Conversion of Exhaust Gases from Dual-Fuel (Natural Gas-Diesel) Engine under Ni-Co-Cu/ZSM-5 Catalysts

Natural gas (NG), which consists of mostly methane, can be co-combusted with diesel fuel in existing compression ignition engines through dual fuel technology with reasonable engine modifications. The removal of short-chain alkanes (e.g. CH₄, C₂H₆ and C₃H₈) of a dual fuel (natural gas and diesel) engine raises a distinctive topic to the exhaust aftertreatment system (ATS). However, there are few studies reported based on tests with real engine exhaust. This present study focuses on the conversion of short-chain alkanes by Co, Ni and Cu/ZSM-5 catalysts, which are commonly used for oxidation/partial oxidation and reforming. These catalysts are tested with exhaust of a dual-fuel (natural gas and diesel) engine. The complicated and dynamic exhaust composition, determined by the engine loading and natural gas substitution, can result in different components in the exhaust and various conversions for species. Co-Ni-Cu/ZSM-5 had the highest conversion of CH₄ and non-methane hydrocarbon (NMHC) at 30000 h^-1 space velocity (SV) when the engine was operated at 1000 RPM, 25% loading, 70% natural gas substitution. Significant amounts of CO and formaldehyde were generated by the dual fuel engine, but can be mostly converted starting at 450 °C. Methane conversion of up to 42% was attainable at a higher temperature of 500 °C by using Co-Ni-Cu/ZSM-5 in the aftertreatment system.