Autoignition modes under premixed combustion conditions are usually studied in constant-volume configurations. However, the autoignition events related to knocking combustion in spark-ignition engines do experience variable volumes in combustion chamber and ever-changing thermodynamic states caused by reciprocating piston motion and main flame front compression. Such combustion situations may lead to different autoignition modes from constant-volume scenarios. Using one-dimensional direct numerical simulations with detailed chemistry and transport of H2/air mixture, the autoignition modes during knocking combustion were studied under different engine combustion boundary conditions. It was the first to identify important influence of variable thermodynamic states on the development of autoignition modes through changing critical temperature gradients. Four autoignition modes—thermal explosion, supersonic deflagration, detonation, and subsonic deflagration—were observed, which, however, were quantitatively different from the constant-volume configurations in regime boundaries. Meanwhile, on comparison with intake temperature and equivalence ratio, intake pressure shows greater impact on detonation formation, characterized by a regime extension under high intake pressures. To classify the autoignition modes responsible for various knocking events with different intensities in a straightforward manner, a regime diagram was proposed based on the temperature gradients and the effective energy density used for universally quantifying various intake conditions. This diagram was found useful to determine the distributions of different autoignition modes (especially for detonation) and the potential approaches for achieving maximum thermal efficiency while suppressing engine knock. In addition, detonation mode was prevailing under high effective energy density conditions, and the underlying reasons were ascribed to the significant reduction of excitation time and pre-flame temperature increases by pressure wave.

中文翻译：

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内燃机变热力学状态下的自燃模式研究

预混燃烧条件下的自燃模式通常在恒定体积配置中进行研究。然而，与火花点火发动机中的爆震燃烧相关的自燃事件确实会经历燃烧室中的可变容积和由往复活塞运动和主火焰前缘压缩引起的不断变化的热力学状态。这种燃烧情况可能会导致与恒定体积情况不同的自燃模式。使用具有详细化学和 H2/空气混合物传输的一维直接数值模拟，研究了不同发动机燃烧边界条件下爆震燃烧过程中的自燃模式。它是第一个通过改变临界温度梯度来确定可变热力学状态对自燃模式发展的重要影响的人。观察到四种自燃模式——热爆炸、超音速爆燃、爆震和亚音速爆燃——但在数量上与区域边界中的恒定体积配置不同。同时，与进气温度和当量比相比，进气压力对爆震形成的影响更大，其特征是在高进气压力下的状态扩展。为了以简单的方式对导致不同强度的各种爆震事件的自燃模式进行分类，基于温度梯度和用于普遍量化各种进气条件的有效能量密度，提出了一个状态图。发现该图可用于确定不同自燃模式（尤其是爆震）的分布以及在抑制发动机爆震的同时实现最大热效率的潜在方法。此外，在高有效能量密度条件下，爆震模式占主导地位，其根本原因归因于压力波引起的激发时间显着减少和预燃温度升高。发现该图可用于确定不同自燃模式（尤其是爆震）的分布以及在抑制发动机爆震的同时实现最大热效率的潜在方法。此外，在高有效能量密度条件下，爆震模式占主导地位，其根本原因归因于压力波引起的激发时间显着减少和预燃温度升高。发现该图可用于确定不同自燃模式（尤其是爆震）的分布以及在抑制发动机爆震的同时实现最大热效率的潜在方法。此外，在高有效能量密度条件下，爆震模式占主导地位，其根本原因归因于压力波引起的激发时间显着减少和预燃温度升高。