Hydraulic characteristics of high temperature hydrocarbon liquid jets with various orifice geometries

Abstract

An experimental study was conducted to investigate the effects of orifice geometry on the hydraulic characteristics of high-temperature aviation fuel jets. Pressurized heated liquid hydrocarbon fuel, simulating fuel used as coolant in the active cooling system of a hypersonic flight vehicle, was injected through a set of plain orifice nozzles of different lengths and diameters. The fuel was heated to close to 573 K (300 °C) using an induction heater at an upstream pressure of up to 1.0 MPa, and discharged to atmospheric downstream pressure conditions. The orifice diameter (D) varies from 0.7 to 1.5 mm and the length (L) from 1.4 to 4.3 mm, which results in length-to-diameter ratios (L/D) from 1.1 to 6.1, and the inlet of the orifice is nominally sharp-edged. Hydraulic characterization in terms of fuel injection temperature (Tinj) was carried out by introducing the discharge coefficient (Cd), and the macroscopic internal flow characteristics were correlated to Reynolds number (Re) and cavitation numbers (K and Ca). The fundamental behaviors of high-temperature liquid fuel jets at the specified operating ranges represented by Cd with respect to Tinj for a given set of injectors revealed that, as Tinj increases above the boiling point, the Cd of the injector with a longer orifice decreases faster than that of a shorter injector of the same orifice diameter, and for injectors of a given orifice length, Cd decreases with Tinj in a similar way irrespective of orifice diameter. Plots of Re vs. Tinj, Cd vs. Re, and Cd vs. K and Ca clearly show the dependence of the cavitation characteristics on the orifice geometry under high temperature injection conditions. In order to quantify the degree of cavitation for various orifice geometries, the Cd vs. Ca curve for each injector configuration has been fitted linearly; the mass flow choking effect in high temperature fuel injection represented by the magnitude of the slope from the linear fit becomes stronger as the orifice is longer in length and/or wider in diameter. This suggests that longer and wider orifices are more susceptible to choked cavitation. It was also found that the geometric effect is maintained for various ΔP, even though the magnitude of the slope increases with ΔP, and the sensitivity of the magnitude to increasing ΔP becomes stronger for longer orifices.