Nano-hardness of the material of thin layers of the injector tip depending on the depth under the precisly finished co-operating surfaces

In this paper, the authors present the results of experimental studies of the nano-hardness and Young's modulus of the injector spray pattern body and needle (the tip of the injector). The nano-hardness of a thin-layer of precisely finished co-operating surfaces was tested according to the depth below the surface of the sample (deep into the material). The quality of precisely finished surfaces of a fuel infector has a very large impact on the proper operation of a diesel engine. Both, the needle and the body of the injector spray pattern, are individually adjusted and lapped to maintain the proper gap between them. The gap between the needle and the injector tip body affects the proper dosage and quality of the sprayed fuel. Impurities in the fuel are of the same order of magnitude or even greater than this gap. Hard particles that penetrate between the side surfaces of the needle and body of the injector tip could result in scratching, which generate leaks and drops of injection pressure, increased fuel consumption, poor spraying of fuel, leaking of fuel to the lubricating oil and reduction of its operating properties. The hardness of the precisely finished surfaces of the injector is essential in the process of wear of these surfaces. The aim of the study was to determine the hardness and Young's modulus of thin layers of precisely finished co-operating surfaces of injector tip and estimation of the thickness of these layers. The nano-hardness measurements were made with the Hysitron TI 950 TriboIdenter, where the test is conducted using a nano-indenter with a mechanical method. The device allows selecting from several to several dozen of measurement points and performs automatic measurement of nano-hardness and Young's modulus in the indicated locations. The study concerns the tip (body and needle) of the non-used Bosch DLLA 160 S 1305 injector. The presented results can be used to develop some new methods of coating the co-operating surfaces with the hard thin layers, e.g. the use of titanium in order to decrease wear and increase scratching resistance.