Cycle-to-cycle combustion variability in spark-ignition engines during normal operation is mainly caused by random perturbations of the in-cylinder conditions such as the flow velocity field, homogeneity of the air-fuel distribution, spark energy discharge, and turbulence intensity of the flame front. Such perturbations translate into the variability of the energy released observed at the end of the combustion process. During normal operating conditions, the cycle-to-cycle variability (CCV) of the energy release behaves as random uncorrelated noise. However, during diluted combustion, in either the form of exhaust gas recirculation (EGR) or excess air (lean operation), the CCV tends to increase as dilution increases. Moreover, when the ignition limit is reached at high dilution levels, the combustion CCV is exacerbated by sporadic occurrences of incomplete combustion events, and the uncorrelation assumption no longer holds. The low or null energy released by partial burns and misfires has an impact on the following combustion event due to the residual gas that carries burned and unburned gases, which contributes to the deterministic coupling between engine cycles. Many residual gas fraction estimation methods, however, only address the nominal case where complete combustion occurs and combustion events are uncorrelated. This study evaluates the efficacy of such methods on capturing the effects of partial burns and misfires on the residual gas estimate for high-EGR operation. The advantages and disadvantages of each method are discussed based on their ability to generate cycle-to-cycle estimates. Finally, a comparison between the different estimation techniques is presented based on their usefulness for control-oriented modeling.

火花点火发动机在正常运行期间的逐周期燃烧变化主要是由缸内条件的随机扰动引起的，例如，流场，空气燃料分布的均匀性，火花能量的排放以及燃料的湍流强度。火焰锋。这种扰动转化为在燃烧过程结束时观察到的释放能量的可变性。在正常运行条件下，能量释放的周期变化（CCV）表现为随机的不相关噪声。但是，在稀薄燃烧期间，以废气再循环（EGR）或过量空气（稀薄运行）的形式，CCV会随着稀薄度的增加而增加。此外，在高稀释水平下达到点火极限时，零星发生的不完全燃烧事件加剧了CCV燃烧，并且不相关假设不再成立。由于残留气体携带着已燃烧和未燃烧的气体，部分燃烧和不点火释放的低能量或零能量会对随后的燃烧事件产生影响，这有助于发动机循环之间的确定性耦合。然而，许多残余气体分数估计方法仅解决发生完全燃烧且燃烧事件不相关的标称情况。这项研究评估了这些方法在捕获部分燃烧和不点火对高EGR运行估计的残留气体的影响方面的功效。基于每种方法生成周期估算的能力，讨论了每种方法的优缺点。最后，