Investigation of the Early Flame Development in Spark Assisted HCCI Combustion Using High Speed Chemiluminescence Imaging
Investigation of the Early Flame Development in Spark Assisted HCCI Combustion Using High Speed Chemiluminescence Imaging
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DOI：
10.4271/2007-01-0212
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发表时间：
2007-04
期刊：
影响因子：
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通讯作者：
H. Persson;Anders Hultqvist;B. Johansson;A. Remon
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文献类型：
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作者：
H. Persson;Anders Hultqvist;B. Johansson;A. Remon
通过用热残余物代替部分新鲜充量，可以实现SI压缩比的自动点火。在这项工作中，发动机运行的负气门重叠（NVO）捕获热残留物。通过增加NVO，从而提高初始充气温度，随着残余量的增加，可以研究SI和HCCI之间的中间区域。最近的研究表明，在某些操作条件下，使用火花辅助来辅助汽油HCCI燃烧，甚至将操作状态扩展到不可能进行无支撑HCCI燃烧的区域。在这项工作中的火花的影响进行了研究，在一个单缸发动机与光学访问。通过缸内压力和同步高速化学发光成像来监测燃烧。可以看出，即使对于大的NVO和因此高的残余分数，也是不断增长的SI火焰与随后的HCCI燃烧相互作用并控制随后的HCCI燃烧。使用火花正时，即使当释放的热量的主要部分来自HCCI燃烧时，也可以使燃烧正时定相。对于较高的NVO，火焰膨胀速度降低，但对于高残余分数也普遍存在。较高的火花提前被发现，以补偿较慢的火焰膨胀到一个点。发现火花辅助HCCI和纯HCCI的自燃过程是分层的。对于纯HCCI的初始前蔓延速度被发现是在同一数量级的SI火焰的膨胀速度。基于汽缸压力信息执行估计自动点火的曲柄角的计算，该汽缸压力信息提供关于SI与HCCI的比例对于不同操作条件如何表现的良好统计。
Auto-ignition with SI-compression ratio can be achieved by replacing some of the fresh charge by hot residuals. In this work an engine is run with a negative valve overlap (NVO) trapping hot residuals. By increasing the NVO, thus raising the initial charge temperature it is possible to investigate the intermediate zone between SI and HCCI as the amount of residuals is increased. Recent research has shown the potential of using spark assistance to aid gasoline HCCI combustion at some operating conditions, and even extend the operating regime into regions where unsupported HCCI combustion is impossible. In this work the influence of the spark is studied in a single cylinder operated engine with optical access. Combustion is monitored by in-cylinder pressure and simultaneous high speed chemiluminescence imaging. It is seen that even for large NVO and thus high residual fractions it is a growing SI flame that interacts with, and governs the subsequent HCCI combustion. Using the spark timing it is possible to phase the combustion timing even when the major part of the released heat is from HCCI combustion. The flame expansion speed is decreases for higher NVO, but prevails also for high residual fractions. A higher spark advance is found to compensate for the slower flame expansion up to a point. The auto-ignition process is found to be stratified for both spark assisted HCCI as well as for pure HCCI. For pure HCCI the initial front spreading velocity is found to be in the same order of magnitude as for the expansion speed of the SI flame. Calculations to estimate the crank angle of auto-ignition are performed based on cylinder pressure information providing good statistics on how the proportion of SI to HCCI behaves for different operating conditions.