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

对预混充气压缩着火机理和产生预混充气的燃气射流湍流混合过程进行了理论分析和实验研究，建立了缸内非均质混合气压缩自燃和燃烧的理论模型。该模型依赖于空间过滤的传输方程，而不是雷诺平均的，集成了一个简化的动力学模型的低温氧化反应和热火焰反应的一步全球模型。该模型的数值计算模拟的空间和时间的波动的速度，燃料浓度和温度的混合液滴的大小几乎是湍流的整数长度尺度的每个实现。该模型再现了低总当量比、EGR气体稀释混合气或已燃气稀释混合气的预混充量压缩着火过程。计算机 ...更多信息 理论分析表明，燃料浓度和温度的不均匀性以及燃气的稀释作用是产生适度整体燃烧而不是压力突然升高的两个同等重要的因素.在实验中，用空间分辨率为18 μm的Nd：YAG激光器拍摄了定常和非定常空气射流中熏香烟雾散射光的平面图像.分析了浓度场沿射流轴线沿着方向的积分长度尺度。结果表明，沿顺流方向，烟气浓度场的积分长度尺度减小，而速度场的积分长度尺度增大。实验也进行了与LIF技术，导致在积分长度尺度相同的趋势。理论研究解释了射流中浓度的湍流混合比动量的湍流混合慢。这一思想表明，燃料射流形成的混合气需要额外的湍流产生时，动量进入良好的扩散状态，以更快的混合气制备。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