Reducing Methane Emissions From Lean Burn Natural Gas Engines with Prechamber Ignited Mixing-Controlled Combustion

Abstract

The oil and gas industry heavily relies on lean burn spark ignited natural gas reciprocating engines. These engines produce pollutants, such as NOx and CO, but due to their premixed nature, also produce relatively large amounts of unburned methane (CH4) emissions. The primary source of methane emissions in lean burn engines are the crevices and near wall quench layers. Thus, one method to dramatically reduce methane emissions is to alter the combustion to be non-premixed, mixing-controlled combustion. In this concept the active prechamber acts as a reliable ignition source for the direct injected natural gas, which is referred to as prechamber ignited mixing-controlled combustion (PC-MCC). The PC-MCC concept enables a ~10x reduction in methane emissions, making it a promising technology for reducing the environmental impact of reciprocating engines. In this study, CFD simulations have been used to compare two modeling approaches for PC-MCC: a pure Eulerian gaseous injection approach and a gas-parcels injection method. Using the parcel method to model the gas injection enables an engineering approach to study and design the PC-MCC concept in a timely manner with coarser computational grids. This study also investigated the impact of several variables that may contribute to the performance and emissions of the PC-MCC strategy. The parameters that were examined include prechamber passageway characteristics like nozzle diameter, number of nozzles, and the orientation of nozzle orifices.