Numerical investigation of premixed hydrogen combustion in dual-fuel marine engines at high load

Abstract

Zero-emission fuels are expected to drive the maritime sector decarbonisation, with hydrogen emerging as a long-term solution. This study aims to investigate by using CFD modelling a hydrogen fuelled marine dual-fuel engine to identify operating settings ranges for different hydrogen energy fractions (HEF), as well as parametrically optimise the diesel fuel injection timing and temperature at inlet valve closing (IVC). A large marine four-stroke engine with nominal power of 10.5 MW at 500 rev/m is considered, assuming operation at 90 % load and hydrogen injection in the cylinders intake ports. CFD models are developed for several operating scenarios in both diesel and dual-fuel modes. The models are validated against measured data for the engine diesel mode and literature data for a hydrogen-fuelled light-duty engine. A convergence study is conducted to select the grid compromising between computational effort and accuracy. Parametric runs for 20 %, 40 % and 60 % HEF with different IVC temperature and diesel start of injection are modelled to quantify the engine performance, emissions, and combustion characteristics. A single parameter optimisation is conducted to determine the most effective pilot diesel injection timings. The results reveal the IVC temperature range for stable hydrogen combustion to avoid incomplete combustion at low IVC temperature and knocking above 360 K. The proposed settings lead to higher peak heat release rate and in-cylinder pressure compared to the diesel mode without exceeding the permissible in-cylinder pressure rise limits for 60 % HEF. However, NOx emissions increase to 12.9 g/kWh in the dual-fuel mode. The optimal start of injection (SOI) for the diesel fuel, in the case of 60 % HEF, is found 8 °CA BTDC resulting in an indicated thermal efficiency of 43.2 % and stable combustion. Advancing SOI beyond the optimal value results in incomplete combustion. This is the first study on hydrogen use in large marine four-stroke engines providing insights for the engine design and operation, and as such it contributes to the maritime industry decarbonisation efforts.