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

点击翻译按钮获取中文摘要

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