Effects of residual burnt gas heterogeneity on early flame propagation and on cyclic variability in spark-ignited engines
Effects of residual burnt gas heterogeneity on early flame propagation and on cyclic variability in spark-ignited engines
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DOI：
10.1016/j.combustflame.2013.01.009
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发表时间：
2013-06
影响因子：
4.4
通讯作者：
C. Pera;S. Chevillard;J. Réveillon
中科院分区：
文献类型：
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作者：
C. Pera;S. Chevillard;J. Réveillon
本文研究了残余燃烧气体（RBG）的非均质性对预混火焰早期传播的影响。目的是量化RBG空间波动对火花点火（SI）发动机在化学计量操作下观察到的循环变化（CCVs）的贡献。本文对异辛烷（29种物质和48种反应）的湍流火焰传播进行了直接数值模拟（DNSs）。为了获得SI发动机的相关结果，从实验数据和发动机大涡模拟计算中提取了代表发动机低负荷运行的气动热化学条件（压力、温度、湍流特性）。主要研究结果如下：(1)RBG异质性结合了两种相反的效应。热的温度袋倾向于局部增加层流火焰的速度，而稀释的混合物减慢火焰的传播。(2) RBG的非均质性在局部增强火焰的传播，因为温度的主导作用大于稀释。(3)即使没有引入明显的焓波动，RBG的非均质性也能够产生额外的火焰起皱。(4) DNS结果包含有价值的信息，可以进一步理解以前在发动机中被误解的实验观测[Sztenderowicz和Heywood， SAE论文902142,1990]。由于对局部混合条件的非线性化学响应，RBG的非均质性对火焰发展过程的影响与它们对热释放波动的贡献相比是次要的，因此对发动机ccv的影响较小。
This paper investigates the effects of Residual Burnt Gas (RBG) heterogeneity on premixed early flame propagation. The aim is to quantify the contribution of RBG spatial fluctuations on Cycle-to-Cycle Variations (CCVs) observed in Spark-Ignited (SI) engines under stoichiometric operation. We performed Direct Numerical Simulations (DNSs) of turbulent flame propagation with a semi-detailed kinetic mechanism for iso-octane (29 species and 48 reactions). To obtain relevant results for SI engines, aerothermochemical conditions (pressure, temperature, turbulence characteristics) representative of low-load engine operation were extracted from experimental data and engine Large Eddy Simulation computations. The main findings are as follows: (1) RBG heterogeneity combines two opposing effects. Hot temperature pockets tend to locally increase the laminar flame speed, while diluted mixtures slow down flame propagation. (2) RBG heterogeneities locally enhance flame propagation because of the dominant effect of temperature over dilution. (3) RBG heterogeneities are able to create additional flame wrinkling even without the introduction of sensible enthalpy fluctuations. (4) DNS results contain valuable information to further our understanding of previously misinterpreted experimental observations in engines [Sztenderowicz and Heywood, SAE paper 902142, 1990]. The influence of RBG heterogeneities on the flame development process is minor compared to their contribution on heat release fluctuations and therefore on engine CCVs as a result of the non-linear chemical response to local mixture conditions.