Abstract: Aiming at the prediction of engine removal time，the engine performance deterioration was studied. Based on the engine gas temperature margin （EGTM） data， a stochastic Wiener model was established， and the severity factor was used to modify the model to characterize the effects of different operating conditions on an engine. The model parameters were worked out by expectation maximum （EM） algorithm combined with Bayes theorem， and finally the average engine removal time was obtained based on the engine performance deterioration. The results show that on the operation condition of severity factor of 1.2696， the average engine removal time caused by performance deterioration of a type engine is 8219 cycles. And， the error between the average engine removal interval estimated by this model and that recommended by the engine manufacturer is 1.7%.

Key words: Aeroengines;Wiener process;Severity factor;Performance deterioration;Engine gas temperature margin

摘要： 针对发动机下发间隔预测的问题，研究了发动机性能衰退规律。基于发动机排气温度裕度（EGTM）数据，建立了随机维纳模型，并使用严酷度因子修正模型，表征不同的工作条件对发动机的影响。利用期望最大化（EM）算法结合贝叶斯定理，对模型参数求解，最终得到了基于性能衰退的发动机平均下发间隔。研究结果表明，在严酷度因子为1.2696的使用条件下，某型号航空发动机性能衰退平均下发间隔为8219循环；基于该模型预测的发动机平均下发间隔与厂商建议的下发时间之间的误差仅为1.7%。

关键词: 航空发动机;维纳过程;严酷度因子;性能衰退;发动机排气温度裕度