End Of Pre-Injection Cycle
The pre-injection cycle ends directly after the injection needle opens. The rising pressure causes the bypass piston to move down, thereby increasing the volume of the high-pressure chamber. The pressure drops briefly as a result and the injector needle closes. The pre-injection cycle is completed. The downwards movement of the bypass piston increases the preload on the injector spring. The fuel pressure required to reopen the injection needle during the subsequent main injection cycle, therefore, is higher than during the pre-injection cycle.