In-Use Efficiency of Oxidation and Three-Way Catalysts Used in High-Horsepower Dual Fuel and Dedicated Natural Gas Engines

Directional drilling rigs and hydraulic stimulation equipment typically use diesel fueled compression ignition (CI) engines. The majority of these engines are compliant with US Environmental Protection Agency (EPA) Tier 2 standards. To reduce fuel costs, industry is investing in dual fuel (DF) and dedicated natural gas (DNG) engines. DF engines use diesel oxidation catalysts (DOCs) to reduce CO and NMHC emissions. DNG engines may be either lean-burn or rich-burn and the latter uses three-way catalysts (TWC) to reduce CO, NMHC, and NOx emissions. This research presents in-use catalyst efficiency data collected pre- and post-catalyst for three DF engines and two DNG engines. One DF engine was converted earlier and did not include a DOC. Data were collected from six Tier 2 engines, two CI drilling engines converted to operate as DF, two CI hydraulic fracturing engines converted to operate as DF, and two SI DNG drilling engines. DF engines with DOCs were able to reduce CO and NMHC during DF operation by > 90 and >50%, respectively. The DOCs did not reduce methane and NOx emissions. One DNG catalyst did not effectively reduce emissions. Properly functioning DNG engines and TWCs decreased engine out CO, NMHC, and NOx emissions all by >90%. It is important to note that DOCs could be added to Tier 2 diesel engines regardless of combustion mode to reduce engine out NMHC and CO emissions. DNG engines offered the lowest NOx emissions, which could be important in certain air districts. Research should focus on improved oxidation of methane emissions from DF engines to realize any benefit of reduced of GHG emissions.