Methane emissions from over 7000 large-bore natural gas engines used for gas compression in the United States result from combustion inefficiency and the escape of unburned methane through the crevices. Methane is a strong greenhouse gas with a warming potential 28 times that of carbon dioxide. The Inflation Reduction Act passed by the Biden administration in 2022 imposes a methane “waste” fee that accumulates yearly to invest in clean energy and climate action starting in 2024. This study aims to reduce the amount of methane emissions from large bore engines through fuel injection techniques, thereby advancing sustainable energy development. The strategies explored investigate fuel injection pressure and timing optimization, crankcase methane emissions quantification and mitigation, and ring-pack methane quantification. While varying injection pressures and injection timing on the engine, the performance and methane emission characteristics were measured. Also, a model of the engine was created for computational fluid dynamics (CFD) simulations using CONVERGE Studio v 3.0. Experimental results showed that methane emissions are minimized with late-cycle fuel injection at 500 psi and 100 degrees BTDC. Computational results showed that the ring pack contributes up to 34% of methane emissions in the large bore engine model.

The diagnostic merits of high-speed (HS) exhaust gas temperature and pressure measurements for indexing engine stability and identifying abnormal combustion cycles are explored through experimental investigations on a low speed, single-cylinder engine. Exhaust temperature and pressure are measured using a fine wire 50 μm thermocouple and a piezoresistive pressure transducer, respectively. Synchronously recorded cylinder pressure data is used to continuously index combustion variations, and then anomalous combustion event detection and engine stability monitoring are attempted using HS exhaust temperature and pressure measurements. Two types of abnormal combustion cycles, namely, misfiring and overload cycles are used to typify low and high intensity anomalous combustion cycles, respectively. The results demonstrate that if suitable cyclic exhaust pressure and temperature metrics are used, anomalous combustion cycles can be identified, and overall combustion variability levels can be indexed. The comparative diagnostic performance of HS measured exhaust pressure and temperature and slow speed measured exhaust temperature are also discussed. A thermodynamic simulation of the engine and the HS thermocouple is used to provide theoretical support for the discussion by comparing measured and simulated “actual” exhaust temperature and identifying the flow, heat transfer, and thermodynamic influences that act as limits to the thermocouple's dynamic performance.

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Although precombustion chambers, or prechambers, have long been employed for improving large-bore two-stroke natural gas engine ignition and combustion stability, their design predates modern analysis techniques. Employing the latest computational fluid dynamics (CFD) modeling techniques, this study investigates the importance of temperature and chemistry for ignition of the main chamber, with an emphasis on eliminating unburned methane. The sensitivity of the ignition and complete combustion to main chamber air/fuel mixture homogeneity was also explored. This study compares the effect of purely thermal ignition, purely chemical ignition, and how their interplay can influence the complete combustion of methane in typical mixtures and in homogeneous distributions of fuel in the combustion chamber. The CFD results demonstrated that temperature and chemistry are equally important in the ignition mechanism, and combining the two phenomena is effective at igniting the main chamber. Reduction of residual methane in the main combustion chamber (MCC) is most effective when chemical intermediates and thermal ignition are combined. A rudimentary analysis of the effect of fuel/air stratification was also conducted, and it demonstrated that a dramatic reduction in methane emissions is observed for homogeneous mixtures. The flow field in the main combustion chamber was shown to create detrimental stratification of the fuel/air mixture, which inhibited complete combustion of the methane in the main chamber. By contrast, in the extreme case of a perfectly homogeneous distribution of both chemical intermediates and fuel in the combustion chamber, it is possible to completely eliminate unburned methane in the main combustion chamber.