High nitrogen oxide levels of the conventional diesel engine combustion often requires the introduction of exhaust gas recirculation at high engine loads. This can adversely affect the smoke emissions and fuel conversion efficiency associated with a reduction of the in-cylinder air-fuel ratio (lambda). In addition, low exhaust gas temperatures at low engine loads reduce the effectiveness of aftertreatment systems necessary to meet stringent emissions regulations. These are some of the main issues encountered by current heady-duty diesel engines. In this work, variable valve actuation–based advanced combustion control strategies have been researched as means of improving upon the engine exhaust temperature, emissions, and efficiency. Experimental analysis was carried out on a single-cylinder heady-duty diesel engine equipped with a high-pressure common-rail fuel injection system, a high-pressure loop cooled exhaust gas recirculation, and a variable valve actuation system. The variable valve actuation system enables a late intake valve closing and a second intake valve opening during the exhaust stroke. The results showed that Miller cycle was an effective technology for exhaust temperature management of low engine load operations, increasing the exhaust gas temperature by 40 °C and 75 °C when running engine at 2.2 and 6 bar net indicated mean effective pressure, respectively. However, Miller cycle adversely effected carbon monoxide and unburned hydrocarbon emissions at a light load of 2.2 bar indicated mean effective pressure. This could be overcome when combining Miller cycle with a second intake valve opening strategy due to the formation of a relatively hotter in-cylinder charge induced by the presence of internal exhaust gas recirculation. This strategy also led to a significant reduction in soot emissions by 82% when compared with the baseline engine operation. Alternatively, the use of external exhaust gas recirculation and post injection on a Miller cycle operation decreased high nitrogen oxide emissions by 67% at a part load of 6 bar indicated mean effective pressure. This contributed to a reduction of 2.2% in the total fluid consumption, which takes into account the urea consumption in aftertreatment system. At a high engine load of 17 bar indicated mean effective pressure, a highly boosted Miller cycle strategy with exhaust gas recirculation increased the fuel conversion efficiency by 1.5% while reducing the total fluid consumption by 5.4%. The overall results demonstrated that advanced variable valve actuation–based combustion control strategies can control the exhaust gas temperature and engine-out emissions at low engine loads as well as improve upon the fuel conversion efficiency and total fluid consumption at high engine loads, potentially reducing the engine operational costs.

中文翻译：

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用于提高重型柴油机效率和排放控制的基于可变气门驱动的燃烧控制策略

传统柴油发动机燃烧的高氮氧化物水平通常需要在高发动机负载下引入废气再循环。这会对与缸内空燃比 (lambda) 降低相关的烟气排放和燃料转换效率产生不利影响。此外，低发动机负载下的低废气温度会降低满足严格排放法规所需的后处理系统的有效性。这些是当前重型柴油发动机遇到的一些主要问题。在这项工作中，研究了基于可变气门驱动的先进燃烧控制策略，作为改善发动机排气温度、排放和效率的手段。对配备高压共轨燃油喷射系统、高压回路冷却废气再循环和可变气门驱动系统的单缸满负荷柴油发动机进行了实验分析。可变气门致动系统能够在排气冲程期间延迟进气门关闭和第二次打开进气门。结果表明，米勒循环是一种有效的发动机低负荷运行排气温度管理技术，当发动机在 2.2 和 6 bar 净指示平均有效压力下运行时，排气温度分别提高了 40 °C 和 75 °C。然而，米勒循环在 2.2 巴指示平均有效压力的轻负载下对一氧化碳和未燃烧的碳氢化合物排放产生不利影响。由于内部废气再循环的存在导致形成相对较热的缸内充气，因此当将米勒循环与第二个进气门打开策略相结合时，可以克服这一问题。与基准发动机运行相比，该策略还使烟尘排放量显着减少了 82%。或者，在米勒循环操作中使用外部废气再循环和后喷射在 6 巴指示平均有效压力的部分负载下将高氮氧化物排放降低了 67%。考虑到后处理系统中的尿素消耗量，这有助于将总流体消耗量减少 2.2%。在 17 bar 的高发动机负载指示平均有效压力下，带有废气再循环的高度提升的米勒循环策略将燃料转换效率提高了 1.5%，同时将总流体消耗降低了 5.4%。总体结果表明，先进的基于可变气门驱动的燃烧控制策略可以在低发动机负载下控制废气温度和发动机排放，并在高发动机负载下提高燃料转换效率和总流体消耗，潜在地减少发动机运行成本。