柴油机变组分进气的燃烧特性研究

发布时间：2018-04-30 03:37

本文选题：柴油机 + 变组分进气　；参考：《吉林大学》2016年硕士论文

【摘要】：本文提出了变组分进气对柴油机燃烧特性和排放特性影响的研究,该项技术通过改变发动机进气中各类组分的浓度,能够有效改善柴油机的燃烧特性,同时降低诸多有害气体的排放,并且能够改善高海拔环境下发动机着火困难、动力性下降、热效率低、燃烧不完全等一系列问题。不过目前该项技术手段还处于研究阶段,距离实际应用还存在很多技术问题。本文研究的变组分进气对柴油机的燃烧特性和排放特性的影响。主要分为两部分,一部分是富氧进气燃烧,另一部分是富氮进气燃烧。为了实现研究目的,本文采用Chemkin-pro和AVL-Fire进行相关的模拟分析。首先是利用Chemkin-pro建立正庚烷化学反应机理,为了能够更好的预测变组分进气对柴油机排放特性的影响,在原有化学反应机理的基础上添加NO生成的机理模型,由此建立了新的化学反应机理。将利用Pro/e建立的几何模型导入AVL-Fire生成动网格。本文在研究富氧进气燃烧的过程中,分别设置了4种不同的富氧进气浓度,分别为23%、25%、27%和29%,研究了与自然进气状态下相比的温度、放热率、累计放热率、压力、压力升高率等相关参数的变化趋势。通过研究发现随着进气氧气浓度的升高,这些参数都有不同程度的升高,因此富氧进气能够有效增加柴油机工作过程中的动力性。在研究富氧进气对柴油机排放特性的影响时发现,低温和缺氧是导致CO生成的主要因素,因此富氧进气可以有效降低CO的排放量。为了研究富氧进气对HC生成量的影响,选取CH3、CH4、CH3O、CH2O、C2H5和C3H6六种主要生成物最为研究对象,通过模拟分析发现,随着氧气浓度的升高,这些HC的生成量不断降低。在研究NO的生成量时发现,随着氧气浓度的升高,NO的生成量急剧升高,并且增长幅度和增长速率都越来越大,NO开始生成的时刻也逐渐提前。为了研究喷油正时对NO生成量的影响,设定了三种不同的喷油持续期,分别为15°CA、20°CA、25°CA,设定了三种不同的喷油提前角,分别是3°CA、7°CA、11°CA。通过研究发现,相同富氧浓度的条件下,随着喷油持续期的缩短,NO的排放量降低,随着喷油提前角的减小,NO的排放量降低,因此可以通过改变喷油正时来优化NO的排放量。本文在研究富氮进气燃烧的过程中,分别设置了2种不同的富氮进气浓度,分别为81%和83%。通过研究发现,富氮进气与自然进气相比,富氮进气会导致燃烧室内的温度峰值和压力峰值下降。同时富氮进气对柴油机的排放特性也有很大的影响,富氮进气会加剧燃料的不完全燃烧,导致CO和HC的生成量升高。在研究不同转速对CO和HC的生成量的影响时发现,随着发动机转速的降低,CO和HC的生成量均不断降低。同时还研究了富氮进气对NO排放的影响,由于氮气的阻燃作用,NO的生成量随着氮气浓度的升高而逐渐降低。
[Abstract]:In this paper, the effect of variable component intake on combustion and emission characteristics of diesel engine is studied. This technology can effectively improve the combustion characteristics of diesel engine by changing the concentration of various components in the intake. At the same time, it can reduce the emission of many harmful gases, and can improve a series of problems such as the difficulty of engine ignition, the decline of power performance, the low thermal efficiency, the incomplete combustion and so on. However, the technology is still in the research stage, and there are still many technical problems in practical application. In this paper, the influence of variable component intake on combustion and emission characteristics of diesel engine is studied. It is mainly divided into two parts, one is oxygen-enriched intake combustion, the other is nitrogen-rich intake combustion. In order to achieve the purpose of the study, Chemkin-pro and AVL-Fire are used to carry out the relevant simulation analysis. Firstly, the mechanism of n-heptane chemical reaction is established by using Chemkin-pro. In order to better predict the effect of variable component intake on diesel engine emission characteristics, the mechanism model of no generation is added on the basis of the original chemical reaction mechanism. A new chemical reaction mechanism was established. The geometric model established by Pro/e is imported into AVL-Fire to generate dynamic mesh. During the study of oxygen-enriched intake combustion, four different oxygen-enriched inlet concentrations were set up, which were 2325% and 29%, respectively. The temperature, heat release rate, cumulative heat release rate and pressure were studied in comparison with natural air intake. Change trend of pressure rise rate and other related parameters. It is found that these parameters increase in varying degrees with the increase of inlet oxygen concentration, so the oxygen-enriched intake can effectively increase the dynamic performance of diesel engine in the working process. It is found that the low temperature and hypoxia are the main factors that lead to CO formation, so the oxygen-enriched intake can effectively reduce the emission of CO in diesel engine by studying the effect of oxygen-enriched intake on the emission characteristics of diesel engine. In order to study the effect of oxygen-enriched air intake on HC production, the six main products of Ch _ 3H _ 4 Ch _ 3O _ 3 Ch _ 3O _ 3 Ch _ 2O _ 3 Ch _ 2O _ 2 H _ 2H _ 5 and C3H6 were selected as the most important research objects. Through simulation analysis, it was found that the HC production decreased with the increase of oxygen concentration. When the amount of no was studied, it was found that with the increase of oxygen concentration, the production of no increased sharply, and the increasing amplitude and growth rate of no increased gradually. In order to study the effect of injection timing on no production, three different fuel injection durations were set up, which were 15 掳CA-20 掳CA-25 掳CAand 3 掳CA-7 掳CA11 掳CA. It is found that under the same oxygen enrichment concentration, no emission decreases with the shortening of fuel injection duration and the decrease of fuel injection advance angle. Therefore, no emission can be optimized by changing the injection timing. In this paper, two different concentrations of nitrogen-rich intake are set up, which are 81% and 83% respectively. It is found that compared with natural air intake, nitrogen-rich intake will lead to the decrease of temperature and pressure peak in the combustor. At the same time, nitrogen-rich intake also has a great influence on the emission characteristics of diesel engine. The nitrogen-rich intake will aggravate the incomplete combustion of fuel and lead to the increase of CO and HC production. It is found that with the decrease of engine speed, the amount of CO and HC is decreasing with the decrease of engine speed, and the effect of different rotational speeds on the production of CO and HC is studied. At the same time, the effect of nitrogen-rich intake on no emission was also studied. The amount of no produced decreased with the increase of nitrogen concentration due to the flame retardation of nitrogen.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK421.2

【参考文献】