Combustion Stability of Offshore Gas Motor Compressors Operating on Associated Petroleum Gas

Reliable combustion is essential for the efficient and reliable operation of aging offshore gas motor compressors fueled by associated petroleum gas (APG). This study investigated the combined influence of fuel composition, scavenging-air pressure, and compressor loading on combustion stability under real industrial conditions. Operational data were obtained from four low-speed 10GKNAM gas motor compressors operating on APG with elevated heavy-hydrocarbon content. Fuel composition was determined by gas chromatography, while combustion stability was evaluated using exhaust-gas temperatures measured in all engine cylinders together with scavenging-air pressure and compressor loading. Two dimensionless diagnostic indicators, the Combustion Stability Index (CSI) and the Temperature Dispersion Coefficient (TDC), were developed using routinely monitored operating parameters, providing a practical combustion-diagnostic approach without additional instrumentation. Although the investigated fuel exhibited increased combustion reactivity, fuel composition did not account for the observed differences in combustion stability because all compressors operated on essentially identical APG. Instead, scavenging-air pressure was identified as the dominant operational factor, whereas higher compressor loading provided an additional stabilizing effect. Increased scavenging-air pressure reduced exhaust-gas temperature dispersion and improved combustion uniformity, whereas the influence of compressor loading became more pronounced under adequate scavenging conditions. The proposed methodology provides a practical basis for quantitative combustion assessment using existing industrial monitoring systems and may support condition-based maintenance, operational optimization, and future development of predictive combustion-diagnostic approaches for aging offshore gas motor compressors.