Fuels, Engines, and Emissions Research Center, Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
Fuels, Engines, and Emissions Research Center, Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Philos Trans A Math Phys Eng Sci. 2015 Feb 13;373(2034). doi: 10.1098/rsta.2014.0088.
Spark-ignited internal combustion engines have evolved considerably in recent years in response to increasingly stringent regulations for emissions and fuel economy. One new advanced engine strategy ustilizes high levels of exhaust gas recirculation (EGR) to reduce combustion temperatures, thereby increasing thermodynamic efficiency and reducing nitrogen oxide emissions. While this strategy can be highly effective, it also poses major control and design challenges due to the large combustion oscillations that develop at sufficiently high EGR levels. Previous research has documented that combustion instabilities can propagate between successive engine cycles in individual cylinders via self-generated feedback of reactive species and thermal energy in the retained residual exhaust gases. In this work, we use symbolic analysis to characterize multi-cylinder combustion oscillations in an experimental engine operating with external EGR. At low levels of EGR, intra-cylinder oscillations are clearly visible and appear to be associated with brief, intermittent coupling among cylinders. As EGR is increased further, a point is reached where all four cylinders lock almost completely in phase and alternate simultaneously between two distinct bi-stable combustion states. From a practical perspective, it is important to understand the causes of this phenomenon and develop diagnostics that might be applied to ameliorate its effects. We demonstrate here that two approaches for symbolizing the engine combustion measurements can provide useful probes for characterizing these instabilities.
近年来，火花点火式内燃机为了应对排放和燃油经济性日益严格的法规，已经有了很大的发展。一种新的先进发动机策略利用高水平的废气再循环（EGR）来降低燃烧温度，从而提高热力学效率并减少氮氧化物排放。虽然这种策略非常有效，但由于在足够高的 EGR 水平下会产生大量的燃烧振荡，因此也带来了重大的控制和设计挑战。以前的研究已经证明，燃烧不稳定性可以通过反应性物种和在保留的残余废气中的热能在单个气缸中的自生成反馈在连续的发动机循环之间传播。在这项工作中，我们使用符号分析来描述在使用外部 EGR 的实验发动机中多缸燃烧振荡。在低水平的 EGR 下，缸内振荡清晰可见，似乎与气缸之间短暂的间歇性耦合有关。随着 EGR 的进一步增加，达到了一个点，其中四个气缸几乎完全锁定在相位上，并同时在两个不同的双稳态燃烧状态之间交替。从实际的角度来看，了解这种现象的原因并开发可能用于改善其效果的诊断方法非常重要。我们在这里证明，两种用于符号化发动机燃烧测量的方法可以为表征这些不稳定性提供有用的探针。
