Port fuel injection (PFI) methanol-diesel dual-fuel is considered a promising retrofit solution for methanol adoption in marine engines. PFI enables fuel flexibility, improved thermal efficiency, and reduced greenhouse gas (GHG), soot, and NOx emissions. This work aims to provide insights for the optimization of PFI methanol-diesel marine engines, contributing to the decarbonization of the maritime sector. For this purpose, Computational Fluid Dynamics (CFD) simulations in CONVERGE-CFD are performed, incorporating spray modeling and combustion kinetics of both methanol and diesel to investigate high-pressure PFI methanol behaviours injected at different locations. The developed CFD model satisfactorily captured methanol-air mixture formation and methanol combustion under low-load dual-fuel operation measured at 3.1 bar Brake Mean Effective Pressure (BMEP). Two distinct phases of dual-fuel combustion are captured: compression ignition of n-heptane, as a surrogate for diesel, and fast flame propagation of premixed methanol, with results being sensitive to blending ratio (BR), start of injection (SOI), and injector location. At 3.1 bar BMEP, varying BR between 45%–65% yielded increased combustion efficiency (91.9%–94.8%) and gross Indicated Thermal Efficiency (ITE) (46.2%–47.3%), while BRs above 75% caused partial burn and efficiency drop. Advancing SOI improved mixture uniformity and flame propagation rate, however, it increased NOx and heat release rate of the second phase. Injecting more methanol from the short runner promoted homogeneity, raising combustion efficiency by up to 8%-points, thermal efficiency up to 4.3%-points, and NOx emissions by 50%. These results highlighted the model's capability to simulate dual-fuel operation and advance the understanding towards efficient and low-emission methanol marine engines.

The maritime sector aims to achieve short and medium-term sustainability targets through the conversion of Internal Combustion Engines to methanol operation. For small to medium sized engines, Port Fuel Injection (PFI) is the most viable injection method to achieve this conversion. However, the knowledge of the behaviour of methanol in combustion engines, particularly its spray characteristics under PFI conditions, is limited. To better understand liquid methanol sprays, this paper studies the injection of methanol in marine PFI conditions through Computational Fluid Dynamics (CFD) modelling. The CFD models use the Lagrangian-Eulerian (LE) coupling method within the Reynolds Averaged Navier Stokes (RANS) turbulence framework. Numerical results were validated using dedicated methanol experiments from the literature for both high and low injection pressures. Subsequently, this predictive CFD framework was used in a number of different injection pressures with scaled injection quantities that represent marine applications. Moreover, we demonstrated that high injection pressure improves atomisation and, thus, evaporation prior to wall impingement. This work strongly contributes to our understanding of marine PFI methanol engines by modelling fuel quantities relevant for ship applications. Our approach can be implemented in full engine simulations to solve evaporation challenges often found in small-bore methanol marine engines.

To reduce emissions, methanol is a favorable carbon-neutrally-producible alternative fuel, which can substitute gasoline in direct-injection spark-ignition (DISI) engines. Robust DISI engine operation relies on a consistent air-fuel mixture. To understand the physical processes that characterize the mixture formation, predictive computational fluid dynamics (CFD) simulations are used to improve the understanding, operation, and emissions of these engines. However, using an alternative fuel such as methanol often poses challenges to the CFD simulations’ validity due to the alteration of the fuel properties. This study presents the validation of a CFD modeling approach that can be applied to the predictive modeling of DISI methanol engines. Our methodology uses Lagrangian-Eulerian methods to model the methanol eight-hole counter-bore style Spray M injector from the Engine Combustion Network (ECN). We used the Spray M1 condition, which represents a late-injection spray under a high ambient pressure and temperature environment. For the present study, we employed both a Reynolds Averaged Navier Stokes (RANS) and a Large Eddy Simulation (LES) turbulence approach in CONVERGE-CFD. To validate our models, we used the projected liquid volume (PLV) maps generated by the tomographic liquid volume fraction (LVF) based on methanol. Subsequently, we tuned our models based on the corresponding numerical predictions of the liquid penetration and LVF distributions. The results demonstrated that both the RANS and LES models could replicate the spray morphology and liquid length. While the RANS model was unable to fully capture the complex phenomena of spray collapse and sweeping in the methanol multi-hole spray, the LES model effectively reproduced these behaviors without excessive tuning effort.