Spray–combustion interaction mechanism of multiple-injection under diesel engine conditions

Abstract

Multiple-injection has shown significant benefits in the reduction of combustion emissions and soot formation. However, there is a need to understand the secondary flow-induced air-fuel mixture formation and subsequent combustion mechanism under multiple-injection. An experiment was performed by changing the dwell time between the pilot and main injections under the conditions of 23 kg/m 3 ambient density with 0% O 2 (noncombusting) and 15% O 2 (combusting) ambient conditions, at an injection pressure of 120 MPa. The mass ratios of pilot and main injections in the study were 15%/85% and 20%/80%. A hybrid shadowgraph and Mie scattering imaging technique in a nearly simultaneous mode along the same line of sight was used to visualize the spray and flame luminosity. Pilot-main spray flame properties including ignition delay, ignition location, and lift-off length were characterized from experimental images. CFD simulation of pilot-main spray combustion was performed under the same experimental conditions to provide additional insights into the combustion process. The air-fuel mixing field and ignition process followed by main injection flame structure are significantly altered at different dwells. The spray-to-flame interaction mechanism model has been established for the development of an optimal multiple-injection scheme for, possibly, low soot formation and emissions. .

Study of the soot quantification for two-stage injection of hydrogenated catalytic biodiesel in a constant-volume combustion chamber

“…It may be caused by the dissatisfaction with the injector needle electromechanical delay due to the such short dwell time. It can also be found that the highest soot concentration located in the middle section of the flame at 0.5 ms AMI that is consistent with the results in [8]. Generally, the high temperature and high C/O location exists near the flame in the diffused flame combustion.…”

“…4 (b), it is shown that the LL overlap in the main evolution in all pilot injection cases. The results were found to be identical with the research in [8]. …”

“…The longer dwell time contributes to more total soot mass while the different pilot injection duration barely affect the total soot mass of the main injection. In non-reacting conditions, the spray of the main injection penetrates faster within a shorter dwell time investigated by Mie-scatter and CFD models [8]. When the two-stage injection duration are same, the second injection vapor phase penetration is longer and faster [9][10][11] [12].…”

“…In the previous literatures, multiple injections have shown potent for simultaneous reduction of NOx and soot emission in the diesel engine [4][5] [6] [7]. In non-reacting conditions, the spray of the main injection penetrates faster within a shorter dwell time investigated by Mie-scatter and CFD models [8]. When the two-stage injection duration are same, the second injection vapor phase penetration is longer and faster [9][10] [11] [12].…”

“…When the two-stage injection duration are same, the second injection vapor phase penetration is longer and faster [9][10][11] [12]. For combustion characteristics, ignition delay of main injection is much shorter than that of the pilot injection and it may be shorter or longer with the dwell time increasing due to the different entrainment of surrounding gas [8]. In the multiple injection strategy investigation, the dwell time between injections and the pilot injection duration were seen as the two main factors.…”