微粒后处理器结构参数对柴油机超细微粒捕集特性的影响

发布时间：2018-03-11 00:30

本文选题：压燃式发动机　切入点：汽油/柴油混合燃料　出处：《吉林大学》2015年硕士论文　论文类型：学位论文

【摘要】：随着环境污染越来越严重， PM2.5、霾逐渐成为社会的关注点。而内燃机排放作为城市大气的重要污染来源也越来越受到重视。相比于汽油机，柴油机的微粒排放是其的几十倍以上，因此，我国乃至全世界范围内都对柴油机排放微粒进行了严格要求。随着排放法规的日益严格，近几年来，新的燃烧理论也逐渐发展。由于汽油燃料挥发性较好，，能很好的解决预混合化的问题，目前已有研究学者对汽油/柴油混合燃料对发动机燃烧与排放的影响进行了研究。而柴油机微粒捕集器（DPF）作为柴油机减少微粒排放的重要手段之一，研究其对使用混合燃料的微粒排放的捕集特性具有重要意义。本文主要采用模拟计算与试验的手段针对DPF对柴油机超细微粒的捕集特性开展研究工作。对DPF内部的两相流运动进行了模拟仿真分析，探讨了边界条件以及微粒捕集器结构参数对气流均匀性的影响。同时试验研究了柴油机在不同工况、不同边界条件以及使用不同汽油添加比例的汽油/柴油燃料时，DPF对不同模态的微粒的捕集效率。研究结果表明： 1）通过使用ANSYS FLUENT软件对DPF内部进行模拟分析，本文主要研究了0.1m及0.3m粒径的微粒在DPF内部的浓度分布。从结果可以看出，随着微粒直径的减小，微粒的惯性相应减小，当微粒足够小时将沿布朗运动轨迹进行运动，因此整个DPF内的微粒浓度分布的均匀性很好。 2）研究了不同壁面渗透率、不同过滤孔道宽度、不同入口进气速度、不同扩张角对DPF内部气流运动均匀性的影响。壁面渗透率与过滤孔道宽度的大小并不影响气相流场分布的均匀性，只影响速度值的大小。减小入口进气速度能提高DPF内流速分布的均匀性，但入口进气速度受到柴油机工况的制约，不能随意的改变。减小扩张角可以迅速的提高流速分布及微粒浓度分布的均匀性。同时采用离散相模型对过滤孔道内的微粒运动轨迹进行了研究，随着DPF轴向位置的增加，气流速度在进气孔道内减小，在排气孔道内增大,在出口处达到最大；而壁面渗流速度也逐渐增大。 3）DPF对不同模态微粒的都具有很高的捕集效率。其中，DPF存在核态和积聚态两个穿透窗口，而当发动机排放微粒在此穿透窗口处存在较多微粒时，会影响DPF对此粒径微粒的捕集，导致DPF后此粒径微粒比例增多。 4）对相同粒径微粒，DPF的捕集效率与发动机工况有关。存在最优工况点。中等转速、中等负荷时，DPF的捕集效率最大。与负荷相比，转速的变化对DPF的捕集效率影响更大。随着发动机主喷定时提前，DPF前后核态微粒比例及超细微粒比例均升高。 5)对于不同汽油添加比例的燃料，相比与纯柴油燃料，使用汽油添加比例为30%的燃料时，DPF前50nm以下的核态微粒比例有所降低，但DPF后核态微粒比例升高，由此可以说明，使用汽油/柴油混合燃料可以有效降低核态微粒的比例，但此时，有大部分核态微粒粒径处于捕集器的核态穿透窗口处，导致DPF后核态微粒比例增多。对于超细微粒，DPF后微粒比例相比于使用纯柴油燃料时在中高负荷时降低显著，微粒数量最多降低了90%。因此，DPF可以有效控制使用汽柴油混合燃料的柴油机的超细微粒排放。
[Abstract]:With more and more serious environmental pollution, PM2.5, haze has gradually become a social concern. As an important source of pollution emissions and combustion atmosphere of the city is attracting more and more attention. Compared to the gasoline engine, the diesel particulate emission is dozens of times, therefore, China and the world within the scope of diesel engine emissions the particles of a strict requirement. With the increasingly stringent emission regulations, in recent years, the new combustion theory has gradually developed. Because of the gasoline fuel volatility is good, can be a good solution to the problem of pre mixing, at present scholars of gasoline / diesel fuel blends on engine combustion and emissions were studied. While the diesel particulate filter (DPF) is one of the important means to reduce the diesel particulate emissions, it is important to study the particulate emission of hybrid capture characteristics.
This paper mainly uses the simulation calculation and test means for DPF capture characteristics of diesel ultrafine particles to carry out research work. The movement of the DPF internal two-phase flow simulation analysis, discusses the boundary conditions and the DPF structural parameters on the flow uniformity influence. At the same time were studied in different diesel engine conditions, different boundary conditions and different proportion of the gasoline gasoline / diesel fuel, DPF of particles of different modes of trapping efficiency. The results show that:
1) by using ANSYS FLUENT software to simulate and analyze the internal DPF, this paper mainly studies 0.1M and 0.3m particle size particle concentration within the DPF distribution. From the results we can see that, with the decrease of particle diameter, particle inertia decreases, when the particle is small enough along the Brown motion trajectory, so uniformity the particle concentration distribution in the DPF is very good.
2) of different wall permeability, different filter channel width, different entrance velocity, different expansion angle of uniform airflow movement. The influence of DPF internal wall permeability and filtration pore width size does not affect the gas flow uniformity, only affect the speed value of the reduced intake speed can improve the entrance. The velocity distribution within the DPF uniformity, but the entrance inlet velocity is restricted by the operating condition of the diesel engine, can not arbitrarily change. Reduce the divergentangle can quickly improve the velocity distribution and particle concentration distribution. At the same time were studied by the particle trajectory, discrete phase model of the filtration pore, with the increase of DPF axial position air velocity in the intake, reduce the pore increases in the exhaust channel, reaches the maximum at the outlet; and the wall seepage velocity increases gradually.
3) DPF of different modal particles have high trapping efficiency. Among them, the existence of DPF nucleation and accumulation mode two through the window, and when there are many particles in the particle emission of the engine through the window at the time, this will affect the capture DPF particles, DPF particles lead to the proportion of increased.
4) on the same particles, the collection efficiency of DPF is related with the operating condition of the engine. The existence of the optimal operating point. Medium speed and medium load, the collection efficiency of DPF. The maximum load and speed compared to the change of DPF trapping efficiency greater impact. With the engine main injection timing, DPF and nuclear the proportion of state particles and ultrafine particles were increased.
5) for different proportion of added gasoline fuel, compared with pure diesel fuel, gasoline mixed with 30% fuel, the proportion of nucleation particles before DPF below 50nm decreased, but DPF increased the proportion of nucleation particles, which can show the use of gasoline / diesel blended fuel can effectively reduce the nucleation particles the proportion, but this time, most of the particle size in the nucleate nucleate collector through the window, resulting in DPF after nucleation particles increased. For ultrafine particles, compared the proportion of particles at DPF after using pure diesel fuel in high load decreased significantly, the largest number of particles reduces 90%. so DPF ultrafine particle emission in diesel engine to effectively control the use of gasoline and diesel fuel.

【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK421.5

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