Ammonia Emissions from Combustion in Gasoline Engines
Ammonia Emissions from Combustion in Gasoline Engines
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DOI：
10.4271/2023-01-1655
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发表时间：
2023-10
期刊：
影响因子：
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通讯作者：
A. Bajwa;Varun Shankar;F. Leach
中科院分区：
文献类型：
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作者：
A. Bajwa;Varun Shankar;F. Leach
即将出台的全球排放法规将开始规范轻型车辆的氨排放。目前，大多数轻型车辆由汽油火花点火发动机提供动力。来自这种发动机的氨排放源可以是缸内反应（即燃烧）或穿过后处理装置（特别是三元催化剂）的下游反应。已知后者是汽油车辆氨排放的主要来源，并已进行了广泛的调查。前者（燃烧），较少，因此是这项工作的主题。一个两区热力学火花点火发动机模型与综合化学动力学框架（C3MechV3.3机制），对实验氨排放数据进行验证后，被用来研究氨的形成在燃烧过程中。分析了导致其产生的反应途径，并探讨了改变以下发动机操作和燃烧参数的影响：发动机负荷、燃烧开始、燃烧持续时间、燃料-空气当量比和废气再循环分数。发现氨的产生比其他主要污染物物种的产生慢-在热释放阶段的后期开始，在汽缸压力和温度处于最高值的时刻附近达到峰值，并且在热释放结束之后具有较晚的、延长的生产阶段。氨浓度直到膨胀过程后期才“冻结”。初始氨的生产是由三体基本反应，涉及从燃料的氧化/还原产生的氢自由基驱动，和后期的生产是由H2O与氨基自由基的反应占主导地位。这些生产途径对氨排放的净效应响应于发动机操作的变化是非单调的，并且取决于特定热条件下的主导途径。但是，总体趋势表明，随着发动机负荷的增加、燃烧持续期的缩短、燃烧提前角的提前、混合气浓度的增加以及废气再循环率的降低，排放量增加。
Forthcoming worldwide emissions regulations will start regulating ammonia emissions from light duty vehicles. At present, most light duty vehicles are powered by gasoline spark ignition engines. Sources of ammonia emission from such engines can be in-cylinder reactions (i.e. combustion) or downstream reactions across aftertreatment devices, particularly three-way catalysts. The latter has been known to be a major source of ammonia emissions from gasoline vehicles and has been extensively investigated. The former (combustion), less so, and thus is the subject of this work. A two-zone thermodynamic spark ignition engine model with a comprehensive chemical kinetics framework (C3MechV3.3 mechanism), after being validated against experimental ammonia emissions data, is used to study ammonia formation during combustion. Reaction pathways responsible for its generation are analysed and the effects of changing the following engine operational and combustion parameters are explored: engine load, start of combustion, combustion duration, fuel-air equivalence ratio, and exhaust gas recirculation fraction.Ammonia production was found to be slower than that of other major pollutant species - starting late during the heat release stage, peaking around the time when the cylinder pressures and temperatures were at their highest, and having a late, prolonged production stage after the end of heat release. Ammonia concentrations did not ‘freeze’ until late into the expansion process. Initial ammonia production was driven by three body elementary reactions involving hydrogen radicals produced from the fuel oxidation/reduction, and the late-stage production was dominated by H2O reactions with amino radicals. The net effect of these production pathways on ammonia emissions in response to changes in engine operation was non-monotonic and depended on the dominant pathway at the particular thermal conditions. However, overall trends suggested that emissions increased when engine load increased, combustion duration shortened, combustion timing advanced, fuel-air mixture became richer and exhaust gas recirculation fraction decreased.