Diesel Injector 320-0677 Fuel Injector 2645A746 Injector Compatible with Caterpillar Cat C6.6 Engine 320dl Excavator

Cavitation Inside High-Pressure Optically Transparent Fuel Injector Nozzles (PART 1)

Introduction Elevated injection pressures and microscopic nozzle orifices are used in injection systems in modern directinjection engines to enhance atomization and deliver sufficient fuel mass quickly. The flow inside the injector must turn abruptly to enter the nozzle orifice, which in many cases causes cavitation to appear on the downstream side of the orifice inlet corner. Cavitation is generally considered a hazard, because collapsing cavitation bubbles can damage the surfaces of durable metals such as hardened steels. In addition, while some forms of cavitation have been shown to be beneficial for atomization, even removing carbon deposits in gasoline injectors, hydraulic flip suppresses atomization completely[1]. Until cavitation is better understood and easier to control, it seems logical to design the injector nozzle in such a way as to prevent cavitation. The most effective way to study nozzle orifice flow cavitation is to construct an injector with an optically accessible nozzle so that the orifice flow can be visualized directly. This is not a simple task. Optically transparent engineering materials are most often brittle at room temperature. While brittle materials often have higher elastic moduli and stronger theoretical strengths, flaws left from the processing required to create the desired geometry can significantly reduce the load capacity of the finished component. An important issue with optical tips is to find a match between the indices of refraction for the nozzle material and the fluid used. If they are not matched, then the edges of the passage will appear dark in a shadowgram. That would make it difficult to image wall cavitation.

Acrylic and quartz have an index that comes close to that of most fuels (and water) but unfortunately they have low tensile strength due to processing flaws. They usually break well below realistic fuel pressures. Sapphire, on the other hand, has thermal and strength properties similar to steel, but it is poorly index matched to the fluids of interest.