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Optimizing the scavenging system for high efficiency and low emissions: A computational approach.

机译：优化扫气系统以实现高效率和低排放：一种计算方法。

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摘要

A free piston internal combustion engine operating on high compression ratio, HCCI combustion is being developed to significantly improve the thermal efficiency and exhaust emissions relative to conventional crankshaft-driven SI and Diesel engines. A two-stroke scavenging process recharges the engine and is key to realizing the efficiency and emissions potential of the device. To ensure that the engine's performance goals can be achieved the scavenging system was configured using Computational Fluid Dynamics, zero-dimensional and one-dimensional modeling, along with single step parametric variations. Visualization of the in-cylinder and port dynamics allowed the flow through the engine to be more completely understood and better controlled.; Through a comprehensive study a wide range of design options were investigated including the use of loop, hybrid-loop and uniflow scavenging methods, different charge delivery options, and various operating schemes. Parameters such as the intake/exhaust port arrangement, valve lift/timing, charging pressure and piston frequency were varied. Operating schemes including a standard uniflow configuration, a low charging pressure option, a stratified scavenging geometry, and an over-expansion (Atkinson) cycle were studied. High scavenging and trapping efficiencies (∼0.85, >0.99, respectively), as well as overall thermal efficiency and exhaust emissions were metrics by which the designs were evaluated.; The computational results indicated that the loop and hybrid-loop arrangements are inadequate, however, the uniflow geometry can produce both high scavenging and high trapping efficiencies. The delivery tank pressure and temperature histories are important to enabling steady charging, high operating compression ratio and low pumping power consumption. Stratified scavenging and over-expansion operating schemes can significantly improve the efficiency of the engine cycle, through increased compression ratio (∼24:1) (by more complete flushing) and additional blowdown recovery, respectively. However, the over-expansion arrangement was calculated to result in large cycle-to-cycle variability for slightly altered operating conditions.; It was found that the in-cylinder flows are important to both NOx and short-circuiting emissions with inadequate mixing (and resulting temperature stratification) the predominant driver of NO production, and fuel penetration to the valve region the main cause of short-circuiting emissions. In addition, early auto-ignition of the charge by the hot residual gases can lead to reduced efficiency potential.
机译：一种自由活塞式内燃机，以高压缩比运行，正在开发HCCI燃烧，以相对于传统的曲轴驱动的SI和柴油发动机显着提高热效率和废气排放。二冲程清除过程为引擎充电，这对于实现设备的效率和排放潜力至关重要。为了确保可以实现发动机的性能目标，使用计算流体动力学，零维和一维建模以及单步参数变化对扫气系统进行了配置。缸内和进气口动力学的可视化使对发动机的流量得到了更全面的了解和更好的控制。通过全面的研究，研究了广泛的设计方案，包括回路的使用，混合回路和单流清除方法，不同的电荷输送方案以及各种运行方案。诸如进气/排气口布置，气门升程/正时，充气压力和活塞频率之类的参数已改变。研究了包括标准单流配置，低充气压力选项，分层扫气几何形状和过度膨胀（阿特金森）循环的操作方案。高效的清除和捕集效率（分别约为0.85和> 0.99）以及总体热效率和废气排放是评估设计的指标。计算结果表明，回路和混合回路的布置是不充分的，但是，单流几何形状既可以产生高的清除效率，又可以产生高的捕集效率。输油箱的压力和温度历史对于实现稳定的充气，高的工作压缩比和低的泵送功率很重要。分层的扫气和过度膨胀操作方案可以分别通过增加压缩比（〜24：1）（通过更彻底的冲洗）和额外的排污恢复来显着提高发动机循环效率。然而，对于稍微改变的工作条件，计算出过度膨胀的布置会导致较大的周期变化。发现缸内流量对于NOx和短路排放均很重要，其中混合不充分（以及由此产生的温度分层）是NO产生的主要驱动力，而燃料渗透到阀区是短路排放的主要原因。此外，热的残留气体过早地自动点燃装料会导致效率潜力降低。

著录项

  • 作者

    Goldsborough, Samuel Scott.;

  • 作者单位

    Colorado State University.;

  • 授予单位 Colorado State University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 199 p.
  • 总页数 199
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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