L51766 Instantaneous Rotational Velocity Development

Considerable effort has been put forth to develop an automated method for balancing the power cylinders of reciprocating integral engines used in the natural gas industry. The benefits to power cylinder balance include reducted emissions and improved cylinder component mechanical integrity (which should lead to reductions in repair costs). The current approach to automate engine balancing uses pressure transducers to measure cylinder pressure, then integrate the signals into the engine fuel /timing management controller to achieve engine balance. Each power cylinder must be instrumented, which quickly leads to an expensive installation package. For large units (12 to 16 power cylinders), the likelihood of transducer failure and / or calibration changes will be problematic to reliable operation of this autobalancing system. A potential alternative to multiple transducers measuring power cylinder pressure is to use a single transducer to measure instantaneous shaft rotational velocity. Instantaneous shaft rotational velocity is driven by engine / compressor torque loads, and therefore is sensitive to changes in both power and compressor cylinder operation. This report summarizes the results of an investigation into the possible use of the flywheel rotational velocity as a surrogate for power cylinder pressure measurements in an autobalancing arrangement, or as a balanced/need-to-balance indicator for integral engines. A fundamental model of the rotational kinetics/dynamics was developed and used to predict the flywheel rotational acceleration. The model was validated and enhanced with data acquired as part of this study. The model was then extended to establish a sensitivity matrix, which established the change in predicted torque as a function of power cylinder imbalance. Using the sensitivity matrix, an algorithm was developed to predict the change in power cylinder peak pressures as a function of the change in the measured shaft rotational velocity.