Accurate predictions of low-temperature heat release (LTHR) are critical for modeling auto-ignition processes in internal combustion engines. While LTHR is typically obscured by deflagration, extremely late ignition phasing can lead to LTHR prior to the spark, a behavior known as pre-spark heat release (PSHR). In this research, PSHR in a boosted direct-injection spark-ignition engine was studied using 3-D computational fluid dynamics (CFD) and detailed chemical kinetics. The turbulent combustion was modeled via a hybrid approach that incorporates the G-equation model for tracking the turbulent flame front, and the well-stirred reactor model with detailed chemistry for assessing the low-temperature reactions in unburnt gas. Simulations were conducted using Co-Optima alkylate and E30 fuels at operating conditions characterized by different PSHR intensities. The predicted in-cylinder pressure and heat release rate were found to agree well with experiments. It was found the estimate of previous-cycle trapped residuals is of utmost importance for capturing PSHR correctly. A simulation best practice was developed which keeps the detailed chemistry solver active throughout the entire simulation, allowing to track the evolution of intermediate species from one cycle to the next. Following the validation, the dynamics of PSHR were analyzed in detail employing the pressure-temperature (P-T) trajectory framework. It was shown that PSHR correlated with the first-stage ignition delay of the fuel, hence showing close relation to the in-cylinder P-T trajectory and the chemical kinetics. Besides, it was indicated that LTHR is a self-limiting process that has the effect of attenuating the thermal stratification in the combustion chamber. Furthermore, it was observed the occurrence of PSHR caused the P-T trajectory of end-gas to overlap with the negative temperature coefficient region of the fuel’s ignition-delay maps. This effect was more significant in the fuel-rich regions where engine knock tendency would be generally higher, with potential implications on knock control and mitigation.

低温放热 (LTHR) 的准确预测对于模拟内燃机中的自燃过程至关重要。虽然 LTHR 通常会被爆燃掩盖，但极晚的点火定相会导致 LTHR 在火花之前出现，这种行为称为预火花放热 (PSHR)。在这项研究中，使用 3-D 计算流体动力学 (CFD) 和详细的化学动力学研究了增压直喷火花点火发动机中的 PSHR。湍流燃烧是通过混合方法模拟的，该方法结合了G- 用于跟踪湍流火焰前沿的方程模型，以及带有详细化学成分的充分搅拌反应器模型，用于评估未燃烧气体中的低温反应。在以不同 PSHR 强度为特征的操作条件下，使用 Co-Optima 烷基化物和 E30 燃料进行了模拟。发现预测的缸内压力和放热率与实验非常吻合。发现前一周期被困残差的估计对于正确捕获 PSHR 至关重要。开发了一种模拟最佳实践，在整个模拟过程中保持详细的化学求解器处于活动状态，从而可以跟踪中间物种从一个循环到下一个循环的演变。验证通过后，使用压力-温度 (PT) 轨迹框架详细分析了 PSHR 的动力学。结果表明，PSHR 与燃料的第一阶段点火延迟相关，因此与缸内 PT 轨迹和化学动力学密切相关。此外，还表明 LTHR 是一种自限过程，具有减弱燃烧室热分层的作用。此外，观察到 PSHR 的发生导致尾气的 PT 轨迹与燃料点火延迟图的负温度系数区域重叠。这种影响在发动机爆震倾向通常较高的富燃料区域更为显着，对爆震控制和缓解具有潜在影响。结果表明，PSHR 与燃料的第一阶段点火延迟相关，因此与缸内 PT 轨迹和化学动力学密切相关。此外，还表明 LTHR 是一种自限过程，具有减弱燃烧室热分层的作用。此外，观察到 PSHR 的发生导致尾气的 PT 轨迹与燃料点火延迟图的负温度系数区域重叠。这种影响在发动机爆震倾向通常较高的富燃料区域更为显着，对爆震控制和缓解具有潜在影响。结果表明，PSHR 与燃料的第一阶段点火延迟相关，因此与缸内 PT 轨迹和化学动力学密切相关。此外，还表明 LTHR 是一种自限过程，具有减弱燃烧室热分层的作用。此外，观察到 PSHR 的发生导致尾气的 PT 轨迹与燃料点火延迟图的负温度系数区域重叠。这种影响在发动机爆震倾向通常较高的富燃料区域更为显着，对爆震控制和缓解具有潜在影响。表明 LTHR 是一种自限性过程，具有减弱燃烧室中热分层的作用。此外，观察到 PSHR 的发生导致尾气的 PT 轨迹与燃料点火延迟图的负温度系数区域重叠。这种影响在发动机爆震倾向通常较高的富燃料区域更为显着，对爆震控制和缓解具有潜在影响。表明 LTHR 是一种自限性过程，具有减弱燃烧室中热分层的作用。此外，观察到 PSHR 的发生导致尾气的 PT 轨迹与燃料点火延迟图的负温度系数区域重叠。这种影响在发动机爆震倾向通常较高的富燃料区域更为显着，对爆震控制和缓解具有潜在影响。