Effects of internal flow in a diesel nozzle on spray combustion

A common rail injection system for diesel engines has a potential to realize low emission and low fuel consumption diesel combustion. The core technology of this system is accumulated on spray characteristics such as mean droplet diameter, spray cone angle and tip penetration. And these characteristics are greatly influenced by internal flow in a diesel nozzle. In order to clarify the internal flow phenomenon such as cavitation, a real-size transparent nozzle had been developed, which can realize simultaneous cavitation visualization during a single-shot injection under high-density and room temperature condition using a high-speed camera. In this article, relationship between internal flow in the nozzle and spray combustion had been investigated. A high pressure and temperature environment in which the spray ignites were achieved in a rapid compression machine, and internal flow in the nozzle and the spray combustion were visualized. Regarding the evaluation of the spray combustion, the formation of the luminous flame triggered by the spray ignition was observed. Two cases of inlet radius of the nozzle hole (R = 0.016 and 0.033 mm) were prepared for this analysis. Under the case of larger inlet radius hole (R = 0.033 mm), probability of the string-type cavitation was greater, spray cone angle was larger and ignition delay was shorter.