Spectroscopic and chemical-kinetic analysis of the phases of HCCI autoignition and combustion for single- and two-stage ignition fuels
Spectroscopic and chemical-kinetic analysis of the phases of HCCI autoignition and combustion for single- and two-stage ignition fuels
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DOI：
10.1016/j.combustflame.2008.03.019
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发表时间：
2008-08
影响因子：
4.4
通讯作者：
W. Hwang;J. Dec;Magnus Sjöberg
中科院分区：
文献类型：
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作者：
W. Hwang;J. Dec;Magnus Sjöberg
在全金属发动机和与之匹配的光学发动机上研究了HCCI发动机的自燃和燃烧时相。汽油，主要参考燃料混合物（PRF80），和几种代表性的实际燃料成分进行了测试。只有两段点火燃料PRF80表现出“冷焰”低温放热（LTHR）阶段。对于所有燃料来说，在中间温度下发生的缓慢放热反应将装药温度提高到热燃点。除了LTHR的量外，这个中温热释放（ITHR）阶段的差异也会影响燃料的点火质量。在这一阶段，异辛烷的化学发光图像显示出微弱而均匀的光发射。接下来是主要的高温放热（HTHR）阶段。最后，观察到一个“燃尽”阶段，具有非常弱的均匀排放和接近零的热释放率（HRR）。为了更好地了解这些燃烧阶段，对单级点火燃料异辛烷和两级燃料PRF80进行了化学发光光谱和化学动力学分析。对于这两种燃料，在ITHR阶段获得的光谱主要是甲醛化学发光。这与PRF80的LTHR光谱相似，但发射强度和温度要高得多，表明两者存在差异。化学动力学模型阐明了LTHR和ITHR相的异同，以及PRF80增强ITHR的原因。两种燃料的HTHR光谱均以广泛的CO连续谱为主，HCO、CH和OH波段也有一定贡献。模拟结果表明，CO+O→CO2+hν反应对HTHR有很好的跟踪作用，解释了HTHR阶段总化学发光与HRR之间的强相关性。CO连续统对thr和LTHR的化学发光没有贡献。在HTHR过程中，在红色和红外区域也检测到H2O和o2的条带，数据表明这很可能是由于热激发引起的。“燃尽”阶段的极弱光发射也表现为H2O和O2的热发射。
The temporal phases of autoignition and combustion in an HCCI engine have been investigated in both an all-metal engine and a matching optical engine. Gasoline, a primary reference fuel mixture (PRF80), and several representative real-fuel constituents were examined. Only PRF80, which is a two-stage ignition fuel, exhibited a “cool-flame” low-temperature heat-release (LTHR) phase. For all fuels, slow exothermic reactions occurring at intermediate temperatures raised the charge temperature to the hot-ignition point. In addition to the amount of LTHR, differences in this intermediate-temperature heat-release (ITHR) phase affect the fuel ignition quality. Chemiluminescence images of iso-octane show a weak and uniform light emission during this phase. This is followed by the main high-temperature heat-release (HTHR) phase. Finally, a “burnout” phase was observed, with very weak uniform emission and near-zero heat-release rate (HRR). To better understand these combustion phases, chemiluminescence spectroscopy and chemical-kinetic analysis were applied for the single-stage ignition fuel, iso-octane, and the two-stage fuel, PRF80. For both fuels, the spectrum obtained during the ITHR phase was dominated by formaldehyde chemiluminescence. This was similar to the LTHR spectrum of PRF80, but the emission intensity and the temperature were much higher, indicating differences between the ITHR and LTHR phases. Chemical-kinetic modeling clarified the differences and similarities between the LTHR and ITHR phases and the cause of the enhanced ITHR with PRF80. The HTHR spectra for both fuels were dominated by a broad CO continuum with some contribution from bands of HCO, CH, and OH. The modeling showed that the CO+O→CO2+hν reaction responsible for the CO continuum emission tracks the HTHR well, explaining the strong correlation observed experimentally between the total chemiluminescence and HRR during the HTHR phase. It also showed that the CO continuum does not contribute to the ITHR and LTHR chemiluminescence. Bands of H2O and O2in the red and IR regions were also detected during the HTHR, which the data indicated were most likely due to thermal excitation. The very weak light emission in the “burnout” phase also appeared to be thermal emission from H2O and O2.