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.

Methanol is considered an alternative fuel for the shipping decarbonisation, the properties of which, however, impact the marine dual-fuel engines ignition and combustion characteristics, especially at low load conditions. This study aims at parametrically optimising a marine dual-fuel engine operating with methanol high energy fraction at low loads to achieve knock-free combustion with the highest efficiency and lowest emissions. Computational Fluid Dynamics (CFD) modelling in the CONVERGE software is employed for the investigated large-bore marine four stroke engine considering four injection strategies including single, two stage and stratified injection. The Reynolds Averaged Navier Stokes (RANS) approach is employed to represent turbulence, the Lagrangian-Eulerian approach is used for the spray formation, and the SAGE detailed chemistry solver is used for modelling combustion. The CFD model was first developed and validated for the engine diesel mode. Subsequently, the validated model was expanded to accommodate the direct injection (DI) of both methanol and diesel fuels. Parametric runs are performed considering the compression ratio (CR) in the range 14–17 and the temperature range at inlet valve closing (T_IVC) 360–400 K. The results reveal that acceptable combustion efficiency and high thermal efficiency are achieved with CR and T_IVC above 17 and 380 K respectively for single injection, above 16 and 380 K respectively for double injection, as well as above 14 and 360 K respectively for stratified injection. Stratified injection is proposed to improve engine performance and reduce NOx emissions. This study provides insights to achieve stable and efficient operation of methanol-fuelled marine engines at low loads, and as such it contributes to the maritime industry decarbonisation.

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.

Renewably produced methanol is a promising fuel for internal combustion engines in long-range transportation thanks to its scalability, liquid storage, and favorable combustion properties. However, the distinction between different injection and ignition strategies for methanol engines and the resulting combustion mechanisms has not been consistently defined. Moreover, diffusion combustion strategies are favored over premixed strategies in large engines because of higher methanol energy fractions, disregarding the advantages of premixed approaches, such as reduced nitrogen oxide emissions and retrofitting opportunities. To address ambiguity in terminology, this paper proposes a classification framework for injection and ignition strategies and applies it to methanol-fueled internal combustion engines. Subsequently, this review focuses on experimental studies of methanol-fueled heavy-duty engines, which are crucial for transitioning to renewable and sustainable energy in long-range transportation. This research summarizes the impact of the reviewed injection and ignition strategies on combustion characteristics, engine performance and emissions to identify key trends. Furthermore, this review highlights how specific design and operating parameters influence premixed dual-fuel combustion, offering insights into optimizing performance and emissions. While mono-fuel and premixed dual-fuel strategies with methanol can significantly promote methanol use in heavy-duty engines and reduce harmful emissions like nitrogen oxides, a rise in unburned hydrocarbon emissions may also be expected, necessitating further research in this area. Additionally, methanol injection location in premixed dual-fuel schemes affects its cooling effect, influencing volumetric and thermal efficiency. Overall, this study deepens our understanding of methanol's impact on heavy-duty engine performance, highlighting critical challenges to be addressed for advancing sustainable transportation.

Methanol is a promising alternative fuel, which can assist in reducing emissions in heavy-duty (HD) dual-fuel (DF) compression ignition (CI) engines. In medium and large bore marine engines, DF operation is achieved through either direct injection (DI) or port fuel injection (PFI) of methanol with diesel acting as a DI pilot fuel for ignition. However, the injection of methanol presents a significant challenge due to its high latent heat of vaporization and decreased lower heating value (LHV) compared to diesel. Therefore, for the same energy content operation, methanol requires around eight times the amount of heat to evaporate completely in comparison to diesel, which results in lower in-cylinder temperatures. This charge cooling effect leads to a strong negative temperature gradient influencing ignition and flame propagation. This paper aims to quantify the cooling effect of methanol in a heavy-duty dual-fuel direct injection compression ignition (DICI) engine environment. The presented methodology uses computational fluid dynamics (CFD) simulations to model methanol sprays with validation originating from the engine combustion network (ECN) Spray D experimental data. The CFD models operate within the Lagrangian–Eulerian framework in CONVERGE-CFD using the Reynolds Averaged Navier Stokes (RANS) turbulence modeling. Compared to diesel, injecting methanol with the same energy content exhibited up to 100 K more decreased temperature within the mixture. Consequently, this cooled mixture may pose challenges to combustion stability due to the intense temperature gradients. Nonetheless, lower mixture temperature decreases NOx emissions, which can prove beneficial for high methanol energy fractions in dual-fuel DICI engines.

Methanol is a promising alternative fuel, which can assist in reducing emissions in heavy-duty dual-fuel (DF) compression ignition (CI) engines. In medium and large bore marine engines, DF operation is achieved through either direct injection (DI) or port fuel injection (PFI) of methanol with diesel acting as a DI pilot fuel for ignition. However, the injection of methanol presents a significant challenge due to its high latent heat of vaporization and decreased lower heating value (LHV) compared to diesel. Therefore, for the same energy content operation, methanol requires around eight times the amount of heat to evaporate completely in comparison to diesel, which results in lower in-cylinder temperatures. This charge cooling effect leads to a strong negative temperature gradient influencing ignition and flame propagation. This paper aims to quantify the cooling effect of methanol in a heavy-duty dual-fuel DICI engine environment. The presented methodology uses Computational Fluid Dynamics (CFD) simulations to model methanol sprays with validation originating from the Engine Combustion Network (ECN) Spray D experimental data. The CFD models operate within the Lagrangian-Eulerian framework in CONVERGE-CFD using the Reynolds Averaged Navier Stokes turbulence modelling. Compared to diesel, injecting methanol with the same energy content exhibited up to 100 K more decreased temperature within the mixture. Consequently, this cooled mixture may pose challenges to combustion stability due to the intense temperature gradients. Nonetheless, lower mixture temperature decreases NOx emissions, which can prove beneficial for high methanol energy fractions in dual-fuel DICI engines.

Methanol has emerged as a cost-effective and scalable alternative fuel for the maritime sector. However, the use of methanol in marine engines is limited by the unknown characteristics of methanol sprays when introduced through retrofitted port fuel injection (PFI) systems. The present study investigates the characteristics of methanol sprays under relevant conditions for marine engines, such as low injection pressure PFI. The primary objective of this research is to advance knowledge into key spray characteristics, including spray penetration, droplet size, atomization quality, and evaporation. The proposed methodology evaluates the efficacy of state-of-the-art computational fluid dynamics (CFD) models in simulating PFI marine engine spray conditions. Moreover, the study compares the performance of the Kelvin-Helmholtz (KH-RT) and Taylor Analogy Breakup (TAB) droplet breakup models under low injection pressure conditions. The results demonstrated that the KH-RT model does not predict any droplet breakup occurrence suggesting that the TAB model is more suitable for the given conditions. Furthermore, the liquid penetration of the spray was observed to align with the outcomes reported in previous experimental literature on methanol sprays. Nevertheless, the droplet sizes for low pressure injectors appear relatively large, indicating poor spray atomization, which impedes rapid evaporation and increases the risk of wall wetting in the inlet manifold and combustion chamber.