共查询到20条相似文献,搜索用时 15 毫秒
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C. B. Yin Z. D. Zhang N. L. Xie Y. D. Sun T. Sun 《International Journal of Automotive Technology》2016,17(4):591-604
In this paper, knocking combustion in dual-fuel diesel engine is modeled and investigated using the CFD code coupled with detailed chemical kinetics. The ethanol/gasoline blend E85 is used as the primary fuel in a dual-fuel combustion concept based on a light-duty diesel engine equipped with a common-rail injection system. The E85 blend is injected and well mixed with intake air in the intake manifold and is ignited by the direct injection diesel fuel. A 46-species, 187-reaction Multicomponent mechanism is adopted to model the auto-ignition process of the E85/air/diesel mixture ahead of the flame front. Based on the model validation, knocking combustion under boost and full load operating condition for 0 %, 20 %, 50 %, as well as 70 % E85 substitute energy is simulated. The effects of E85 substitute rate and two stage injection strategies on knock intensity, power output, as well as location of the auto-ignition initiation is clearly reproduced by the model. The calculation result shows that, for a high E85 rate of 50 % and 70 % with single injection strategies, the most serious knock and the origin of auto-ignition always occurs far away from where the flame of diesel spray is first generated, at the center of combustion chamber, due to higher pressure wave, relatively richer E85 mixture and longer distances of flame propagation. The two stage injection strategies with a small amount of diesel pilot injection ahead of the main injection primarily influence the ignition behavior of the directly injected fuel, leads to a lower pressure rise rate and a reduced propagation distance, both of which contribute to the attenuation of knock intensity for a higher E85 rate. 相似文献
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《JSAE Review》1998,19(4):319-327
This study aimed to reduce NOx and soot by creating a more homogeneous lean fuel distribution in a diesel spray using high-pressure fuel injection and a micro-hole nozzle. This injection system shortened the ignition delay, but a homogeneous lean fuel distribution in the diesel spray was not achieved. Using a lower cetane number fuel, the resulting longer ignition delay made a uniform, lean fuel distribution in the diesel spray possible with this injection system. Ignition and combustion were analyzed by the combustion chamber pressure history, and flame temperatures and KL values were analyzed by the two-color method. 相似文献
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J. Lee S. Choi H. Kim D. Kim H. Choi K. Min 《International Journal of Automotive Technology》2013,14(4):551-558
Recent studies on dual-fuel combustion in compression-ignition (CI) engines, also known as diesel engines, fall into two categories. In the first category are studies focused on the addition of small amounts of gaseous fuel to CI engines. In these studies, gaseous fuel is regarded as a secondary fuel and diesel fuel is regarded as the main fuel for combustion. The objectives of these studies typically involve reducing particulate matter (PM) emissions by using gaseous fuel as a partial substitution for diesel fuel. However, the addition of gaseous fuel raises the combustion temperature, which increases emissions of nitrogen oxides (NOx). In the second category are studies focused on reactivity-controlled compression-ignition (RCCI) combustion. RCCI combustion can be implemented by early diesel injection with a large amount of low-reactivity fuel such as gasoline or gaseous fuel. Although RCCI combustion promises lower NOx and PM emissions and higher thermal efficiency than conventional diesel combustion, it requires a higher intake pressure (usually more than 1.7 bars) to maintain a lean fuel mixture. Therefore, in this study, practical applications of dual-fuel combustion with a low air-fuel ratio (AFR), which implies a low intake pressure, were systemically evaluated using propane in a diesel engine. The characteristics of dualfuel combustion for high and low AFRs were first evaluated. The proportion of propane used for four different operating conditions was then increased to decrease emissions and to identify the optimal condition for dual-fuel combustion. Although the four operating conditions differ, the AFR was maintained at 20 (? approximately equal to 0.72) and the 50% mass fraction burned (MFB 50) was also fixed. The results show that dual-fuel combustion can reduce NOx and PM emissions in comparison to conventional diesel combustion. 相似文献
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C. W. Park H. C. Oh S. D. Kim H. S. Kim S. Y. Lee C. S. Bae 《International Journal of Automotive Technology》2014,15(4):525-533
To comply with reinforced emission regulations for harmful exhaust gases, including carbon dioxide (CO2) emitted as a greenhouse gas, improved technologies for reducing CO2 and fuel consumption are being developed. Stable lean combustion, which has the advantage of improved fuel economy and reduced emission levels, can be achieved using a sprayguided-type direct-injection (DI) combustion system. The system comprises a centrally mounted injector and closely positioned spark plugs, which ensure the combustion reliability of a stratified mixture under ultra-lean conditions. The aim of this study is to investigate the combustion and emission characteristics of a lean-burn gasoline DI engine. At an excess air ratio of 4.0, approximately 23% improvement in fuel economy was achieved through optimal event timing, which was delayed for injection and advanced for ignition, compared to that under stoichiometric conditions, while NOx and HC emissions increased. The combustion characteristics of a stratified mixture in a spray-guided-type DI system were similar to those in DI diesel engines, resulting in smoke generation and difficulty in three-way catalystutilization. Although a different operating strategy might decrease fuel consumption, it will not be helpful in reducing NOx and smoke emissions; therefore, alternatives should be pursued to achieve compliance with emission regulations. 相似文献
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《JSAE Review》1998,19(4):305-310
An instrument to measure time-resolved fuel–air ratio in the vicinity of a spark plug was developed. Properties of absorption and scattering at the wavelengths of visible and infrared rays were utilized to determine the fuel–air ratio in the mixture including liquid and vaporized fuel. The measurement error of the instrument was within 10% as a result of comparison between the overall and the measured fuel–air ratio at the vicinity of the spark plug under the inlet port injection, which forms a relatively homogeneous mixture. The instrument was applied to a direct injection gasoline engine and the mixture formation process was clarified. 相似文献
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针对二甲醚燃料饱和蒸气压高、黏度低、易与空气形成混合气等特性,开发了低压共轨燃油系统。主要进行了系统的总体设计、电子控制单元(ECU)的软硬件开发和在油泵台架上的试验。试验结果表明,在新开发系统的驱动下,喷油器启合及时,喷射有力,雾化效果好;并获取供油量的MAP图,实现了对喷油量和喷油定时的外触发、外同步的反馈控制。 相似文献
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柴油微引燃乙醇发动机采用进气道喷射乙醇、缸内直喷微量柴油引燃的方式进行燃料供给。基于单缸四冲程柴油机,对其燃烧、性能及排放特性进行研究,固定引燃柴油喷射量为发动机能实现压燃着火的最小值,在进气压力为0.15 MPa时比较不同乙醇喷射量的工况组,通过改变柴油喷射时刻进行工况扫描。结果表明,引燃柴油的喷射时刻对发动机的燃烧、性能和排放影响显著。柴油微引燃乙醇发动机在中高负荷能够稳定运行,指示热效率可达34%以上,通过适当调节柴油喷射时刻,可以有效控制未燃碳氢(UHC)、NO_x与CO排放,同时可以实现极低的炭烟排放。柴油微引燃乙醇发动机燃烧模式为预混合或部分预混合燃烧,燃烧有两阶段放热特征,改变引燃柴油喷射时刻,可以有效控制燃烧相位。 相似文献
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B. H. Lee J. H. Song Y. J. Chang C. H. Jeon 《International Journal of Automotive Technology》2010,11(6):783-791
The diesel combustion process is highly dependent on fuel injection parameters, and understanding fuel spray development is
essential for proper control of the process. One of the critical factors for controlling the rate of mixing of fuel and air
is the number of injector holes in a diesel engine. This study was intended to explore the behavior of the formation of spray
mixtures, combustion, and emissions as a function of the number of injector hole changes; from this work, we propose an optimal
number of holes for superior emissions and engine performance in diesel engine applications. The results show that increasing
the number of holes significantly influences evaporation, atomization, and combustion. However, when the number of holes exceeds
a certain threshold, there is an adverse effect on combustion and emissions due to a lack of the air entrainment required
for the achievement of a stoichiometric mixture. 相似文献
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《JSAE Review》1999,20(1):31-39
In a direct injection gasoline engine, in order to achieve good stratified combustion, an extremely advanced control of air–fuel mixture is required. For this purpose, the method of diagnosing the quality of the state of mixture formation in combustion chambers becomes necessary. In this research, the state of air–fuel mixture in the combustion chamber of a TOYOTA D-4 was analyzed in space and time by visualization, A/F multi-point measurement and A/F high response measurement, and thus the effects that injection timing, swirl and fuel pressure exerted on mixture formation were elucidated. 相似文献
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利用三维仿真软件Ansys Fluent建立了GDI汽油机的仿真计算模型,就变气门升程耦合不同喷油策略对缸内气流运动和混合气形成的影响进行了模拟计算。结果表明,与大气门升程工况相比,小气门升程工况的缸内湍流运动强度、燃油蒸发和湿壁情况以及点火时刻混合气质量都明显改善;在小气门升程工况,采用两段喷油会缩短油气混合时间,过度推迟二次喷油时刻会恶化混合气质量和燃油湿壁情况;在大气门升程工况,两段喷油会改善混合气均匀性,随着二次喷油时刻推迟,燃油蒸发量增加,湿壁情况加剧,混合气质量得到改善;小气门升程工况下采用二次喷油时刻为470°曲轴转角,前后两次喷油量比例为7∶3的两段喷油方案在燃油蒸发和湿壁以及点火时刻缸内混合气质量这几个方面的效果都很好,是最合理的方案。 相似文献
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U. Egüz N. C. J. Maes C. A. J. Leermakers L. M. T. Somers L. P. H. De Goey 《International Journal of Automotive Technology》2013,14(5):693-699
The objective of new combustion concepts is to meet emission standards by improving fuel air mixing prior to ignition. Since there is no overlap between injection and ignition, combustion is governed mainly by chemical kinetics and it is challenging to control the phasing of ignition. Reactivity Controlled Compression Ignition (RCCI) combustion aims to control combustion phasing by altering the fuel ratios of the high- and low octane fuel and injection timings. In this study the dual fuel blend is prepared with gasoline and diesel fuels. The applied injection timings of the diesel are very early (90 to 60° CA bTDC). In the detailed reaction mechanism, n-heptane and iso-octane represent diesel and gasoline fuel, respectively. A multi-zone model approach is implemented to perform RCCI combustion simulation. Ignition characteristics are analyzed by using CA50 as the main parameter. In the experiments for the early direct injection (DI) timing advancing the injection time results in a later ignition. Qualitatively, the trend effect of the diesel injection timing and the effect of the ratio gasoline/diesel are captured accurately by the multi-zone model. 相似文献