Search Results

Within a public founded project test cell investigations were undertaken to identify parameters which predominantly influence the development of critical deposits in injection nozzles. A medium-duty diesel engine was operated in two different coking cycles with a zinc-free lubricant. One of the cycles is dominated by rated power, while the second includes a wide area of the operation range. During the experiments the temperatures at the nozzle tip, the geometries of the nozzle orifice and fuel properties were varied. For a detailed analysis of the deposits methods of electron microscopy were deployed. In the course of the project optical access to all areas in the nozzle was achieved. The experiments were evaluated by means of the monitoring of power output and fuel flow at rated power. The usage of a SEM (scanning electron microscope) and a TEM (transmission electron microscope) revealed images of the deposits with a magnification of up to 160 000.

It is the objective of this work to characterize mixture formation in the sprays emanating from Multi-Layer (ML) nozzles under approximately engine-like conditions by quantitative, spatially, and temporally resolved fuel-air ratio and temperature measurements. ML nozzles are cluster nozzles which have more than one circle of orifices. They were introduced previously, in order to overcome the limitations of conventional nozzles. In particular, the ML design yields the potential of variable spray interaction, so that mixture formation could be controlled according to the operating condition. In general, it was also a primary aim of the cluster-nozzle concepts to combine the enhanced atomization and pre-mixing of small nozzle holes with the longer spray penetration lengths of large holes. The applied diagnostic, which is based on 1d spontaneous Raman scattering, yields the quantitative stoichiometric ratio and the temperature in the vapor phase.

In open jet wind tunnels with high blockage ratios a sharp rise in drag is observed for models approaching the nozzle exit plane. The physical background for this rise in drag will be analyzed in the paper. Starting with a basic analysis of the dependencies of the effect on model and wind tunnel properties, the key parameters of the problem will be identified. It will be shown using a momentum balance and potential flow theory that interaction between model and nozzle exit can result in significant tunnel-induced gradients at the model position. In a second step, a CFD-based investigation is used to show the interaction between nozzle exit and a bluff body. The results cover the whole range between open jet and closed wall test section interaction. The model starts at a large distance from the nozzle, then moves towards the nozzle, enters the nozzle and is finally completely inside the nozzle.

The reference pressures are determined in automotive wind tunnels by measurement of pressures and pressure differences at upstream positions along the wind tunnel nozzle. For closed wall wind tunnels usually the so called nozzle method is used, where the volume flux is calculated from a pressure difference measured at the nozzle contour and a calibration factor determined in the empty test section. For open jet wind tunnels a choice is available between nozzle and plenum method. For the plenum method the reference static pressure is taken from the plenum chamber and the dynamic pressure also refers to the plenum conditions. The static reference pressure in closed wall tunnels is calculated by subtracting the dynamic pressure from the total pressure in the settling chamber. In this paper, the definitions and the differences between the two methods are discussed in detail.

This paper deals with the correction of aerodynamic interference effects taking place between the nozzle of an open jet wind tunnel and a test model. In order to deduce correct aerodynamic coefficients these interference effects have to be allowed for in the determination of the correct wind tunnel speed. In open jet wind tunnels basically two different methods are used to determine the tunnel speed. One is the so-called nozzle-method, utilizing the pressure difference down the nozzle to determine the nozzle exit velocity or tunnel speed. The other procedure is the so-called plenum-method, where the pressure difference between the settling chamber and the surrounding plenum chamber of the test section is measured and used. In this paper it is shown that both methods yield a systematic error, since the velocity distribution in the nozzle differs from the velocity distribution in an unbounded stream measured at the same distance from the model.