Study on the Unsteady Turbulent Combustion Process Using Statistical Methods

发展了基于统计方法的非定常湍流燃烧诊断新技术，并应用于描述往复式内燃机的湍流流动特性和火焰结构。本研究的要点可归纳为以下几点。通过估计湍流中粒子的随机运动来预测局部波动速度，表明了激光同差法测量非定常湍流的巨大优势。采用基于图像分析的瞬时湍流检测技术获得了柴油火焰湍流的强度和空间，研究了涡流和高压喷射对湍流混合速率的影响。利用氩离子激光和高速摄影技术对压缩点火发动机燃烧过程中形成的烟灰云进行了表征。结果表明，在发光火焰的外缘上烟灰云分布较多，火焰中富燃料点在此被冷却。此外，从不同燃料量、喷射时间和燃烧室几何形状下测量的烟尘云分布考虑了气体运动和湍流对烟尘形成的影响。考虑预混料的形成和燃烧气体的夹带，对描述浓度非均质性和湍流混合过程的随机模型进行了修正。预测结果表明，该模型能较好地再现大范围条件下放热全过程和污染物排放的实测结果。采用瑞利散射法测量了混合气浓度的非均质性对火花点火发动机爆震的影响。结果表明，在化学计量的情况下，均质混合物容易产生硬撞击，因此压缩比低于非均质混合物。少

New technologies based on statistical methods are developed for diagnosing unsteady turbulent combustion and are applied to describe the characteristics of turbulent flows and flame structures in reciprocating internal combustion engines. The main points of the study may be surmarized as follows.1. Random motion of particles in turbulent flows was estimated to predict the local fluctuating velocity, and the great advantage of laser homodyne method for measuring the unsteady turbulence was shown. Another technique for instantaneous turbulence detection using image analysis was applied to obtain the intensity and the sace of turbulence in diesel flames, by which the effects of swirl and high-pressure injection on the rate of turbulent mixing were investigated.2. Soot clouds formed during combustion in a compression-ignition engine were characterized by a laser-light sheet method using an argon-ion laser and high-speed photography. The obtained results showed that soot clouds were distrib … More uted on the outer edges of the luminous flames, at which the fuel-rich spots in the flame were cooled. In addition, the effects of the gas motion and turbulence on soot formation were considered from the distribution of soot clouds measured in various fuel quantities, injection timings and chamber geometries.3. Stochastic model which describes the concentration heterogeniety and the turbulent mixing process was modified by considering the premixture formation and the entrainment of burnt gas into spray. The predicted results showed that this model can well reproduce the measured results of the entire courses of heat release and the pollutant emissions under wide-spread conditions.4. Effects of the heterogeniety of mixture concentration on knock in a spark ignition engine were measured by using Rayleigh scattering method. The results showed that in the case of stoichiometry the homogeneous mixture easily causes a hard knock, thereby the compression ratio being lower than that in the heterogeneous mixture. Less