Soot processes in compression ignition engines
Soot processes in compression ignition engines
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DOI：
10.1016/j.pecs.2006.03.002
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发表时间：
2007-06
影响因子：
29.5
通讯作者：
D. Tree;K. Svensson
中科院分区：
文献类型：
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作者：
D. Tree;K. Svensson
虽然柴油发动机在效率、扭矩和整体驾驶性能方面可以说优于运输行业的任何其他发电设备，但它们在噪音、氮氧化物和颗粒物排放方面的性能较差。大多数颗粒物源自燃烧柴油机的富含燃料区域中形成的烟灰颗粒。在过去的二十年中，我们对柴油燃烧中碳烟形成过程的理解已经从基于排气测量和实验室火焰的推论转变为直接缸内观察，这导致了柴油发动机燃烧的转变。缸内测量显示柴油喷雾产生喷射，形成升力、部分预混合、湍流扩散火焰。已发现烟灰的形成强烈依赖于喷气机提升部分中的空气夹带以及燃料中的氧气，并且在较小程度上依赖于燃料中碳氢化合物的组成和结构。燃烧过程中幸存下来并从排气中排出的烟灰主要是来自富含燃料的区域的烟灰，这些烟灰在排气门打开之前没有时间混合和燃烧。燃烧结束时的较高温度会促进烟灰的燃尽，而喷射时的高温会减少空气夹带并增加烟灰的形成。使用基于缸内烟灰和燃烧测量的概念模型，可以解释排气颗粒中的趋势。当前柴油发动机排放控制的趋势涉及多喷射燃烧策略，该策略将柴油燃烧的情况迅速转变为一系列低温、分层充气、预混燃烧事件，其中由于低温而避免了氮氧化物的形成，并且通过在点火前倾斜混合物或增加空气夹带来避免烟灰的形成。
While diesel engines are arguably superior to any other power-production device for the transportation sector in terms of efficiency, torque, and overall driveability, they suffer from inferior performance in terms of noise, NOxand particulate emissions. The majority of particulate originates with soot particles which are formed in fuel-rich regions of burning diesel jets. Over the past two decades, our understanding of the formation process of soot in diesel combustion has transformed from inferences based on exhaust measurements and laboratory flames to direct in-cylinder observations that have led to a transformation in diesel engine combustion. In-cylinder measurements show the diesel spray to produce a jet which forms a lifted, partially premixed, turbulent diffusion flame. Soot formation has been found to be strongly dependent on air entrainment in the lifted portion of the jet as well as by oxygen in the fuel and to a lesser extent the composition and structure of hydrocarbons in the fuel. Soot surviving the combustion process and exiting in the exhaust is dominated by soot from fuel-rich pockets which do not have time to mix and burn prior to exhaust valve opening. Higher temperatures at the end of combustion enhance the burnout of soot, while high temperatures at the time of injection reduce air entrainment and increase soot formation. Using a conceptual model based on in-cylinder soot and combustion measurements, trends seen in exhaust particulate can be explained. The current trend in diesel engine emissions control involves multi-injection combustion strategies which are transforming the picture of diesel combustion rapidly into a series of low temperature, stratified charge, premixed combustion events where NOxformation is avoided because of low temperature and soot formation is avoided by leaning the mixture or increasing air entrainment prior to ignition.