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约20-30%，从而减少二氧化碳排放。然而，在实际发动机中，凹模现象是非常复杂和困难的。因此，为了从根本上研究每一种现象，有必要使场易于分析。在本研究中，在圆盘式定容容器内产生旋流，通过在燃烧室中心供应丙烷燃料在中心点火来轴对称地发展火焰。在不同的湍流和浓度场中进行了实验。用激光多谱勒风速仪测量湍流，用激光诱导荧光法测量燃料浓度场。用3.39微米波长的激光对燃烧过程进行了吸收测量，利用高速摄像机拍摄了燃烧过程中火焰发展的碳氢化合物，主要结果如下：(1)实验中，湍流流场和浓度场都发生了变化。然而，由于平均燃料浓度几乎相同，但湍流浮团却不同，因此，只考察了湍流强度的影响。(2)当总当量比大于0.7时，燃烧效率可达97%以上，而当当量比小于0.7时，燃烧效率在某些情况下表现为较低的0.3。(3)当燃烧室中心附近存在较丰富的燃料时，观察到火焰的发展与初始燃烧相比，火焰中含有大量的发光部分，主要结果如下：(4)混合气甚至可以在可燃极限之外点火和火焰传播，这是因为非均匀混合气中包含了许多在可燃极限内的较浓淡的部分，包括化学计量条件。

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.