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首页> 外文会议>SAE International Powertrains, Fuels and Lubricants Meeting >Some Insights on the Stochastic Nature of Knock and the Evolution of Hot Spots in the End-Gas During the Engine Cycle from Experimental Measurements of Knock Onset and Knock Intensity
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Some Insights on the Stochastic Nature of Knock and the Evolution of Hot Spots in the End-Gas During the Engine Cycle from Experimental Measurements of Knock Onset and Knock Intensity

机译：从爆震发作和敲击强度的实验测量中发动机循环过程中爆震随机性质的一些见解及最终气体的进化。

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Knock in spark ignition engines is stochastic in nature. It is caused by autoignition in hot spots in the unburned end-gas ahead of the expanding flame front. Knock onset in an engine cycle can be predicted using the Livengood-Wu integral if the variation of ignition delay with pressure and temperature as well as the pressure and temperature variation with crank angle are known. However, knock intensity (KI) is determined by the evolution of the pressure wave following knock onset. In an earlier paper (SAE 2017-01-0689) we showed that KI can be approximated by KI = Z ({partial deriv}T/{partial deriv}x)-2 at a fixed operating condition, where Z is a function of P_(ko), the pressure, and ({partial deriv}T/{partial deriv}x) is the temperature gradient in the hot spot at knock onset. Then, from experimental measurements of KI and P_(ko), using five different fuels, with the engine operating at boosted conditions, a probability density function for ({partial deriv}T/{partial deriv}x) was established. In this paper the knock data for two other non-boosted operating conditions for the same fuels at the same engine speed in the same engine are analyzed. The crank angle at knock onset for a given fuel is more advanced at these two new conditions because of the more advanced spark timing needed to obtain knock, and this enables some insights to be gained on how the hot spots evolve during an engine cycle. With increasing crank angle, the mean absolute value of ({partial deriv}T/{partial deriv}x) decreases and its distribution narrows. This is consistent with a simple picture that at the start of compression in the engine cycle there is a wide distribution of scales in the turbulent temperature field and the mean temperature gradient is large but conditions become more homogenized with time (crank angle). The paper presents distributions in terms of normalized counts in histograms for other parameters related to knock onset as well as knock intensity which might be of use in modeling knock stochastically.
机译：敲入火花点火发动机的性质上是随机的。它是由在膨胀火焰前面的未燃烧的终端气体中的热点中的自燃引起的。如果点火延迟与压力和温度的变化以及具有曲柄角的压力和温度变化，则可以使用Livengood-Wu积分预测发动机循环中的敲击发动机循环中的敲击。然而，爆震强度（ki）由撞击后的压力波的演变决定。在早期的纸张（SAE 2017-01-0689）中，我们展示了Ki Qu = Z（{Partial deriv} T / {Partive Deriv} x）-2可以在固定的操作条件下近似，其中z是一个函数P_（ko），压力和（{部分eriv} t / {partive deriv} x）是敲击时热点中的温度梯度。然后，从Ki和P_（KO）的实验测量，使用五种不同的燃料，发动机在提升条件下运行，建立了（{部分DERIV} T / {PERALIAL DERIV} X）的概率密度函数。在本文中，分析了在同一发动机中相同发动机速度的相同发动机速度的相同燃料的两个其他非升压操作条件的爆震数据。由于获得敲击所需的更先进的火花正时，在这两个新条件下，撞击燃烧的曲柄角在这两个新条件下更进一步，这使得这使得能够在发动机循环期间发出一些洞察力。随着曲柄角度的增加，（{Partial deriv} t / {partive deriv} x）的平均绝对值降低，其分布缩小。这与一个简单的图像一致，在发动机循环中的压缩开始时，湍流温度场中的尺度广泛分布，平均温度梯度大，但条件变得更加均匀（曲柄角）。本文提出了与爆震发作相关的其他参数的直方化的标准化计数，以及爆震强度，这些参数可能在随机建模敲击时使用。

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