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An experimental study of negative valve overlap injection effects and their impact on combustion in a gasoline HCCI engine

机译：汽油HCCI发动机负气门重叠喷射效应及其对燃烧影响的实验研究。

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摘要

This study pertains to negative valve overlap (NVO) phenomena and subsequent combustion of gasoline in a direct injection homogeneous charge compression ignition (HCCI) engine. Experiments were performed at variable valvetrain settings, which resulted in NVO crank angle (CA) values ranging from 157° to 182°. Fuel was injected directly into the cylinder in a single dose applied during the NVO period, and injection timings were varied from the early stage of exhaust compression to the later stage of exhaust expansion. During the experiments, air excess ratio values were varied from a stoichiometric mixture to lean mixtures, limited by misfires occurrence. A Fourier transform infrared analytical system and simple gas sampling method from the intake port were applied in order to analyze changes in fuel composition resulting from the reforming process during the NVO period. As a result of reforming, which took place after fuel injection during exhaust compression, up to 10.2% of fuel carbon was converted into CO carbon. Auto-ignition promoting species were also identified in considerable quantities, where fuel conversion into acetylene was 26.5 g, ethylene - 133.7 g and formaldehyde - 13.5 g per kilogram of fuel. Certain quantities of other light unsaturated hydrocarbons and methane were identified in the fuel as well. Furthermore, reforming products were present in the exhaust gases, where the fractional composition of unburned hydrocarbons was correlated with the composition of reformed fuel after NVO. Also, the influence of both NVO injection timing and air excess ratio on combustion was studied. It was found that retard of fuel injection during exhaust compression advanced combustion timing, while retard of fuel injection during exhaust expansion retarded combustion due to thermal NVO effects. The examination of combustion timings at a variable air excess ratio and two injection strategies: early and late NVO injections, showed the effect of mixture strength and NVO thermochemistry on the main event. At late NVO injection, applied 20 ℃A after top dead center (TDC), the combustion timing was retarded both for the stoichiometric and lean mixtures, due to the mixture strength itself, while for early NVO injection, applied 40 ℃A before TDC, the thermal effects of NVO played a dominant role in combustion control. However, the presence of reforming products in the mixture increased the heat release rate.
机译：这项研究涉及负气门重叠（NVO）现象以及随后在直喷均质充量压缩点火（HCCI）发动机中汽油的燃烧。在可变气门机构设置下进行了实验，这导致NVO曲柄角（CA）值的范围从157°到182°。在NVO期间以单剂量将燃料直接喷射到气缸中，喷射时间从排气压缩的早期到排气膨胀的后期有所变化。在实验过程中，空气过量比值从化学计量的混合物变化为稀薄的混合物，受失火限制。为了分析在NVO期间由于重整过程而产生的燃料成分变化，应用了傅立叶变换红外分析系统和进气口的简单气体采样方法。作为重整的结果，该重整是在排气压缩期间在燃料喷射后进行的，将高达10.2％的燃料碳转化为CO碳。还发现了自燃促进物质，每千克燃料的燃料转化成乙炔的量为26.5克，乙烯为133.7克，甲醛为13.5克。燃料中还发现了一定数量的其他轻质不饱和烃和甲烷。此外，重整产物存在于废气中，其中未燃烧碳氢化合物的分数组成与NVO后重整燃料的组成相关。此外，还研究了NVO喷射正时和空气过量比对燃烧的影响。发现在排气压缩期间的燃料喷射延迟使燃烧正时提前，而在排气膨胀期间的燃料喷射延迟由于热NVO效应而使燃烧延迟。在可变的空气过量比和两种喷射策略下进行的燃烧正时检查：早期和晚期NVO喷射，显示了混合强度和NVO热化学对主要事件的影响。在上死点（TDC）后20℃A处进行NVO后期喷射时，由于混合气本身的影响，化学计量和稀薄混合气的燃烧正时都被延迟，而在NVO早期时，在TDC之前40℃处进行喷射， NVO的热效应在燃烧控制中起主要作用。然而，混合物中重整产物的存在增加了放热速率。

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  • 来源
    《Fuel》 |2014年第ptaa期|236-250|共15页
  • 作者

    Jacek Hunicz;

  • 作者单位

    Institute of Transport, Combustion Engines and Ecology, Lublin University of Technology, Nadbystrzycka 36, 20-618 Lublin, Poland;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    HCCI; Gasoline; Direct injection; Negative valve overlap; Fuel reforming;

    机译：HCCI;汽油;直接注射;负气门重叠;燃料重整;

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