INFLUENCE OF POST-INJECTION PARAMETERS ON SOOT FORMATION AND OXIDATION IN A COMMON-RAIL-DIESEL ENGINE USING MULTI-COLOR- PYROMETRY
INFLUENCE OF POST-INJECTION PARAMETERS ON SOOT FORMATION AND OXIDATION IN A COMMON-RAIL-DIESEL ENGINE USING MULTI-COLOR- PYROMETRY
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使用多色高温测定法研究喷射后参数对共轨柴油发动机中烟灰形成和氧化的影响
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
K. Boulouchos
中科院分区：
文献类型：
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作者：
C. Barro;F. Tschanz;P. Obrecht;K. Boulouchos
碳烟和氮氧化物之间的排放权衡是车用柴油应用中的一个主要问题。发动机和后处理方面都需要采取措施，以便在保持尽可能高的效率的同时优化发动机的排放。众所周知，二次喷射具有减少废气碳烟的潜力，而不会对NOx排放产生任何重大影响。然而，关于如何对后喷射进行参数化以使其最大限度地减少烟尘排放的准确而一般的规则并不存在。此外，其潜在的机制还没有得到详细的了解。本文的实验研究揭示了在不同的湍流和反应动力学条件下，二次喷射碳烟形成和减少的基本机理。在测量排气中的碳烟元素碳的同时(使用光声碳烟传感器)，用光学探头(OLP)研究了气缸内碳烟的形成和氧化过程。该传感器提供了气缸内碳烟演化的曲轴角度分辨信息。实验证实了早期工作的结论，即后喷油导致的碳烟减少主要基于两个原因：碳烟氧化过程中的湍流增加(来自后喷油)，以及在相似负荷条件下，由于主燃烧中的燃料量较少而导致的碳烟生成减少。文献中经常提到的在烟尘氧化过程中增加热量的第三种效应不能得到证实。此外，实验还表明，湍流(涡流)和反应动力学的变化对扩散控制放热速率的影响很小。然而，碳烟演化的时间阶段性受这些变化的影响很大，碳烟峰值浓度变化很小。结果表明，一次喷油的碳烟降低率与喷油时间有关。更准确地说，后喷射的碳烟减少能力一旦在碳烟氧化阶段的后期就会迅速下降。只有在气缸内碳烟峰值出现之前的一段时间内，通过增加后喷油的湍流和热量添加，才能提高碳烟氧化速率。根据EGR和涡流水平，可以定义最大停留时间，在该时间之后，后喷射效应相对于碳烟氧化速率变得相反。
The emission trade-off between soot and NOx is an issue of major concern in automotive diesel applications. Measures need to be taken both on the engine and on the aftertreatment sides in order to optimize the engine emissions while maintaining the highest possible efficiency. It is known that post injections have a potential for exhaust soot reduction without any significant influence in the NOx emissions. However, an accurate and general rule of how to parameterize a post injection such that it provides a maximum reduction of soot emissions does not exist. Moreover, the underlying mechanisms are not understood in detail. The experimental investigation presented here provides insight into the fundamental mechanisms of soot formation and reduction due to post injections under different turbulence and reaction kinetic conditions. In parallel to the measurement of soot elementary carbon in the exhaust (using a Photo Acoustic Soot Sensor), the in-cylinder soot formation and oxidation process have been investigated with an Optical Light Probe (OLP). This sensor provides crank angle resolved information about the in-cylinder soot evolution The experiments confirm conclusions of earlier works that soot reduction due to a post injection is mainly based on two reasons: increased turbulence (from the post injection) during soot oxidation and lower soot formation due to lower amount of fuel in the main combustion at similar load conditions. A third effect of heat addition during the soot oxidation, which was often mentioned in the literature, could not be confirmed. In addition, the experiments show that variations of turbulence (from swirl) and reaction kinetics have a minor influence on the diffusion controlled heat release rate. However, the time phasing of the soot evolution is highly influenced by these variations with only small changes in the peak soot concentration. It is shown that the soot reduction of a post injection depends on the timing. More precisely, the soot reduction capability of a post injection decreases rapidly as soon as its timing is late in the soot oxidation phase. The soot oxidation rate can only be improved by increased turbulence and heat addition from the post injection in a time window before the in-cylinder soot peak occurs. Depending on EGR and swirl level, a maximum dwell time can be defined after which the post injection effect becomes counterproductive with respect to the soot oxidation rate.