多组分蒸发模型以独立计算混合燃料中各组分的蒸发速率。采用高压共轨柴油机测试数据对模型进行验证，研究结果表明，石化-生物柴油碳烟模型耦合KIVA3V程序对燃料组分、供油定时、EGR率等多种条件下燃烧和碳烟形成的预测与试验结果吻合；提高生物柴油掺混比例或推迟供油时刻将导致碳烟生成反应速率降低，碳烟净质量峰值减小、柴油机碳烟排放降低。增大EGR率，环境氧浓度降低，碳烟氧化反应速率降低，碳烟排放升高，EGR率在42%时的碳烟排放较无EGR时提高了1.7倍。本文发展了石化柴油现象学碳烟模型，提出了生物柴油现象学碳烟模型，构建了生物柴油碳烟生成简化机理，并在广泛的试验条件下加以验证，这对于发展更为完善的生物柴油碳烟模型有重要的理论意义和应用价值。更多还原

【Abstract】 In order to in-depth study the soot evolution mechanisms of diesel and biodieselfuels under various combustion boundary conditions, both computational andexperimental research was employed. Simulations through three dimensional CFDprogram (KIVA3V-R2) as well as experiments conducted in optical constant volumechamber and common rail diesel engine are adopted to investigate the time relatedevolution and spatial distribution of soot and intermediate species with different initialambient temperature, ambient oxygen concentrations, biodiesel ratio, start of fuelsupply timings and EGR rates.Initially, a laser diagnostic technology known as FILE (Forward illuminationlight extinction) was applied to investigate the combustion and soot evolution ofdiesel and biodiesel fuels with different initial ambient temperature or ambient oxygenconcentrations in constant volume chamber. Measurements showed that withdecreasing initial ambient temperature, the ratio of premixed combustion increased,which was evidenced by the transaction from two-peak diffusion dominantcombustion to one-peak premixed dominant combustion in heat release rate traces,and soot net mass decreased. At700K initial ambient temperature, the normalizedtime integrated soot mass (NTISM) was close to zero, so the combustion is sootless.As ambient oxygen concentration decreased, soot net mass of biodiesel increasedwithin high temperature environment, but decreased within low temperatureenvironment. Compared to diesel fuel, the combustion pressure peak of biodieseldecreased, so does the soot net mass.In order to interpret soot evolution of diesel fuel, a diesel phenomenological sootmodel was revised to describe the effects of surface oxidation reactions on sootnumber density. Computational results predicted by the revised soot model wasvalidated by time-related quantitive soot mass diagnostic results under various initialambient temperature and ambient oxygen concentrations, and the predictive capacity of revised soot model was compared with the Hiroyasu-NSC two-step soot model.Results showed that the soot lift off length, soot net mass and its spatial distributionpredicted by KIVA3V program compiled with revised diesel phenomenological sootmodel matched the measurements pretty well, and they were better than thosepredicted by Hiroyasu-NSC two-step soot model. As ambient oxygen concentrationdecreased, oxidation mechanism dominated soot evolution. Therefore, the peaks ofsoot net mass, net number, net mass of intermediate species increased with decreasingambient oxygen concentration, soot mean mole weight decreased. As initial ambienttemperature decreased, soot formation reaction pathways were restricted step by step:soot formation rates reduced first, and then the formation rate of soot precursor beganto decrease. Finally, peaks of soot net mass and net number became smaller withlower initial ambient temperature, soot mean mole weight got larger. At700K initialambient temperature, the largest local equivalence ratio was lower than2, sootformation rate was close to zero.Based on the revised phenomenological diesel soot model, a biodieselphenomenological soot model was proposed and the chemical effects of esterstructure of biodiesel on soot evolution were included. A bunch of experimentalresults conducted in constant volume chamber with various initial ambienttemperature and ambient oxygen concentrations was applied to validate new biodieselphenomenological soot model. Agreements between computational and experimentalresults were observed, which indicated that KIVA3V program complied with biodieselsoot model was capable to precisely predict the effects of temperature and oxygenconcentrations on biodiesel combustion and soot evolution. As ambient oxygenconcentration decreased, time related soot mass trace showed reverse changingtendency. Within high temperature, soot oxidation rate decreased, while sootformation rate increased. As a result, soot net mass and net number increased withdecreasing ambient oxygen concentration. However, soot formation and oxidation rateboth decreased within low temperature, while soot formation mechanism wasdominant, so soot net mass and net number decreased with ambient oxygenconcentration. Nevertheless, the difference in acetylene net mass with various ambientoxygen concentrations under low temperature was negligible because of a largerformation region observed in temperature and equivalence ratio map. Variation inbiodiesel soot evolution caused by decreasing initial temperature was similar to dieselfuel. Also, the analysis of combustion process and the evolution of soot and intermediates species proved that the effects of fuel chemical characteristics seemedto be larger than physical characteristics.Through the combination of diesel and biodiesel phenomenological soot model,a phenomenological soot model that could be applied to predict soot evolution ofblend fuels was built. Moreover, a multi-component evaporation model was proposedto predict the evaporation rate of each fuel component independently. Through thecomparison with measurements recorded in common rail diesel engine, it is clear tonotice that the new phenomenological soot model was reliable for wide operationconditions, such as different biodiesel ratio, start of fuel supply timings and EGR rates.As biodiesel ratio increased or start of fuel supply timing retarded, soot formation rateand then the peaks of soot net mass decreased, so soot emission went down. WhenEGR rate increased, the ambient oxygen concentration became lower, so the sootoxidation rates decreased and soot emission increased sharply: soot emission with42%EGR rate was1.7times higher than that without EGR.In a word, a diesel phenomenological soot model was revised and a biodieselphenomenological soot model was proposed, in which a simplified soot formationmechanism of biodiesel was built. All models were validated with a number ofexperimental results. And this work is of profound theoretical and practicalsignificance for further development of biodiesel soot model.更多还原