Effects of Spark Component on Free Radical Formation in Spark Ignition Process of Combustible Mxture.

对火花点火初期OH自由基的形成进行了实验研究。目的是阐明火花放电对OH自由基初始形成的影响以及OH自由基在燃烧化学反应引发中的作用。用双单色仪和带通滤光片的超高速摄影机，通过OH自由基的自发射（306 nm）观察OH自由基的行为。利用超高速摄影机对火焰核的生长过程进行了纹影摄影观察。丙烷-空气预混合物用作可燃气体：对于所有测试，丙烷的浓度为4.7体积%。采用电容火花点燃预混物。电极由不锈钢制成，直径为0.5mm，火花间隙调节为0.8mm，火花能量在15 ~ 80 mJ范围内变化，在火花放电后1.2 ~ 40 μ s内成功地观察到OH自由基的行为。OH自由基的浓度是高的火花放电后，从10 μ s逐渐减少。随着火花能量的增加，在火花点火开始时形成的OH自由基的量增加，火焰核的增长率增加。结果表明，当火花能量较大时，初始火焰核中OH自由基含量较少，且主要存在于火焰核边缘附近。从火焰核的纹影照片中可以观察到，随着火花能量的增加，火焰核中心的高温区持续时间变长。高温区的寿命比火花持续时间的两倍还要长。有人建议，这个高温区加速OH自由基的形成在高温区和丙烷-空气预混合物之间的边界。

Study on OH radical formation at the beginning of spark ignition has been performed experimentally. The purpose is to declare the effect of spark discharge on the initial formation of OH radical and the role of OH radical in the initiation of combustion chemical reaction. A double monochromator and an ultra-high-speed camera with a band pass filter were employed to observe the behavior of OH radical by its self-emission (306nm). The growth of a flame kernel was observed by schlieren photography with the ultra-high-speed camara. Propane-air premixture was used as a combustible gas : The concentration of propane was 4.7 vol% for all tests. Capacitance spark was employed to ignite premixtures. Electrodes were made of stainless steel and their diameter were 0.5 mm. Spark gap was adjusted to be 0.8 mm. The energy of spark was varied from 15 to 80 mJ.The behavior of OH radical was observed successfully from 1.2 to 40 mus after a spark discharge. The concentration of OH radical is high just after a spark discharge and decreases gradually from 10 mus. As spark energy increases, amount of OH radical formed at the beginning of spark ignition increases and growth rate of a flame kernel increases. It was found that, when the spark energy is large, there is little OH radical in the initial flame kernel and it exists near the edge of the initial flame kernel. From schlieren photographs of flame kernels, it was observed that high temperature region in the center of the flame kernel remains longer as spark energy increases. The life time of the high temperature region is longer than double the spark duration. It is suggested that this high temperature region accelerates the formation of OH radical at the boundary between the high temperature region and the propane-air premixture.