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Numerical study of air-fuel mixing in direct-injection spark-ignition and diesel engines.

机译：直喷式火花点火和柴油发动机中空燃混合的数值研究。

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摘要

A numerical study is carried out of engine in-cylinder air-fuel mixing phenomena using multidimensional computer models. Submodels to describe turbulence and convective wall heat transfer of engine flows and to treat the disintegration processes and vaporization of hollow-cone sprays are developed and validated using available experiments. These models are implemented in the KIVA codes and are applied to diesel and direct-injection spark-ignition (DISI) engines.; A modified RNG k-{dollar}varepsilon{dollar} turbulence model and a temperature wall model are proposed to include the effects of flow density variation. In addition, a sheet spray model is developed for computing sheet atomization and the subsequent drop breakup processes of hollow sprays. The predicted spray characteristics of a gasoline-engine pressure-swirl atomizer such as spray structures, spray tip penetrations, drop Sauter mean diameters and drop size distributions agree well with experimental data.; The present models are first applied to diesel engine combustion simulations. The demonstrated improvements in combustion and emissions predictions of both single and split fuel injection schemes obtained using the present models lead to a study of the mechanisms of soot and NOx reduction using multiple injections. It is shown that the reduced soot formation using multiple injections is due to the fact that the soot-producing fuel-rich regions at the spray tip are not replenished when the injection is terminated and then restarted. With multiple injections, the subsequently injected fuel burns rapidly and does not contribute significantly to soot production.; As the final application of the models, a direct-injection spark-ignition engine is simulated to study the air-fuel mixing processes. The induction and compression processes with early fuel injection are computed in which realistic engine port/chamber geometry, intake-valve motion and pressure-swirl atomized sprays are considered. The in-cylinder gas flow structures, gas/spray interactions and evolution of the liquid and vapor phases of the injected fuel are characterized. The effects of fuel injection timing on gas/spray interactions, turbulence generation, spray/wall impingement, vaporization rate, air-fuel distribution and thermodynamic characteristics of the mixture are studied.
机译：使用多维计算机模型对发动机缸内空燃混合现象进行了数值研究。子模型描述了发动机流的湍流和对流壁传热，并处理了中空圆锥形喷雾的崩解过程和汽化过程，并利用现有实验进行了验证。这些模型在KIVA代码中实现，并适用于柴油和直喷式火花点火（DISI）发动机。提出了一种改进的RNG k- {美元} varepsilon {美元}湍流模型和温度壁模型，以包括流量密度变化的影响。此外，还开发了一种薄板喷雾模型，用于计算薄板雾化和随后的中空喷雾液滴破碎过程。汽油发动机压力旋流雾化器的预测喷雾特性，例如喷雾结构，喷雾尖端渗透，液滴索特平均直径和液滴尺寸分布，与实验数据吻合良好。本模型首先应用于柴油机燃烧模拟。使用本模型获得的单燃料和分开燃料喷射方案在燃烧和排放预测方面的已证明的改进导致对使用多次喷射减少烟灰和NOx的机理的研究。示出了使用多次喷射减少的烟灰形成是由于以下事实：当喷射终止并且然后重新开始时，在喷嘴尖端处的产生烟灰的燃料富集区域没有被补充。通过多次喷射，随后喷射的燃料迅速燃烧，对烟灰的产生没有显着贡献。作为模型的最终应用，对直喷式火花点火发动机进行了仿真，以研究空燃混合过程。计算了早期燃油喷射的进气和压缩过程，其中考虑了实际的发动机进气道/腔室几何形状，进气门运动和压力旋流雾化喷雾。表征了缸内气流结构，气体/喷雾相互作用以及所喷射燃料的液相和气相的演变。研究了燃料喷射正时对气体/喷雾相互作用，湍流产生，喷雾/壁撞击，汽化速率，空气-燃料分布和混合物的热力学特性的影响。

著录项

  • 作者

    Han, Zhiyu.;

  • 作者单位

    The University of Wisconsin - Madison.;

  • 授予单位 The University of Wisconsin - Madison.;
  • 学科 Engineering Mechanical.; Engineering Automotive.
  • 学位 Ph.D.
  • 年度 1996
  • 页码 246 p.
  • 总页数 246
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;自动化技术及设备;
  • 关键词

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