A numerical and experimental study of diesel fuel sprays impinging on a temperature controlled wall

Paper in proceeding, 2006

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.