Phase-locked masking-based vibration cyclostationarity analysis for wear characterization of cylinder liner-piston ring in simulated ammonia engine environment

Online wear monitoring of the cylinder liner–piston ring (CL-PR) in engines is inherently challenging since friction-induced vibration is masked by reversal impacts and background disturbances. This challenge is further exacerbated in ammonia engines. In this study, a series of experiments were conducted under simulated ammonia-contaminated lubrication conditions, and vibration and friction signals were obtained online. Subsequently, a phase-locked masking method was proposed to extract the sliding region vibration signal, and second-order cyclostationary behavior was quantified using the indicator of cyclostationarity (ICS2). Combining the 1/3-binary tree filter bank with ICS2 to select the optimal frequency band, the cyclic modulation intensity associated with the reciprocating motion period in the vibration signal was quantitatively characterized. Results show that the ICS2 of the sliding region signal is sensitive to lubricant degradation and shows a positive linear fitting relationship with wear volume (R 2 = 0.7887), with a higher fitting performance than conventional indicators such as RMS and kurtosis. The proposed method suppresses reversal region interference and highlights friction-induced periodic modulation in the sliding region. These results provide a potential characteristic parameter and an analytical basis for future online vibration monitoring of abnormal CL-PR wear in ammonia engines.