A Double-Diaphragm Shock Tube for Hydrocarbon Disintegration Studies (original) (raw)

Abstract

F or gaining deeper insight in the process of fuel evaporation in dense fuel sprays, understanding the fluid disintegration mechanisms at high chamber pressures and temperatures is of particular importance. This paper describes a newly commissioned double-diaphragm shock tube (DDST) facility, developed at the Institute of Aerospace Thermodynamics (ITLR) of the Universität Stuttgart. A shock tube is an ideal tool to investigate disintegration and evaporation processes, as it can provide a uniform and well-defined thermodynamic state over a wide range of pressures and temperatures. The double-diaphragm shock tube at ITLR consists of five major components: driver, buffer, driven section, test section, and dump tank. Driver, buffer, and driven section have a cylindrical inner diameter. The introduction of the short buffer between the driver and the driven section reduces the initial pressure load on each of the two diaphragms and improves the controllability and triggering of the experiments. The test section has a square cross section to allow the application of flat fused-silica windows for optical access. The observable length within the test section is 100 mm. In order to partially dispose the boundary layer and to accomplish the transition from the cylindrical driven section to the square test section, a skimmer is mounted at the beginning of the test section realising a semi-direct connection between these two parts. The driver section is 3 m long, the driven section is about 9.5 m long leading to an overall facility length of about 12.5 m. The new shock tube facility was characterised for several representative conditions, using a helium/argon mixture as the driver gas and argon as the test gas. Pressure levels of up to 50 bar have been attained and temperatures greater than 2000 K were achieved. These values are suitable to investigate most hydrocarbon fuels of interest (e.g. n-dodecane as a kerosene substitute) over a wide range of different thermodynamic regimes (sub,-transand supercritical). In the endwall of the shock tube, a fast-acting high-pressure injection system is mounted to rapidly introduce the fuel into the test section, as test-times are limited to about 4-5 ms. First spray characterisation experiments are currently ongoing.

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