A Visualization Study of Soot Production and Oxidation Characteristics under Diesel Engine like Conditions
A Visualization Study of Soot Production and Oxidation Characteristics under Diesel Engine like Conditions
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DOI：
10.4271/2017-32-0126
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发表时间：
2017-11
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影响因子：
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通讯作者：
Huynh Thanh Cong;Takahiro Kashima;Daisuke Komasaki;Y. Saito;A. Azetsu
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作者：
Huynh Thanh Cong;Takahiro Kashima;Daisuke Komasaki;Y. Saito;A. Azetsu
为了探索在与直喷式柴油机相当的条件下，柴油射流火焰中碳烟的生成和氧化特性，对3个重要参数（喷射压力、喷射持续时间和氧浓度）的影响进行了实验研究。为此，小型CVCC为了获得碳烟生成和氧化的实验数据，在实验中，对环境温度、温度、温度通过贫氢混合气的燃烧来准备喷射正时之前的压力和氧浓度（在8个火花塞的帮助下）在大约1000 K和4.5MPa的高温和高压条件下。现代柴油机用8孔共轨式喷油器安装在该容器上。注射压力设定为80、100和120 MPa。分析了三个重要因素对喷射过程的影响：（1）在喷射量不变的情况下，不同的喷射压力;（2）在喷射持续时间不变的情况下，不同的喷射压力;（3）氧气体积分数分别为21%和17%。光学窗口连接在该容器的一侧，并且喷雾火焰的完整图像可以通过该窗口由高速彩色摄像机可视化并记录。从柴油机火焰的可视化彩色图像中，可以用双色法定量地计算火焰温度和火焰内的碳烟量。该方法基于烟尘云的光辐射是灰体的热辐射，灰体的热辐射是烟尘温度和烟尘量指标KL因子的函数的理论原理，计算结果表明，喷射持续时间和喷射速率是影响热释放速率的主要因素。而在实验条件下，喷油压力和环境氧浓度对放热率的影响主要集中在燃烧后期。喷射压力和喷射持续时间对火焰温度的影响较小，而环境氧气浓度对火焰温度的影响较大。对于碳烟的产生和氧化，所有考虑的参数都有很大的影响。有趣的结果是，喷射压力和环境氧浓度对总KL因子的最大值的影响不是很大。但随着喷射压力的降低和环境氧浓度的降低，碳烟生成速率降低，导致总KL因子最大值出现时间延迟。通过与HRR曲线的对比，发现在低喷射压力和氧浓度条件下，碳烟氧化反应发生在很低的HRR燃烧下。
To explore the production and oxidation characteristics of soot in the flame of diesel jet under the condition equivalent to the direct injection diesel engine condition, the effect of three different important parameters (including injection pressure, injection duration, and oxygen concentration) are experimentally examined. For these purposes, a small CVCC (constant volume combustion chamber) with the volume of 60cc equivalent to the volume of combustion chamber of automotive diesel engine is used.To obtain the experimental data of soot production and oxidation, in experiments, the ambient condition of temperature, pressure and oxygen concentration before injection timing are prepared by the combustion of lean hydrogen mixture (with help of 8 spark plugs) at a high temperature and pressure condition around 1000K and 4.5MPa. The common rail type injector with 8 injection holes for modern diesel engine is attached to this vessel. Injection pressures are set up at 80, 100, and 120 MPa. The effects of three important factors are analyzed including: (1) different injection pressures with constant injection mass; (2) different injection pressures with constant injection duration; (3) oxygen concentrations of 21% and 17% in volume. The optical window is attached on one side of this vessel and the full image of the spray flames can be visualized and recorded through this window by a high-speed color video camera. From the visualized color image of diesel flame, the flame temperature and the amount of soot inside the flame can be quantified by the two color method. This method is based on the theoretical principle that the light emission from the soot cloud is a thermal radiation of gray body which is a function of soot temperature and the KL factor, an index of the amount of soot.The obtained results show that the injection duration and the injection rate are the dominant factors for heat release rate (HRR). On the contrary, within the experimental condition, the heat release rate is affected by both of the injection pressure and the oxygen concentration of ambient mainly at late combustion phase. The injection pressure and the injection duration give small effect on the level of flame temperature; however, the ambient oxygen concentration gives a large effect on the flame temperature.Concerning the soot production and oxidation, all of the considered parameters have large effect. The interesting result is that the effect of injection pressure and ambient oxygen concentration on the maximum value of total KL factor is not so large. However, the soot production rate becomes lower as the decrease of injection pressure and as the decrease of ambient oxygen concentration, and results in the delayed arrival of the maximum total KL factor. Comparing with the HRR curve, it is revealed that the soot oxidation reaction is occurred under the very low HRR combustion in the case of low injection pressure and oxygen concentration condition.