柴油引燃缸内直喷天然气发动机燃料喷射对燃烧过程的影响研究

发布时间：2019-03-01 09:20

【摘要】：柴油引燃缸内直喷技术作为当前最新的天然气发动机技术,除了具有传统天然气发动机技术的优点之外,还可以弥补其动力性不足和充量系数下降等问题,成为当前研究的重点领域。对于柴油引燃缸内直喷天然气发动机,引燃柴油和天然气的喷射过程对发动机的燃烧过程和排放具有重要的影响。而目前国内外在引燃柴油和天然气喷射对缸内混合气的形成和燃烧过程方面的研究还比较少。因此本文通过仿真的方法研究了引燃柴油和天然气的喷射对缸内混合气的形成和燃烧过程,以及NO的排放性所产生的影响,为以后产品开发奠定一定的基础。在发动机工作过程中,混合气的浓度、引燃柴油所占比例,引燃柴油和天然气的喷射时刻、喷射持续期,喷孔的位置、喷孔直径的大小、以及喷孔之间的夹角都会对混合气形成和燃烧产生重要影响。为深入研究柴油引燃缸内直喷天然气发动机燃料喷射对混合气形成和燃烧过程的影响规律,本文通过FIRE软件建立了柴油引燃天然气发动机仿真系统,在发动机转速为2100r/min,全负荷工况,过量空气系数为1.7,柴油和天然气喷射间隔为5°CA,引燃柴油量比例为5%的情况下,对引燃柴油的喷射持续期和喷孔直径、天然气喷孔夹角和喷射持续期四个因素进行仿真研究,对混合气形成过程中的缸内浓度分布、缸内流场分布,燃烧过程中的缸内温度和压力、放热特性,以及NO的生成进行了深入分析。研究结果表明,在保持引燃柴油喷射量一定的情况下,随着引燃柴油喷射持续期的延长,喷射速度从引燃柴油喷射持续期为0.5°CA的274m/s下降到喷射持续期为2°CA时的65m/s。缸内温度和压力的峰值下降的最大值分别为2.6%、7.5%;随着引燃柴油喷孔直径的变大,燃料喷射速度从喷孔直径为0.15mm情况下的234m/s,下降到喷孔直径为0.25mm时的90.5m/s,缸内温度和压力的峰值下降的最大值分别是2.8%、6.9%,而NO的浓度随着引燃柴油喷孔直径的增大逐渐降低;天然气喷孔夹角为130°时,缸内燃烧的温度和压力峰值最高,其他夹角下缸内温度和压力峰值下降的最大值为8.6%、8.2%,燃烧持续期从天然气喷孔夹角为130°下的45°CA延长到150°CA下的103°CA,最大延长了58°CA。在130°时缸内NO的生成量最高,随着喷孔夹角的变化,生成量降低;随着天然气喷射持续期延长,燃料喷射速度从4°CA时的最大值318m/下降到持续期为10°CA时的288.7m/s,相比于持续期为4°时,缸内温度和压力峰值、燃烧放热率峰值下降的最大值分别是5.5%、13.8%、35.3%,温度峰值出现的时刻最大滞后期为4°CA。随着天然气喷射持续期的延长,NO生成量总量逐渐降低。
[Abstract]:Diesel in-cylinder direct injection technology, as the latest natural gas engine technology at present, not only has the advantages of traditional natural gas engine technology, but also can make up for the lack of power performance and the decrease of filling coefficient, and so on. It has become the focus of current research. The injection process of diesel fuel and natural gas plays an important role in the combustion process and emission of diesel engine. At present, there is little research on the formation and combustion process of diesel fuel and natural gas injection in cylinder at home and abroad. In this paper, the effects of diesel fuel and natural gas injection on the formation and combustion process of in-cylinder mixture and the emission of NO are studied by simulation method, which lays a certain foundation for future product development. In the course of the engine operation, the concentration of the mixture, the proportion of diesel fuel ignited, the injection time of diesel and natural gas, the duration of injection, the location of the nozzle, the diameter of the injection hole, As well as the angle between the nozzle holes will have an important impact on the formation and combustion of the mixture. In order to study the influence of fuel injection on mixture formation and combustion process in diesel ignition cylinder, a simulation system of diesel ignition natural gas engine was established by FIRE software, and the engine speed was 2100r / min, the fuel injection rate was 2100rmin, and the fuel injection rate was 2100r / min. Under full load condition, the injection duration and the diameter of injection hole of diesel fuel are 5 掳CA with excess air coefficient of 1.7, 5 掳CA of interval between diesel and natural gas injection, and 5% of fuel quantity. Four factors, including angle and duration of natural gas injection hole, are simulated and studied. The distribution of concentration in cylinder, flow field in cylinder, temperature and pressure in cylinder during combustion, and heat release characteristics in the process of gas mixture formation are studied, and the temperature and pressure in the cylinder and the heat release characteristics in the process of combustion are studied. And the generation of NO is deeply analyzed. The results show that with the increase of injection duration, the injection speed decreases from 274m/s of 0.5 掳CA to 65 m / s of 2 掳CA under the condition of constant injection amount of diesel fuel from ignited diesel fuel to diesel fuel injection duration of 2 掳diesel fuel injection duration, and the injection speed decreases from 0.5 掳diesel injection duration to 2 掳diesel injection duration of 2 掳diesel injection duration, with the injection duration of 0.5 掳diesel. The maximum values of the peak drop of temperature and pressure in the cylinder are 2.6% and 7.5%, respectively. With the increasing diameter of diesel fuel injection holes, the fuel injection speed decreases from 234m / s in the case of 0.15mm to 90.5m / s when the diameter of the injection holes is 0.25mm, and the fuel injection speed decreases from 234m / s to 90.5m / m / s when the diameter of the nozzle is 0.25mm. The maximum values of peak drop of temperature and pressure in cylinder are 2.8% and 6.9%, respectively, while the concentration of NO decreases gradually with the increase of the diameter of injection hole of diesel fuel. When the angle of natural gas injection hole is 130 掳, the peak temperature and pressure of combustion in cylinder is the highest, and the maximum drop of peak temperature and pressure in cylinder under other angles is 8.6% and 8.2%, respectively. The combustion duration extends from 45 掳CA at 130 掳angle to 103 掳CA at 150 掳CA, with a maximum extension of 58 掳CA.. At 130 掳, the generation of NO in cylinder is the highest, and with the change of nozzle angle, the amount of formation decreases. With the prolongation of natural gas injection duration, the fuel injection velocity decreased from the maximum 318m/ at 4 掳CA to 288.7 m / s at 10 掳CA, compared with the peak in-cylinder temperature and pressure at 4 掳duration. The maximum decrease of combustion exothermic rate is 5.5%, 13.8%, 35.3%, respectively. The maximum lag time of the peak temperature is 4 掳CA.. With the prolongation of the duration of natural gas injection, the total amount of NO formation decreases gradually.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U464

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