Influence of Nozzle Design Upon the Primary Jet Breakup of High-Viscosity Fuels for Entrained Flow Gasification

Abstract

The research work of the present study is focused on the influence of design parameters of twin-fluid nozzles used for the atomization of high-viscosity fuels with respect to the primary breakup of the liquid jet. Two external mixing twin-fluid nozzles, which have already been investigated in previous studies [1, 2], were chosen as basic design. Based on the previous findings the web thickness between fuel and oxidizer supply was varied. In addition both designs were extended by a channel for internal mixing of gas and liquid with a length to diameter ratio of one. Moreover one of the basic nozzles was scaled by decrease of the effective areas in a way that momentum flux ratio as well as gas to liquid mass flow ratio was kept constant. The newly designed atomizers were subsequently investigated with regard to the influence of the changes upon the primary jet breakup using CFD simulations. The numerical simulations were conducted by means of the open source package OpenFOAM. The Volume of Fluid method was used for the determination of the gas-liquid interface. These simulations were then compared with experimentally validated simulations of the basic nozzle designs with regard to the breakup morphology of the jet and the mode of the primary surface instability. In addition, the liquid structure was examined by comparison of breakup length and frequency. The results of these simulations showed that small changes in the atomizer design heavily influence the primary breakup, which in turn influences the overall performance of the atomizer (e.g. SMD). Moreover, these findings will contribute to a better understanding of the physics of the breakup of high-viscosity liquid jets and as well to create an experimentally validated CFD based tool for future burner development and optimization.