Study on the Formation Processes of Polycyclic Aromatic Hydrocarbon in a Fuel Spray Flame via Excitation Emission Matrix spectroscopy

为了研究作为烟尘前体的多环芳烃（PAHs）在喷射火焰中的形成过程，开发了一种适用于高温高压瞬态燃油喷射的激发发射矩阵（EEM）光谱技术。本研究的后半部分，将激光诱导荧光光谱和2-S成像技术应用于快速压缩机的喷雾火焰。所得结果总结如下：(1)226 nm激发时，喷射火焰入射侧的发射比355nm激发时的发射强。这表明在266 nm激发下比在3555 nm激发下被激发并发出荧光的物质种类更多。(2)在335 nm激发下，在热点燃前检测到燃料低温氧化过程中甲醛产生的LIF，甲醛产生的LIF迅速消失，多环芳烃产生的LIF在热点燃后立即出现。在266 nm激发下，热点燃前未检测到甲醛的LIF，但观察到燃料中杂质的LIF。热点燃后，多环芳烃产生了与355nm激发相同的强LIF。(3)在266 nm和355 nm激发下，多环芳烃热点燃后在距喷嘴孔35 ~ 45 mm的喷雾火焰中心区域均可观察到LIF。在距喷嘴口55mm处，烟灰颗粒的LII与多环芳烃的LIF重叠。

In order to investigate the formation processes of the polycyclic aromatic hydrocarbons (PAHs) which are considered as soot precursors in a spray flame, Excitation Emission Matrix (EEM) spectroscopy which can be applied to the transient fuel spray at high temperature and high pressure was developed. The latter half of this study, the laser-induced fluorescence spectroscopy and 2-S imaging were applied to the spray flame in a rapid compression machine. The summary of the obtained results are followings(1)The stronger emission was observed in the incident side of the spray flame in the case of excitation by 226 nm wavelength than that in the case of 355 nm excitation. This indicates that the more kinds of species are excited and emit the fluorescence in the case of 266 nm excitation than that of 355 nm excitation.(2)In the case of 335 nm excitation, the LIF from formaldehyde formed in the low temperature oxidation process of fuel was detected before the hot ignition, this LIF from formaldehyde disappears rapidly and the LIF from PAHs are appears immediately after the hot ignition. In the case of 266 nm excitation, the LIF from formaldehyde was not detected before the hot ignition, but the LIF from impurities in fuel was observed. After the hot ignition, the strong LIF from PAHs appears which has the same spectrum as the case of 355 nm excitation.(3)In the both cases of 266 nm and 355 excitations, the LIF from PAHs can be observed in the central region of a spray flame between 35 mm and 45 mm from the nozzle orifice after the hot ignition. At the 55 mm from the nozzle orifice, the LII from soot particles is overlapped to the LIF from PAHs.