Cycle-to-cycle variations (CCV) of engine (or other power sources) effective power output is a crucial parameter for engine itself and connecting machines, but limited by the response characteristic of measuring instrument, it is still an unattainable parameter. In the current study, an approach is proposed to estimate the cyclic variations of engine effective power output. We designed two experiment scenarios to measure in-cylinder parameters in cyclic level and engine friction loss. Then, friction loss modeling is calibrated by this experimental data, such that in-cylinder parameters (especially maximal pressure) and engine operating parameters (such as speed) can be integrated into FMEP in cyclic level. Thus, cyclic variation of effective power output can be finally deduced. We found that Chen-Flynn friction loss model can well predict FMEP after careful calibration. The FMEP keeps synchronously with P_max against cycle and FMEP generally decreases cycle fluctuation of BMEP, the average COV of BMEP is lower than that of IMEP by ∼33% and ∼32% at 60% and 100% load, respectively. CCV of BMEP shows nonsynchronous characteristics relative to that of IMEP, this is affected by cycle evolution feature of FMEP. So, CCV of in-cylinder parameters cannot be directly used to assess CCV of effective power output. Finally, when the CCV output is considered in analysis of connecting machines, the transmission accuracy for connecting machines is deteriorated largely, and the vibration and sound will be more intense. Thus, the engine CCV output cannot be ignored in assessment of connecting machines.

发动机（或其他动力源）有效功率输出的周期变化（CCV）是发动机本身和连接机器的关键参数，但受测量仪器响应特性的限制，它仍然是一个无法达到的参数。在当前的研究中，提出了一种估计发动机有效功率输出循环变化的方法。我们设计了两个实验场景来测量循环水平和发动机摩擦损失中的缸内参数。然后，通过这些实验数据校准摩擦损失模型，从而可以将缸内参数（尤其是最大压力）和发动机运行参数（例如速度）循环集成到 FMEP 中。因此，最终可以推导出有效功率输出的循环变化。我们发现 Chen-Flynn 摩擦损失模型经过仔细校准后可以很好地预测 FMEP。FMEP 与 P 保持同步_max against cycle 和 FMEP 通常会降低 BMEP 的循环波动，在 60% 和 100% 负载下，BMEP 的平均 COV 分别比 IMEP 低约 33% 和约 32%。BMEP 的 CCV 表现出相对于 IMEP 的非同步特性，这受 FMEP 循环演化特征的影响。因此，缸内参数的CCV不能直接用于评估有效功率输出的CCV。最后，在连接机分析中考虑CCV输出时，连接机的传动精度大大恶化，振动和声音会更加强烈。因此，在评估连接机器时不能忽略发动机 CCV 输出。