Characterization of Crankcase Ventilation Gas on Stationary Natural Gas Engines

Natural gas stands out as a prominent alternative fuel, boasting a well-established infrastructure for extraction and transport, substantial cost advantages, and potential for mitigating greenhouse gas (GHG) emissions. Its primary component, methane (CH₄), offers lower CO₂ emissions per unit of energy due to its high hydrogen-to-carbon ratio. However, it’s crucial to note that CH₄ is a potent greenhouse gas, with a heat-trapping capacity approximately 28 times greater than CO₂, subject to strict regulation by agencies like the Environmental Protection Agency (EPA). Over the last decade, the industry has diligently pursued CH₄ emission reductions, focusing on enhancing in-cylinder combustion efficiency and aftertreatment systems. Yet, further opportunities for mitigating CH₄ emissions through engine vent gas recirculation have emerged. This research presents a preliminary investigation into crankcase vent emissions, comprehensively characterizing field-engine, and lab-engine crankcase gas properties, including composition, flow rates, temperatures, pressures, and oil concentration/distribution. This study focuses on evaluating three engine types: Caterpillar G3516 ULB (four-stroke lean-burn), Caterpillar CG137-8 (four-stroke stoichiometric), and Copper Bessemer GMV-4TF (two-stroke lean-burn). A custom crankcase sampling probe, equipped with sensors, an isokinetic probe, a vortex-shedding flowmeter, and an FTIR spectrometer for gas speciation, facilitated this study. Findings highlight the significance of crankcase gas ventilation in contributing to CH₄ emissions for four-stroke engines, ranging from 17% to 69% of total engine CH₄ emissions. Additionally, entrained oil concentration ranged from 213.2 to 288.8 mg/m³-std, with oil particle sizes from 0.010 μm to 10 μm for four-stroke engines. Ongoing research aims to utilize these insights to develop an optimized closed recirculation system with efficient oil removal, preventing air-system fouling while effectively curtailing unnecessary CH₄ emissions.