Study on the effects of hydrogen nozzle diameter on the combustion and emission characteristics of hydrogen-blended methanol engines.

In this study, three-dimensional modelling and simulation of a high-power six-cylinder hydrogen-blended methanol engine with direct hydrogen injection and methanol port injection were conducted using the simulation software CONVERGE. The control variable method was used to study the effects of hydrogen nozzle diameters of 1, 2, 3, and 4 mm on the in-cylinder airflow movement, hydrogen distribution, combustion, and emission characteristics of the hydrogen-blended methanol engine. The results showed that, with an increase in the hydrogen nozzle diameter, the injection duration was shortened, the distribution of hydrogen in the cylinder tended to be uniform, and the speed of flame propagation in the cylinder decreased. When the nozzle diameter was small, noticeable hydrogen accumulation occurred near the spark plug at the time of ignition, which accelerated flame propagation. Compared with increasing the diameter of the hydrogen nozzle, reducing the diameter of the nozzle caused the peak cylinder pressure and peak heat release rate to increase significantly; the ignition delay period was shortened; the mean indicated pressure and indicated thermal efficiency increased; and the emissions of CO, HC, and unburned methanol decreased, but the NO x emissions increased. Compared with pure methanol engines, hydrogen blending can optimise the combustion of methanol engines to a certain extent, improve power performance, and reduce the emissions of unburned methanol and formaldehyde. Therefore, a hydrogen nozzle diameter of 2 mm is considered the best solution for a hydrogen-blended methanol engine. • Hydrogen direct injection and methanol port injection. • Hydrogen-blended methanol engine has better combustion characteristics. • The hydrogen distribution under different hydrogen nozzle diameters was compared. • The engine with a hydrogen nozzle diameter of 2 mm has the best overall performance. [ABSTRACT FROM AUTHOR]