The short circuit of fresh air is a more and more extended strategy to deal with low-end torque issues, very common in small turbocharged and spark-ignited four-stroke engines. Therefore, from the author’s point of view, it is interesting to check whether the after-treatment system can work properly under these conditions. In the present study, the effect of the fresh air short-circuit on engine emissions has been assessed through its impact on the wideband λ sensor and the three-way catalyst behaviour, which are the key elements of the fuel-to-air ratio control strategy. In particular, the analysis of the sensor dynamic response shows that the λ sensor overestimates the fuel-to-air ratio under short-circuit conditions. The sensor overestimation leads the actual fuel-to-air ratio out of the proper three-way catalyst window; in this sense, results show a non-negligible emissions increase, especially in terms of NOx. Regarding the impact on the three-way catalyst behaviour, the study shows how short-circuit pulses change the exhaust gas composition for a given fuel-to-air ratio at catalyst inlet, which also contributes to a penalty in the three-way catalyst efficiency.

中文翻译：

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短路对火花点火发动机后处理和空燃比控制的影响

新鲜空气短路是处理低端扭矩问题的越来越广泛的策略，在小型涡轮增压和火花点火四冲程发动机中很常见。因此，从作者的角度来看，检查后处理系统在这些条件下是否能正常工作是很有趣的。在本研究中，新鲜空气短路对发动机排放的影响已通过其对宽带 λ 传感器和三元催化剂行为的影响进行评估，这是燃料空气比控制的关键要素战略。特别是，传感器动态响应的分析表明，λ传感器高估了短路条件下的燃料空气比。传感器高估导致实际燃料空气比超出适当的三元催化剂窗口；在这个意义上，结果显示排放增加不可忽视，尤其是在氮氧化物方面。关于对三元催化剂行为的影响，该研究显示了在催化剂入口处，对于给定的燃料空气比，短路脉冲如何改变废气成分，这也有助于降低三元催化剂的效率.