Effect on flash boiling spray characteristics in the far-field and near-field and nozzle tip wetting with multi-hole LPDI injector

Abstract

Flash boiling spray, which has a wider spray width and enhanced interactions plume to plume is likely to favor nozzle tip wetting. To understand the effect of flash boiling spray, this study was aimed that the spray characteristics and nozzle tip wetting of n-heptane and Liquefied petroleum gas (LPG) fuel on LPG direct injection (LPDI) system under various fuel temperature. In addition, the novelty of this study is providing a more detailed understand of spray characteristics affected the fuel properties in the far-field and near-field and nozzle tip wetting by comparing n-heptane and summer LPG under flash boiling conditions. The sprays were divided to three conditions (sub-cooled, transitional, flare flash boiling) based on the degree of superheat. Macroscopic spray characteristics such as spray penetration, spray angle, spray area, and spray length to width ratio were studied in the far-field. Near-field visualization was used to analyze the spray width and spray area. In addition, the wet area and wet boundary on the nozzle tip were visualized using a high-speed camera equipped with a Long-distance microscope (LDM). The experimental results showed that the spray plumes expand and developed in the central axis as fuel temperature increased for both fuels, and the spray plumes were significantly widened in the axial and radial direction for both fuels. The wet area and boundary increased under sub-cooling and transitional conditions as a result of nozzle tip wetting with n-heptane, but the wet area and boundary decreased under transitional and flare conditions. Like n-heptane fuel, the wet area of summer LPG decreased under transitional and flare conditions.