Alf Magnusson

Numerical and Experimental Analysis of the Wall Film Thickness for Diesel Fuel Sprays Impinging on a Temperature-Controlled Wall

Analysis of spray-wall interaction is a major issue in the study of the combustion process in DI diesel engines. Along with spray characteristics, the investigation of impinging sprays and of liquid wall film development is fundamental for predicting the mixture formation. Simulations of these phenomena for diesel sprays need to be validated and improved; nevertheless they can extend and complement experimental measurements. In this paper the wall film thickness for impinging sprays was investigated by evaluating the heat transfer across a temperature-controlled wall. In fact, heat transfer is significantly affected by the wall film thickness, and both experiments and simulations were carried out to correlate the wall temperature variations and film height. The numerical simulations were carried out using the STAR-CD and the KIVA-3V, rel. 2, codes. Different wall impingement models and liquid film approaches were analyzed and numerical results were compared with measurements available in the literature and with experiments carried out at Chalmers. The conditions for which the simulations were performed correspond to those found during the compression stroke in a diesel engine. The fuel used was a 2-component model fuel (Idea, 70% n-decane and 30% α methylnaphthalene). The experiments were carried out in the Chalmers high-pressure/high-temperature spray rig for non-evaporating and evaporating conditions. The spray chamber was equipped with a temperature-controlled wall, including coaxial thermocouples for recording the surface temperature. The time histories of the surface temperatures were used to calculate the local heat fluxes applying a 1-dimensional transient heat conduction model.

A Numerical and Experimental Study of Diesel Fuel Sprays Impinging on a Temperature Controlled Wall

Spray-wall as well as spray-spray interactions in direct injection diesel engines have been found to influence both the rate the heat release and the formation of emissions. Simulations of these phenomena for diesel sprays need to be validated and an issue is investigating what kind of fuels can be used in both experiments and spray calculations. The objective of this work is to compare numerical simulations with experimental data of sprays impinging on a temperature controlled wall, regarding spray characteristics and heat transfer. The numerical simulations were carried out using the STAR-CD and KIVA 3V codes. The CFD simulations accounted for the actual spray chamber geometry and operating conditions used in the experiments. Particular attention has been devoted to the fuel used for the simulations. Firstly a single component model fuel (n heptane) has been adopted; subsequently a 2 component model fuel (Idea, 70% n-decane and 30 % α methylnaphthalene) has been implemented into the code fuel libraries in order to account for the fuel used in the experiments. Finally, different break-up and wall impingement models were analyzed. The experiments were performed in the high pressure, high temperature spray rig at Chalmers with conditions corresponding to those found during the compression stroke in a heavy duty diesel engine. The temperature controlled wall was equipped with three coaxial thermocouples for recording the surface temperature. The time histories of the surface temperatures were used to calculate the local heat fluxes applying a 1 dimensional transient heat conduction model. The spray characteristics were measured using two different optical methods; Phase Doppler Anemometry and high speed imaging. Image analysis gave the characteristics of the general behavior of the axial and radial penetration. PDA-data gave the characteristics of droplet penetration before and after impinging the wall.

Spray-Wall Interaction: Diesel Fuels Impinging on a Tempered Wall

Heat transfer from impinging sprays in direct injected diesel engines has been found to influence the rate of heat release and the formation of emissions. The use of multiple injections may also affect heat transfer. The objective of this work is to study heat transfer between the wall and the spray, and how the surface temperature of the wall affects spray behaviour in single and split injections. Two different diesel fuels were used in the experiments, noteworthy is that the diesel fuel had a higher radial penetration rate than the Idea fuel at evaporating conditions but not at non-evaporating conditions. The wall temperature has no measurable influence on radial penetration but does have a significant influence on the heat transfer.

An Experimental Investigation of Spray-Wall Interaction of Diesel Sprays

Wall wetting can occur irrespective of combustion concept in diesel engines, e.g. during the compression stroke. This action has been related to engine-out emissions in different ways, and an experimental investigation of impinging diesel sprays is thus made for a standard diesel fuel and a two-component model fuel (IDEA). The experiment was performed at conditions corresponding to those found during the compression stroke in a heavy duty diesel engine. The spray characteristics of two fuels were measured using two different optical methods: a Phase Doppler Particle Analyzer (PDPA) and high-speed imaging. A temperature controlled wall equipped with rapid, coaxial thermocouples was used to record the change in surface temperature from the heat transfer of the impinging sprays. This work demonstrated that the two different fuels used in the experiments have spray characteristics that behave in a similar way for a relatively wide range of air temperatures and air pressures, before and after wall impingement.