Engine Hot Spots: Modes of Auto-ignition and Reaction Propagation
Engine Hot Spots: Modes of Auto-ignition and Reaction Propagation
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DOI：
10.1016/j.combustflame.2016.01.002
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发表时间：
2016-04
影响因子：
4.4
通讯作者：
L. Bates;D. Bradley;Günter Paczko;N. Peters
中科院分区：
文献类型：
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作者：
L. Bates;D. Bradley;Günter Paczko;N. Peters
许多直接数值模拟的球形热点自燃，与不同的燃料，已确定不同的自燃制度。这些范围从良性的自动点火，与小幅度的压力波，以超级爆震与破坏性的过压的产生。这种模拟的结果概括图解，绘制边界值的，声学自燃速度的比率，对的。后一个参数是在半径为r o的热点中发展的声波的停留时间，即r o/a，由化学热释放的激发时间τ e归一化。这个比率控制能量转移到发展中的声阵面。第三个相关参数涉及活化温度E/R与自燃延迟时间τ i的乘积，由混合物温度归一化。T、比值τ i/τ e和无量纲热点温度梯度（τ ln T/τ r <$$>），其中r <$是无量纲半径。这些参数定义的边界制度的热爆炸，亚音速自燃，发展爆震，和非自燃爆燃，在图中的爆炸对爆燃。发展中的爆轰区在整个区域形成一个半岛和等高线。乘积参数（E/RT）（τ i/τ e）/λ ln T/λ r反映了热点温度梯度和燃料特性的影响，其唯一值可作为自燃区和爆燃区的分界线。还可以识别其他燃烧状态，包括自动爆燃和“正常”爆燃燃烧的混合状态。本文探讨了一些不同的发动机的性能，在制度的控制自动点火，正常燃烧，燃烧与轻度爆震，并最终，超级爆震。热点的可能起源进行了讨论，它表明，单独的湍流能量的耗散是不太可能直接导致足够的精力充沛的热点。还讨论了燃料的爆震特性。
Many direct numerical simulations of spherical hot spot auto-ignitions, with different fuels, have identified different auto-ignitive regimes. These range from benign auto-ignition, with pressure waves of small amplitude, to super-knock with the generation of damaging over-pressures. Results of such simulations are generalised diagrammatically, by plotting boundary values of ξ, the ratio of acoustic to auto-ignition velocity, against ɛ. This latter parameter is the residence time of the developing acoustic wave in the hot spot of radius r o, namely r o/a, normalised by the excitation time for the chemical heat release, τ e. This ratio controls the energy transfer into the developing acoustic front. A third relevant parameter involves the product of the activation temperature, E/R, for the auto-ignition delay time, τ i, normalised by the mixture temperature. T, the ratio, τ i/τ e, and the dimensionless hot spot temperature gradient,(∂ ln T/∂ r¯), where r¯ is a dimensionless radius. These parameters define the boundaries of regimes of thermal explosion, subsonic auto-ignition, developing detonations, and non-auto-ignitive deflagrations, in plots of ξ against ɛ. The regime of developing detonation forms a peninsula and contours, throughout the field. The product parameter (E/R T)(τ i/τ e)/∂ ln T/∂ r¯ expresses the influences of hot spot temperature gradient and fuel characteristics, and a unique value of it might serve as a boundary between auto-ignitive and deflagrative regimes. Other combustion regimes can also be identified, including a mixed regime of both auto-ignitive and “normal” deflagrative burning. The paper explores the performances of a number of different engines in the regimes of controlled auto-ignition, normal combustion, combustion with mild knock and, ultimately, super-knock. The possible origins of hot spots are discussed and it is shown that the dissipation of turbulent energy alone is unlikely to lead directly to sufficiently energetic hot pots. The knocking characterisation of fuels also is discussed.