Numerical investigation on the effects of pilot fuel and natural gas injection pressures on methane slip in a large marine dual-fuel engine

Reducing methane slip takes on a critical significance in marine two-stroke diesel-natural gas engines especially in natural gas low-pressure injection configuration. This paper aims to use CFD numerical simulation methods to study the pilot fuel injection pressure, natural gas injection pressure, and hydrogen-blended strategy to reduce methane slip. The results indicate that optimizing the injection pressures of natural gas and pilot fuel can reduce the methane slip. As the pilot fuel injection pressure increases, the fuel spray penetration distance increases, the atomized droplets become finer and the ignition point increases. When the pressure is 1400 bar, the maximum reduction of methane is 8.02 %. Enhancing the natural gas injection pressure could increase the concentration of methane in the central region of the cylinder, which is beneficial for gas combustion. As the natural gas injection pressure increases, the greatest decrease in methane slip is 10.39 %. Adjusting the injection pressures of pilot fuel and natural gas in the hydrogen-blended natural gas reduced the methane slip by a maximum of 47.06 %, and the equivalent CO2 reduction is 311.04 g/kW∙h. Therefore, fuel injection pressure and fuel composition need more attention in reducing methane slip from the engine.