A new track for high-efficiency marine diesel engines: Initiative air jet and post-split injection combined

In pursuit of adequate mixing with a high volume of fuel injection, a re-intake scheme is proposed to promote the diffusion of combustibles and flames by using the disturbance of high-pressure air jets after the pressure peak. The results indicate that during the power stroke, an additional air jet enhances combustion by penetrating the spray and disturbing the flame front. The high-pressure air jet's obstruction of the atomization of local sprays achieves a longer combustion duration, while intensifying the vortex and temperature at the cylinder center, which enhances the evaporation of fuel near the nozzle. However, excessively high fuel injection pressure brings in more cold air, causing a temperature drop. It is necessary to have sufficient flame expansion before re-intake to eliminate the impact on pressure. By adjusting the re-intake pressure and timing, the air jet, when it reaches half the cylinder diameter, can exert its maximum advantage. By introducing post-injection and increasing the pressure of the first fuel injection, the air-spray impingement duration is extended, thereby improving thermal efficiency. This work, at 190 MPa injection pressure without changing the duration, and combined with a 5°CA re-intake, achieved a 1.82 % increase in thermal efficiency.