Transient measuring method for injection rate of each nozzle hole based on spray momentum flux

For a diesel engine equipped with multi-hole injectors, its combustion process, pollutant formation and thermal load consistency of combustion chamber are directly influenced by the differences in injection rates among nozzle holes. However, there are few measuring methods and equipments suitable for the determination of injection rate of each nozzle hole. The aim of this paper is to evaluate a measuring method proposed based on the spray momentum measurement of each nozzle hole that could be used to determine its injection rate. For this purpose, a conventional injection system of pump-line-nozzle was utilized and a dedicated experimental rig was constructed. Under different operating conditions, the cycle fuel injection quantities of the measured injector and the transient injection rate of each nozzle hole were measured successively. Based on the experimental results, the reliability and stability of the proposed measuring method were validated, and the differences in injection rates among nozzle holes were analyzed. In order to further understand the measuring method proposed, the influence of the measurement procedure details such as the distance between the outlet and the target and the angle between the target and spray axis on the determination of the transient injection rate of each nozzle hole was experimentally studied. The experimental results show that when the distance between the outlet and the target is less than 12 mm and the angle between the target and spray axis is lower than 100°, the transient injection rate of each nozzle hole could be measured accurately using the measuring method proposed, and that with a higher injection pump speed or more cycle fuel supply quantity, the consistency of cycle fuel injection quantities among nozzle holes is improved gradually. The further increase of the distance or the angle will result in the reduction of the peak injection rate and cycle fuel injection quantity of the measured nozzle hole. Besides, the injection start, injection end, and the corresponding phase of peak injection rate of the measured nozzle hole will be delayed little by little with the further increment of the distance.