Implementation and Use of a Secondary Droplet Break-Up Model Under Diesel Engine Conditions

Abstract

The diesel engine combustion process is very complex in nature. On the order of milliseconds, a high-pressure liquid spray is injected into a cylinder with a moving boundary. The spray undergoes break-up, dispersion, phase change and combustion. Accurate spray modeling is a prerequisite to modeling the diesel combustion process. Droplet break-up is governed by both primary and secondary break-up mechanisms. The Taylor Analogy Break-Up (TAB) Model was employed, in a self-contained simulation environment, to study the secondary break-up of a droplet flowing in a range of aerodynamic environments. The model, which describes the droplet distortion/break-up in an analogy to a spring-mass-damped system, was not formulated to solve the entire spray from start of injection to combustion, which is typically done with a PDF treatment. The developed simulation code provides a fundamental environment to parametrically study the effects of different break-up forcing functions (aerodynamic etc.) as well as provides the ability to refit power-law expressions that can then be used in phemonological diesel engine simulations. The paper first discusses the key physical mechanisms associated with breakup, the formulation/implementation of the numerical model, demonstrates its use to understand droplet parameter tradeoffs and how it can be used to construct reduced order break-up residence time models. Finally, the model is extended to a multi-DOF formulation to facilitate the understanding of the impact of additional breakup forces, which could be aerodynamic, collision-induced etc., on the droplet.