Exhaust gas recirculation (EGR) technology can be used in internal combustion engines to reduce NOx emission and improve fuel economy. However, it also affects the end-gas autoignition and engine knock since NOx in EGR can promote ignition. In this study, effects of NOx addition on autoignition and detonation development in dimethyl ether (DME)/air mixture under engine-relevant conditions are investigated. Numerical simulation considering both low-temperature and high-temperature chemistry is conducted. First the kinetic effects of NOx addition on the negative temperature coefficient (NTC) regime are assessed and interpreted. It is found that NOx addition greatly promotes both low-temperature and high-temperature ignition stages mainly through increasing OH production. Then the autoignitive reaction front propagation induced by either local NO accumulation or a cold spot within NTC regime with different amounts of NO addition is investigated. For the first time, supersonic autoignition modes including detonation induced by local NO accumulations are identified. This indicates that local accumulation of NOx in end gas might induce super-knock in engines with EGR. A new parameter quantifying the ratio of sound speed to average reaction front propagation speed is introduced to identify the regimes for different autoignition modes. Compared to the traditional counterpart parameter used in previous studies, this new parameter is more suitable since it yields a detonation development regime in a C-shaped curve which is almost unaffected by the initial conditions. The results in this study may provide fundamental insights into knocking mechanism in engines using EGR technology.

排气再循环（EGR）技术可用于内燃机，以减少NOx排放并提高燃油经济性。但是，由于EGR中的NOx会促进点火，因此也会影响终端气体的自动点火和发动机爆震。在这项研究中，研究了在发动机相关条件下，NOx添加对二甲醚（DME）/空气混合物中自燃和爆轰发展的影响。进行了同时考虑低温和高温化学性质的数值模拟。首先，评估和解释NOx添加对负温度系数（NTC）的动力学影响。发现添加NOx主要通过增加OH的产生极大地促进了低温和高温点火阶段。然后研究了由不同浓度的NO引起的NTC区域内局部NO积累或冷点引起的自燃反应前沿传播。首次确定了包括局部NO累积引起的爆轰在内的超音速自燃模式。这表明，最终气体中NOx的局部积累可能会在具有EGR的发动机中引起超爆震。引入了量化声速与平均反应前沿传播速度之比的新参数，以识别不同自燃模式的状态。与先前研究中使用的传统对应参数相比，此新参数更合适，因为它在C形曲线中产生了几乎不受初始条件影响的爆轰发展机制。