Experimental investigations on the spray structure and nozzle tip wetting using various fuels with an LPDI injector

초록

Unlike the conventional liquid phase LPG injection (LPLI) system, an LPG direct injection (LPDI) system directly injects fuel into the combustion chamber, so the temperature inside the combustion chamber decreases due to the latent heat of vaporization of the fuel. Therefore, the direct injection (DI) system has the advantage of increasing fuel efficiency and power performance. However, a classic problem of the DI system is that a large amount of particle numbers (PNs) is emitted due to the nozzle tip wetting, which is affected by the spray characteristics related to the fuel properties. Therefore, research on nozzle tip wetting using an LPDI injector is needed. The purpose of this study is to investigate the macroscopic spray characteristics of four test fuels: n-heptane, gasoline, LPG winter, and LPG summer, using Mie scattering visualization, Schlieren visualization, and nozzle tip wetting using a long-distance microscope (LDM). The experiments were conducted using a three-hole LPDI injector with a step hole. In the comparison of n-heptane, gasoline, and the LPG fuels, the vapor pressure of the test fuels was high, in the order of LPG winter > LPG summer > gasoline > n-heptane. In addition, the surface tension of the test fuels was low, in the order of LPG winter < LPG summer < n-heptane < gasoline. The results revealed that the spray penetration of the LPG fuels was longer than that of n-heptane and gasoline because of flash boiling. Also, by comparing the nozzle tip wetting of these fuels, the wet area was wider in the order of LPG winter > LPG summer > n-heptane > gasoline.

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