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A reduced chemical kinetic mechanism for computational fluid dynamics simulations of high brake mean effective pressure, lean-burn natural gas engines.

机译：用于高制动平均有效压力，稀薄燃烧天然气发动机的计算流体动力学模拟的简化化学动力学机制。

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摘要

Recent developments in numerical techniques and computational processing power now permit time-dependent, multi-dimensional computational fluid dynamics (CFD) calculations with detailed chemical kinetic mechanisms using commercially available software. Such computations have the potential to be highly effective tools for designing lean-burn, high brake mean effective pressure (BMEP) natural gas engines that achieve high fuel efficiency and low emissions. Specifically, these CFD simulations can provide the analytical tools required to design highly optimized natural gas engine components such as pistons, intake ports, pre-combustion chambers, fuel systems and ignition systems. To accurately model the transient, multi-dimensional chemically reacting flows present in these systems, detailed chemical kinetic mechanisms are needed that accurately reproduce measured combustion data at high pressures and lean conditions, but are of reduced size to enable reasonable computational times. Prior to the present study, these CFD models could not be used as accurate design tools for application in high BMEP lean-burn gas engines because existing reduced chemical kinetic mechanisms failed to accurately reproduce experimental flame speed and ignition delay data for natural gas at high pressure (40 atm and higher) and lean (0.6 equivalence ratio and lower) conditions. Existing methane oxidation mechanisms had typically been validated with experimental conditions at atmospheric and intermediate pressures (1 to 20 atm) and relatively rich stoichiometry. Accordingly, these kinetic mechanisms were not adequate for CFD simulation of natural gas combustion for which elevated pressures and very lean conditions are typical. This thesis describes an analysis, based on experimental data, of the laminar flame speed computed from numerous, detailed chemical kinetic mechanisms for methane combustion at pressures and equivalence ratios necessary for accurate high BMEP, lean-burn natural gas engine modeling. A reduced mechanism that was shown previously to best match data at moderately lean and high pressure conditions was updated for the conditions of interest by performing sensitivity analysis using CHEMKIN. The reaction rate constants from the most sensitive reactions were appropriately adjusted to obtain better agreement at high pressure lean conditions. An evaluation of two new reduced chemical kinetic mechanisms for methane combustion was performed using Converge CFD software. The results were compared to engine data and a significant improvement on combustion performance prediction was obtained with the new mechanisms.
机译：数值技术和计算处理能力的最新发展现在允许使用可商购的软件，通过具有详细的化学动力学机理的时间相关的多维计算流体动力学（CFD）计算。这样的计算有可能成为设计稀燃，高制动平均有效压力（BMEP）天然气发动机的高效工具，从而实现高燃料效率和低排放。具体而言，这些CFD模拟可以提供设计高度优化的天然气发动机部件（例如活塞，进气口，预燃烧室，燃料系统和点火系统）所需的分析工具。为了准确地模拟这些系统中存在的瞬态，多维化学反应流，需要详细的化学动力学机制来精确地再现高压和稀薄条件下测得的燃烧数据，但要减小尺寸以实现合理的计算时间。在本研究之前，这些CFD模型不能用作用于高BMEP稀薄燃烧发动机的精确设计工具，因为现有的降低的化学动力学机制无法准确地再现高压下天然气的实验火焰速度和点火延迟数据（40 atm或更高）和稀（0.6当量比及更低）条件。现有的甲烷氧化机制通常已在大气压和中压（1至20个大气压）和相对丰富的化学计量比的实验条件下得到验证。因此，这些动力学机制不足以进行天然气燃烧的CFD模拟，因为在这种情况下，典型的是高压和非常稀薄的条件。本文基于实验数据，对层流火焰速度进行了分析，该层流火焰速度是由许多详细的甲烷动力学化学动力学机制计算得出的，该机理是在精确的高BMEP稀燃天然气发动机建模所需的压力和当量比下进行的。通过使用CHEMKIN进行灵敏度分析，针对感兴趣的条件更新了先前显示的在中等程度的稀薄和高压条件下与数据最佳匹配的简化机制。对来自最敏感反应的反应速率常数进行适当调整，以在高压贫油条件下获得更好的一致性。使用Converge CFD软件对甲烷燃烧的两种新的还原化学动力学机理进行了评估。将结果与发动机数据进行比较，并通过新机制获得了燃烧性能预测的显着改进。

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  • 作者

    Martinez Morett, David.;

  • 作者单位

    Colorado State University.;

  • 授予单位 Colorado State University.;
  • 学科 Chemistry Physical.;Engineering Chemical.;Engineering General.
  • 学位 M.S.
  • 年度 2012
  • 页码 94 p.
  • 总页数 94
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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