Characterization of Crankcase Ventilation Gas on Stationary Natural Gas Engines

Abstract

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.