For the fuel injection system of a pilot-ignited direct-injection natural gas engine

the influence of different natural gas pre-injection strategies on the combustion and emission characteristics of the engine was studied to explore the potential of natural gas pre-injection to improve the combustion system of low speed marine engines using a single-cylinder simulation model established by a Converge software. The combustion and emission data were verified by experiments and calculated at different pre injection intervals and pre-injection ratios. Results show that the use of pre-injection strategy affects the proportion of premixed combustion in the combustion process

thus affecting the exothermic phase and isovolumetric combustion. Moreover

the pre-injection ratio has a more significant influence on the combustion process than the pre-injection interval

and the latter only affects the combustion exothermic process at a larger pre-injection ratio. In terms of emissions

the optimized pre-injection strategy can control the premixed combustion so as to achieve simultaneous improvement of NOx and fuel consumption. On the other hand

different pre-injection strategies allow different soot distributions in the cylinder. Compared with non-pre-injection solution

the use of pre-injection strategies leads to higher soot emissions.