摘 要

作为一种清洁的气体替代燃料，天然气被广泛应用于内燃机等各种燃烧系统中。燃用天然气不仅能够调整国家的能源消费结构，还可以降低污染物排放。天然气是一种组成复杂的可燃混合气，其主要组分燃料为甲烷、乙烷、丙烷和丁烷。对于不同气源开采的天然气，其成分存在波动。目前，国内外学者已经对特定组分的天然气以及天然气模拟燃料的预混层流燃烧特性展开了一些研究，但关于天然气成分波动对其层流燃烧特性的影响的研究非常有限。因此，本文以成分变化的天然气为研究对象，基于详细的天然气氧化机理对其预混层流燃烧特性展开了数值模拟研究。

本文借助CHEMKIN PRO气相化学动力学软件构建出一维平面火焰模型，在298K、0.1MPa的初始条件下，以甲烷掺混乙烷、丙烷和丁烷的烷烃混合燃料模拟天然气，通过改变当量比和天然气模拟燃料中C1-C4烷烃组分的含量，研究了天然气成分波动对其层流燃烧速度的影响规律，并利用火焰结构分析和敏感性分析等动力学分析方法，从化学动力学的角度解释了天然气成分波动引起其层流燃烧特性变化的本质原因，得到的主要结论如下：

（1）当量比保持不变时，天然气的层流燃烧速度的随乙烷、丙烷和丁烷含量的增加而上升。相对于丙烷和丁烷，乙烷含量波动对层流燃烧速度的影响更加明显。当天然气组分保持恒定时，随着当量比的增加，其层流燃烧速度先增加后减小并在当量比1.1附近达到最大值。

（2）火焰结构分析表明，天然气的层流燃烧速度与火焰中OH基和H基浓度之和的最大值之间有较强的相关性，其成分波动时各主要活性基的浓度峰值均发生变化，其中H基浓度峰值的变化最为明显。H基浓度的改变是造成天然气层流燃烧速度变化的本质原因。

（3）敏感性分析和净反应速率分析表明，成分波动会影响天然气燃烧过程中的重要基元反应，通过正影响的基元反应和负影响的基元反应之间的竞争，使得火焰中H基的浓度峰值发生变化，乙烷含量波动对H基浓度的影响最大，因此层流燃烧速度随乙烷含量的变化最明显。

关键词：天然气；成分波动；层流燃烧速度；化学动力学分析

Abstract

As a clean gas alternative fuel, natural gas is widely used in various combustion systems, like the internal combustion engine. Natural gas not only can adjust the country’s energy consumption structure, but also can reduce the pollutant emission. Natural gas is a kind of combustible mixture with the primary component of methane and other minor ones, like ethane, propane and butane. The components of natural gas that is mined by different gas sources are fluctuant. At present, the domestic and foreign scholars have conducted some studies on the premixed laminar combustion characteristics of natural gas with specific sources and natural gas simulated fuels, but the researches on the influence of natural gas component fluctuations on the laminar combustion characteristics are quite few. Therefore, this paper, taking the natural gas with changing components as the research object and based on the detailed natural gas oxidation mechanism, conducts a numerical simulation study on the premixed laminar combustion characteristics.

This paper builds a one-dimensional planar flame model via the CHEMKIN PRO gas-phase chemical kinetics software, uses the alkane mixed fuel constituted with methane, ethane, propane and butane to simulate the natural gas at the initial temperature of 298K and the initial pressure of 0.1MPa, and studies the influence rule of natural gas component fluctuations on the laminar burning velocity through changing the equivalence ratio and the C1-C4 alkane component contents in the natural gas simulated fuel, and explains the essential reason that the natural gas component fluctuations cause the change of laminar combustion characteristics from the point of view of chemical kinetics by using the flame structure analysis, sensitivity analysis and other kinetics analysis methods. The main conclusions are as follows:

(1) When the equivalence ratio remains constant, the laminar burning velocity of natural gas will rise with the increasing contents of ethane, propane and butane. Compared to propane and butane, the influence of ethane content fluctuations on the laminar burning velocity is more obvious. When the natural gas components remain constant, as the equivalence ratio increases, the laminar combustion velocity will increase firstly and then decrease, and reach the maximum value at the equivalent ratio of 1.1.

(2) The flame structure analysis shows that there is a strong correlation between the laminar burning velocity of natural gas and the maximum values of the total concentrations of OH radical and H radical in the flame; when the components fluctuate, the concentration peak of each main reactive radical will also change and the H radical concentration peak changes most obviously. The change of H radical concentration is the essential reason that causes the change of the natural gas laminar burning velocity.

(3) The sensitivity analysis and the net reaction velocity analysis show that the component fluctuations will affect the important elementary reactions in the natural gas combustion process. The competition between the elementary reactions with positive impacts and the ones with negative impacts changes the concentration peak of H radicals in the flame and the fluctuations of ethane contents have the greatest influence on the concentration of H radicals. Therefore, the laminar burning velocity varies most obviously with the change of ethane contents.

Keywords: natural gas; component fluctuation; laminar burning velocity; chemical kinetics analysis

目 录

摘要 I

Abstract II

第1章 绪论 1

1.1 研究背景 1

1.1.1 石油基燃料与替代燃料 1

1.1.2 天然气的优势与应用 1

1.2 研究的目的与意义 3

1.3 国内外研究现状 4

1.3.1 天然气和天然气中主要组分燃料的层流燃烧特性研究现状 4

1.3.2 天然气成分波动对其层流燃烧特性的影响的研究现状 4

1.4 本文的主要工作和技术路线 7

1.4.1 本文的研究对象和研究内容 7

1.4.2 本文的目标 7

1.4.3 拟采用的研究方案和技术路线 7

1.5 本文的章节安排 9

第2章 本文的研究方法 10

2.1 计算机数值模拟 10

2.1.1 数值模拟方法的发展 10

2.1.2 CHEMKIN软件包的介绍 10

2.2 化学反应动力学机理 11

2.2.1 天然气燃烧化学反应动力学机理的简介 11

2.2.2 化学反应动力学机理的验证与选择 12

2.3 本章小结 14

第3章 乙烷含量对甲烷-乙烷混合燃料层流燃烧特性的影响 15

3.1 乙烷含量波动对甲烷-乙烷混合燃料层流燃烧速度的影响 15

3.2 乙烷含量对甲烷-乙烷-空气层流火焰影响的动力学分析 16

3.2.1 对火焰结构和化学反应路径的影响 16

3.2.2 对基元反应敏感性和化学反应速率的影响 21

3.3 本章小结 24

第4章 乙烷和丙烷含量对甲烷-乙烷-丙烷混合燃料层流燃烧特性的影响 25

4.1 乙烷含量波动对甲烷-乙烷-丙烷混合燃料层流燃烧速度的影响 25

4.2 丙烷含量波动对甲烷-乙烷-丙烷混合燃料层流燃烧速度的影响 27

4.3 丙烷含量对甲烷-乙烷-丙烷-空气层流火焰影响的动力学分析 28

4.3.1 对火焰结构和化学反应路径的影响 28

4.3.2 对基元反应敏感性和化学反应速率的影响 33

4.4 乙烷和丙烷含量波动对天然气-空气层流火焰影响效果的对比 35

4.5 本章小结 36

第5章 C2-C4烷烃含量波动对天然气层流燃烧特性的影响 37

5.1 丁烷含量波动对C1-C4烷烃混合燃料层流燃烧速度的影响 37

5.2 丁烷含量对C1-C4烷烃混合气-空气层流火焰影响的动力学分析 38