摘 要

随着环境污染和能源危机的不断加剧，LNG-柴油双燃料发动机也越来越受到重视。目前对柴油的模拟大多数都是通过构建柴油替代物模型，TRF混合物是比较典型的柴油替代物模型，本文模拟研究TRF组分燃料的掺混对甲烷着火特性的影响。通过对正庚烷-甲烷、异辛烷-甲烷、甲苯-甲烷混合燃料的模拟研究，研究双燃料发动机的着火特性。通过模拟数据与实验数据的对比，选择了LLNL Version 3.1的正庚烷详细机理、LLNL Version 3的异辛烷详细机理以及含有甲苯机理的汽油替代物机理。利用Chemkin软件进行数值模拟，研究了初始温度、初始压力、当量比、掺混比例等对混合燃料着火延迟时间的影响，并对混合燃料着火特性影响较大的初始温度和掺混比进行了基元反应敏感性分析。研究发现：

（1）正庚烷-甲烷、异辛烷-甲烷混合燃料的着火延迟时间随温度的变化分为低温、中温、高温三个阶段。在低温、高温区，混合燃料的着火延迟时间随温度的升高而缩短，在中温区，混合燃料的着火延迟时间出现明显的负温度区域现象，并且随着压力的增大，负温度区域有向高温区偏移的趋势。当量比对混合燃料的影响在负温度区域最大。正庚烷掺混比例低于3%~5%之间的某个值时，负温度区域现象消失。相比较而言，初始温度对混合燃料着火的影响最大。

（2）甲苯-甲烷混合燃料的着火延迟时间随温度的升高而缩短，当量比对混合燃料着火延时的影响较小。在低温区和中温区，随着甲苯掺混比例的增大，混合燃料的着火延迟时间延长。当温度到达大于1100K的高温区，随着甲苯掺混比例的增大，混合燃料的着火延迟时间缩短。

（3）通过对初始温度和掺混比的敏感性分析发现，反应CH₃ HO₂=CH₄ O₂消耗甲基转化为稳定的烷烃对着火的影响较大，反应H₂O₂( M)=2OH( M)生成大量的OH标志着火。正庚烷的异构反应、脱氢反应对着火的影响较大。异辛烷的不同脱氢反应对着火的作用不同。G24在模拟的初始温度条件下均是抑制甲苯-甲烷混合燃料着火最主要的反应，并且对着火的抑制作用随着温度的升高而略微减弱。甲苯的加氢反应G5521在不同掺混比条件下，均是抑制着火的主要反应。

关键词：柴油替代物；TRF；甲烷；着火延迟时间；敏感性分析

Abstract

With the increasingly serious energy crisis and environmental pollution, LNG-diesel dual-fuel engine draws more and more attention. At present, most of the simulation of diesel oil is through the construction of diesel substitute model, TRF mixture is a typical diesel substitute model, this paper simulates the effect of the blending of TRF components on the ignition characteristics of methane. The ignition characteristics of dual-fuel engines were investigated by simulating the mixture fuels of n-heptane-methane, isooctane-methane and toluene-methane. Through the comparison of simulation data with experimental data, the n-heptane detailed mechanism of LLNL Version 3.1, the isooctane detailed mechanism of LLNL Version 3 and the mechanism of gasoline substitution with toluene mechanism were selected eventually. The effects of initial temperature, initial pressure, equivalent ratio and blending ratio on the ignition delay time of mixture fuels were investigated by performing numerical simulation using Chemkin software, the sensitivity analysis of the initial temperature and blending ratio were also studied. The result as follows:

(1)The ignition delay time of n-heptane-methane and isooctane-methane mixed fuels is divided into three stages: low temperature, medium temperature and high temperature. In the low temperature and high temperature region, the ignition delay time of the mixture fuels is shortened with the increase of the temperature. In the middle temperature region, the ignition delay time of the mixture fuels appears negative temperature coefficient phenomenon obviously, and as the pressure increases, the negative temperature coefficient region tends to approach the high temperature region. The effect of the equivalent ratio on the mixed fuels is greatest in the negative temperature coefficient region. When the n-heptane blending ratio is less than 3% to 5%, the negative temperature coefficient phenomenon disappears. In contrast, the initial temperature has the greatest impact on the ignition of mixed fuels.

(2)The ignition delay time of the toluene-methane mixed fuel is shortened with the increase of the temperature, and the negative temperature coefficient does not appear, the equivalent ratio has little effect on the ignition delay of the mixed fuel. In the low temperature and the middle temperature region, with the increase of the proportion of toluene, the ignition delay time of the mixed fuel is prolonged. When the temperature reaches high temperature region more than 1100K, with the increase in the proportion of toluene, the fuel ignition delay time is shortened.

(3) Through the sensitivity analysis of the initial temperature and blending ratio, it was found that the reaction CH₃ HO₂=CH₄ O₂ had a great effect on the ignition, and the dissociation reaction H₂O₂ ( M) =2OH ( M) produced a large amount of OH. The isomerization of n-heptane and the dehydrogenation reaction have a greater effect on ignition. The different dehydrogenation reactions of isooctane have different effects on ignition. G24 is the most important reaction to suppress the ignition of toluene-methane mixed fuel under the simulated initial temperature conditions, and the inhibition of ignition is slightly weakened with the increase of temperature. Toluene hydrogenation reaction G5521 is the main reaction to suppress the ignition under different mixing conditions.

Key Words：diesel alternative；TRF；methane；ignition delay time；sensitivity analysis

目 录

摘要 I

Abstract II

第一章 绪论 1

1.1 研究背景 1

1.2 TRF柴油替代物组分燃料着火特性的国内外研究现状 2

1.2.1 国外研究现状 2

1.2.2 国内研究现状 3

1.3 研究内容和技术方案 4

1.3.1 研究内容 4

1.3.2 技术方案 4

第二章 混合燃料着火特性的数值模拟方法 5

2.1 Chemkin简介 5

2.2 敏感性分析方法 6

2.3 TRF组分燃料化学动力学机理的验证和筛选 6

2.3.1 正庚烷机理的验证和筛选 6

2.3.2 异辛烷机理的验证和筛选 8

2.3.3 甲苯机理的验证和筛选 9

第三章 初始条件对混合燃料着火特性影响的模拟研究 11

3.1 初始温度和压力对混合燃料着火特性的影响 11

3.2 当量比对混合燃料着火特性的影响 13

3.3 掺混比例对混合燃料着火特性的影响 14

3.4 TRF单一组分掺混和多组分掺混甲烷的比较 16

第四章 混合燃料燃烧的化学反应动力学分析 18

4.1 正庚烷-甲烷混合燃料的敏感性分析 18

4.2 异辛烷-甲烷混合燃料的敏感性分析 20

4.3 甲苯-甲烷混合燃料的敏感性分析 21

第五章 总结与展望 24

5.1 全文总结 24

5.2 工作展望 26

参考文献 27

致谢 29

绪论

研究背景

随着世界范围内气候变暖、极端天气频发、雾霾天气增多等一系列环境问题不断加剧，国际上陆续制定了相关的法律法规。为了降低船舶排放物中氮氧化物（NO_x）、微粒物（PM）、未燃的碳氢化合物（HC）等的排放，国际海事组织对船舶排放出台了较为严格的限制措施。目前，欧洲和美洲一些国家的水域已经开始推行较为严格的船舶废气排放法规，且排放法规日益严格。天然气能够有效地减少污染物的排放，受到广泛关注和研究。天然气的辛烷值^[1]较高，可使燃用天然气的发动机在更高压缩比下运行。