共查询到17条相似文献,搜索用时 625 毫秒
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本文简要介绍了发动机均质充量压缩着火(HCCI)燃烧的概念和特点,并进一步着重分析了柴油机HCCI燃烧的特点,以及影响柴油机HCCI燃烧的一些重要因素,如混合气形成方式、进气温度、负荷、废气再循环(EGR)、气门正时及压缩比等因素。 相似文献
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1 HCCI控制发动机排放的基本原理
HCCI,亦称可控自燃着火(CAI,Controlled Auto Ignition),它是指大量燃料和稀释物(空气和再循环废气等)在进气过程中预先混合成均质混合气,当压缩行程活塞运动到上止点附近时,均质混合气自燃着火的一种燃烧过程. 相似文献
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在乙醇HCCI发动机中,随着EGR率的提高,燃烧始点提前。并且在引入EGR后,燃烧变得柔和,有效地避免了爆震的发生。但由于引入EGR后缸内燃烧温度升高,使得氮氧化物的排放增加。加入EGR后,混合气中二氧化碳、水、惰性气体等成分浓度的变化对燃烧有一定的影响。在增加混合气中二氧化碳和水的含量后,缸内的压力和温度都有所降低,且着火始点也都有延迟。混合气中惰性气体的作用则相反,惰性气体使得燃烧始点提前,且缸内压力、温度都升高。 相似文献
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对预燃室壁涂有催化剂的均质压燃(HCCI)发动机的燃烧过程进行了数值计算,分析了催化燃烧对HCCI发动机燃烧特性的影响;同时分析了预燃室内催化剂种类、过量空气系数、进气温度、进气速度、缸径以及预燃室壁温对HCCI发动机燃烧特性的影响。结果表明,预燃室存在催化燃烧时对HCCI发动机的着火时刻有很大的影响:随着过量空气系数及预燃室进气速度的增加,HCCI发动机的着火时刻提前;催化剂种类、预燃室缸径以及预燃室壁温对HCCI发动机着火时刻影响不显著,但对缸内燃烧温度影响显著。 相似文献
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二甲醚均质压燃燃烧的详细化学动力学模拟研究 总被引:5,自引:0,他引:5
采用由美国Lawrence Livermore国家实验室提出的二甲醚(DME)详细化学动力学反应机理及其开发的HCT化学动力学程序,对均质充量压缩着火(HCCI)发动机燃用DME的着火和燃烧过程进行了分析。为考虑壁面传热的影响,在HCT程序中增加了壁面传热子模型。采用该方法研究了燃空当量比、进气充量加热、发动机转速和EGR等因素对HCCI着火和燃烧的影响。结果表明,DME的HCCI燃烧过程有明显的低温反应放热和高温反应放热两阶段;增大燃空当量比、提高进气充量温度使着火提前;提高发动机转速和采用冷却EGR使着火滞后。 相似文献
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对比研究HCCI汽油机在不同空燃比下采用混合气分层策略时的极限负荷、NOx排放量和燃油经济性,考察了在此策略下过量空气系数λ和EGR率对HCCI发动机燃烧特性的影响。结果表明,混合气分层压缩燃烧模式能有效降低HCCI燃烧的压力升高率,具有拓展负荷范围的潜力,但同时也使NOx排放增加;适当的过量空气系数能在一定程度上改善HCCI发动机的燃烧特性,采用9%的EGR率时发动机油耗率最低,具有明显节油效果。 相似文献
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There has been recent interest in a new engine type, Homogeneous Charge Compression Ignition (HCCI), to combine the advantages
of SI and CI engines. In this paper, a locally deterministic approach is employed to consider spatial inhomogeneities using
the KIVA-CHEMKIN package. Validation is performed for two experimental HCCI engines fueled, respectively, by hydrogen and
n-heptane. The full mechanism for hydrogen and a skeletal mechanism for n-heptane are used for combustion chemistry. Differences
in the reaction flow paths are shown at ignition and the heat release reaction stages of the two fuels. Results show good
agreement between measured and calculated pressures for different initial mixture temperatures with estimated residual fractions.
A parametric study is performed in both engines to consider the influences of the physical parameters wall temperature, swirl
ratio and global equivalence ratio. The ignition time of n-heptane is shown to be relatively insensitive to variations in
these parametric due to its two-stage ignition behavior. 相似文献
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Y. Tsutsumi A. Iijima K. Yoshida H. Shoji J. T. Lee 《International Journal of Automotive Technology》2009,10(6):645-652
The Homogeneous Charge Compression Ignition (HCCI) engine has attracted much interest because it can simultaneously achieve
high efficiency and low emissions. However, the ignition timing is difficult to control because this engine has no physical
ignition mechanism. In addition, combustion proceeds very rapidly because the premixed mixture ignites simultaneously at multiple
locations in the cylinder, making it difficult to increase the operating load. In this study, an HCCI engine was operated
using blended test fuels comprised of dimethyl ether (DME) and methane, each of which have different ignition characteristics.
The effects of mixing ratios and absolute quantities of the two types of fuel on the ignition timing and rapidity of combustion
were investigated. Cool flame reaction behavior, which significantly influences the ignition, was also analyzed in detail
on the basis of in-cylinder spectroscopic measurements. The experimental results revealed that within the range of the experimental
conditions used in this study, the quantity of DME supplied substantially influenced the ignition timing, whereas there was
little observed effect from the quantity of methane supplied. Spectroscopic measurements of the behavior of a substance corresponding
to HCHO also indicated that the quantity of DME supplied significantly influenced the cool flame behavior. However, the rapidity
of combustion could not be controlled even by varying the mixing ratios of DME and methane. It was made clear that changes
in the ignition timing substantially influence the rapidity of combustion. 相似文献