Compensation for the differences in LHV of diesel-OME blends by using injector nozzles with different number of holes: Emissions and combustion
Compensation for the differences in LHV of diesel-OME blends by using injector nozzles with different number of holes: Emissions and combustion
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DOI：
10.1016/j.fuel.2019.116166
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发表时间：
2020
期刊：
影响因子：
7.4
通讯作者：
M. Parravicini;C. Barro;K. Boulouchos
中科院分区：
文献类型：
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作者：
M. Parravicini;C. Barro;K. Boulouchos
减少颗粒物质（PM）排放已成为压缩点火（CI）发动机发展的一个重要课题。采用微粒捕集器（DPF）对废气进行后处理，取得了良好的效果。然而，反压力和再生的必要性导致燃料消耗和运营成本的增加。降低这一成本的一个可能的策略是通过使用含氧燃料来减少发动机废气的PM水平。这种解决方案减少了排气中的背压，也减少了昂贵的燃料再生事件。本文在一台单缸、直喷、四冲程重型柴油机上，研究了两种由柴油和聚氧亚甲基二甲醚（OME、POMDME或PODE）组成的不同混合物在燃烧和排放方面的性能。为了尽量减少对燃烧特性的影响（即点火延迟，预混和扩散燃烧部分等），通过增加喷油器喷嘴孔数来补偿混合燃料与柴油相比的较小热值。选择这种策略是为了避免由于延长喷射时间、增加燃油压力或增加喷嘴直径而对排放造成的影响。总共测试了三种不同数量的喷嘴孔，一种是参考柴油壳体（7孔），另两种是不同的混合物（8孔，约22% OME； 9孔，约42% OME）。结果表明，随着OME比例的增加，扩散燃烧速率加快，指示比油耗（- 5.7%）得到改善。此外，主要由于减少了高达90%的烟尘排放，氮氧化物和烟尘的权衡也得到了改善。氧化程度越低，NOx排放量越低，而氧化程度越高，NOx排放量越高。这种行为归因于更快的燃烧，这一方面减少了形成NOx的停留时间，另一方面提高了温度，这再次增强了NOx的形成。研究更短的停留时间和更高的温度之间的权衡只能在不同燃料之间恒定的喷射参数（喷射能量、燃油压力和喷射持续时间）下进行。
The reduction of particulate matter (PM) emissions has become a major topic in the development of compression ignition (CI) engines. The aftertreatment of exhaust gases by means of particulate traps (DPF) has given promising results in terms of effectiveness. However, the backpressure and necessity to regenerate causes an increase in fuel consumption and operational cost. A possible strategy to reduce this cost is the abatement of PM levels of engine out exhaust gases by employing oxygenated fuels. This solution reduces the backpressure in the exhaust as well as fuel expensive regeneration events. In the present work the performances, in terms of combustion and emissions, of two different blends composed of diesel and a mixture of polyoxymethylene dimethyl ether (OME, POMDME or PODE) were investigated in a single-cylinder, direct injection, 4-stroke, heavy duty diesel engine. In order to minimize the influence on combustion characteristics (i.e. ignition delay, premixed and diffusion combustion portion, etc.), the compensation for the smaller caloric value of the blends in comparison to diesel was performed with an increased number of injector nozzles holes. This strategy was chosen to avoid effects on emissions caused by a prolonged duration of injection, increased fuel pressure or increased nozzle diameter. In total three different number of nozzle holes were tested with a reference diesel case (7-hole) and two with according blends (8-hole, ca. 22% OME; 9-hole, ca. 42% OME). The results show an acceleration of the diffusion combustion rate and the resulting improvements in the indicated specific fuel consumption (−5.7%) with increasing OME portion. In addition, mainly due to a reduction of up to 90% of the soot emissions, the NOx-soot trade-off improved as well. The NOx emissions showed decreased values for the less oxygenated, and increased values for the stronger oxygenated blend. This behaviour is attributed to the faster combustion, which, on the one hand reduces the residence time to form NOx and on the other hand increases the temperature, which enhances NOx formation again. The investigation of the trade-off between shorter residence time and higher temperature can only be performed with constant injection parameters (injected energy, fuel pressure and duration of injection) among the different fuels.