Effect of EGR on diesel premixed-burn equivalence ratio
Effect of EGR on diesel premixed-burn equivalence ratio
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DOI：
10.1016/j.proci.2006.08.022
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发表时间：
2007
影响因子：
1.3
通讯作者：
C. Idicheria;L. Pickett
中科院分区：
文献类型：
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作者：
C. Idicheria;L. Pickett
试验研究了废气再循环（EGR）对柴油机燃烧过程中预混燃烧混合气当量比的影响。在恒定体积的燃烧室中，环境氧浓度从21%系统地降低到10%，以模拟发动机中的EGR效应。采用压力测量和高温化学发光时间分辨成像技术研究了正庚烷柴油射流着火和预混燃烧的时间和空间特性。随着EGR的增加，点火延迟增加，预混燃烧的位置发生在喷嘴的下游。首次点火后，高温反应稳定在一个准稳态提离长度，表明提离是确定预混燃烧区的边界参数。利用平面激光瑞利散射测量了预混燃烧区燃料与环境混合物的当量比。燃料-氧气质量分布函数表明，随着EGR率的增加，更多的质量被混入预混燃烧区，但这种混合物的当量比相同。该研究表明，随着EGR的增加而增加的点火延迟不一定会降低当量比，这对于减少低温燃烧发动机中的碳烟形成是期望的。然而，改善燃料-环境混合的措施，如缩短喷射持续时间和长点火延迟，可能会降低当量比。
The effect of exhaust-gas recirculation (EGR) on the equivalence ratio of premixed-burn mixture in diesel combustion was investigated experimentally. The ambient oxygen concentration was systematically decreased from 21% to 10% in a constant-volume combustion vessel to simulate EGR effects in engines. Pressure measurements and time-resolved imaging of high-temperature chemiluminescence were used to characterize the temporal and spatial ignition and premixed burn characteristics of n-heptane diesel jets. With increasing EGR, ignition delay increases and the location of premixed burn occurs further downstream from the nozzle. Subsequent to first ignition, high temperature reactions stabilize at a quasi-steady lift-off length, showing that lift-off is a bounding parameter for determining premixed-burn region. The equivalence ratio of the fuel–ambient mixture in the premixed-burn region was measured using planar laser Rayleigh scattering. Fuel–oxygen mass distribution functions show that more mass is mixed into the premixed-burn region with increasing EGR, but the equivalence ratio of this mixture is the same. The study shows that an increasing ignition delay with increasing EGR does not necessarily decrease the equivalence ratio as would be desired for reducing soot formation in low-temperature combustion engines. However, measures to improve fuel–ambient mixing, such as shortened injection durations coupled to long ignition delay, could decrease equivalence ratio.