Retrofitting a high-speed marine engine to dual-fuel methanol-diesel operation: A comparison of multiple and single point methanol port injection

As a result of climate change and increasingly stringent emission legislation the shipping industry has started with a transition to sustainable propulsion. Methanol is a viable fuel to reach this goal: it is a great engine fuel (high octane number, high heat of evaporation, and absence of carbon to carbon bonds) and a simple molecule that can be produced in a renewable way. The dual-fuel methanol-diesel technology with methanol injection in the intake has proven to be a promising retrofit solution for vessels. In this concept methanol injectors can be at multiple locations: single point injection (SPI) in the intake duct (assumed to be easier to install) or multiple point injection (MPI) at the intake ports of the cylinders (assumed to give additional in-cylinder cooling to suppress knock). This paper compares MPI and SPI with a focus on maximum methanol energy fraction (MEF), brake thermal efficiency (BTE) and NOx emissions; and compares both injection modes with diesel-only operation. The highest MEF was measured in SPI: 84%. BTE was significantly higher in SPI for high MEFs due to a better combustion phasing resulting from higher intake temperatures. Higher intake temperatures in SPI resulted in higher NOx emissions. Independent of the injection mode, NOx mainly decreased compared to diesel-only operation. It is concluded that SPI is preferred from a cost point of view (maximizing BTE and minimizing retrofit cost) and that MPI is preferred from a sustainability point of view (maximizing MEF and minimizing NOx emissions).