Analysis of Mechanism of and Model for Compression Ignition Diffusion Combustion in Burned Gas Diluted Mixture

对产生预混装药的燃料气体射流的预混压燃机理和湍流混合过程进行了理论和实验分析，建立了气缸内燃料和空气非均质混合物压缩自燃和燃烧的理论模型。该模型依赖于空间滤波的输运方程，而不是雷诺平均的输运方程，集成了低温氧化反应的简化动力学模型和热焰反应的一步全局模型。模型的数值计算模拟了混合气气泡的速度、燃料浓度和温度的时空起伏的各种实现，其尺寸几乎是湍流的整体长度尺度。该模型再现了在低总当量比或掺入EGR气体或燃烧气体的混合气中预混充气压缩着火过程的整体适度燃烧。The Comput…更多的分析表明，燃料浓度和温度的不均匀以及燃烧气体的稀释是产生中等体积燃烧而不是突然压力升高的两个同样重要的因素。在实验中，用空间分辨率为18μm的激光拍摄了稳态和非稳态空气射流中香烟散射光的平面图像，并对沿射流轴线的浓度场进行了积分长度尺度分析。结果表明，烟道浓度积分长度尺度沿汽流方向减小，而速度场积分长度尺度增大。用LIF技术也进行了实验，结果在积分长度尺度上也有相同的趋势。理论研究解释了射流中浓度的湍流混合慢于动量的湍流混合。这一想法表明，燃料射流形成混合气需要在动量进入良好扩散状态时产生额外的湍流，以便更快地制备混合气。较少

Theoretical and experimental analyses were made for the mechanism of premixed charge compression ignition and turbulent mixing process of gas jet of fuel for producing the premixed charge.Theoretical model was developed for compression-autoignition and combustion of heterogeneous mixture of fuel and air in a cylinder. The model relies on the spatially-filtered transport equations, instead of Reynolds averaged ones, integrating a reduced kinetic model for the low temperature oxidation reaction and a one-step global model for the hot flame reaction. The numerical computation of the model simulated each realization of spatial and temporal fluctuations of velocities, fuel concentrations and temperatures of the mixture blobs in sizes of almost the integral length scale of turbulence. The model reproduced the moderate combustion in a bulk, which features the premixed charge compression ignition process in low total-equivalence ratios or mixtures diluted with EGR gas or burned gas. The comput … More ational analyses showed that the heterogeneity in fuel concentration and temperature, and the dilution with burned gas are two equally dominant factors to give the moderate bulk combustion instead of abrupt pressure rise.In the experiments, plane images of scattered light from incense smoke in steady and unsteady air jets were photographed with a Nd : YAG laser in spatial resolution of 18 μm. The integral length scale was analyzed for the concentration field along the jet axis. It was revealed that flue integral length scale of concentrations decreases in a down steam direction, while the integral length scale of the velocity field increases. Experiments were conducted also with LIF technique to result in the same tendency in the integral length scale. Theoretical study gives an explanation that the turbulent mixing of concentrations is slower than that of momentum in a jet. This idea suggests that mixture formation by fuel jet needs additional turbulence generation when the momentum comes into well diffused state for faster mixture preparation. Less