【作者】 张波；

【导师】 舒歌群；

【作者基本信息】 天津大学 ， 动力机械及工程， 2007， 博士

【摘要】 均质压燃(HCCI)结合了传统汽油机和柴油机的优点,能够同时降低氮氧化物(NOX)和微粒(PM)排放而且具有较高的热效率,被认为是最有潜力的新一代内燃机燃烧方式,是目前国际内燃机燃烧学研究的热点。HCCI着火和燃烧主要受到混合气燃烧化学反应动力学的控制,燃料特性以及燃烧边界条件对HCCI燃烧过程有决定性影响。为了研究不同特性燃料的HCCI燃烧反应机理、探索有效的HCCI燃烧控制策略以及寻找适合HCCI燃烧的特性燃料,最终实现对HCCI燃烧着火时刻和燃烧反应速率的精确控制以及拓宽其运转工况范围,本文对燃料特性和燃烧边界条件(负荷、转速、EGR、进气温度和压力等)对HCCI燃烧特性、运转工况范围、发动机性能以及排放特性等的影响规律进行了系统的试验研究。首先,本文采用由正庚烷和异辛烷混合而成的不同辛烷值基础燃料(PRF)研究燃料辛烷值和燃烧边界条件对HCCI燃烧过程、运转工况范围以及排放特性等的影响。基础燃料的HCCI燃烧过程表现了明显的双阶段放热特点,燃料辛烷值越低,低温反应放热越明显。燃料辛烷值对HCCI燃烧过程的影响与燃烧边界条件有关,且随燃烧边界条件变化而变化,负荷越低、发动机转速和EGR率越高,燃料辛烷值对HCCI燃烧过程的影响越明显。提高燃料辛烷值和EGR率可使HCCI运转工况范围向大负荷区域拓宽。HCCI对燃料辛烷值的要求介于汽油燃料和柴油燃料之间,在本研究试验条件下,辛烷值为60燃料的HCCI运转工况范围及高效率运转区域覆盖的工况范围均为最宽,能够实现的最高指示效率也最高。HCCI的HC排放与燃料辛烷值和工况有关,大负荷时主要来源于缸内的缝隙容积,但低负荷时,缸内大范围的淬熄是HC排放的主要来源;与HC排放不同,CO排放主要取决于缸内温度,并与它具有很好的一致性。采用研究法辛烷值近似相同但理化特性不同的燃料研究燃料特性和燃烧边界条件对HCCI燃烧过程、运转工况范围以及排放特性等的影响。研究法辛烷值相同但理化特性不同的燃料即使在相同燃烧边界条件下其燃烧特性参数也有较大的差别,而且在不同的燃烧边界条件下燃料特性对HCCI燃烧特性参数的影响也不同,即燃料特性对HCCI燃烧过程的影响与燃烧边界条件有关,且随燃烧边界条件变化而变化。OI是比研究法辛烷值和马达法辛烷值相对全面的燃料抗爆性能的相对度量指标,它在各种运转工况条件下均能较好的表征不同燃料在相同工况条件下的抗爆性能的相对强弱。相同运转工况条件下,燃料的OI越高,其抗爆性能相对越强,HCCI主燃烧着火时刻越晚。最后,作者采用模拟增压研究进气压力和燃料特性对HCCI燃烧过程、运转工况范围以及排放特性等的影响。进气压力升高,主燃烧着火时刻提前,缸内最大爆发压力增大,但不同进气压力条件下,燃料特性对HCCI燃烧过程也有不同的影响。提高进气压力可使HCCI的正常运转工况范围同时向高负荷和低负荷拓宽。进气压力对燃烧效率的影响与燃料辛烷值以及运行工况有关,对于燃烧效率和指示效率均存在一个最佳进气压力,燃料辛烷值和运行工况不同,该最佳进气压力的值不同;而不同进气条件下,燃料特性对燃烧效率和指示效率的影响均与燃料的OI有关。不同进气条件下,燃料特性对HC和CO比排放的影响也与OI有关,但进气压力和燃料特性对HCCI NOX比排放的影响均不明显。更多还原

【Abstract】 Combined the advantages of Gasoline engine and Diesel engine, with ultra-low NOx and PM emissions and high thermal efficiency, homogeneous charge compression ignition (HCCI) was considered as a new combustion process with the strongest potential in internal combustion engine and a focus in the field of combustion study in the world. Its ignition and combustion are mainly controlled by combustion chemistry reaction kinetics of mixture; therefore, the fuel properties and combustion boundary condition have dominant effect on HCCI combustion process.To learn the combustion reaction mechanism of different characteristic fuel and the effects of fuel physical and chemical properties on HCCI combustion, find effective controlling strategy of HCCI combustion, the effects of fuel properties and combustion boundary condition on the HCCI combustion characteristics, operation region, engine performance and emission characteristics were systematically investigate by experiments. The purpose of this study is to realize the exact control to HCCI ignition timing and combustion reaction rate and the extended of operation region.Firstly, Primary Reference Fuels (PRFs) with different octane number (ON), obtained by mixing with n-heptane and isooctane, were applied to learn the effects of ON and combustion boundary condition on HCCI combustion process, operation region and emission characteristics. The HCCI combustion process of PRFs was characteristic by two-stage heat release. The lower the ON is, the more obvious the heat release of low temperature reaction. The influence of ON of fuel on HCCI combustion process has relations with combustion boundary condition, and change with the variation of combustion boundary condition. With the load lower, the engine speed and EGR rate higher, the influence becomes more obvious. The increase of RON of fuel and ratio of EGR would expend the HCCI operation region to high load range. The demanded ON of fuel for HCCI is between that of gasoline fuel and diesel fuel. In the experiment condition of this paper, both the HCCI operation load region and the high efficiency operation region get the broadest area when the fuel ON is 60, the highest indicated efficiency is the highest, too. The HC emissions of HCCI are related to fuel ON and operation condition. At high load condition HC emissions mainly come from crevice in the cylinder while at the low load condition mainly from quenching. Different to HC, CO emissions are related to the in-cylinder temperature, and there is the good consistent relation between CO and in-cylinder temperature.Fuels, with the almost same Research Octane Number (RON) but different physical and chemical properties, were used to learn the effects of fuel property and combustion boundary condition on HCCI combustion process, operation region and emission characteristics. With the same combustion boundary condition, the fuels with same RON but different physical and chemical characteristics have large differences in combustion characteristic parameters. If combustion boundary condition changed, the fuel has different effects on HCCI combustion characteristic parameters. It means that the effects of fuel properties of HCCI combustion process are relate with combustion boundary condition. Octane Index (OI) is relatively measurement of antiknock performance, more comprehensive than RON and Motor Octane Number (MON). No matter what operation condition, it could relatively indicate the antiknock performance of fuel in the same operation condition. In the same condition, the higher OI is, the stronger the capability is, the later the ignition timing is.Finally, simulated boost was applied to learn the effects of intake pressure and fuel properties on HCCI combustion process, operation region and emission characteristics. The intake pressure increased, the main combustion ignition timing advanced, the maximum cylinder pressure rise. But with different intake pressures, the fuel properties have different effects on HCCI combustion process. The increase of intake pressure would expand the normal operation region of HCCI to both high load condition and low load condition. The effects of intake pressure on combustion efficiency are related to the ON of fuel and operation condition. For the combustion efficiency and indicated efficiency, exits an optimum intake pressure. When operation condition changed, the optimum intake pressure changed. At different intake pressure conditions, the influences of fuel properties on both combustion efficiency and indicated efficiency are related to OI. In different intake pressure conditions, its influences on HC and CO emissions are also related to OI, while the influences of intake pressure and fuel properties are not obvious on NOx emissions.更多还原