柴油机燃用BED多组份燃料的燃烧过程研究

【作者】 刘少华；

【导师】 申立中；

【作者基本信息】 昆明理工大学 ， 车辆工程， 2013， 博士

【摘要】 生物柴油和乙醇作为石化柴油的替代燃料,在世界各国得到了广泛的研究。在研究过程中还存在一些不足,主要表现在：生物柴油燃油雾化效果差,NOx排放增加,乙醇与柴油互溶性差,对排放物的研究结论不一致,缺乏系统研究等。针对以上问题,利用生物柴油、乙醇和柴油之间的理化特性互补性,将三者以一定比例混合形成生物柴油-乙醇-柴油(简称为BED)多组份燃料。利用生物柴油和乙醇的燃料优势以及高压共轨系统的技术潜力,通过替代燃料和控制技术两种途径的有机结合,研究BED多组份燃料对柴油机性能的影响规律及其燃烧控制规律,并进行不同海拔对BED多组份燃料燃烧过程的影响研究,开展的研究工作如下：(1)进行了BED多组份燃料的稳定性和理化特性研究针对乙醇和柴油互溶性较差的问题,在乙醇柴油中加入生物柴油,系统研究了不同温度下BED多组份燃料的稳定性和三相互溶性。研究了不同生物柴油比例和不同温度对BED多组份燃料稳定性的影响规律。对生物柴油和乙醇掺混比例对BED多组份燃料的主要理化指标的影响关系进行了研究和分析。(2)进行了柴油机燃用BED多组份燃料的性能试验研究在高压共轨柴油机上燃用纯柴油和六种BED多组份燃料(在柴油中掺混10%-25%的生物柴油和3%-5%的乙醇),在81kPa大气压力下进行了对比试验研究,分析了不同比例BED多组份燃料对柴油机动力性、经济性、排放特性以及燃烧特性的影响规律及其与燃用纯柴油时的差异性。从各种燃烧过程的场分布情况分析了BED多组份燃料与柴油喷雾与燃烧过程的差异性。研究结果表明,未对柴油机作任何调整的情况下,燃用BED多组份燃料会造成动力性下降。当生物柴油掺混比例在15%以内时,经济性有1.3%-2.1%的改善；有利于降低柴油机的CO,THC,烟度和PM排放,NOx排放有增加趋势,最高增幅达到17%。当生物柴油比例增加至25%时,经济性下降；排放物改善效果变差甚至高于柴油。推迟喷油正时和采用EGR技术能够有效降低BED多组份燃料的NOx排放。气缸压力和燃烧温度均有所下降；燃烧始点与柴油差别不大,燃烧持续期明显缩短；放热率峰值随着生物柴油比例的增加而逐渐增大。(3)研究了BED多组份燃料的燃烧控制规律进行了主要喷射控制参数预喷正时,预喷油量,主喷正时,主喷油量及喷油压力对柴油机燃用BED多组份燃料燃烧特性的影响试验研究。试验结果表明,适当推迟预喷正时,可以降低主喷燃烧的剧烈程度。增加预喷油量有利于提高气缸压力,同时会增加预喷燃烧的放热率峰值和最大压力升高率。主喷正时提前,BED多组份燃料的燃烧始点随之提前；最大气缸压力,最高燃烧温度以及最大放热率都随之增大,出现的时刻也随之提前；压力升高率增大,增加了燃烧的激烈程度。随着掺混生物柴油和乙醇比例的增加,主喷阶段放热率峰值随着主喷定时的提前,出现先增大后减小的趋势。最高气缸压力和放热率峰值均随着主喷油量的增加而逐渐增大,燃烧持续期延长。随着喷油压力的提高,最高气缸压力和放热率峰值基本随之增大,燃烧持续期缩短。燃烧初期的放热速度先增大后减小,导致燃烧初期的气缸压力也出现同样的变化趋势。(4)研究了不同海拔对BED多组份燃料燃烧过程的影响进行了高压共轨柴油机在不同海拔下燃用BED多组份燃料的试验研究。结果表明,不对柴油机进行任何调整的前提下,大气压力的变化在整体上对动力性影响不大；在低负荷下,大气压力的升高对经济性的改善效果不大甚至有负面影响；在高负荷下,经济性改善。随着大气压力的增加,柴油机的CO和THC排放基本逐渐降低；中低负荷下NOx排放随之降低,全负荷下升高；PM排放在全负荷时降低。随着大气压力的升高,最大气缸压力,最高燃烧温度和放热率峰值均随之增大,且增加幅度随不同的气压变化区间而不同。燃烧速度加快,燃烧持续期缩短。气缸压力升高率增大,但仍在平稳运转范围内。(5)研究了不同形式含氧量的变化对柴油机性能的影响进一步比较了BED多组份燃料的含氧量和不同海拔变化引起的大气含氧量对柴油机性能影响的差异性。研究结果表明,海拔变化引起的空气含氧量变化对柴油机燃用纯柴油时的动力性影响不大；随着大气压力的升高,柴油机比油耗逐渐下降。随着BED多组份燃料含氧量的增加,动力性和有效燃油消耗率降低,有效热效率提高。BED多组份燃料含氧量的增加对经济性的改善幅度高于海拔变化引起的大气含氧量增加对经济性的改善幅度。更多还原

【Abstract】 As alternative fuels to petroleum diesel fuel, biodiesel and ethanol have been widely researched in many countries and regions. There exist some problems in the process of these researches. The main problems were as follows:the poor fuel atomization effect of biodiesel, the increased NOx emissions, the poor solubility of diesel fuel and ethanol, the inconsistent study conclusions of the emissions and the lack of systematic research and so on. Aiming at the above problems, the biodiesel-ethanol-diesel (abbreviated as BED) multi-component fuel was prepared with certain proportions of biodiesel, ethanol and diesel fuel by using the physicochemical properties complementarity of the three fuels. Taking into account the advantages of biodiesel and ethanol and the technical potential of high pressure common rail system, the researches on the effect of the BED multi-component fuel on the engine performance and it’s combustion control law were performed, and the effect of different altitude levels on the combustion process was studied when the BED multi-component fuel was used by the organic combination of alternative fuel and control technology. The researches were investigated as follows:(1) Conducting the investigation on stability and physicochemical properties of the BED multi-component fuelAiming at the problem of poor solubility of ethanol and diesel fuel, the biodiesel was added to the ethanol-diesel fuel. And the experimental investigation on stability and three phase solubility of the BED multi-component fuel at different temperatures was carried out. The effect of different proportions of biodiesel and different temperatures on the stability of the BED multi-component fuel was studied. And the effect of the blending ratio of the biodiesel and ethanol on the main physicochemical properties of the BED multi-component fuel was researched and analyzed.(2) Conducting the experimental investigation on the engine performance when the BED multi-component fuel was usedThe comparative experiments were performed on a high pressure common rail diesel engine fueled with pure diesel and the BED multi-component fuel with10%-25%biodiesel and3%-5%ethanol in volume percentage at81kPa atmospheric pressure. The effect of the BED multi-component fuel with different proportions of biodiesel, ethanol and diesel fuel on engine power, fuel economy, emissions and combustion characteristics and the difference between the BED multi-component fuel and the diesel fuel were analyzed. The difference of the spray and combustion process between the BED multi-component fuel and the diesel fuel was analyzed by comparing the fields’distribution.The test results showed that if the engine was kept unchanged, the engine power was lower than that of pure diesel when the BED multi-component fuel was used. And the fuel economy was improved by1.3%-2.1%when the proportion of biodiesel in the BED multi-component fuel was kept within15%. On the meanwhile, the CO, THC, soot and PM emissions decreased, while the NOx emissions had increasing trend with a maximum of17%. If the volume percentage of biodiesel reached25%, the fuel consumption increased, the improving effect of the BED multi-component fuel on emissions was weakened and the emissions even increased. Retarding injection timing and using EGR technology can reduce the NOx emissions of the BED multi-component fuel effectively. The cylinder pressure and combustion temperature were decreased. There was no significant difference in the start of combustion. And the combustion duration was shortened obviously. With the increase of biodiesel component in the BED multi-component fuel, the peak heat release rate increased.(3) Researching the combustion control law of the BED multi-component fuelThe effects of the key fuel injection control parameters including the pilot injection timing and quantity, the main injection timing and quantity and the injection pressure on the combustion characteristics of the diesel engine were investigated when the BED multi-component fuel was used.The results indicated that if the pilot injection timing was retarded properly, the intensity of the main injection fuel combustion process would reduce. The increased pilot injection quantity was helpful to improve the cylinder pressure, while the peak heat release rate and the maximum rate of pressure rise increased. The advanced main injection timing led to the advanced start of combustion and higher values in the maximum cylinder pressure, the maximum combustion temperature and the peak heat release rate, and they would appeared in advance. The rate of pressure rise increased, which resulted in a violent combustion process. With the increase of the biodiesel and ethanol components in the BED multi-component fuel, the peak heat release rate in the main injection phase increased firstly and then decreased as the main injection was made in advanced timing. Both of the maximum cylinder pressure and the peak heat release rate increased with the increasing main injection quantity. The combustion duration extended accordingly. As the injection pressure increased, the maximum cylinder pressure and the peak heat release rate both increased. And the combustion duration was shortened. The heat release rate increased firstly and then decreased at the early stage of the combustion, leading to the same trend in the cylinder pressure.(4) Researching the effect of different altitude levels on the combustion process of the BED multi-component fuelThe experiments on the high pressure common rail diesel engine fueled with the BED multi-component fuel at different altitude conditions were performed. The experimental results indicated that when the engine was kept unchanged, the influence of atmospheric pressure variation on the engine power was not significant on the whole. At low loads, with the increase of atmospheric pressure, the improvement of fuel economy was not significant and the fuel consumption even increased. At high loads, the fuel economy was improved. With the increase of atmospheric pressure, the CO and THC emissions decreased basically, and the NOx emissions decreased at medium and low loads while increased at full load. The PM emissions decreased at full loads. With the decrease of the altitude level and the increase of atmospheric pressure, the maximum cylinder pressure, the maximum combustion temperature and the peak heat release rate were all increased. The degree of their increase varied with the different variation intervals of the atmospheric pressure. The burning speed was accelerated and the combustion duration was shortened. The rate of pressure rise increased, but still within the scope of smooth running.(5) Researching the effect of different types of oxygen content variation on the engine performanceA further comparison of the different effects of fuel oxygen content in the BED multi-component fuel and intake oxygen content caused by altitude variation on diesel engine performance was made. The results indicated that when the pure diesel fuel was used, the influence of altitude variation on the engine power was not significant and the brake specific fuel consumption (BSFC) decreased with the increase of atmospheric pressure. When the BED multi-component fuel were used, the engine power and brake specific fuel consumption reduced with the increase of fuel oxygen content, and the effective thermal efficiency was improved. Compared to the effect of increasing atmospheric oxygen content by altitude variation, the improvement in fuel consumption due to the increase of BED multi-component fuel’s oxygen content was greater.更多还原