Effect of Turbulent Flow Field on Flame Developing in Fuel Gradient Field in a Constant-Volume Vessel

在直喷式火花点火发动机中，低负荷时热效率可提高20-30%左右，导致二氧化碳排放量下降。然而，在实际发动机中，模具现象是非常复杂和困难的。因此，为了从根本上考察每一种现象，有必要使场易于分析。在本研究中，在圆盘型等容容器内产生旋流，火焰在中心点燃，在燃烧室中心提供丙烷燃料，形成轴对称火焰。在不同的湍流场和浓度场中进行了实验。用激光多普勒风速仪测量了湍流，用激光诱导荧光法测量了燃料浓度场。利用高速摄像机捕捉燃烧后的火焰发展过程，利用波长为3.39微米的激光吸收法测量燃烧后的碳氢化合物。总体燃烧的主要结果如下：(1)在本次实验中，湍流场和浓度场都发生了变化。然而，发现平均燃料浓度几乎相同，但湍流流动不同，因此只研究了湍流强度的影响。(2)当总当量比大于0.7时，燃烧效率可达97%以上，而当总当量比小于0.7时，燃烧效率仅为0.3。(3)当燃烧室中心附近存在较丰富的燃料时，火焰的发展中含有大量的发光部分。对于初始燃烧，主要的结果总结如下：(4)由于不均匀混合物中含有大量在化学计量条件下的可燃极限内的较丰富和较稀薄的部分，因此混合物即使在可燃极限外也能着火并火焰传播。

In direct injection spark-ignition engine, thermal efficiency can increase about 20-30% in low load, leading to decrease in carbon dioxide. However, die phenomena are very complicated and difficult in actual engines. Therefore, in order to investigate each phenomenon fundamentally, it is necessary to make the fields easy to analyze. In this study, a swirl flow was produced in a constant-volume vessel of disk type and a flame developed axisymmetrically by igniting at the center with supplying fuel of propane at the center of the combustion chamber. Experiments were done in various turbulent flow and concentration fields. Turbulent flow was measured with a laser Doppler anemometer and fuel concentration field was measured with a laser induced fluorescence method. A high-speed video camera was used to capture the flame development Hydrocarbon after the combustion was measured with absorption method using a laser of 3.39 micrometer wavelength.Main results for overall combustion are as follows: (1) In this experiment, both turbulent flow and concentration fields were changed. However, it was found that average fuel concentration is almost the same but the turbulent floe is different Therefore, only the effect of turbulence intensity was investigated. (2) The combustion efficiency was over 97% when overall equivalence ratio is larger man 0.7 while the combustion efficiency presented lower value of 0.3 in some cases at lower equivalence ratio less than 0.7. (3) When richer fuel existed near the center of The combustion chamber, it was observed that the flame developed with a lot of luminous parts in it As for initial combustion, main result is summarized as follows: (4) The mixture can ignite and flame propagates even outside the flammable limits because inhomogeneous mixture includes a lot of richer and leaner parts that are within the flammable limits including stoichiometric condition.