ID 299

Effect of realistic multicomponent diesel surrogates on predicted in-nozzle flow and cavitation

 

Abstract:

In-nozzle flow dominates primary break-up characteristics and therefore the combustion efficiency. Predictive methods of the internal nozzle flow and its link with the spray characteristics have traditionally assumed constant fuel properties, which may lead to inaccuracies. Surprisingly enough, the effect of using realistic fuel surrogates has not been closely examined. In this work, the fuel property variation as function of pressure of three diesel surrogates is modelled using the PC-SAFT EoS; these include n-dodecane and two mixtures comprising four and eight components, named V0 and V1 respectively, based on a grade no. 2 diesel emissions-certification fuel. Then, the surrogates properties are utilised in simulations for a common rail 5-hole tip injector nozzle. The needle is assumed to be still at a lift of 105µm, which is representative of the lift reached during pilot injection. The injector operating pressure is 180MPa and the collector back pressure is 5MPa. The density of the bulk fluid is assumed to vary according to a barotropic-like scheme, following an isentropic expansion. Results show that the mixture surrogates V0 and V1 have a greater vapour pressure than that of n-dodecane, although they are significantly heavier both in density and viscosity. Predicted cavitation clouds occupied a ∼14% larger volume for V1 than that for n-dodecane. Slight differences were observed on the calculated mass flux, where V1 gave an increase of ∼7% with respect to n-dodecane. Interestingly, the amount of vaporised components which appear simultaneously in the two mixtures were not the same, which indicates that there exists an interaction between the components during the vaporisation process. Despite its exploratory nature, this study offers some insight for the first time into the use of complex EoS and surrogate mixtures, which may be worth to capture the particular properties of diesel fuel during high pressure injections.