Accurate prediction of in-cylinder heat transfer processes within internal combustion engines (ICEs) requires a comprehensive understanding of the boundary layer effects in the near-wall region (NWR). This study investigates near-wall temperature fluctuations of an optical reciprocating engine using a combined approach of planar laser-induced fluorescence (PLIF) thermometry and numerical conjugate heat transfer modeling. Single-line excitation of toluene and subsequent one-color emission detection is employed for PLIF thermometry, while large-eddy simulations (LES) using commercial CFD software (CONVERGE v2.4.18) is utilized for modeling. The PLIF signal is calibrated to predicted in-cylinder temperatures from a GT-POWER simulation, and precision uncertainty of temperature is found to be ±1.5 K within the calibration region. Near-wall temperature fluctuations are determined about the multi-cycle mean, and the development of thermal stratification is captured in the NWR under motored and fired conditions during the compression stroke. Regions of the largest cycle-to-cycle temperature fluctuations are identified closer to the in-cylinder head surface indicating the unsteadiness of the thermal boundary layer. Analysis includes an assessment of cyclic variability of near-wall temperature fluctuation, and the effects of compression on temperature fluctuations. Additionally, thermal stratification is found to be similar under motored and fired conditions before ignition timing. Lastly, spatial correlation analysis of temperature fluctuations is performed in the wall-normal direction, and it reveals higher correlations under fired conditions. Spatial correlations experience an initial drop outside of the buffer layer in the NWR, and the location of the drop is well captured in the simulations. Analysis of fluctuating temperatures needs to be extended to fluctuations about the spatial average temperature which directly affects the spatial thermal gradients relevant to engine heat transfer.

内燃机（ICE）内缸内传热过程的准确预测需要全面了解近壁区域（NWR）中的边界层效应。这项研究使用平面激光诱导荧光（PLIF）测温和数值共轭传热建模相结合的方法，研究了光学往复式发动机的近壁温度波动。PLIF测温采用甲苯的单线激发和随后的单色发射检测，而使用商用CFD软件（CONVERGE v2.4.18）的大涡模拟（LES）进行建模。通过GT-POWER仿真将PLIF信号校准为预测的缸内温度，发现校准区域内温度的精度不确定度为±1.5K。确定多壁均值附近的近壁温度波动，并在压缩冲程期间在机动和燃烧条件下在NWR中捕获热分层的发展。循环温度波动最大的区域被识别为更靠近缸盖表面，表明热边界层不稳定。分析包括评估近壁温度波动的周期性变化，以及压缩对温度波动的影响。另外，发现在点火正时之前的机动和点火条件下，热分层是相似的。最后，在壁法线方向上进行了温度波动的空间相关性分析，它揭示了在燃烧条件下的较高相关性。空间相关性在NWR的缓冲层外部经历了初始下降，并且在模拟中可以很好地捕获到下降的位置。波动温度的分析需要扩展到关于空间平均温度的波动，该波动会直接影响与发动机传热相关的空间热梯度。