Using a new generation of thermal fluid analysis software(CONVERGE)

the three dimensional computational fluid dynamics(CFD) model for high pressure direct injection marine natural gas engines was developed to study the effect of natural gas post injection strategies on engine combustion and emissions. Results show that the rise in post injection ratio slightly increases the maximum combustion pressure coupled with the extension of combustion duration. Increasing the interval between the main injection and post injection would delay the post injection combustion phase

and extend the combustion duration

while the maximum combustion pressure remains unchanged. Compared with the operation without natural gas post injection

increasing the proportion of post injection to 10% and 20%

respectively can reduce soot emissions by 7.7%～13.5% and 1.5%～11.5% with an increase of NOx emissions by 12.0%～15.0% and 5.0%～7.0% and an increase of indicated specific fuel consumption by about 0.1% and 1.0%. However

increasing the proportion of post injection to 30% obtains a strong increase of soot emissions by 2.0%～8.0% with a reduction of NOx emissions by 5.0%～7.7% and an increase of indicated specific fuel consumption by approximately 2.3%.