The effects of turbulence on knock development and intensity for a thermally inhomogeneous stoichiometric ethanol/air mixture at a representative end-gas autoignition condition in internal combustion engines are investigated using direct numerical simulations with a skeletal reaction mechanism. Two- and three-dimensional simulations are performed by varying the most energetic length scale of temperature, $$l_T$$ l T , and its relative ratio with the most energetic length scale of turbulence, $$l_T/l_e$$ l T / l e , together with two different levels of the turbulent velocity fluctuation, $$u'$$ u ′ . It is found that $$l_T$$ l T / $$l_e$$ l e and the ratio of ignition delay time to eddy-turnover time, $$\tau _{ig}/\tau _t$$ τ ig / τ t , are the key parameters that control the detonation development. An increase in either $$l_T$$ l T or $$l_e$$ l e enhances the detonation propensity by allowing a longer run-up distance for the detonation development. The characteristic length scale of the temperature field, $$l_T$$ l T , is significantly modified by high turbulence intensity achieved by a large $$l_e$$ l e and $$u'$$ u ′ . The intense turbulence mixing effectively distributes the initial temperature field to broader scales to support the developing detonation waves, thereby increasing the likelihood of the detonation formation. On the contrary, high turbulence intensity with a short mixing time scale, achieved by a small $$l_e$$ l e and a large $$u'$$ u ′ , reduces the super-knock intensity attributed to the finer broken-up structures of detonation waves. Either $$\tau _{ig}/\tau _t$$ τ ig / τ t less than unity or $$l_e = l_T$$ l e = l T even with a large $$u'$$ u ′ is found to have no significant effect on super-knock mitigation. Finally, high turbulent intensity may induce high-pressure spikes comparable to the von Neumann spike. Increased temperature and pressure by combustion heating, noticeably after the peak of heat release rate, significantly enhance the collision and interaction of multiple emerging autoignition fronts near the ending combustion process, resulting in localized high-pressure spikes.

中文翻译：

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湍流和温度波动对乙醇/空气混合物爆震发展的影响

使用具有骨架反应机制的直接数值模拟，研究了湍流对内燃机中具有代表性的尾气自燃条件下热不均匀化学计量乙醇/空气混合物的爆震发展和强度的影响。二维和三维模拟通过改变温度的最大能量长度尺度 $$l_T$$l T 及其与湍流能量最大长度尺度的相对比率 $$l_T/l_e$$ l T / le ，连同两个不同水平的湍流速度波动 $$u'$$u ′ 。发现$$l_T$$ l T / $$l_e$$ le 和点火延迟时间与涡旋时间的比值$$\tau _{ig}/\tau _t$$ τ ig / τ t ，是控制爆轰发展的关键参数。$$l_T$$l T 或$$l_e$$ le 的增加通过允许用于爆轰发展的更长的助跑距离来增强爆轰倾向。温度场的特征长度尺度 $$l_T$$l T 被大 $$l_e$$ le 和 $$u'$$ u ′ 实现的高湍流强度显着修改。强烈的湍流混合有效地将初始温度场分布到更广泛的尺度以支持发展中的爆震波，从而增加了爆震形成的可能性。相反，通过小 $$l_e$$ le 和大 $$u'$$ u ′ 实现的短混合时间尺度的高湍流强度降低了归因于更精细破碎结构的超级爆震强度的爆震波。$$\tau _{ig}/\tau _t$$ τ ig / τ t 小于 1 或 $$l_e = l_T$$ le = l T 即使有一个大 $$u'$$ u ′ 被发现对超级爆震缓解没有显着影响。最后，高湍流强度可能会引起与冯诺依曼尖峰相当的高压尖峰。燃烧加热导致的温度和压力升高，尤其是在放热率峰值之后，显着增强了结束燃烧过程附近多个新兴自燃锋的碰撞和相互作用，导致局部高压尖峰。